C26 overhaul advice?

pete1729

pete1729

Super Member
I have overhauled a few point to point wired tube pieces, this will be my first SS project.

The preamp has a bad variable static noise in one channel of the phono section. Imagine draining an air compressor complete with the spitting punctuation from water condensed in the compressor's tank.

Like everything in my house, this preamp probably needs to have a bunch of capacitors replaced. But which ones?

Also, could my noise be the result of a failed transistor? I need some help here.

I have linked to a schematic in the AK database, would any of you be kind enough to look at it and suggest a program of parts to replace?

http://akdatabase.org/AKview/display...album=7&pos=54
 
I usually replace the phono preamp transistor's with modern lower noise ones it is not uncommon for them to be noisy.

This vintage of unit deserved a electrolytic recap 10 years ago.......
 
c_dk said:
I usually replace the phono preamp transistor's with modern lower noise ones it is not uncommon for them to be noisy.

This vintage of unit deserved a electrolytic recap 10 years ago.......
Click to expand...

Thanks for the advice. So in the schematic were talking about Q1, Q2, Q3, Q4, Q5, and Q6. Do I have that right?

http://akdatabase.org/AKview/displayimage.php?album=7&pos=54

I picked this unit up a year and a half ago at an estate sale for $75. I've just now found the time to turn my attention to it.
 
Clean and deox all switches and controls first.

Then you can start looking to see if you have a thermally noisy semiconductor.
 
c_dk said:
Clean and deox all switches and controls first.

Then you can start looking to see if you have a thermally noisy semiconductor.
Click to expand...

I did that in the first 48 hours after I bought it.

I have New Muse electrolytics sitting in my virtual cart at Mouser along with an assortment of bypass caps that I plan to do some crossover experiments with. I'd like to order them all at once.

I'd rather have a half a dozen fresh transistors on hand if it turns out that they're necessary rather than put it off any longer. The fact that the noise exists only one channel of both phono input circuits leads me to believe there's a component failure.
 
Back in the 80s Mac engineering used the Toshiba 2sc2240bl and 2sa970bl to replace dozens of old transistors. These Toshibas, there are others out there, are getting more and more difficult to find.

The ksc1845 and ksa992 have worked well as readily available subs.
 
c_dk said:
Back in the 80s Mac engineering used the Toshiba 2sc2240bl and 2sa970bl to replace dozens of old transistors. These Toshibas, there are others out there, are getting more and more difficult to find.

The ksc1845 and ksa992 have worked well as readily available subs.
Click to expand...

Thanks so very much! They seem to be available from B&D Enterprises.

http://www.bdent.com/2sc2240bl-toshiba-audio-transistor.html

http://www.bdent.com/2sa970bl-toshiba-audio-transistor.html

According to this thread the lead orientation is different. My thanks to the 'mostly functional' MisterFishy for this information.
 
I may be selling the thing. I'd rather be able to say it's been recapped and has fresh low noise transistors in the phono section.

I have an MX117 that will likely remain but the internal speaker control relay in the C26 makes me sort of want to keep it.
 
Update.

I replaced the electrolytic caps on both boards and it sounds fine. The bad hiss in that one channel is gone. There is some noise out of both channels of the phono amp when I turn it way up with no signal, but at reasonable volume it's quiet.

I did get some new transistors, but I looked at those solder pots they sit in and decided to put it off for a while.
 
pete1729 said:
....I did get some new transistors, but I looked at those solder pots they sit in and decided to put it off for a while.
Click to expand...

Solution: Hakko 808

Anyone doing wholesale restorations or re-cap projects should have this or something like it.

If you have had to futz around with rebuilding a circuit board because the runs pulled up from too much heat while desoldering or clearing through holes, the investment is worth it, IME.

Don't set up a bench with out one!

Cheers,

David
 
dshoaf said:
Solution: Hakko 808

Anyone doing wholesale restorations or re-cap projects should have this or something like it.

If you have had to futz around with rebuilding a circuit board because the runs pulled up from too much heat while desoldering or clearing through holes, the investment is worth it, IME.

Don't set up a bench with out one!

Cheers,

David
Click to expand...

Thanks, Dave. Just another $300 indispensable tool for my entirely dispensable hobby. In carpentry we joke about having a 'knot extractor', that desoldering gun looks like the concept of that dream realized.

All joking aside, thanks for the information.

I put the new signal path caps in it and it quieted the unit right down. I sold it this morning to a man assembling a Mac system for himself, he already has a 2105. I was sort of sad to see it go.
 
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