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    Replacement driver board for MK III

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    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Replacement driver board for MK III

    Post by GlacierJohn on Fri May 23, 2014 5:37 pm

    When I rebuilt my MK IIIs a couple months ago, Chad (recently deceased Crying or Very sad ), recommended I keep the original driver boards and just concentrate on the power supply which I did. Now human beings the way we are I just have to tinker, plus I notice a little hiss out of my right amp at idle. The trouble shooting sticky above says that is likely a driver tube or bad resistor on the driver board. Buying a new driver tube would be too easy, so I'm thinking about replacing both driver boards with a new tubes4hifi, or Poseidon driver boards. I'm pretty happy with the Dynaco sound, but am open to other options, what can I expect to hear with new drivers?

    Thanks,

    John

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Replacement driver board for MK III

    Post by Bob Latino on Fri May 23, 2014 6:23 pm

    Hi John,

    The original Dynaco Mark III circuit was designed to use just one driver tube to "save a tube" and "save a tube socket". The original pentode/triode 6AN8 driver tube is not the best solution for best sound quality in light of what is available today. The 6AN8 tube is noted for not being linear at all drive levels. Either the Poseidon or the Tubes4hifi driver board would be a better choice over the original driver circuit. Both modern boards use all triode 12**7 driver tubes. The advantage of the Tubes4hifi board is that it has its own "on board" power supply to run just the board. This leaves the quad cap (or underchassis power supply board) free to supply power to just the output transformer. The Poseidon board uses the amp's main power supply for B+ high voltage to run the board AND the power transformer. The Tubes4hifi board also has an octal board option if you favor octal driver tubes like a 6SN7.

    The original Mark III driver circuit, while OK for it's day (circa 1957), is easily improved on by modern driver circuitry using all triode type tubes. Modern circuits would give your amps better and more solid bass and also more treble extension. The original circuit also used a lot of feedback (about 20 dB) to keep the amp linear. Modern all triode circuits do not need as much feedback because they are inherently linear to begin with. The Tubes4hifi driver circuit only uses 13 dB of feedback and is linear at all drive levels and with any reasonable speaker load.

    Bob

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: Replacement driver board for MK III

    Post by zx on Fri May 23, 2014 6:57 pm

    just concentrate on the power supply which I did......
    You put new caps in right.??..even if you go with a other frontend ......whats your B+???...If its over 500-550V like my 3pr are.....i have 125AC comeing from the wal here in Fl... you well wont to drop  it to about 480V thats what the amps were made to run at....for the best sound out these amps....
    Well sounds best to me.....
    Otheres can say on the sound of the new boards....the 6SN7 one look good to me....an a vary fair $$..if you dont think it sounds better than stock not out a lot .....i like the stock 6AN8-7199...one tube makes less noise.. so my ears say.... others ears may say diff....an thay can speaker for there self......hehe ....have fun with tubes.........

    Thanks for the site Bob......

    snav

    Posts : 18
    Join date : 2011-05-18

    Re: Replacement driver board for MK III

    Post by snav on Sun Jun 15, 2014 1:37 am

    [quote="zx"]just concentrate on the power supply which I did......
    You put new caps in right.??..even if you go with a other frontend ......whats your B+???...If its over 500-550V like my 3pr are.....i have 125AC comeing from the wal here in Fl... you well wont to drop  it to about 480V thats what the amps were made to run at....for the best sound out these amps....
    Well sounds best to me.....
    Otheres can say on the sound of the new boards....the 6SN7 one look good to me....an a vary fair $$..if you dont think it sounds better than stock not out a lot .....i like the stock 6AN8-7199...one tube makes less noise.. so my ears say.... others ears may say diff....an thay can speaker for there self......hehe ....have fun with tubes.........

    I know this topic is a bit old but I want to say that I saw the high voltage on my Cap and after much experimenting, I found that a 5U4GB and a 30s delay for the rectifier filament, so no surge, gives me just the drop I need so that my voltages under load are 488 before and 480 after the choke with 124v line. Drops to 478-470 when the line drops to 119-120.

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: Replacement driver board for MK III

    Post by zx on Sun Jun 15, 2014 8:43 am

    Good job.....now youll get good tube life...an better sound...well to me with lower B+!
    You got spend lots of $$ to get better sound .....than the old Mk3s...
    I also like the tone of the 5u4...with or with out the choke................have fune with tubes


    thanks for the site Bob...................

    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Re: Replacement driver board for MK III

    Post by GlacierJohn on Thu Feb 19, 2015 3:36 pm

    Ok, I'm bumping this thread from last year. I'm too busy with outdoors stuff to do anything but listen to my stereo from May-December. Now in late winter I'm ready to play with my MK IIIs again, been listening to my wonderful MC225 since last spring.

    I installed the SDS power supply mod last winter and with your help got them up and running. Now I'm ready to order the tube 4 hifi driver boards and try Snav's idea for lowering my B+ voltage. My line voltage out the wall is 123 volts and my B+ is plus and minus 564 volts. Will Snav's suggestion drop that B+ voltage enough? I'm about 90 volts higher than spec right now. I biased the amp at an even 1.50 volts. My amp runs pretty hot, not too hot to touch but way hotter than my 225. Any other ideas? What about installing that mod for switching to triode mode? Or the separate bias pots?

