Flipped board over--no solder bridges or burnt marks on rectifiers. I put in new rectifiers and the problem still exists.

Yes, all the secondary taps  disconnected and the lightbulb shines very dimly at 120V so all appears well. Will check for solder bridges, open traces...

Okay, back to getting 1.4VDc on supply rail and other side of rectifiers....light bright as ever.

Thanks Enzo, greatly appreciated. So I replaced the rectifiers and am now getting a mere .31 vDC on the rectifiers and on the rails. The 100 W bulb  is shining very brightly, at 90 V on the variac

I was getting 1.4 volts with the shorted rectifiers...

Thanks gents!  So the AC voltage off the transformer is good. Checked the diodes using  a resistance check and they don't look so good. D36--8.45Mohm, 5.9Mohm  D34 .1ohm, 0 ohm,
D37 3.67 Mohm, 7.95 Mohm D35 0ohm, 0ohm. The voltage that is fed from the diodes is only 1.4 volts which is what I'm getting on the rails. The diodes look good visually. My readings were with the diodes in circuit.

I checked all the resistors in the power amp circuit and they checked out good except for R97 which should be 4.7K but reads as .8k, again, in circuit. How important is this to getting the amp up and running?

I'm including a photo of something wierd that I found. C53 and 54 don't exist in the amp. C53 only has the leads left, and C54 looks like a resistor and measures like one, 107kohm?. My friend didn't give this amp to anyone else to fix and it's been sitting in his basement for 20 years. I suppose C53 could  have broken off after I opened up the amp but I wasn't tinkering with that side of the amp. Could C53 have anything to do with the amp not working?

.7V AC across 42 volt supply, line side. 3.5v AC across 15v supply. As an aside I orginally checked all the Output Transistors and all the others on the power amp side and they checked out okay but one which was shorted and I replaced it and the other in last stage with a matched set from Peavey.
42 v supply diodes check out okay. What kind of resistance should I find across the 42 volt transformer winding?   Info so far...

So, thought about it some more and fired up the amp with the limiter and slowly brought up the voltage to about 94 volts using a 100 W bulb. Bulb is very bright, current draw reads approx. .6 volts, 1mv DC on output which seems reasonable. But the rails are reading -/+ 1.47 volts. Seems way too low. Any thoughts? Ground to  Collector Voltage on Transistors 6,7,12 shows 1.47V, and the emitter voltage on 10,11,and 13 show -1.47.  Rail voltage on Schematic, when operating normally, is  +42 volts.  How much voltage is being dropped across the lightbulb? I checked the line volts on the amp and it reads 11 volts. hmmm,not a lot of voltage, the amp has far to go, so we should see an increase in rail voltage, but is this voltage too low at this stage and should I be concerned?

Quoteyes in tube radio world it is known as a Dim Bulb Tester.  high current is dropped across the bulb protecting your equipment instead of high current across expensive delicate components such as transformers.  you can gage the bulb size by device power consumption.  100W power consumption = 100W bulb.  not to be confused with power output which is not close to power consumption

Replaced power output transistor. So, according to this statement above, I need to have a 450 watt bulb as the Renown Amp is rated at 120V/450 Watts. Not sure this statement agrees with some of the other info on the current limiter info discussed in this forum.  I read the info but not sure exactly how to proceed. I have a current limiter and a variac. I know that SS amps can operate at lower voltages so would it be okay to start with a 60W/100 W bulb? The amp  has a 5 Amp fuse.
I also have a current monitor.

Thanks.

Thanks guys.

QuoteI rarely have to remove these to determine if they are faulty.

Well, from what I've read most people say to get a proper reading the transistor must be removed from circuit. Enzo, I'd rather not for sure. So, how would you have tested this one in-circuit to save you the hassle of removing it? Would none of the associated circuit effect the reading?  Thanks!

I will certainly try your method to save future removals...

Best techniques to save transistor legs from breaking!!!

In the images I attached (sorry one is blurry but you'll see that the middle leg broke off), I removed the transistors to test out of circuit and they both tested good. So I was feeling good about that. But when I tried inserting the 5331 the middle leg broke off. I had kept the transistor screwed down and had pried the legs out as I applied the iron from the other side of the board. After testing, I tried to slide the legs back into the holes using a small screwdriver--the middle leg wore out very quickly and broke.
Is it best to have the transistor standing at a 90 degree angle to the board when removing then simply pull upwards? When re-inserting should I insert legs through holes, solder, then bend the entire trans. down to the heatsink and screw it down??

On the smaller transistor, when I removed it, the legs soon became bent at odd angles that were very hard to straighten out and after trying several times to get all three legs in the hole the transistor looked like an arthritic octopus and the middle leg broke off. What is the best method for taking out and re-insertion with these small sensitive resistors??

I've ordered duplicates from Peavey and I don't want to screw up putting the new ones back in the board.

What have the experts been doing for years that works?  Thanks for  your input in advance!


Also, when I ordered a replacement transistor (Q13) from Peavey they told me it had to be a matched pair so I purchased two.  So, like output tubes, does this mean I have to replace Q12 with the other new transistor?

Thanks for everyone's input. I've learned a lot as usual. Will print off this thread and attach to schematic for future reading for future solid state repair work.

Will order parts and power up with my current meter, variac, and limiter and let everyone know my results.  Thanks :dbtu:

CR28 reads .014v one way and the other, in circuit?? As LateDev suggest testing diodes out of circuit so will try that.

QuoteProtection circuit is CR29, Q4, Q8, CR30, R105, R106. These act as clamps on the bases of Q5 and Q9, which are the drivers, via R107 and R108 . All transistors and diodes should be checked out of circuit

. Okay, good.

Thanks for the post on parallel diode readings. :cheesy:

QuoteNo one said to run an amp with one O/P transistor removed.  What was said was that when there are multiple pairs, extra pairs can be removed, for test purposes at lower power levels.  We do this all the time in the repair world.  You saw the caution about power levels when doing this?

If, for example, you mean Q3, Q12 and Q7, Q11, and Q6, Q10 then I get it. Correct?

QuoteOperating with one pair of the output transistors missing is not one less gain stage, it is less current gain.  This translates to less power available to the load, and more strain on the other output transistors at higher power levels.

Understood!

Also, fed a 1khz sinewave to do some signal tracing from the input on the pre-amp. Starts off as a nice clean sinewave, tests as showing in multiple locations throughout pre-amp and beyond, but the sign wave is fuzzy, although its retains its original shape and amplitude.

In fact, now that I'm testing other diodes I'm getting the same mixed messages. Can't imagine all these diodes are fried.

Re: CR9 and CR10. Other diodes that I tested in circuit test normal using the diode checker function on my meter. But with these two, in circuit, I get a read of .553v in one direction and .555v in the other direction. So that would be incorrect. But just to make sure should I  take one leg out of circuit and re-test just to make sure these are indeed fried?