My sca-35

[tech_fanatic]

2nd owner of this piece. Needs some cleaning at the moment, seems to be in decent shape functionally minus the burn-out power bulb. Not sure what the original owner used it for radio phono? It's currently used occasionally with my turntables.

Any tips or recommendations would be appreciated. Thanks!

-Kevin

Some pics from today:

[TomMcNally]

There has been a lot of discussion about the SCA-35 on here and
other places on the net. Yours in in nice original shape, you
can either clean it up and keep in in "original condition" or modify
the heck out of it. Many guys remove the tone controls from
the circuit, replace all of the resistors and capacitors, replace the
too-closely-spaced RCA jacks, new selector switch, new circuit boards, etc.

I have one in similar condition to yours, I am going to keep
it original.

[Geek]

I love those finds

Not much more to add to Tom's suggestion, just wanted to drool

Cheers!

[TerrySmith]

The main thing on a SCA-35 is they run really HOT! If the main amp boards aren't totally cooked, replace the coupling caps. Someone on ebay sells 6GH8 replacement boards that looks to be good quality.

[tech_fanatic]

Thanks for the input!

I don't think I'm up for modding, just basic resto.
Would like to fix the power light, 1 or 2 of the pots need Deoxit and maybe the rear in-outs, but that's about it. Boards/tube sockets/pots seem good. So, do the tubes look OK? I thought maybe I'd need to replace them at this point, however they're orange still? I assume that's a good thing right?

-Kevin

[mesherm]

Replace the pilot light with a red LED and resistor rather than the original tungsten filament bulb. The power tranny is the same as in a ST-35 and is pretty much maxed out without the extra current draw from the bulb.

[tech_fanatic]

More background info on the tubes... and questions.

the smaller ones say sylvania, which are 7199's and which are 12AX7's? Should I upgrade to better/newer?

The larger say dynaco. I see one looks like the glass got really hot once (hence the leaning tower of pisa) Should I replace/upgrade to better/newer el84's?
If I do, can I just pop in new tubes or do I have to re-adjust bias?

-Kevin

[mesherm]

The PCB with just the two small tubes is the phono/preamp section and both tubes are 12AX7s. Good modern 12AX7s are available for about $15 apiece. NOS 12AX7s run much more as they are highly prized by both guitar and hifi amp people.
The four large power tubes are 6BQ5/EL84s and are also easily available. Those I would replace first. They are cathode biased so there is no bias adjustment to make. Electro Harmonix or Sovtek are good inexpensive brands.
The small tubes on the two 3 tube PCBs are 7199s and are NOT easy or cheap to find in NOS. There are some Russian 7199s made but general opinion is the older tubes sound much better.
My recommendation is to replace the 4 power tubes first and give the amp a listen before replacing the small signal tubes. The life span on the 7199 and 12AX7 is much greater than on the 6BQ5/EL84 power tubes.

[tech_fanatic]

Thanks for all the help guys! I'll keep this thread updated with my progress.
-Kevin

[dcgillespie]

I would definitely replace the four EL84/6BQ5 output tubes right away. The pictures of your unit clearly shows that on at least three of these tubes the flashing within the tube has had significant evaporation take place, which is a visual indicator that the tubes are very well spent. If you have the means to test these tubes on any good Gm tube tester (Hickok, etc.), they will test very poorly.

David G.

[tech_fanatic]

David, I assume you mean the reddish-brown looking tubes? I thought maybe they were on the way out since they look different than the others. Sorry tOOb nOOb still at this point LOL.
-Kevin

[dcgillespie]

Kevin --

Yes -- those are the tubes I mean. At the level of deteriorated performance they visually indicate, those tubes also have an increased danger of internal arcing as well. Would not want to see you lose an output transformer from that!

David G.

[Ty_Bower]

I dunno how much faith I put in tube testing via visual inspection. Would you say the pair of tubes on the right are bad, based solely on the yucchy brown stains coming out of the plate holes?

[TerrySmith]

The two on the right are Mullards, that's normal for those. They will probably get much darker before they wear out.

[tech_fanatic]

Well it sounds like test the originals, then buy.

I know a guy with a tester and tube stock, he's an hr drive away. There's decent stock to choose from, just not sure WHICH are true NOS. There's just no way I'm spending $xx.xx and them not be NOS.

Just in case, can anyone point me to an alternative supplier - specifically guaranteed NOS stock?

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As for other non-tube related updates, I bought a new fuse holder to swap in and looking into a simple, yet classy alternative to the the speaker terminals (which I have grown to despise LOL)
-K