    I have three matched sets of 6550s on hand, and the amp sounds good right now, though not as good as my restored Mc225, but what is. The MK IIIs have very strong tight bass and extended airy highs, I guess my point is I'm happy with the sound so any improvement is bonus, while running cooler and driving the 6550s a little easier would be good.

    snav

    Posts : 18
    Join date : 2011-05-18

    Re: Replacement driver board for MK III

    Post by snav on Thu Feb 19, 2015 6:01 pm

    I believe the peak voltage before my investigation was around 564v also. I have to say the delay on the filament of the rectifier is key. Mine is set at 25sec and 1s reset on power loss. The power xfmr is rated for the extra 5v current required as well.

    Bob Latino
    Admin

    Posts : 2378
    Join date : 2008-11-26
    Location : Massachusetts

    Re: Replacement driver board for MK III

    Post by Bob Latino on Thu Feb 19, 2015 7:07 pm

    GlacierJohn wrote:Ok, I'm bumping this thread from last year. I'm too busy with outdoors stuff to do anything but listen to my stereo from May-December. Now in late winter I'm ready to play with my MK IIIs again, been listening to my wonderful MC225 since last spring.

    I installed the SDS power supply mod last winter and with your help got them up and running. Now I'm ready to order the tube 4 hifi driver boards and try Snav's idea for lowering my B+ voltage. My line voltage out the wall is 123 volts and my B+ is plus and minus 564 volts. Will Snav's suggestion drop that B+ voltage enough? I'm about 90 volts higher than spec right now. I biased the amp at an even 1.50 volts. My amp runs pretty hot, not too hot to touch but way hotter than my 225. Any other ideas? What about installing that mod for switching to triode mode? Or the separate bias pots?

    I have three matched sets of 6550s on hand, and the amp sounds good right now, though not as good as my restored Mc225, but what is. The MK IIIs have very strong tight bass and extended airy highs, I guess my point is I'm happy with the sound so any improvement is bonus, while running cooler and driving the 6550s a little easier would be good.

    If you run an older Mark III that was supposed to run on 1957 voltage (115 - 117 VAC USA line voltage) and then run that at 123 volts, the B+ voltage will be sky high as you have found out. 563 volts DC will shorten tube life. That voltage should be about 490 VDC. I bet if you measure across pins 2 and 7 of each output tube, your filament voltage will be much higher than 6.3 VAC. Probably up in the 7+ volt AC range. If you continue to run the amp(s) like that, tube life will be noticeably shortened.

    Suggestions ..
    1. If you are using a 5AR4 tube rectifier switch to a 5U4. This will drop all the DC voltages in the amp but will not the AC voltages. If you are using the SDS's power supply ALSO for solid state rectification > switch back to tube rectification. The worst thing you can to to an OLDER ORIGINAL Mark III or ST-70 is to use solid state rectification. Using solid state rectification causes even a higher B+ than a GZ34/5AR4 and your much higher than normal 123 VAC line voltage is making things even worse.

    2. Get a VARIAC and set it to give an output of about 117 - 118 VAC. Now use tube rectification and your voltages should be pretty much normal again ...

    Bob

    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Re: Replacement driver board for MK III

    Post by GlacierJohn on Thu Feb 19, 2015 7:48 pm

    Bob Latino wrote:
    GlacierJohn wrote:Ok, I'm bumping this thread from last year. I'm too busy with outdoors stuff to do anything but listen to my stereo from May-December. Now in late winter I'm ready to play with my MK IIIs again, been listening to my wonderful MC225 since last spring.

    I installed the SDS power supply mod last winter and with your help got them up and running. Now I'm ready to order the tube 4 hifi driver boards and try Snav's idea for lowering my B+ voltage. My line voltage out the wall is 123 volts and my B+ is plus and minus 564 volts. Will Snav's suggestion drop that B+ voltage enough? I'm about 90 volts higher than spec right now. I biased the amp at an even 1.50 volts. My amp runs pretty hot, not too hot to touch but way hotter than my 225. Any other ideas? What about installing that mod for switching to triode mode? Or the separate bias pots?

    I have three matched sets of 6550s on hand, and the amp sounds good right now, though not as good as my restored Mc225, but what is. The MK IIIs have very strong tight bass and extended airy highs, I guess my point is I'm happy with the sound so any improvement is bonus, while running cooler and driving the 6550s a little easier would be good.

    If you run an older Mark III that was supposed to run on 1957 voltage (115 - 117 VAC USA line voltage) and then run that at 123 volts, the B+ voltage will be sky high as you have found out. 563 volts DC will shorten tube life. That voltage should be about 490 VDC. I bet if you measure across pins 2 and 7 of each output tube, your filament voltage will be much higher than 6.3 VAC. Probably up in the 7+ volt AC range. If you continue to run the amp(s) like that, tube life will be noticeably shortened.

