I agree completely. I like the idea of using the holes already in the chassis, and want to keep the adjustment from the top for sure. Are there any special considerations for the pots themselves that I need to know about? Whatever the solution, I really have to thank you for the great tutorial, @paulbottlehead! I've wanted to get a handle on this amp for years, but had little reason.That's not a head scratcher at all. Those pots are supposed to be mounted to a PC board, and yours are not. The little tiny leads on those pots are not intended to have wires connected to them, and you have to be extremely careful when you do that.
The ultimate solution would be to fabricate a new piece of metal that holds four panel mount potentiometers with solder lugs, or attempt to install some in the holes I see in the chassis that are already there. Another option is to make a proper PC board to hold pots that are made to be adjusted from the top when looking down on the PC board.
Whatever you do, I wouldn't just solder it back together as it is, as I'd expect that same thing to happen again.
The math is pretty easy. With 78v across a 100K pot, the dissipated power is V^2 / R = 78x78/100K = 0.06W. Giving a 2x margin just to be safe, the calculation tells you that 1/8W or higher should be fine.So, I'm guessing I should use 100K linear potentiometers, but what wattage is adequate? 1/2W, lesser, or greater?
What impedance are the trim pots that are in there now? 100K seems very high for a bias trim pot, but I would certainly replace them with the same value.
Mouser has a few different sizes of Alpha pots that are available with solder lugs, I would encourage you to use them and probably to order both sizes just to see what fits properly.
Not a problem. I'm a journeyman toolmaker (retired). I could just turn something down on the lathe as an extension, too. I'll keep the adjustable bias so I can still roll tubes if I'd like.If you need to slot the pot, you can do it by hand with a small hacksaw.
Yep. The 3590 series are what I mentioned in my earlier post. The amp is absolutely worth the 80+ dollars to me.Single turn is going to be "touchy"......google search for solder lug multi turn pot I found...
Now is it worth 20 bucks each, thats up to you
So, I further narrowed down the test probe sockets and pots to these:
3542-2 Pomona Electronics | Connectors, Interconnects | DigiKey
3549S-1AA-104A Bourns Inc. | Potentiometers, Variable Resistors | DigiKey