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    WOW, what a difference

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    mcgyver74

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    WOW, what a difference

    Post by mcgyver74 on Wed Apr 19, 2017 9:18 pm

    So after a productive discussion with Jim McShane I decided to make some small upgrades in the Tubes...

    We decided.

    1) Leave the 6550 Outputs alone for now, they really need to break in.
    2) Replace the 3 Driver tubes as follows.
    a. In the left/right sockets a matched pair if 12AX7LP's (Sovtek)
    b. In the center socket a 12BH7 (Sylvania)
    3) Replace the Chinese Rectifier with a Genelex re-issue GZ34


    Tonight I received the new tubes, and after doing some work on the amp that needed to be done (replacing a tube socket I bungled with solder Smile ) I popped in the new tubes, re-biased the amp to .500 all around and "put the needle on da record" Smile

    At which point my jaw dropped, it was noticeably stronger and clearer, more well defined.... Even my wife looked up and said "what did you do, that sounds way better"

    Just WOW Smile

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    Kentley

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    Re: WOW, what a difference

    Post by Kentley on Wed Apr 19, 2017 10:09 pm

    Are you certain about the 12AX7s? I'm not sure how much it matters, as they are (mere?) phase inverters, but these are specified as 12AU7s.
    Undoubtedly, the improvement can be traced to the 12BH7. Sylvania made some real good ones. FYI my personal fave is the old TungSol. Simply the best to my ears.

    Dogstar

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    Join date : 2014-06-23

    Re: WOW, what a difference

    Post by Dogstar on Thu Apr 20, 2017 5:52 am

    I haven't experimented with tubes other that 12AU7's in my VTA ST-120 but after building my Akido Tube Buffer I was given a few 12AX7's to play with. I tried them in the tube buffer and they really made the sound open up. They also glowed a lot brighter so I imagine their life won't be as long. The AE-2 was developed to be used with 12AU7's so I switched back to those after trying them out.

    Mcgyver74 do you have an ST-70 that you put the 12AX7's and 12BH7 in?


    Last edited by Dogstar on Thu Apr 20, 2017 2:08 pm; edited 1 time in total

    mcgyver74

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    Re: WOW, what a difference

    Post by mcgyver74 on Thu Apr 20, 2017 8:07 am

    I have an ST-120, and they not only look good but there is a noticeable improvement in the sound Smile

    I still need to get this sucker on a signal analyzer and see what THD is etc...but so far very happy. Smile

    Just a few issues to track down (One of my tubes is running a lot "cooler" then the others, I need to check voltages tonight) And I still need to install the Varistor on the power line..(I had ordered a terminal lug set to do that but accidentally ordered one too small LOL )

    wildiowa

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    Re: WOW, what a difference

    Post by wildiowa on Thu Apr 20, 2017 8:42 am

    I will probably be torn up greatly on this from a tech standpoint but it seems we went through the 12ax7/12au7/12at7 sequence to tame a wild guitar amp that had too much juice in the preamp stage. The Fender Deville came stock with a 12ax7 that was way too hot, as you reached maximum volume at like 3 or 4 on the gain and nothing much past that. It was designed to hook kids playing it in a music store and made them think, if it's THIS loud at 4, it will SCREAM at 10 when I play on stage! Not so. It topped out early. So, we were advised to use a 12au7. Supposedly, this cut the gain approximately in half from the 12ax7. You could also go with a 12at7, which supposedly cut the gain on half from the 12au7. All very confusing to me, but it did seem we were able to get more range out of the volume control using these different tubes. Not sure how this applies to the Dynas in this case but if each cuts the gain somehow this would explain the differences in volume tone etc...just adding to the conversation here....IA.
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    deepee99

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    Re: WOW, what a difference

    Post by deepee99 on Thu Apr 20, 2017 10:56 am

    Kentley wrote:Are you certain about the 12AX7s? I'm not sure how much it matters, as they are  (mere?) phase inverters, but these are specified as 12AU7s.
    Undoubtedly, the improvement can be traced to the 12BH7. Sylvania made some real good ones. FYI my personal fave is the old TungSol. Simply the best to my ears.