    Suggestions ..
    1. If you are using a 5AR4 tube rectifier switch to a 5U4. This will drop all the DC voltages in the amp but will not the AC voltages. If you are using the SDS's power supply ALSO for solid state rectification > switch back to tube rectification. The worst thing you can to to an OLDER ORIGINAL Mark III or ST-70 is to use solid state rectification. Using solid state rectification causes even a higher B+ than a GZ34/5AR4 and your much higher than normal 123 VAC line voltage is making things even worse.

    2. Get a VARIAC and set it to give an output of about 117 - 118 VAC. Now use tube rectification and your voltages should be pretty much normal again ...

    Bob

    Thanks Bob, I am using the GZ34 Rectifier, so what's better the VARIAC or 5U4 rectifier tube? Both, to cover all bases? Also Snav has PM'd me the following advise, I'm not sure how to do that exactly.

    Snav's note:
    - Thu Aug 14, 2014 2:24 pm
    If you can get a flux pen or other source It would seem to me that Rehitting each of the solder joints would be wise, Allow good sleep. Wink

    I have high voltage at my home and discovered that Using a 5U4GB rectifier instead of the 5AR4 drops the final voltage to 479 from 516 with line voltage of 124. I did however add a 25s delay to the rectifier filament to prevent the unloaded voltage from spiking to over 565v. Very simple RC delay which resets in .5s after power off. Hope you get many years of use from your MK3.


    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Re: Replacement driver board for MK III

    Post by GlacierJohn on Wed Feb 25, 2015 9:02 pm

    I've decided to completely rewire my Mk III when I install the new driver board but I have a few concerns. My plan is to remove all the wiring except the hard wires out of the transformers, pull out the old driver board, the old tube sockets, speaker connecting strip and input jack. I would keep the original transformers and choke, power switch and the SDS power supply board I installed last winter. I am also thinking of installing the dual bias set up tubes 4 hifi sells and would like to install that triode/pentode switch.

    My concerns or questions:
    1) With that rather large SDS board in place and set pretty tight to the speaker terminals, is there room in the chassis for everything I want to do?
    2) If I plan on buying a Variac and setting it at 117 volts anyway, should I still change out that rectifier tube to lower the voltage?
    3) What is the sonic difference between the standard Tubes 4 hifi driver board and the Octal board?
    4) Any other ideas or suggestions while I dig into these two amps.
    Thanks,
    John

    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Re: Replacement driver board for MK III

    Post by GlacierJohn on Thu Feb 26, 2015 11:02 am

    Here's a pic of my fairly crowded amp...


    You can see how tight the SDS board is to the speaker terminal connections.

    Tiziano73

    Posts : 29
    Join date : 2012-09-11
    Location : Italy

    Re: Replacement driver board for MK III

    Post by Tiziano73 on Mon Mar 02, 2015 4:31 am

    zx wrote:just concentrate on the power supply which I did......
    You put new caps in right.??..even if you go with a other frontend ......whats your B+???...If its over 500-550V like my 3pr are.....i have 125AC comeing from the wal here in Fl... you well wont to drop  it to about 480V thats what the amps were made to run at....for the best sound out these amps....
    Well sounds best to me.....
    Otheres can say on the sound of the new boards....the 6SN7 one look good to me....an a vary fair $$..if you dont think it sounds better than stock not out a lot .....i like the stock 6AN8-7199...one tube makes less noise.. so my ears say.... others ears may say diff....an thay can speaker for there self......hehe ....have fun with tubes.........

    Thanks for the site Bob......


    I am in agreement, i prefer stock boards with good 6AN8 matching (same triode current and same Gm on pentode). The best thing to do it's control the power supply.

    Tiziano.

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: Replacement driver board for MK III

    Post by MontanaWay on Mon Mar 02, 2015 12:31 pm

    Tiziano73 wrote:
    zx wrote:just concentrate on the power supply which I did......
    You put new caps in right.??..even if you go with a other frontend ......whats your B+???...If its over 500-550V like my 3pr are.....i have 125AC comeing from the wal here in Fl... you well wont to drop  it to about 480V thats what the amps were made to run at....for the best sound out these amps....
    Well sounds best to me.....
    Otheres can say on the sound of the new boards....the 6SN7 one look good to me....an a vary fair $$..if you dont think it sounds better than stock not out a lot .....i like the stock 6AN8-7199...one tube makes less noise.. so my ears say.... others ears may say diff....an thay can speaker for there self......hehe ....have fun with tubes.........

    Thanks for the site Bob......


    I am in agreement, i prefer stock boards with good 6AN8 matching (same triode current and same Gm on pentode). The best thing to do it's control the power supply.

    Tiziano.

    It is important to have a good, clean and steady power supply, no argument there. But that is, I feel, only about half way there. Updating the driver board, in my opinion, will make the biggest change in sound.
    To me, there is no comparison between the old driver circuit design to the updated Tubes4Hifi design, the latter being head and shoulder above the original. Some people prefer to keep a circuit as original as possible, and thats OK, but I feel that by doing that, you would not get the best sound out of your system. And don't forget, sound is extremely subjective as well!
    Like a lot of original/early Dynaco designs, it was a compromise, one of the main aims being saving $.
    For us, paying a little extra for two tubes and additional resistors etc is no big deal, but when you start talking about 100's even 1000's of kits, it makes a huge difference to the bottom line.

