• 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.

Dynaco SCA-35 fixer-upper

hi all,
being a solid state guy, i'm not up on my tube amp history... is a Dynaco SCA-35 any good as a fixer-upper platform for a modest tube amplifier? not looking for the ultimate in hifi performance obviously, just some tube thrills on the cheap. my friend has one he's giving away and i'm wondering it's worth the time to recondition/modify. he already spent a couple hundred on new tubes last year, so those may be worth salvaging.

thanks,
dorkus
 
Yes. Reasonably nice iron (outputs are 8K with UL taps, very hefty for the power rating), but you'll end up doing pretty much a wholesale replacement of the circuitry. The circuit is crude and the circuit boards are awful quality. Same with switches and plugs.

There's plenty of room to work in, though, and you can turn it into a very nice-looking unit.
 
The SCA35 is a great donor, but as SY says the circuit and quality of boards & chassis is suspect.

I have an SCA35 project... iron is going on another chassis and i'll build up a circuit with a long-tailed pair on the front... mine will also borrow a PS Trafo from another unit to give me dual mono (the trafo on the SCA35 is reputed to be just a tad undersize)

dave
 
A ccs-loaded long tail is a good approach. If I were doing one, I'd consider a 12AT7- it's small, lowish distortion, cheap, and has enough gain that you can throw some feedback around the whole shmeer. In VA3, Morgan Jones shows a very nice little circuit (Bevois Valley), also a 1 tube input stage, that would fit just fine in the SCA-35 chassis.

Add a potentiometer and a switch and you've got a nice line-level integrated amp.
 
Originally posted by SY
A ccs-loaded long tail is a good approach. If I were doing one, I'd consider a 12AT7- it's small, lowish distortion, cheap, and has enough gain that you can throw some feedback around the whole shmeer.


I'll probably start with 6H23pi or 6AU6 strapped in triode... EF86 is i can come across enuff of them.

dave
 
Definitely.
Simply bypass the tone control circuit and short out the ceramic cap at the amp input (not needed unless your signal source has DC offset) will make the SCA-35 sound a whole lot better without spending a dime.
Replacing those light greenish blue color caps with polyproplene caps will further improve the sound.

dorkus said:
hi all,
being a solid state guy, i'm not up on my tube amp history... is a Dynaco SCA-35 any good as a fixer-upper platform for a modest tube amplifier? not looking for the ultimate in hifi performance obviously, just some tube thrills on the cheap. my friend has one he's giving away and i'm wondering it's worth the time to recondition/modify. he already spent a couple hundred on new tubes last year, so those may be worth salvaging.

thanks,
dorkus