Sca35 tone controls

[denny9167]

In the process of rebuilding a Dynaco SCA-35 w new boards and transformers, I was going to do away with the tone controls, but decided to keep as close to the original design as I could,but have decided to at least to either re-build the PEC's or go with a different passive design altogether,below I have a design I'm considering that has a flatter response,and fewer controls,I'm eliminating all e switches except for the power of course,but was curious about the source and load using the modified tone control,thanks for any advice.

 

[TBL]

Sorry I am not advising on this one coz I too am doing an SCA-35 project without too much clue.

I am contemplating using an EICO HF-85 tone circuit on the SCA-35. Some ppl on the EICO discussion thread pointed out that the HF-85 performs better than SCA-35 as an integrated. But on another weblink, where someone did a shoot-out on output transformers' performance from one amp to another, and on modern productions (e.g. One Electron) it was found that the SCA-35's OPTs are far batter than the EICO HF-85's.

I got the impression that the 85 performs better coz, arguably, it has a superior active tone circuit driven by one 12AX7 tube. I have to agree. Now I have an HF-85 (which is virtually the preamp part in the HF-81), an HF-1, and an SCA-35. Sadlyt, the worst sound really comes from the Dynaco SCA-35 and it has insuficient gain even on the line amp.

But if you aim at rebuilding it to original spec and topology, forget about my suggestion.

 

[denny9167]

Sorry I am not advising on this one coz I too am doing an SCA-35 project without too much clue.

I am contemplating using an EICO HF-85 tone circuit on the SCA-35. Some ppl on the EICO discussion thread pointed out that the HF-85 performs better than SCA-35 as an integrated. But on another weblink, where someone did a shoot-out on output transformers' performance from one amp to another, and on modern productions (e.g. One Electron) it was found that the SCA-35's OPTs are far batter than the EICO HF-85's.

I got the impression that the 85 performs better coz, arguably, it has a superior active tone circuit driven by one 12AX7 tube. I have to agree. Now I have an HF-85 (which is virtually the preamp part in the HF-81), an HF-1, and an SCA-35. Sadlyt, the worst sound really comes from the Dynaco SCA-35 and it has insuficient gain even on the line amp.

But if you aim at rebuilding it to original spec and topology, forget about my suggestion.

Appreciated anyway, I will check that schematic out.

 

[Triodethom]

Sorry I am not advising on this one coz I too am doing an SCA-35 project without too much clue.

I am contemplating using an EICO HF-85 tone circuit on the SCA-35. Some ppl on the EICO discussion thread pointed out that the HF-85 performs better than SCA-35 as an integrated. But on another weblink, where someone did a shoot-out on output transformers' performance from one amp to another, and on modern productions (e.g. One Electron) it was found that the SCA-35's OPTs are far batter than the EICO HF-85's.

I got the impression that the 85 performs better coz, arguably, it has a superior active tone circuit driven by one 12AX7 tube. I have to agree. Now I have an HF-85 (which is virtually the preamp part in the HF-81), an HF-1, and an SCA-35. Sadlyt, the worst sound really comes from the Dynaco SCA-35 and it has insuficient gain even on the line amp.

But if you aim at rebuilding it to original spec and topology, forget about my suggestion.

HF 85 has a pentode output and the SCA-35
is an ultra-linear . So no screen taps on the HF-85 ones. I my self like the el84 run in pentode over ultra- linear . The one electron transformer are very good much better the the things Hafler used.

 

[rmyauck]

One Electron transformers are SE so you can't directly compare.

 

[denny9167]

How did we go from discussing tone controls to OPT's? Can we get back on topic here?

 

[rmyauck]

I'm just ccorrecting the mistake in Trio's reply. Defending the Z-565 trans!

Dave Gillespie whom knows the SCA-35 like the back of his hands may be able to help you. He has the EFB mod on the Tronola site and diytube sites. He also posts on AK.

 

[denny9167]

I'm just ccorrecting the mistake in Trio's reply. Defending the Z-565 trans!

Dave Gillespie whom knows the SCA-35 like the back of his hands may be able to help you. He has the EFB mod on the Tronola site and diytube sites. He also posts on AK.

I have read the article by Dave on the SCA35,the EFB circuit seems like a possible route also, and That's quite alright. I understand.

I think I have decided to go with new PEC's following Dynaco's circuit scheme, the pots are still in good shape, otherwise I would have to redo the driver input circuit to allow for less gain.