Hello,
I own 2 wyetech Topaz amplifiers, both stereo. The first one I got was based around the 572-10 output tube, after 10 years I blew an output transformer. This lead to Roger (amp designer, since passed away) telling me about a 211 topaz with the same issue as mine, a bad output transformer. I acquired it and Roger thought it best to take my good 572 output transformer and move it to the 211 chassis as the 211 sounds better and it is a much more long term reliable tube. Last week I opened the 572 chassis to look at the circuit and noticed that he changed the HV PSU for even better filtration and really made some very positive changes on the 572 tube filament circuit adding much more filtration. In fact on my current 211 filament circuit I measure 52.7 mVac at the filaments and when I fired up the filament transformer for the 572 I measured 3.3mVac at the filament. Hence I feel converting the 572B amp to a 211 amp is a worthwhile project. I am skilled as to physically working on this amp and very careful around the very high B+ and Driver tubes PSU's. I am NOT a knowledgeable tech, just a experienced hobbyist.
Looking at the circuits of the 2 amps, other than the HV PSU circuit, the circuits are pretty close to each other and the HV of the 572 only differs in that he used 3 large ASC propylene in oil caps vs. 6 solen metalized polypropylene caps in the 211 HV supply. Both amps put 1200Vdc on the B+ line, both amps use the same 10K primary output transformers, both amps put 450Vdc on the 6bx7 driver tube and 400 Vdc on the 6sn7 input tube. The input/output board components are almost exactly the same for both amps with only a few minor changes that should not matter, I believe. (bypass cap of 1uF vs .53uF, bypassing the 470uF cap), 470uF cap on the cathode of the 572 vs 500uF on the 211, 200K resistor from input to ground on 572B and 79K resistor in same spot for 211 amp.
So to change this amp from a 572 to 211 amp I think all I would really need to do is 1) change the power triodes filament toroidal transformer to one that can supply 10Vdc and 3.5A on the filaments of the 211 tube vs. 6.3 Vdc and 4A for the 572 filaments. 2) change the power tube sockets from 572 to 211 tubes.
I will also need 2 new output transformers for this amp, without going crazy cost wise I am thinking 10K transformers from either Hammond or Edcor. The amps originally had audio note uk transformers. Wyetech changed the output transformers on his Ruby amps (created after my topaz amps) to Hammond so I'll probably go that route.
The serial # of my current 211 amp is 9, the 572 amp is 28. Based on my observations Roger learned more about PSU circuits as he built amps the 028 has a better PSU circuit than 009. If the conversion works as I expect then some day I may pull the uk audionote output transformers from the #9 211 amp to the now converted #028 amp. For ultimate sonic bliss.
Am I missing anything in my conversion?
I own 2 wyetech Topaz amplifiers, both stereo. The first one I got was based around the 572-10 output tube, after 10 years I blew an output transformer. This lead to Roger (amp designer, since passed away) telling me about a 211 topaz with the same issue as mine, a bad output transformer. I acquired it and Roger thought it best to take my good 572 output transformer and move it to the 211 chassis as the 211 sounds better and it is a much more long term reliable tube. Last week I opened the 572 chassis to look at the circuit and noticed that he changed the HV PSU for even better filtration and really made some very positive changes on the 572 tube filament circuit adding much more filtration. In fact on my current 211 filament circuit I measure 52.7 mVac at the filaments and when I fired up the filament transformer for the 572 I measured 3.3mVac at the filament. Hence I feel converting the 572B amp to a 211 amp is a worthwhile project. I am skilled as to physically working on this amp and very careful around the very high B+ and Driver tubes PSU's. I am NOT a knowledgeable tech, just a experienced hobbyist.
Looking at the circuits of the 2 amps, other than the HV PSU circuit, the circuits are pretty close to each other and the HV of the 572 only differs in that he used 3 large ASC propylene in oil caps vs. 6 solen metalized polypropylene caps in the 211 HV supply. Both amps put 1200Vdc on the B+ line, both amps use the same 10K primary output transformers, both amps put 450Vdc on the 6bx7 driver tube and 400 Vdc on the 6sn7 input tube. The input/output board components are almost exactly the same for both amps with only a few minor changes that should not matter, I believe. (bypass cap of 1uF vs .53uF, bypassing the 470uF cap), 470uF cap on the cathode of the 572 vs 500uF on the 211, 200K resistor from input to ground on 572B and 79K resistor in same spot for 211 amp.
So to change this amp from a 572 to 211 amp I think all I would really need to do is 1) change the power triodes filament toroidal transformer to one that can supply 10Vdc and 3.5A on the filaments of the 211 tube vs. 6.3 Vdc and 4A for the 572 filaments. 2) change the power tube sockets from 572 to 211 tubes.
I will also need 2 new output transformers for this amp, without going crazy cost wise I am thinking 10K transformers from either Hammond or Edcor. The amps originally had audio note uk transformers. Wyetech changed the output transformers on his Ruby amps (created after my topaz amps) to Hammond so I'll probably go that route.
The serial # of my current 211 amp is 9, the 572 amp is 28. Based on my observations Roger learned more about PSU circuits as he built amps the 028 has a better PSU circuit than 009. If the conversion works as I expect then some day I may pull the uk audionote output transformers from the #9 211 amp to the now converted #028 amp. For ultimate sonic bliss.
Am I missing anything in my conversion?
This project is to create one working amp out if the two chassis? Is the rewinding of the OPT not an option?
No, that was the intent when I got first the 211 chassis, it was missing its bad transformer. Roger suggested I take my good 572 transformer and move it to the 211 chassis. Thus making 1 working amp from 2 chassis. Now I would like to get the 572 chassis working, and convert it to a 211 based amp. I only have 1 bad audio note uk transformer so rewinding, if it can be done as they don't make OT's anymore, does not solve my issue of needing 2 OT transformers for this project.
Type 211 can really benefit from a Rod Coleman type filament supply. It requires some space and some airflow, but you'll need to make some kind of new supply anyway. Worth doing, if practical.
All good fortune,
Chris
All good fortune,
Chris
Thank you I'll look into that, first glance looks very interesting. Roger (amps designer, now deceased) for the ruby line used LM78xx regulators for the filaments of the 300B tubes. I measured 3.3 mVac at the filament of the 572, but with a good regulator it would be well below that as well.
The Coleman regulators are different from conventional voltage regulators in that they present a high impedance source to the filament, removing themselves from the signal path. They also provide automatic current limiting, for slowed cold startup. They do require space and airflow though, and considerable voltage overhead. For type 211 they are doable if not easy.
All good fortune,
Chris
All good fortune,
Chris