    So, if you have the $ to upgrade the driver board, do it.

    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Re: Replacement driver board for MK III

    Post by GlacierJohn on Mon Mar 02, 2015 12:58 pm

    MontanaWay wrote:
    Tiziano73 wrote:
    zx wrote:just concentrate on the power supply which I did......
    You put new caps in right.??..even if you go with a other frontend ......whats your B+???...If its over 500-550V like my 3pr are.....i have 125AC comeing from the wal here in Fl... you well wont to drop  it to about 480V thats what the amps were made to run at....for the best sound out these amps....
    Well sounds best to me.....
    Otheres can say on the sound of the new boards....the 6SN7 one look good to me....an a vary fair $$..if you dont think it sounds better than stock not out a lot .....i like the stock 6AN8-7199...one tube makes less noise.. so my ears say.... others ears may say diff....an thay can speaker for there self......hehe ....have fun with tubes.........

    Thanks for the site Bob......


    I am in agreement, i prefer stock boards with good 6AN8 matching (same triode current and same Gm on pentode). The best thing to do it's control the power supply.

    Tiziano.

    It is important to have a good, clean and steady power supply, no argument there. But that is, I feel, only about half way there. Updating the driver board, in my opinion, will make the biggest change in sound.
    To me, there is no comparison between the old driver circuit design to the updated Tubes4Hifi design, the latter being head and shoulder above the original. Some people prefer to keep a circuit as original as possible, and thats OK, but I feel that by doing that, you would not get the best sound out of your system. And don't forget, sound is extremely subjective as well!
    Like a lot of original/early Dynaco designs, it was a compromise, one of the main aims being saving $.
    For us, paying a little extra for two tubes and additional resistors etc is no big deal, but when you start talking about 100's even 1000's of kits, it makes a huge difference to the bottom line.

    So, if you have the $ to upgrade the driver board, do it.

    Obviously a matter of opinion, but having googled the topic and read every related thread on various forums going back 15 years, your opinion seems to predominate. As stated I have already upgraded the power supply with the SDS mod, now I am committed to going whole hog with new tube sockets, speaker jacks, input plug, triode/pentode switch and driver board. The question was which driver board was the best, there is no definitive answer to that, whether it is the Poseidon, Tunes4Hifi, Octal whatever, everyone seems to think they are all an upgrade over the original. As a bonus, with the new driver board I will get two bias pots and that replacement terminal to bias each tube separately.

    BTW, I just re-measured my pin voltages, my heater voltage is still too high 6.7 volts, but the B+ voltages now measure around 490 volts, much closer to spec.

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: Replacement driver board for MK III

    Post by MontanaWay on Mon Mar 02, 2015 1:06 pm

    GlacierJohn wrote:
    MontanaWay wrote:
    Tiziano73 wrote:
    zx wrote:just concentrate on the power supply which I did......
    You put new caps in right.??..even if you go with a other frontend ......whats your B+???...If its over 500-550V like my 3pr are.....i have 125AC comeing from the wal here in Fl... you well wont to drop  it to about 480V thats what the amps were made to run at....for the best sound out these amps....
    Well sounds best to me.....
    Otheres can say on the sound of the new boards....the 6SN7 one look good to me....an a vary fair $$..if you dont think it sounds better than stock not out a lot .....i like the stock 6AN8-7199...one tube makes less noise.. so my ears say.... others ears may say diff....an thay can speaker for there self......hehe ....have fun with tubes.........

    Thanks for the site Bob......


    I am in agreement, i prefer stock boards with good 6AN8 matching (same triode current and same Gm on pentode). The best thing to do it's control the power supply.

    Tiziano.

    It is important to have a good, clean and steady power supply, no argument there. But that is, I feel, only about half way there. Updating the driver board, in my opinion, will make the biggest change in sound.
    To me, there is no comparison between the old driver circuit design to the updated Tubes4Hifi design, the latter being head and shoulder above the original. Some people prefer to keep a circuit as original as possible, and thats OK, but I feel that by doing that, you would not get the best sound out of your system. And don't forget, sound is extremely subjective as well!
    Like a lot of original/early Dynaco designs, it was a compromise, one of the main aims being saving $.
    For us, paying a little extra for two tubes and additional resistors etc is no big deal, but when you start talking about 100's even 1000's of kits, it makes a huge difference to the bottom line.

    So, if you have the $ to upgrade the driver board, do it.

    Obviously a matter of opinion, but having googled the topic and read every related thread on various forums going back 15 years, your opinion seems to predominate. As stated I have already upgraded the power supply with the SDS mod, now I am committed to going whole hog with new tube sockets, speaker jacks, input plug, triode/pentode switch and driver board. The question was which driver board was the best, there is no definitive answer to that, whether it is the Poseidon, Tunes4Hifi, Octal whatever, everyone seems to think they are all an upgrade over the original. As a bonus, with the new driver board I will get two bias pots and that replacement terminal to bias each tube separately.