    The 12BH7/A is definitely the "flavour" of the ST-120, but don't skimp on the side tubes, either. Since I haven't picked a fight with Kentley lately, I gotta say the NOS Sylvanias Bob supplied for the front tubes of the M-125s and centre tube of the ST-120 are the cat's meow. If you've got noval drivers, have a stash on hand. Not because they're short-lived, but because there's no such thing as too many tubes.

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    sKiZo

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    Re: WOW, what a difference

    Post by sKiZo on Thu Apr 20, 2017 11:18 am

    Color me confused ... we're saying the 12AX7 is a drop in substitute for a 12AU7?

    - much lower plate dissipation
    - much higher gain factor

    The fact that it can apparently improve sound in an ST120 with no mods is baffling at best. Then again, a 12BH7 isn't exactly to spec for these boxes either, and maybe there's some happy accidental kinda synergy going on that makes it work.

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    corndog71

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    Re: WOW, what a difference

    Post by corndog71 on Thu Apr 20, 2017 11:24 am

    I keep a handy list of the mu or amplification factor of various tubes.

    12BH7 - 16.5
    12AU7 - 17
    6CG7, 6FQ7 - 20
    6922, 6DJ8 - 33
    6BQ7 - 35
    12AY7 - 40
    5965 - 47
    12AT7 - 60
    5751 - 70
    12AX7 - 100

    This is useful for voltage amplification stages but not so much for cathode follower or phase splitter stages. This isn't to say all of these are interchangeable either. The 6XXX tubes have different heater connections than the 12XXX tubes.

    mcgyver74

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    Re: WOW, what a difference

    Post by mcgyver74 on Thu Apr 20, 2017 11:44 am

    Some interesting stuff here, I am trying to understand exactly what I did here (From an electronic perspective, I know what I physically did). I was just following Jim's advice here and noticed a great improvement.

    It's possible that my wife's perception of the improvement is synonymous effect people perceive when they push the "Loudness" button on their stereos since she doesn't understand audio, she just likes music, but in my case I don't think so, Yes it was louder at lower volume levels, and I suspect if I hook it to a scope it would be pushed into clipping much sooner but as I don't ever crank the volume up (I live in apartment) that's not a problem. But in my case I am hearing a difference on specific areas..

    1) Bass is more pronounced and feels "tighter", a bass drum has a more pronounced "thump"
    2) Sibilants are clearer
    3) HighHat "clink" is a much more defined sound...

    Etc...

    But now that I am reading some responses, I am wondering if my uneven output tube heat could be because of this.

    When I get home I'll pull it apart and measure the heater/Plate/Grid voltages across all 4 and see if they are balanced....


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    Bob Latino
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    Re: WOW, what a difference

    Post by Bob Latino on Thu Apr 20, 2017 11:46 am

    Just a word to the wise .. The only recommended noval (9 pin) driver tubes for the VTA amps are 12AU7, 12BH7, 5963, 5814, 6189 and the Mullard CV4003. 12AT7 and 12AX7 tubes, although pin compatible, have different (higher) gain characteristics than 12AU7 type tubes. Yes - You might insert one into one of the VTA amps and you might get music out but the resistor set on the driver circuit is optimized for the lower gain 12AU7 type tubes.

    I do not recommend using 12AX7, 12AT7, 5751 or any other noval tubes that have higher gain characteristics than the 12AU7 in any of the VTA amps.

    Bob
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    j beede

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    Location : California

    Re: WOW, what a difference

    Post by j beede on Thu Apr 20, 2017 11:51 am

    Which tube is running cool? How are you measuring its temperature?
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    deepee99

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    Re: WOW, what a difference

    Post by deepee99 on Thu Apr 20, 2017 12:52 pm

    j beede wrote:Which tube is running cool? How are you measuring its temperature?
    Get a cheap little hand-held temp sensor.
    https://www.amazon.com/Etekcity-Lasergrip-774-Non-contact-Thermometer/dp/B00837ZGRY/ref=sr_1_5?ie=UTF8&qid=1492707107&sr=8-5&keywords=digital+temperature+sensor

    mcgyver74

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    Re: WOW, what a difference

    Post by mcgyver74 on Thu Apr 20, 2017 1:02 pm

    j beede wrote:Which tube is running cool? How are you measuring its temperature?

