Uh, yes the driver card has the predriver transistors Q100 changed to MJE15032 and Q104 to MJE15033. R110 and R220 go from 10 to 33 ohm. R102, R127, R202, R227, go from 1.5 kohms to 4.7k. The MJE parts have more gain than the Chinese transistors (SA968b, SC2238b) specified in 1994.
The output board, there are pricing pressures on the output transistors. To save $20 I replaced MJ15024 and MJ15025 with MJ21193 and MJ21194. Someone else may have used something different depending on the price that day and what is available. I find the output transistor cold idle current deficient and may do something about replacing R110 with a potentiometer before I put the top on.
Enzo always recommends buying the transistors from Peavey as they come matched up, but you have to have a phone with long distance service to order from them. My phone with long distance service is a pay phone at the gas station, and shouting out part numbers and my debit card number over the diesel cooler noise is a real nuisance, so I bought from newark.
The output board, there are pricing pressures on the output transistors. To save $20 I replaced MJ15024 and MJ15025 with MJ21193 and MJ21194. Someone else may have used something different depending on the price that day and what is available. I find the output transistor cold idle current deficient and may do something about replacing R110 with a potentiometer before I put the top on.
Enzo always recommends buying the transistors from Peavey as they come matched up, but you have to have a phone with long distance service to order from them. My phone with long distance service is a pay phone at the gas station, and shouting out part numbers and my debit card number over the diesel cooler noise is a real nuisance, so I bought from newark.
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Oh be fair now, Peavey has ALWAYS had toll free telephone numbers. If your phone is on the wall at the gas station and it for some reason will not allow toll free calling, that is not Peavey's fault. So unless you have a long line if guys behind you waiting to use that phone for parts orders, I don;t think it is proper to tell people not to ordeer thiungs from Peavey because of that.
And let's be straight. I always suggest Peavey as one source, because they will have real parts - the same parts they use in their products. They will not be counterfeits, and they will not be mis-matched stuff like NTE sells. I don;t worry about matching, Peavey transistors are not sold by grade. But Peavey prices are usually reasonable, maybe not the lowest, but not a rip off. And last I checked the Peavey parts price included shipping, so consider that in your calculations, because the Mousers and Newarks of the world generally charge you $10 and up to ship.
MY first choice is buying my MJ power transistor stock from a reliable supplier like Mouser.
Current pricing on parts does change so indeed it pays to check. But today at Mouser MJ15024 and MJ21193 are both selling for the same $4.72 each in lots of 10. I have absolutely nothing against the MJU21193 as a sub, however it is a different transistor, so I consider it a bad idea to mix it with the existing MJ15024s, so if you plan to use the 21193, in my view you need to be replacing ALL of the parallel outputs with them. They all need to be the same type, regardless of which, so they share current well and thermally track each other.
And let's be straight. I always suggest Peavey as one source, because they will have real parts - the same parts they use in their products. They will not be counterfeits, and they will not be mis-matched stuff like NTE sells. I don;t worry about matching, Peavey transistors are not sold by grade. But Peavey prices are usually reasonable, maybe not the lowest, but not a rip off. And last I checked the Peavey parts price included shipping, so consider that in your calculations, because the Mousers and Newarks of the world generally charge you $10 and up to ship.
MY first choice is buying my MJ power transistor stock from a reliable supplier like Mouser.
Current pricing on parts does change so indeed it pays to check. But today at Mouser MJ15024 and MJ21193 are both selling for the same $4.72 each in lots of 10. I have absolutely nothing against the MJU21193 as a sub, however it is a different transistor, so I consider it a bad idea to mix it with the existing MJ15024s, so if you plan to use the 21193, in my view you need to be replacing ALL of the parallel outputs with them. They all need to be the same type, regardless of which, so they share current well and thermally track each other.
I bought 22 MJ21193/4 at onesies prices because 19 out of 20 OT's were blown. Two were .01V off Vce when energized with a 100 ohm base resistor and 10 ohm collector resistor, so those became the MJ15020/1 driver.
Newark has sales on old stock sometimes, even parts that don't age like transistors. I usually need something else besides transistors; this Radio Shack bargain pack collection from 1974 is missing a lot of values and wattages. Newark's metal film resistor prices from Thailand and India (Vishay, multicomp) are way better than Mouser's Xicor prices from C****.
