• 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.


I just got an old sca-35amp, and it sounds great!! I must not have the hi-fi sensitive ears that some others have. It definitely sounds better than my old early 90's solid state amp/tuner. I was going to rebuild it as an ST-35, but I dont know if I should even bother.

If anything, this amp is a little bass HEAVY.

Man.. so when I finish my se 300b I bet Im in for a real treat.
I like the chassis, tho.
My wife is an architect, and is really into "mid century modern" design, which this amp chassis is.
I'd like to put one of the new improved st-35 pcb's into this case, but I don't think it will fit.
The original st-35 pcb's will fit, but they still have some issues. I guess I could kludge the improvements hanging off the old style st-35 pcb and fit it all in this case.
sorenj07 said:
gut it and build a new amp into a new chassis, that's what i'm doing. PP 6F6G's driven by a 6SL7 LTP.

That is what i'm doing... if you like the SCA35 stock, you will be stunned by how good it can get done up properly. You do have to watch how much you load down the power trafo. I'm going to use 2 SCA35 power trafos to make sure i have no problems ther.

That does leave me with a spare pair of OPTs and i have some nice 6F6G i was wondering what to do with... can you tell me more?


I agree with the gut rehabilitation idea. However, I suggest you put a tweaked RCA phono circuit in and that you use "El Cheapo" as a model for the power amp portion. I concur with eliminating the nasty tone controls. Really good tone control circuitry would consume the space the phono section occupies.

Don't worry about PCBs. Close the openings in the chassis with some sheet Aluminum. Then, wire the new stuff up point to point.

Please respond to the EMail I'm going to send. After I get your reply, I'll forward some schematics for your consideration.
I already removed the tone control. That was the first thing I did when I pulled it out of the box..
I'm not using the phono preamp, so I pulled those tubes.

P2P is a good idea, but would be sort of awkward in this situation, since there is very little clearance. (for now the original chassis is a requirement for this amp. Im building a nice new SE amp which will be in the current popular style w/ tubes up top)
I'd still have to mount the tubes to something that would bring the connections up to tube level (rather than usual p2p with all the soldering done under the tube socket)
Tone control replacing the preamp is a good idea too. I dont think I care enough, though.

What is the easiest way to replace the pilot light w/ an led? It's 6v ac. I guess I'd need to bridge rectify it...
I guess I wouldn't actually need full rectification.. 1/2 would give me 60hz flicker. (I dont really know what Im talking about here, but it makes sense to me)


2006-05-04 9:15 pm
planet10 said:

That does leave me with a spare pair of OPTs and i have some nice 6F6G i was wondering what to do with... can you tell me more?



tentative schematic. change the top 6SL7 plate resistor to 180K, and the bottom one to 187K, to bias the tube at -3V or so to protect the diode from causing current to run away if the input stage were to clip on CD input... also, change coupling capacitors to .22uF instead. haven't built it yet, but some parts are on their way.

bias adjustment will probably be done with 25K multi-turn pots and 10K resistors from the other end to ground.
Got the LED in.. In case anyone else finds this thread wondering the same thing:

I took 2 diodes, one in series w/ the led, and one in parallel. The polarity is reversed from the led on the parallel diode.
I added a small value resistor in series w/ the led, and it works! It flickers a little, but that could be fixed w/ a small capacitor.