Really funny you mention that particular transistor... I was looking at it and wondering "What is that forth lead for?"... Thank you for pointing me to that website, kinda worrying to think there may well be 'tin whiskers' growing inside that case! Does cutting the forth lead necessarily future proof it from any issues? Noticed that was a solution on that page...
I'm also guessing that the film caps of that age may well contribute to the 'sound' of the tone circuit, something that may appeal to a future owner...
Perhaps I should've gone straight to 2200/3300uF... but I will audition it with the 1000uFs and see what it sounds like in terms of bass response...
Will definitely have to check the bias current on the outputs next...
Wonder if it's worth checking the old carbon resistors for drift?
And now I'm terrified of tin whiskers lol
The carbon comp resistors that looked bubbled or dark brown in my ST70 and organ power supplies were definitely reading high, as much as 15% overrange. No other carbon comp resistors that I have pulled from the dynakit & hammond equipment (because metal film is quieter) have been off tolerance. I've been using $.07-.12 multicomp and vishay metal film resistors, and yes, they hiss less over 100000 ohms (plate resistors in the tube amps).
With a DVM you obviously don't have to pull the shunt to read the O.T. bias, just use clip leads to jumper the 0.47 ohm resistor. The 1000 ohm/volt meters your average hobbiest (like me) had in 1964 had would have changed the readings considerably.
I think I would leave well alone if it all works OK. Although a problem, it by no means suggests all will develop this problem... it was just something to be aware of.
The AFxxx transistors were often used in radio front ends and ran at very low voltages and currents where the problems would be very noticeable. It's possible (and I'm only guessing here) is that the currents and voltage swings when used as a driver transistor may well prevent these "whiskers" forming.
Enjoy the amp 🙂
I found the study on those transistors quite interesting (if not worrying!)
But yes, they seem to be working and so I will leave well alone... although germanium transistors are obsolete as betamax, I still find it a bit baffling that there aren't any on the (niche) market, and replacing them means finding originals from the early 60s! A shame!
Now then, I had two Sony SLC9 Beta machines in daily use until around 7 years ago. That's another story 🙂
You can still get germanium devices although the choice is limited. I built this from old parts I had,
http://www.diyaudio.com/forums/head...rmanium-single-ended-class-headphone-amp.html
Loving your putting to use of the germaniums! 😉 Why should they sit on the shelf when you can put something nice together out of them?!
Just finished the rest of the electrolytic recap... yet to test it as it's a bit late/ Also wired the voltage selector out and hard wired for 250V (I don't know why I have a habit of doing this, I just find them annoying!) and removed the absolutely pointless 'AC Outlet' socket... one less bunch of needless mains leads running through the loom! Starting to look neater... was going to tackle the inputs/switches but my mind exploded when I had a look and so I'll leave it for a day I actually have the mental energy 😉
An externally hosted image should be here but it was not working when we last tested it.
Here's how it looks now... fingers crossed it was worth it. A small amount of the old electrolytics had leaked/were looking corroded around their bases...
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Last year RS in UK had Germanium signal transistors at about L2 each. Or was it RB? whoever is #2 distributor over there, not Tandy corporation. Not that you know you need them yet. The only thing in the US (newark, mouser) was germanium doped silicon RF transistors, which is something else entirely.
FM radios used to run off the power outlet before they invented the power socket strip. You could turn off the whole system at your control hub (the amp). My PAS2 preamp had the power amp plugged into it for decades, one switch did it all. You don't need a preamp, it is all built into this unit. With the attendant selector switch problems.
FM radios used to run off the power outlet before they invented the power socket strip. You could turn off the whole system at your control hub (the amp). My PAS2 preamp had the power amp plugged into it for decades, one switch did it all. You don't need a preamp, it is all built into this unit. With the attendant selector switch problems.
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Potentiometer failure
I wonder if you could help me with the Leak Stereo i have too.I'm experience a faulty Potentiometer and i would like to replace it but cannot find anything close to that.It is a Log Pot 20k with a power switch 2A 250V.Also it says 3-6 0.8db.
Hello there
I wonder if you could help me with the Leak Stereo i have too.I'm experience a faulty Potentiometer and i would like to replace it but cannot find anything close to that.It is a Log Pot 20k with a power switch 2A 250V.Also it says 3-6 0.8db.
Not a common item these days...
What is the problem with yours ? If it's the switch then probably not much you can do.
If it's just a "noisy" or worn track then you can sometimes open these old style pots up and clean them properly (cotton bud and WD40) and slightly bend the wiper so it runs on an unused bit of track. Depends how it's put together.
22K dual gang pots are available in this old style but I haven't found any with a switch,
OMEG|OW2G20BU22KB|POT, DUAL GANG, LOG, 22K | CPC From This Range
Even a 47K should be OK too but I can't find any with switches. If I come up with anything I'll update this...
Edit... you might get more luck on parts here,
http://www.vintage-radio.net/forum/index.php?
you have to register before you can view the forum I think but there are some very helpful folk on there.
And this,
http://www.diyaudio.com/forums/parts/186127-where-find-dual-pots-switches.html
although the switch might not be up to whats required.
What is the problem with yours ? If it's the switch then probably not much you can do.
If it's just a "noisy" or worn track then you can sometimes open these old style pots up and clean them properly (cotton bud and WD40) and slightly bend the wiper so it runs on an unused bit of track. Depends how it's put together.
22K dual gang pots are available in this old style but I haven't found any with a switch,
OMEG|OW2G20BU22KB|POT, DUAL GANG, LOG, 22K | CPC From This Range
Even a 47K should be OK too but I can't find any with switches. If I come up with anything I'll update this...
Edit... you might get more luck on parts here,
http://www.vintage-radio.net/forum/index.php?
you have to register before you can view the forum I think but there are some very helpful folk on there.
And this,
http://www.diyaudio.com/forums/parts/186127-where-find-dual-pots-switches.html
although the switch might not be up to whats required.
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