And from Newark South Carolina to Louisville, a newark package UPS is usually $7 surface since my house counts as a "business". Many times if the order goes in by 1000, the package is there by 1630 tomorrow, surface rate. Distance really counts on UPS charges, and there is a residence surcharge, so your location and status matter a lot on shipping cost. Interesting about the free Peavey shipping, maybe I'll buy a fan likely to be better than the 16 year old one in my box.
If you're watching Enzo, do you have to measure all 5 emitter resistors per side to calculate idle bias current? I've measured the two emitter resistor I can reach of the five per push or pull, and I'm getting 2 to 4 mv with input tuned down to zero. I don't suppose this matters much if one is whomping out table shaking bass in a bar, but my real application involves 1 Vpp music in the living room, so no crossover distortion at low power would be nice. I bought some 120 ohm cold NTC resistors (GE CL-90) to put on the heat sink instead of 33 ohm R110, thinking of putting a pot across R110, but that is getting out in the way beyond my design expertise zone.
Newark has sales on old stock sometimes, even parts that don't age like transistors. I usually need something else besides transistors; this Radio Shack bargain pack collection from 1974 is missing a lot of values and wattages. Newark's metal film resistor prices from Thailand and India (Vishay, multicomp) are way better than Mouser's Xicor prices from C****.
And from Newark South Carolina to Louisville, a newark package UPS is usually $7 surface since my house counts as a "business". Many times if the order goes in by 1000, the package is there by 1630 tomorrow, surface rate. Distance really counts on UPS charges, and there is a residence surcharge, so your location and status matter a lot on shipping cost. Interesting about the free Peavey shipping, maybe I'll buy a fan likely to be better than the 16 year old one in my box.
If you're watching Enzo, do you have to measure all 5 emitter resistors per side to calculate idle bias current? I've measured the two emitter resistor I can reach of the five per push or pull, and I'm getting 2 to 4 mv with input tuned down to zero. I don't suppose this matters much if one is whomping out table shaking bass in a bar, but my real application involves 1 Vpp music in the living room, so no crossover distortion at low power would be nice. I bought some 120 ohm cold NTC resistors (GE CL-90) to put on the heat sink instead of 33 ohm R110, thinking of putting a pot across R110, but that is getting out in the way beyond my design expertise zone.
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Obviously one has to consider all the logistical questions while shopping. I always make up a grid sheet: part I need down the left, supplier names across the top. Then I fill in the prices for each thing at each supplier. I then figure out the best OVERALL order to place.
I don't usually worry about idle current, I am more inclined to watch crossover distortion and heat.
I don't usually worry about idle current, I am more inclined to watch crossover distortion and heat.
That sentence with its use of both past and future tense is not English as I understand it.
I had to replace U100 and U101 and U102 on one board but only 101 and 102 on the other. One board the power supply bypass cap to U100 was blown. 50 v rated caps are subject to 180 v when one of the output transistors has failed shorted C to B, along with the driver and predriver transistors.
I don't see a U103. U102, half provides a signal to the variable gain IC U101, the other half drives the DDT LED.
One DC tests op amps by shorting the input at the 1/4 phone connector, and seeing if the output of the op amp fits the equation Vo= A((V+)-(V-)). A is Ri/Rf. U101 is a variable gain amp, not an op amp.
Then if you still have problems, put music in through a radio or something and check that the AC flows and uniformly gets bigger through the various stages. If you use rock music the beats of the music on the meter pointer distinguish signal from possible oscillations. DVM are useless for the AC test, they average over 2 to 4 seconds, make 8's when the signal moves dynamically, and most I have bought produce random numbers on the AC scale for music frequencies. I use a Simpson 260-6XLPM VOM with 20 VAc and 2 vac scales. Scopes can be nice when they actually work, which is seldom in my experience. I have not bought any new Teks; when your employer can afford one a 465 or 466 works nicely.
U100 had a bad solder joint between the socket and board, and kept whanging the output to +180 v and lock when I touched that pin with a meter probe.