    The right front 6550, and I have an infra thermometer Smile
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    j beede

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    Re: WOW, what a difference

    Post by j beede on Thu Apr 20, 2017 1:20 pm

    mcgyver74 wrote:
    j beede wrote:Which tube is running cool? How are you measuring its temperature?

    The right front 6550,  and I have an infra thermometer Smile  

    That's why I asked... IR thermometers are okay for measuring solid/opaque surfaces but may give curious results when pointed at glass enclosed vacuum tubes for obvious reasons. FYI: I get reliable and repeatable results when I use a thermocouple-based pyrometer to measure tube temperatures.

    How different is the temp of the "cool" tube? Proximity to the power transformer or tube rectifier (if you are using one) can make a measurable difference.

    ...j
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    peterh

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    Re: WOW, what a difference

    Post by peterh on Thu Apr 20, 2017 1:27 pm

    mcgyver74 wrote:
    j beede wrote:Which tube is running cool? How are you measuring its temperature?

    The right front 6550,  and I have an infra thermometer :)  
    A thermometer will report the glass temp. It might or might not cooncidence
    will internal heating.
    Internal losses can be measured via the cathode current aka bias. Correct bias
    is what to aim for.

    mcgyver74

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    Location : Jersey City, NJ

    Re: WOW, what a difference

    Post by mcgyver74 on Thu Apr 20, 2017 1:31 pm

    Ok I'll take a squiz tonight with a thermocouple (I actually have one Smile ) I'm also planning to measure the voltages at the tubes to ensure they are what I should be seeing.

    Also I re-biased the amp last night before the temp measure, so I know they are close to dead on .500 (Within 0.002 v anyway)

    Jim McShane

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    Re: WOW, what a difference

    Post by Jim McShane on Thu Apr 20, 2017 1:46 pm

    mcgyver74 wrote:So after a productive discussion with Jim McShane I decided to make some small upgrades in the Tubes...

    We decided.

    1) Leave the 6550 Outputs alone for now,  they really need to break in.
    2) Replace the 3 Driver tubes as follows.
                a. In the left/right sockets a matched pair if 12AX7LP's (Sovtek)
                b. In the center socket a 12BH7 (Sylvania)
    3) Replace the Chinese Rectifier with a Genelex re-issue GZ34


    Tonight I received the new tubes, and after doing some work on the amp that needed to be done (replacing a tube socket I bungled with solder Smile ) I popped in the new tubes,  re-biased the amp to .500 all around and "put the needle on da record" Smile

    At which point my jaw dropped, it was noticeably stronger and clearer, more well defined....  Even my wife looked up and said "what did you do, that sounds way better"

    Just WOW Smile



    I need to clarify a couple things here...

    1. The 12AX7 tubes I sent were 12AX7LPS, not 12AX7LP. LPS stands for "long plate, spiral" (meaning spiral wound hum reducing heater construction).

    2. I did NOT send the 12AX7s for use in an amp. On my invoice it said "12AX7LPS - Sovtek matched/balanced/low noise tube pair for phono". These tubes were intended for a Pro-Ject phono stage. I'm not sure how they ended up where they did.

    Just so Bob and everyone else knows I did not recommend them for a VTA amp. It looks like some confusion was at work!


    Last edited by Jim McShane on Thu Apr 20, 2017 5:26 pm; edited 1 time in total
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    arledgsc

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    Re: WOW, what a difference

    Post by arledgsc on Thu Apr 20, 2017 1:59 pm

    In circuit a 12AX7 will have about 10dB more gain (10x voltage gain) than the 12AU7.  But please consider that everything will get amplified including noise.  With no input you will have a 10dB rise in your noise floor with a 12AX7.

