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    Prototype 125 watt monoblock tube amplifier KIT

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    xlr8

    Posts : 68
    Join date : 2010-02-09

    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by xlr8 on Mon Oct 11, 2010 10:03 am

    I was wondering if it would be just plain silly to optimize one of these for guitar duties? Reason I ask is because my buddy and I ran the line out of my little Fender Super Champ to a crown XLS 402 driving a cabinet loaded with 4 Celestion G12t-100's yesterday with great results, just without the overall body and tone of tubes. Just wondered...

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Mon Oct 11, 2010 10:21 am

    Hi,

    If you just change out the RCA input jack to a guitar input jack there is no reason why one M-125 could not be used as a guitar amp. With the two or four output tube alternative combined with the triode/pentode switch, the amp would give you a few power/tone options.

    I know at least two people who have built the VTA ST-70 from a kit with the primary intention of using the amp with their electric guitar.

    Bob

    tubehd4life

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    Join date : 2010-10-11

    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by tubehd4life on Mon Oct 11, 2010 8:31 pm

    Will these amps be ready for kit purchase before the new year? PLEASE!

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Mon Oct 11, 2010 9:04 pm

    tubehd4life wrote:Will these amps be ready for kit purchase before the new year? PLEASE!

    Hi,

    Yes - The production M-125 amp KITS should be ready by Dec 1, 2010 ... I will make a short post on this thread when they are ready ..

    Bob

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Wed Oct 13, 2010 4:00 pm

    I now have two production chassis. Photos below ... A couple of holes still have to be moved just a hair one way or the other but in general everything is where it should be now. Below is the front face, rear face and what the interior layout looks like.

    Bob






    Last edited by Bob Latino on Wed Oct 13, 2010 7:06 pm; edited 1 time in total

    Luddite

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Luddite on Wed Oct 13, 2010 6:19 pm

    That looks great, Bob. Of course, you might want to twist those quad cap locking tabs before doing any wiring! Wink

    Best Regards,
    Charlie

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Wed Oct 13, 2010 7:09 pm

    Hi Charlie,

    Yes - I had just temporarily dropped the quad cap in there and taped it on from the other side just to hold it for the photograph. Because you wanted those tabs locked in, however, I "digitally twisted" the tabs and changed the photo above.

    Bob

    Luddite

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Luddite on Wed Oct 13, 2010 9:37 pm

    Bob Latino wrote:Hi Charlie,

    Yes - I had just temporarily dropped the quad cap in there and taped it on from the other side just to hold it for the photograph. Because you wanted those tabs locked in, however, I "digitally twisted" the tabs and changed the photo above.

    Bob

    LOL...That's very clever, Bob! cheers

    Charlie

    Gregg357

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    Join date : 2010-10-15

    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Gregg357 on Fri Oct 15, 2010 7:17 pm

    Bob, Your work is impressive. I'm sold on either your ST-120 or these new mono blocks. I am new to tubes. This will be my first amp. I have no experience with building an amp. Am I foolish to make your mono blocks my first forray? Should I purchase a ST-120 assembled and tested, by you, from your lab? I feel the peace of mind of an expert build might be worth it. I'm drunk with the idea of 125W mono blocks, but with my craftsmanship I'm second guessing it. I would surely be excited to own a ST-120 instead. Thank you and sorry to highjack your thread. Gregg

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Fri Oct 15, 2010 7:36 pm

    Gregg357 wrote:Bob, Your work is impressive. I'm sold on either your ST-120 or these new mono blocks. I am new to tubes. This will be my first amp. I have no experience with building an amp. Am I foolish to make your mono blocks my first forray? Should I purchase a ST-120 assembled and tested, by you, from your lab? I feel the peace of mind of an expert build might be worth it. I'm drunk with the idea of 125W mono blocks, but with my craftsmanship I'm second guessing it. I would surely be excited to own a ST-120 instead. Thank you and sorry to highjack your thread. Gregg

    Hi Gregg,

    The monoblocks are even easier to put together than either the ST-70 or ST-120. The assembly manual for the M-125 is being written in detail for the beginner. I have had four people now build the ST-70 or ST-120 amp kit who have never even soldered before. Only one of the 4 needed a little help from me by Email. For the other 3 - they turned the amp on and it worked.

    You only have one channel on the M-125 amp instead of two which makes for a lot less wiring. The chassis on the M-125 is 10 X 12 inches and there are no real tight spots, cramped spaces etc.

    I won't be making up WIRED versions of the M-125. I just won't have the time with packing and arranging parts for 3 different KIT amps. The M-125 will only be available as a kit. Added on 1/3/13 > The M-125 amps are now available as wired amps. Check the link for more info > VTA M-125 monoblocks

    If you can solder and use simple hand tools (screwdriver, pliers, and a wire stripper/cutter) and solder with a $15 30 watt Radio Shack soldering pencil - you can do it. If you do run into an issue, I am here by Email or phone to help you out.

