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SAE Amplifiers and Quiescent Current

hamrules

hamrules

AK Subscriber
Subscriber
This is for the 01 series as the 00 & Mark series seem to work out.
I’ve rebuilt a few of these, A501 2401 and now a P500(A1001). I’ve always had issues with getting the quiescent current to what is called out on the schematic. I have of late even put in a trimmer. Most of the time most parts have been replaced. As I think about it if the resistors, caps & diodes are all good weather replaced or original those items shouldn’t cause any issue. Now the transistors that’s another story possibly. Examples are in the A501’s I usually get to low 700ma range. The last one (P500) it shows 1.7VDC and I can get to maybe 1.5vdc on a good day. Is it that the gain in the transistors isn’t as much as the original factory ones right out of the factory possibly? Some specific spec on certain parts I’m not watching?
Best example is this P500, it had 470K resistor installed. I installed a 2.5M trimmer. You’d think I could reach the voltage but no! Again the only items I changed that, to me anyway, make any sense of causing this would be transistor subs.
Any ideas ?
 
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Try increasing R14 and R15 to the next size up that you have on hand. What were the Q5,6,7 and 8 you removed and what did you replace them with?
 
MPSA56, 06, 2SA1859A & 2SC4883A
Those are for the A501 / 2401’s

2SA1507, 2SC3902, 2SB755 & 2SD845
Those are for the P500

I keep thinking if SAE had it that way and the resistors, caps and diodes are new or original but the same values and working it leaves the transistor subs. Maybe I’m simplifying it too much…….
 
It could be the gain of the transistors is different. The lower the Ohms in that circuit the lower the current. Increasing R14/15 should get it to where you can adjust it.
 
llwhtt said:
It could be the gain of the transistors is different. The lower the Ohms in that circuit the lower the current. Increasing R14/15 should get it to where you can adjust it.
Click to expand...
That makes sense to me. I will take a look into that. Time to work on Charlie Tuner so I will order a few resistor sizes along with the caps I will need.
 
Your care package arrived today, thank you very much!!!! How did you end up a Thaedra Head Amp board? I know what the yellow relays are for but what do the others fit?

Craig
 
llwhtt said:
Your care package arrived today, thank you very much!!!! How did you end up a Thaedra Head Amp board? I know what the yellow relays are for but what do the others fit?

Craig
Click to expand...
It was a leftover board from a project I had. I think it is missing some transistors, I probably have them in the parts drawer somewhere. The other relays are for the early production SAE amps, I got a case of them real cheap. I still have a couple dozen left; I will probably use a couple if that.
 
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