    I had the same issue in reverse with an 18-watt Marshall type guitar amp.  Too much gain with 12AX7 cathode follower and substituting a 12AU7 gave the amp more control and lowered noise to boot.
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    j beede

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    Re: WOW, what a difference

    Post by j beede on Thu Apr 20, 2017 2:01 pm

    I wonder what replacing 12AU7 with 12AX7 does to the VTA amp's frequency response. I can guess based on the observed "improvements" in bass output, "thump", and exaggerated treble.
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    sKiZo

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    Re: WOW, what a difference

    Post by sKiZo on Thu Apr 20, 2017 2:04 pm

    Bob Latino wrote:12AT7 and 12AX7 tubes, although pin compatible, have different (higher) gain characteristics than 12AU7 type tubes. Yes - You might insert one into one of the VTA amps and you might get music out but the resistor set on the driver circuit is optimized for the lower gain 12AU7 type tubes.


    So ... we're talking circuit mods to get it right, as I expected. I'd be concerned about long term damage to the components downstream of the tube. As stated earlier, amplification factor isn't the only major excursion when comparing ...

    Also, I wouldn't expect a resistor swap at the R38 jumper to do the job properly. I've seen boards optimized for the 12BH7, and that was a lot more complex than that, and you lose a lot of flexibility when it comes to swapping for other "compatible" tube types in the family.

    ** I put compatible in quotes, because it's worth remembering that many of the tubes we use for audio were never intended for home audio use ... we just got lucky. ;-}
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    sKiZo

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    Re: WOW, what a difference

    Post by sKiZo on Thu Apr 20, 2017 2:13 pm

    Jim McShane wrote:
    I need to clarify a couple things here...

    1. The 12AX7 tubes I sent were 12AX7LPS, not 12AX7LP. LPS stands for "long plate, spiral" (meaning spiral wound hum reducing heater construction).


    I'll vouch for the LPS spiral wound being the sh!t for tube positions that are more prone to hum. I've got an Eico HF series mono amp here that will do three part harmony with a standard tube in the lead driver position ... dead quiet with a Sovtek 12AX7LPS in place.


    We now return control of your television set. pirat

    mcgyver74

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    Re: WOW, what a difference

    Post by mcgyver74 on Thu Apr 20, 2017 3:17 pm

    Jim McShane wrote:

    I need to clarify a couple things here...

    1. The 12AX7 tubes I sent were 12AX7LPS, not 12AX7LP. LPS stands for "long plate, spiral" (meaning spiral wound hum reducing heater construction).

    2. I did NOT send the 12AX7s for use in an amp. On my invoice it said "12AX7LPS - Sovtek matched/balanced/low noise tube pair for phono". These tubes were intended for a Fisher receiver phono stage. I'm not sure how they ended up where they did.

    Just so Bob and everyone else knows I did not recommend them for a VTA amp. It looks like some confusion was at work!


    So I have the wrong tubes???? (DIdn't mean to start a Poopstorm here Sad )

    mcgyver74

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    Re: WOW, what a difference

    Post by mcgyver74 on Thu Apr 20, 2017 5:06 pm

    OK
    So I went back and reviewed my emails.

    I had asked for the 12AX7's for my PHONO stage and I like a complete ID10T put them in the amp.

    I will be putting the 12ax7's into the Phonostage when i get home and restoring the 12au7's to their rightful place! (Leaving the 12bh7 in the center position)

    DOH!!! (I feel like a dope!!!)
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    sKiZo

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    Re: WOW, what a difference

    Post by sKiZo on Thu Apr 20, 2017 5:19 pm

    dOHp! of the Day!

    (Hey, that's MY job!)

    PS ... can't wait to hear your immediate impressions after you get the right tubes back in the amp.

    mcgyver74

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    Re: WOW, what a difference

    Post by mcgyver74 on Thu Apr 20, 2017 11:07 pm

    Well I put the 12AU7's back in and put the 12BH7 in the center socket (Still trying to figure out what that socket does)

    The amp still sounds amazing, not as "crisp" as it did with the 12ax7 but it's a noticeable improvement over the 12au7 in the center socket (I swapped back and forth to see...well after a few minute cool down anyway Smile ) the 12bh7 was def a good improvement.

    now I need to get these 12ax7's into my phono stage but I would like to find out WHO designed this pre and freaking smack them..It's a Project tube box ds and not only are the tubes sunk way down inside the chassis they have a heatsink on them that is the exact size of the holes they go in, so I cannot figure out for the life of me how to get these puppies out.... Sad

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