    Bob


    Last edited by Bob Latino on Thu Jan 03, 2013 9:50 pm; edited 2 times in total

    Gregg357

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Gregg357 on Fri Oct 15, 2010 7:52 pm

    Bob, Thanks for the quick reply. Are there sound quality or safety (fire) concerns with a poor wiring job? Gregg

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Fri Oct 15, 2010 8:06 pm

    Gregg357 wrote:Bob, Thanks for the quick reply. Are there sound quality or safety (fire) concerns with a poor wiring job? Gregg

    Hi Gregg,

    If you wire the amp the way it should be there should not be any issues. You get a "pictorial photograph" that comes with the kit that shows the location of every wire in the amp. You do the step and then check what you just did against the pictorial. If you made an error you will see it immediately. If you haven't soldered recently - maybe practice soldering on some old radio or old piece of electrical parts ..

    Bob

    Gregg357

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Gregg357 on Fri Oct 15, 2010 8:09 pm

    Bob, Thanks again. You can expect an email "about Dec 1st". Gregg

    Gregg357

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Gregg357 on Mon Oct 18, 2010 9:24 am

    Bob, I understand you are not supplying the tubes and WZ68 for the M-125 kit. In anticipation of Dec. deliveries and with my limited tube knowledge in mind, could you refer a couple honest internet tube dealers to do business with? I live on the Cape, if there might be any local to Massachusetts. Thanks, Gregg

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Mon Oct 18, 2010 9:46 am

    Hi Gregg,

    I don't know of any local tube suppliers here in Massachusetts... For the M-125 amp you will need FOUR KT88 or 6550 tubes (KT90, KT100 or KT120 also OK), 2 X 12BH7 (recommended) or 12AU7 driver tubes and 1 X Weber WZ68 copper cap for EACH amp of a stereo pair.

    The Weber WZ68 Copper cap is available directly from Weber. Link below ..

    Weber Copper Caps

    One online vendor that I know who is very reputable is Jim McShane. Link below.

    Jim McShane tubes

    Another is Jason Pang of NewquestSound who sells on Ebay. Link below ..

    Newquestsound on Ebay

    Another reliable seller on Ebay is "bnb_tubes". Link below ...

    BNB TUBES

    Bob

    davidness

    Posts : 39
    Join date : 2010-09-15

    Prototype 125-150 watt monoblock tube amplifier

    Post by davidness on Tue Oct 19, 2010 9:51 am

    Is there a difference between the 12BH7 and the 12BH7A, and which is better?


    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Tue Oct 19, 2010 10:05 am

    Hi,

    I believe that the "A" version is a later version of the tube designed for higher maximum plate voltages. Someone can correct me if you have any info other than this. If you have your choice get the "A" version.

    ElectroHarmonix makes an "A" version that is supposed to be a copy of the old GE gray plate. I am using four of them to test out the two monoblocks. Very good tubes ..

    Bob

    Gregg357

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    Join date : 2010-10-15

    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Gregg357 on Tue Oct 19, 2010 2:32 pm

    Bob,
    Am I correct, that given your two bias pins, that purchasing matched quads or even octets is unnecessary? But that it is advisable to purchase matched pairs of KT88's? Also, what is your opinion on 12bh7 tubes? I've read that matched sets on the board don't make an audible difference. Obviously, if they were matched, there would be the theoretical performance difference, however in practicality it produces little audible betterment. Thank you, Gregg.

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Tue Oct 19, 2010 2:50 pm

    Gregg357 wrote:Bob,
    Am I correct, that given your two bias pins, that purchasing matched quads or even octets is unnecessary? But that it is advisable to purchase matched pairs of KT88's? Also, what is your opinion on 12bh7 tubes? I've read that matched sets on the board don't make an audible difference. Obviously, if they were matched, there would be the theoretical performance difference, however in practicality it produces little audible betterment. Thank you, Gregg.

    Hi Gregg,

    If you were to run the amp with FOUR output tubes I recommend a matched quad. If you run the amp with just TWO output tubes only a matched pair is really necessary.

    If you have eight output tubes - four per monoblock then the matched quad of one amp doesn't have to match the matched quad of the other amp. There are, however, tube vendors online that will match up all eight for you if you ask them. On Ebay I have seen vendors advertise a matched "OCTET" of KT88's or 6550 tubes.

    That said, I have run both amps with some older mismatched KT88 tubes. I biased them up, played the amps and honestly couldn't hear any real difference in the sound. Although you may have purchased some matched tubes, sometime down the road after 1000+ hours of play the tubes can and will wear differently. Two years of playing and your matched set of tubes is probably not well matched anymore.

    On the driver tubes IMHO it is less important that the two 12BH7 (or 12BH7A) driver tubes be matched. That said, it may be worth it to purchase from a specialty vendor one "low noise" tube for the front 12BH7. On the M-125 the front tube is the initial voltage amplifier and is much more sensitive to noise/hum etc. than the rear 12BH7 which is the phase splitter/phase inverter tube. One of the four ElectroHarmonix 12BH7A tubes that I am testing these amps with was a little noisy. All I did was swap the tubes front to back on that one amp and the noise went away.