    BTW, I just re-measured my pin voltages, my heater voltage is still too high 6.7 volts, but the B+ voltages now measure around 490 volts, much closer to spec.

    heater voltage of 6.7V should still be ok, don't forget, it all tends to swing with your mains voltage too.
    My personal preference by far is the octal. I love the 6SN7/6SL7's, to me, they have a really full sound yet still give you a clarity difficult to get out of the 12AU7/12BH7 etc., again, that is my 'subjective' sound preference! Smile

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: Replacement driver board for MK III

    Post by zx on Mon Mar 02, 2015 3:07 pm

    I... get better sound with one pot for the outputs........... I have tube amps setup bouth ways...
    The sound of the amps with a pot for each tube .....to me is like... if you were trying to dance with one foot nailed to the ground....the outputs cant talk to each other...an it sound like you Dont get full output.....
    when the outputs cathoides are tied to gather then grounded... thay can talk to each other.... the sound is sweeter an fuller....to me!
    The B+ being to high... like  over 500v....kills the sound!
    480v is a sweet spot..........
    With any drive board.... that has pot for ea output... can ezzly be setup for one pot for the outputs....
    40 years I have had a lot of tube amps old an new......it all about the sound to me...
    An as for the sound of the 6AN8/7199 frount end.....one tube has less noise!
    but I have 6sn7 in preamps....... front ends of amps .....big tone..great tube...some say the best driver.
    The only way I have found the sound I have an like......is by trying ever thing I could...
    so this is just one mans o-pine.....if you don't go you don't know.....hehe have fun with tubes
    An thanks for any an all info on getting better sound out of tubes


    thanks for the site Bob...................

    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Re: Replacement driver board for MK III

    Post by GlacierJohn on Mon Mar 02, 2015 6:34 pm

    zx wrote:I... get better sound with one pot for the outputs........... I have tube amps setup bouth ways...
    The sound of the amps with a pot for each tube .....to me is like... if you were trying to dance with one foot nailed to the ground....the outputs cant talk to each other...an it sound like you Dont get full output.....
    when the outputs cathoides are tied to gather then grounded... thay can talk to each other.... the sound is sweeter an fuller....to me!
    The B+ being to high... like  over 500v....kills the sound!
    480v is a sweet spot..........
    With any drive board.... that has pot for ea output... can ezzly be setup for one pot for the outputs....
    40 years I have had a lot of tube amps old an new......it all about the sound to me...
    An as for the sound of the 6AN8/7199 frount end.....one tube has less noise!
    but I have 6sn7 in preamps....... front ends of amps .....big tone..great tube...some say the best driver.
    The only way I have found the sound I have an like......is by trying ever thing I could...
    so this is just one mans o-pine.....if you don't go you don't know.....hehe have fun with tubes
    An thanks for any an all info on getting better sound out of tubes


    thanks for the site Bob...................

    Now my heads starting to spin. So individual bias pots is a bad thing? I'm not worried about voltage now because I will install a Variac and run the system at 117 volts. Currently my tubes are matched, so maybe the bias isn't an issue, but it seemed like a harmless option to keep open. The one tube driver vs two tube drive. Sound of the octal 6SN7/6SL7 vs 12AU7/12BH7. I don't know if it means anything, but I love the sound of my Mcintosh MC-225 which has 12BH7 driver tubes. I was just getting to order everything from Roy. I know it's not an end of the world decision, I'm sure they all sound good, but anybody else have an opinion on this?

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: Replacement driver board for MK III

    Post by MontanaWay on Mon Mar 02, 2015 6:38 pm

    GlacierJohn wrote:
    zx wrote:I... get better sound with one pot for the outputs........... I have tube amps setup bouth ways...
    The sound of the amps with a pot for each tube .....to me is like... if you were trying to dance with one foot nailed to the ground....the outputs cant talk to each other...an it sound like you Dont get full output.....
    when the outputs cathoides are tied to gather then grounded... thay can talk to each other.... the sound is sweeter an fuller....to me!
    The B+ being to high... like  over 500v....kills the sound!
    480v is a sweet spot..........
    With any drive board.... that has pot for ea output... can ezzly be setup for one pot for the outputs....
    40 years I have had a lot of tube amps old an new......it all about the sound to me...
    An as for the sound of the 6AN8/7199 frount end.....one tube has less noise!
    but I have 6sn7 in preamps....... front ends of amps .....big tone..great tube...some say the best driver.
    The only way I have found the sound I have an like......is by trying ever thing I could...
    so this is just one mans o-pine.....if you don't go you don't know.....hehe have fun with tubes
    An thanks for any an all info on getting better sound out of tubes


    thanks for the site Bob...................

