• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Sca35 tone controls

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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.
 

Attachments

  • image.jpg
    image.jpg
    42.8 KB · Views: 267

TBL

Member
2012-02-13 2:44 pm
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.
 
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.
 
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.
 
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.
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.