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I have 2 Dynaco mkIII's I am restoring. One has a bad power x-former. I need input on replacing X-formers. Should I replace both the power and the audio output transformers so they would be matched? Just the power? I haven't dug into the 2nd amp, if the x-formers on that component are good should I leave well enough alone? Or, again to have a matched pair should I replace them also. I'm interested to what everyone has to say.
Thanks,
Gronboi
RSTucker
Follow Ups:
I restored Mark III's using Triode's Poseidon boards, but it has been a while. One thing I remembered was the voltage exceeds the PS cap voltage at turn on before the tubes start conducting. A simple fix are thermsitors, if you search Dynako Mark III and thermistor it should come up.
The power transformers on Dynaco products were stressed to the limit of reliability. These products were built to a price point and that mandated certain compromises in the components. Those compromises did not extend to the output transformers, fortunately. If I were rebuilding a pair of Mk. IIIs I would, without question, replace the power transformers on both monoblocks with modern parts. The P782 S replacement power transformer from Triode Electronics will run cooler than the stock transformer and has greater current capacity than the original Dynaco part making for greater reliability and greater power on dynamic music passages.
With respect to the driver board on the Mk III, it too should be replaced, not just for reliability and practicality, but for superior sound. The original circuit used a 6AN8 which is a combined pentode/triode in the same bottle. The 6AN8 is an obsolete part and is a serious compromise to the sound quality of the amplifier. Triode Electronics makes a driver board to replace the original that allows the builder to select separate pentode and triode tubes to perform the exact same function in the same circuit topology. The only difference is that instead of being confined to the obsolete triode/pentode, the builder has a wide selection of current production tubes to fulfill the function of the obsolete tube.
Finally, if rebuilding a Mk III I would address the power supply. Again, these products were engineered to a price point, but also in the last 50 years there have been dramatic improvements in the quality of capacitors. What this means is that a builder can use higher quality parts, but also can fit a much improved filter network into the power supply. Once again Triode Electronics and others come to the rescue with uprated filter capacitor boards engineered to improve the performance of the Mk III and make it more reliable.
If all these updates and refinements to the original Dynaco Mk. III are implemented the user will have a dramatic improvement in sound quality allowing these ancient relics to outperform many of today's high end products.
Thanks so much Palustris. Exactly the kind of input that I need.
Rodney
RSTucker
I recommend replacing both power transformers. The original ones have a 115V rated primary causing filament and B+ overvoltage at todays voltages, whereas the new replacements are rated 120V primary. Also, be ready to give the new PTs a lengthy break in period. After replacing mine I was struggling for a long period to try and find why the amps were hard sounding. After a couple of hundred hours they smoothed out and all is wonderful.
Jack
I get 124 volts on the line typically. I had an older Perreau amplifier once that I realized was overvolted. When you design for other countries, maybe even, third-world countries, I suspect that 115 volts is more normal.
not only is there absolutely no reason to replace the output, but an original Dyna output transformer is valued more highly by the market than a reproduction. Simply replace the shorted power transformer and adjust all voltages in both amps so that they are within 10-20% of each other. Then call it a day. If your amp with the original trannies uses a gray one then paint the reproduction to match, or just paint both with a new coat of gray paint.
Edits: 04/23/15 04/23/15
First of all - Great audio pieces. I used them for years at one time. Unfortunately I sold them off at a moment of anger and frustration in my audio dazes. One of the "bad" moves I made in audio.
charles
Welcome! Gronboi,
post this request in the 'tubes' forum as well.
Why would the power transformer have to be 'matched' to the output transformers??
I suggest that you just replace the bad power transformer with a known good one (maybe from a salvaged Dynaco transformer).
Are these monoblocks? Then, I suggest matching the left to the right, certainly.
First off, you may get more responses at the Tubes or Tubes/DIY forums. If it were me, I'd replace both of the power trannys for starters so you're starting out on equal terms. I'd leave the output trannys as is provided they're in good shape. As I've said however, best consult the experts over at the tube related forums.
...the Dynaco Doctor
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