    Now my heads starting to spin. So individual bias pots is a bad thing? I'm not worried about voltage now because I will install a Variac and run the system at 117 volts. Currently my tubes are matched, so maybe the bias isn't an issue, but it seemed like a harmless option to keep open. The one tube driver vs two tube drive. Sound of the octal 6SN7/6SL7 vs 12AU7/12BH7. I don't know if it means anything, but I love the sound of my Mcintosh MC-225 which has 12BH7 driver tubes. I was just getting to order everything from Roy. I know it's not an end of the world decision, I'm sure they all sound good, but anybody else have an opinion on this?

    individual biasing of the output tubes is preferred....absolutely. This way you can 'match' the output tubes to the best.
    As has been said many times here, sound is extremely subjective. What I know though is that for many people, who have heard the 12BH7 then the 6XX7 series in a similar amp, mostly prefer the 6XX7's.

    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Re: Replacement driver board for MK III

    Post by GlacierJohn on Mon Mar 02, 2015 6:44 pm

    MontanaWay wrote:
    GlacierJohn wrote:
    zx wrote:I... get better sound with one pot for the outputs........... I have tube amps setup bouth ways...
    The sound of the amps with a pot for each tube .....to me is like... if you were trying to dance with one foot nailed to the ground....the outputs cant talk to each other...an it sound like you Dont get full output.....
    when the outputs cathoides are tied to gather then grounded... thay can talk to each other.... the sound is sweeter an fuller....to me!
    The B+ being to high... like  over 500v....kills the sound!
    480v is a sweet spot..........
    With any drive board.... that has pot for ea output... can ezzly be setup for one pot for the outputs....
    40 years I have had a lot of tube amps old an new......it all about the sound to me...
    An as for the sound of the 6AN8/7199 frount end.....one tube has less noise!
    but I have 6sn7 in preamps....... front ends of amps .....big tone..great tube...some say the best driver.
    The only way I have found the sound I have an like......is by trying ever thing I could...
    so this is just one mans o-pine.....if you don't go you don't know.....hehe have fun with tubes
    An thanks for any an all info on getting better sound out of tubes


    thanks for the site Bob...................

    Now my heads starting to spin. So individual bias pots is a bad thing? I'm not worried about voltage now because I will install a Variac and run the system at 117 volts. Currently my tubes are matched, so maybe the bias isn't an issue, but it seemed like a harmless option to keep open. The one tube driver vs two tube drive. Sound of the octal 6SN7/6SL7 vs 12AU7/12BH7. I don't know if it means anything, but I love the sound of my Mcintosh MC-225 which has 12BH7 driver tubes. I was just getting to order everything from Roy. I know it's not an end of the world decision, I'm sure they all sound good, but anybody else have an opinion on this?

    individual biasing of the output tubes is preferred....absolutely. This way you can 'match' the output tubes to the best.
    As has been said many times here, sound is extremely subjective. What I know though is that for many people, who have heard the 12BH7 then the 6XX7 series in a similar amp, mostly prefer the 6XX7's.

    Thank you, that is helpful. Is it snowing down your way? Just started up here in Bigfork.

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: Replacement driver board for MK III

    Post by MontanaWay on Mon Mar 02, 2015 6:47 pm

    GlacierJohn wrote:
    MontanaWay wrote:
    GlacierJohn wrote:
    zx wrote:I... get better sound with one pot for the outputs........... I have tube amps setup bouth ways...
    The sound of the amps with a pot for each tube .....to me is like... if you were trying to dance with one foot nailed to the ground....the outputs cant talk to each other...an it sound like you Dont get full output.....
    when the outputs cathoides are tied to gather then grounded... thay can talk to each other.... the sound is sweeter an fuller....to me!
    The B+ being to high... like  over 500v....kills the sound!
    480v is a sweet spot..........
    With any drive board.... that has pot for ea output... can ezzly be setup for one pot for the outputs....
    40 years I have had a lot of tube amps old an new......it all about the sound to me...
    An as for the sound of the 6AN8/7199 frount end.....one tube has less noise!
    but I have 6sn7 in preamps....... front ends of amps .....big tone..great tube...some say the best driver.
    The only way I have found the sound I have an like......is by trying ever thing I could...
    so this is just one mans o-pine.....if you don't go you don't know.....hehe have fun with tubes
    An thanks for any an all info on getting better sound out of tubes


    thanks for the site Bob...................

    Now my heads starting to spin. So individual bias pots is a bad thing? I'm not worried about voltage now because I will install a Variac and run the system at 117 volts. Currently my tubes are matched, so maybe the bias isn't an issue, but it seemed like a harmless option to keep open. The one tube driver vs two tube drive. Sound of the octal 6SN7/6SL7 vs 12AU7/12BH7. I don't know if it means anything, but I love the sound of my Mcintosh MC-225 which has 12BH7 driver tubes. I was just getting to order everything from Roy. I know it's not an end of the world decision, I'm sure they all sound good, but anybody else have an opinion on this?

    individual biasing of the output tubes is preferred....absolutely. This way you can 'match' the output tubes to the best.
    As has been said many times here, sound is extremely subjective. What I know though is that for many people, who have heard the 12BH7 then the 6XX7 series in a similar amp, mostly prefer the 6XX7's.