To answer the second question which appeared as I was answering the first, rail voltage should appear on the case of both Q105 and Q106. It comes in through pins 3 and 6 of the 10 pin connector, which is not built of the world's most reliable technology, having push in back connection. One person was bedeviled by an ittermittant ground pin on one of those connectors in a PV800. The pins and blocks are still for sale from TE connectivity I believe, I bought some gold ones for the VI limiter circuit.
Another possible reason for assymetric voltage on Q105 Q106 is that the flying rails have flown off to 180, 1.5, due to the output transistors being stuck on on one side. At idle rails should be +85 -85.
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Thank you for the reply and this a break down of what I have done,replace every semi on the bad driver board and on the out put board,check and double check every solder joint,left out triac tell everything is correct.The driver board that I am having a problem with is the good board.going to trace out signal path out later today with scope to verify
There will be rail voltage at Q100 and Q104 collectors. The question is, is the rail voltage with no signal centered around 0 v (+85, -85) or is it unbalanced in one direction or the other. these are "flying rails". The signal ground flies too, and the two channels don't have center voltage at the same value.
Your "assumption" that a semiconductor is the fault is not valid. There are lots of 50v capacitors that won't withstand 180 v or minus 180v when the voltage latches one way or the other. There are 1/4 watt resistors that won't stand a long time with the rail voltages unbalanced. I replaced 104 parts many of them resistors and capacitors.
To keep output transistors from blowing dies to the ceiling, I worked the amp with a 1500 watt room heater in series with the AC at the input board in the back. This kept the rail voltages down to + and - 72 v, but allowed the +16 and -16 supplies to reach full value.
Did you figure out the trick of stacking the B channel driver on top of the A channel input board if you want to work on that one? Took me a long time to figure that out. Either can be on top.
Are your +-16 on the power board okay, also the flying +-15 on the driver boards? All of mine were blown up. Lots of diodes were blown. I made 16 v regulator diodes by stacking a 1n4148 on top of a 15 v zener I had in stock, instead of buying special 16 v zener diodes. Line to line.
Your "assumption" that a semiconductor is the fault is not valid. There are lots of 50v capacitors that won't withstand 180 v or minus 180v when the voltage latches one way or the other. There are 1/4 watt resistors that won't stand a long time with the rail voltages unbalanced. I replaced 104 parts many of them resistors and capacitors.
To keep output transistors from blowing dies to the ceiling, I worked the amp with a 1500 watt room heater in series with the AC at the input board in the back. This kept the rail voltages down to + and - 72 v, but allowed the +16 and -16 supplies to reach full value.
Did you figure out the trick of stacking the B channel driver on top of the A channel input board if you want to work on that one? Took me a long time to figure that out. Either can be on top.
Are your +-16 on the power board okay, also the flying +-15 on the driver boards? All of mine were blown up. Lots of diodes were blown. I made 16 v regulator diodes by stacking a 1n4148 on top of a 15 v zener I had in stock, instead of buying special 16 v zener diodes. Line to line.
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I also for got to mention that the rail voltage was showing up at q100 and q104 , on the heatsink after doing some more digging I had found r133 and r134 showing that they were shorted somehow,but when test they show proper resistance ?? .install new ones, circuit show ok these resistor are the flame proof ones but I installed one watt resistor,hope this my cure the problem
I tend to trust resistor measurements made at 2 v to predict performance any any voltage. The exception is dust on the outside + atmospheric humidity. That can lead to shorts around the case.
Capacitors, the way the dielectric breaks down and leaves a carbon track in the plastic, I don't trust meter measurements made at 2 v to predict results at 50 v or 180 v. Especially where the capacitor has been subjected to more than rated voltage through breakdown of various transistors. If you read the peavey parts list in the schematic available from eserviceinfo.com, there are a lot of 50 v capacitors on the driver boards. If you can read the little letters with a convex lens, capacitors with an A or B suffix is a tipoff for low voltage capacitors.
Capacitors, the way the dielectric breaks down and leaves a carbon track in the plastic, I don't trust meter measurements made at 2 v to predict results at 50 v or 180 v. Especially where the capacitor has been subjected to more than rated voltage through breakdown of various transistors. If you read the peavey parts list in the schematic available from eserviceinfo.com, there are a lot of 50 v capacitors on the driver boards. If you can read the little letters with a convex lens, capacitors with an A or B suffix is a tipoff for low voltage capacitors.
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