    Bob

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Thu Oct 21, 2010 1:38 pm



    I took the M-125's to the larger downstairs system that I have that uses two Magnepan 3.6R planar magnetic speakers. These speakers are very inefficient with a "stated" efficiency of 85 dB. Some tests of these speakers indicate though that they may be more like 83 or 84 dB efficient. The load these speakers present to the amp is also more difficult to drive than most box speakers. I normally use a 500 WPC Bryston SS amp to run these speakers because they eat up a lot of power.

    For this test I also ran the M-125's with four Tung-Sol KT120's per amp. The KT120's draw more current and put a greater strain on the amp's power supply. I am also still experimenting with the Mullard GZ33 tube rectifier as seen in the photo. Later I swapped over to the Weber WZ68 SS rectifier and I still think it does a better job at driving the amp - especially as the volume goes up.

    I placed the amps right on floor and hitched them up to the BAT VK30-SE preamp and played the amps for 3 hours. Things that I noticed ..

    1. The ribbon tweeter on the Maggie 3.6 brought out a little more top end detail than my upstairs Tyler Acoustic Linbook II speakers. The Tylers use the Seas Millenium tweeter and it is a very good tweeter but the ribbon on the Maggie is a little better.

    2. At normal listening levels the M-125 kept right up with then Bryston amp. When I cranked it up to pretty loud volumes you could tell that the M-125 was straining a little. The Bryston has 4 times the power which equates to 6 dB more headroom on the Bryston.

    3. At normal listening levels the bass of the M-125 amp was as good as the Bryston amp. Playing some of the same tunes I noticed a tiny bit more bass on the Maggies over the smaller Tyler speakers. The Maggies are - 3dB @ 34 Hz and the Tylers have a -3 dB at maybe 38 Hz. Very close on this one.

    4. I thought that soundstaging was a little wider and more "pinpoint" on the M-125's. Vocals and solo acoustic instruments IMHO sounded more like the real thing. Miles Davis' trumpet sounded more like a real trumpet.

    Bob


    Last edited by Bob Latino on Sun Oct 24, 2010 4:56 pm; edited 1 time in total

    River

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    Join date : 2010-07-26

    Slippery Slope.

    Post by River on Sun Oct 24, 2010 3:58 pm

    Hi Bob,
    I am new to DIY valve amps - and have just ordered your SL120 kit.

    (Talk about a slippery slope,.... I am already planning the upgrade. bounce )
    The M-125s look awesome. Is it possible to make the chassis 'handed' ?
    Regards
    River.


    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Sun Oct 24, 2010 4:54 pm

    River wrote:Hi Bob,
    I am new to DIY valve amps - and have just ordered your SL120 kit.

    (Talk about a slippery slope,.... I am already planning the upgrade. bounce )
    The M-125s look awesome. Is it possible to make the chassis 'handed' ?
    Regards
    River.


    Hi River,

    To add "handles" to the M-125 amp would add to its cost. I am not sure that people would want to pay $20+(?) for matching stainless steel handles ..

    You do bring up something though that many tube amp users probably already know but if some don't ... > You should always pick up and carry a tube amplifier from the transformer side of the amp. Usually the transformers are on the rear of the amp. With the transformers usually on one side, the amp's center of gravity is pretty far "off center". While I haven't done it myself, I have heard stories of neophyte tube amp owners picking the amp up from the front and having the amp flip out of their hands onto the floor because the amp's center of gravity was so off center.

    Bob

    anbitet66

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by anbitet66 on Sun Oct 24, 2010 6:52 pm

    Bob,

    I think he meant "Right handed" and "Left handed". As in mirror images of each other.

    Bob Latino
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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by Bob Latino on Sun Oct 24, 2010 7:16 pm

    anbitet66 wrote:Bob,

    I think he meant "Right handed" and "Left handed". As in mirror images of each other.

    OK - Sorry for my misunderstanding of the word "handed" ... Thank you for clearing this up ..

    Where I have the chassis made they give me a better price the more chassis that I order. There would be a noticeable difference in price in the cost of 50 "left" and 50 "right" chassis as compared to 100 of either style. In a kit amp such as the M-125, I am not sure whether the average kit builder would really care that the two chassis be mirror images. Another issue is that some of the build instructions would have to be changed since now (for instance) the left side choke would now become the right side choke on a mirror chassis and vice versa. In the manual there are also references in some instructions to the left and right sides of the chassis. IMHO this *could* cause confusion on the part of the kit builder. In short, the amps won't be available as mirror copies of each other.

    Bob

    dynacophil

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    Re: Prototype 125 watt monoblock tube amplifier KIT

    Post by dynacophil on Sun Oct 31, 2010 10:47 am

    how much will the fish be...? I like what I see...

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