    Thank you, that is helpful. Is it snowing down your way? Just started up here in Bigfork.

    you're welcome!
    not much at all...its been one of the mildest winters ever here....and when we do get snow, it is not much and does not last long....

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: Replacement driver board for MK III

    Post by zx on Mon Mar 02, 2015 9:34 pm

    With Bias...if the tubes are not matched.....as most are an vary close to day...with the pot for each output tube.....when the tubes is pushed... one well pull more bias V....from where?? the other output tube!.....
    This is not too tell anyone what thay hear.....or need!
    I like the Sound of the Stock MK3s I have.....I have hard to drive speakers like Apogee an Acoustats ESL...An Magnepans........So getting all the output I can out of the Amps I drive them with.. is a must.....so having the Cathoides ran togather befor the one res ... gives me that...
    But like I said....try it all....are you may never know......or find the sound that's for you....that's all that matters in the end....by the way a lot of people think the MC225 is the best sounding tube peace MC ever made....even me....but not a nef power for my speakers....but if your into horns....sweet sound ...I have never got out of a Dynaco
    An as for the 6AN8/7199 Dynaco stock driver tube.....costing less....so that was why thay were used...Hehe...
    I don't buy it!.....in 1959 the 12xx7 an even the 6XX7 cost 10-20 cent ea...at the drug store....I used to buy tubes for my grandfather TV....you could say ....if you need a lot of tubes back then......thay were a dime a dozen.....hehe.....have fun with tubes



    thanks for the site Bob..............

    I not saleing any thing...........good luck

    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Re: Replacement driver board for MK III

    Post by GlacierJohn on Mon Mar 02, 2015 10:48 pm

    zx wrote:With Bias...if the tubes are not matched.....as most are an vary close to day...with the pot for each output tube.....when the tubes is pushed... one well pull more bias V....from where?? the other output tube!.....
    This is not too tell anyone what thay hear.....or need!
    I like the Sound of the Stock MK3s I have.....I have hard to drive speakers like Apogee an Acoustats ESL...An Magnepans........So getting all the output I can out of the Amps I drive them with.. is a must.....so having the Cathoides ran togather befor the one res ... gives me that...
    But like I said....try it all....are you may never know......or find the sound that's for you....that's all that matters in the end....by the way a lot of people think the MC225 is the best sounding tube peace MC ever made....even me....but not a nef power for my speakers....but if your into horns....sweet sound ...I have never got out of a Dynaco
    An as for the 6AN8/7199 Dynaco stock driver tube.....costing less....so that was why thay were used...Hehe...
    I don't buy it!.....in 1959 the 12xx7 an even the 6XX7 cost 10-20 cent ea...at the drug store....I used to buy tubes for my grandfather TV....you could say ....if you need a lot of tubes back then......thay were a dime a dozen.....hehe.....have fun with tubes



    thanks for the site Bob..............

    I not saleing any thing...........good luck

    Thank you. Just to be clear I listened to them in stock form from 1988 to 1995 when I got away from two channel for a bit. I actually traded a very nice Conrad Johnson straight across for the MK IIIs, probably not smartest monetary decision, but I liked the sound better. At the time I was running three pair of speakers from four different power amps. My 1975 JBL L-65s, Martin Logan CLS's and a pair of B&W DM 2000s. Driving them I switched around between Conrad Johnson, Dynaco Pat 5 and Van Alstine Super Pas III pre amps and the MV 75 - Mark IIIs, Dynaco ST 400, Hafler DM 2000 that was modified by Musical Concepts and my favorite of all time McIntosh MC225. Slowly over the years my tubes burned out and living where I do I would just set each amp up on a shelf until there was only my Yamaha CR2020 receiver.

    Point is I am very familiar with the stock MK III sound as well as others and would like to try something different. I would like a little more sweetness but with medium power. I don't need a lot since I'm set up in a small 10'x12' room, just a change of pace amp from the sweet little Mc225.


    GlacierJohn

    Posts : 38
    Join date : 2014-04-17

    Re: Replacement driver board for MK III

    Post by GlacierJohn on Mon Mar 02, 2015 10:59 pm

    GlacierJohn wrote:
    zx wrote:With Bias...if the tubes are not matched.....as most are an vary close to day...with the pot for each output tube.....when the tubes is pushed... one well pull more bias V....from where?? the other output tube!.....
    This is not too tell anyone what thay hear.....or need!
    I like the Sound of the Stock MK3s I have.....I have hard to drive speakers like Apogee an Acoustats ESL...An Magnepans........So getting all the output I can out of the Amps I drive them with.. is a must.....so having the Cathoides ran togather befor the one res ... gives me that...
    But like I said....try it all....are you may never know......or find the sound that's for you....that's all that matters in the end....by the way a lot of people think the MC225 is the best sounding tube peace MC ever made....even me....but not a nef power for my speakers....but if your into horns....sweet sound ...I have never got out of a Dynaco
    An as for the 6AN8/7199 Dynaco stock driver tube.....costing less....so that was why thay were used...Hehe...
    I don't buy it!.....in 1959 the 12xx7 an even the 6XX7 cost 10-20 cent ea...at the drug store....I used to buy tubes for my grandfather TV....you could say ....if you need a lot of tubes back then......thay were a dime a dozen.....hehe.....have fun with tubes



    thanks for the site Bob..............

    I not saleing any thing...........good luck

    Thank you. Just to be clear I listened to them in stock form from 1988 to 1995 when I got away from two channel for a bit, then again this past year since I upgraded the power supply. I actually traded a very nice Conrad Johnson straight across for the MK IIIs, probably not smartest monetary decision, but I liked the sound of the old Dynaco's better. At the time I was running three pair of speakers from four different power amps. My 1975 JBL L-65s, Martin Logan CLS's and a pair of B&W DM 2000s. Driving them I switched around between Conrad Johnson, Dynaco Pat 5 and Van Alstine Super Pas III pre amps and the MV 75 - Mark IIIs, Dynaco ST 400, Hafler DM 2000 that was modified by Musical Concepts and my favorite of all time McIntosh MC225. Slowly over the years my tubes burned out and living where I do I would just set each amp up on a shelf until there was only my Yamaha CR2020 receiver.

    Point is I am very familiar with the stock MK III sound as well as others and would like to try something different. I would like a little more sweetness but with medium power. I don't need a lot since I'm set up in a small 10'x12' room, just a change of pace amp from the sweet little Mc225.


    Tiziano73

    Posts : 29
    Join date : 2012-09-11
    Location : Italy

    Re: Replacement driver board for MK III

    Post by Tiziano73 on Tue Mar 03, 2015 3:33 am

    MontanaWay wrote:
    Tiziano73 wrote:
    zx wrote:just concentrate on the power supply which I did......
    You put new caps in right.??..even if you go with a other frontend ......whats your B+???...If its over 500-550V like my 3pr are.....i have 125AC comeing from the wal here in Fl... you well wont to drop  it to about 480V thats what the amps were made to run at....for the best sound out these amps....
    Well sounds best to me.....
    Otheres can say on the sound of the new boards....the 6SN7 one look good to me....an a vary fair $$..if you dont think it sounds better than stock not out a lot .....i like the stock 6AN8-7199...one tube makes less noise.. so my ears say.... others ears may say diff....an thay can speaker for there self......hehe ....have fun with tubes.........

    Thanks for the site Bob......


    I am in agreement, i prefer stock boards with good 6AN8 matching (same triode current and same Gm on pentode). The best thing to do it's control the power supply.

    Tiziano.

    It is important to have a good, clean and steady power supply, no argument there. But that is, I feel, only about half way there. Updating the driver board, in my opinion, will make the biggest change in sound.
    To me, there is no comparison between the old driver circuit design to the updated Tubes4Hifi design, the latter being head and shoulder above the original. Some people prefer to keep a circuit as original as possible, and thats OK, but I feel that by doing that, you would not get the best sound out of your system. And don't forget, sound is extremely subjective as well!
    Like a lot of original/early Dynaco designs, it was a compromise, one of the main aims being saving $.
    For us, paying a little extra for two tubes and additional resistors etc is no big deal, but when you start talking about 100's even 1000's of kits, it makes a huge difference to the bottom line.

    So, if you have the $ to upgrade the driver board, do it.

    Sure! the original design was a little compromise but the reference at the time was McIntosh MC75 e Marantz Model 9 and the story say that it was a very good compromise.
    Now.... i'm sure that there are other driver circuit than the stock schematic but after we should see with oscilloscope and at the listening the difference between to make a true comparison.
    In my opinion New Dynakitparts Boards with metal resistors and matched 6AN8 NOS tubes are a good and cheap upgrade for an old dynakit that comes from ebay and a good idea it's chose also Dynakitparts Bias Balance Control Kit to achieve the best biasing of power tubes. This solution also keeps the original aspect that will certainly be useful in the future if you decide to sell it for a new power amplifier.

    It's only my opinion.

    Good listening with dynaco gear to everybody.

    Tiziano

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: Replacement driver board for MK III

    Post by zx on Tue Mar 03, 2015 9:30 am

    One more thing about the sound of the MC tube amps......
    as you may know the rave about the sound...has a lot to do with the way the Cathoides of the output tubes are ran thought the output tranfourmers...it lets the output tubes cathoids works part of the output.......in a feedback setup.....an as for the MC225 being one of the best sounding....like the 6an8/7199 driver can also work great........................hhscott an others used the 6an8/7199 that's good a nef for me..
    in Audio an other things in life....smaller/less...can be more...
    Just one mans O-pine......
    But the tubes4hifi ......boards look great an the $$ is right...I wont one of ea.....hehe
    ARC is about the only other Co. that uses there output tubes cathoides  in the output trasfourmers ........
    I don't care for there sound...I am more of a CJ guy...MC just makes some of the best transfourmer ever made....I have had Diyed tube amps with With MC output tranfourmers ....sound was vary close to the MC stock sound.......




    Thanks for the site Bob.....................
    Hehe An yes thay had cloth coverd wires.....

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