Hi
Please refer to attached schematic. Refer to Q5 (7205, pos pre-driver) and Q6 (7204, neg pre-driver). I would like to know what is the actual part number for this transistor, is it 2N, 2SC,2SD etc. Is there a replacement. Please assist.
Thanks
Please refer to attached schematic. Refer to Q5 (7205, pos pre-driver) and Q6 (7204, neg pre-driver). I would like to know what is the actual part number for this transistor, is it 2N, 2SC,2SD etc. Is there a replacement. Please assist.
Thanks
The schematic has 6451 or 6343 above the transistors Q5 power transistor. A quick search pulled up jfets as 2N6451.
I believe these are the TO-220 package. Peavey is subbing MJE15032 MJE15033 which are the toughest out there. I think in the nineties they were buying 2sa968b 2sc2238b but with the prevalence of fakes from ***** you are better off buying ON semi parts from farnell or RS (in the UK). Peavey had an incoming inspection department that could check for SOA and Ft of the ****ese parts, you don't.
With your incoming insp. department not sorting for gain or Vbe match, you may have to change R30 to eliminate cold crossover distortion. Look for vertical outputs on a scope at low wattage sine wave, decrease R30 with a pot until it disappears. Then replace pot with a fixed resistor.
Best of luck with your repair. Incidently, on the PA forum there are lots of threads about CS800's. PA Systems - diyAudio
With your incoming insp. department not sorting for gain or Vbe match, you may have to change R30 to eliminate cold crossover distortion. Look for vertical outputs on a scope at low wattage sine wave, decrease R30 with a pot until it disappears. Then replace pot with a fixed resistor.
Best of luck with your repair. Incidently, on the PA forum there are lots of threads about CS800's. PA Systems - diyAudio
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Early BGW and others used TO5/TO39 with stud cup mounting as the need for thermal mounting on the VAS was needed. The TO202 still needed some extra heatsinking and it was not easy to mount to the heatsink directly. Later Motorola came out with MJE 340/350 and other devices that were easy to secure to the heatsink. We made the changes and better VAS reliability was greatly improved. I think that Jack did the same for Peavey.
Duke
Duke
cs800 slow start
This Peavey CS800 had not been used for a long time. A few days back, I took out the amp, cleaned it dismantle the the preamp and power amp boards. All the power and driver transistors are OK. I checked all the diodes, transistors and resistors on both the preamp boards and they seem OK. I did not check only the capacitors. I did some resoldering here and there and cleaned all the contacts and sockets. I put back everything and turned on the amp. After about 3 to 4 secs, both the relays turned on and the green power LEDs are on. I tried switching the amp ON and OFF a few times, connected the signal and speakers and both channels work fine. The next day, when I turned on the amp, it refuse to turn on, the fan is working, but both the relays and the green power LEDs are OFF. After about 5mins, the right relay and power LED turned on, but it took about 15mins for the left relay and power LED to turn ON. Once both channels have turned ON, then switching the amp ON and OFF repeatedly at time intervals is not a problem .Both channels turn ON within 2secs. Then the same problem repeats, when turning the amp ON the next day. After the 10 to 15 mins delay, the amp comes back to normal operation. Is the problem on the power amp board, preamp board or the power supply board. Please assist.
Thanks
This Peavey CS800 had not been used for a long time. A few days back, I took out the amp, cleaned it dismantle the the preamp and power amp boards. All the power and driver transistors are OK. I checked all the diodes, transistors and resistors on both the preamp boards and they seem OK. I did not check only the capacitors. I did some resoldering here and there and cleaned all the contacts and sockets. I put back everything and turned on the amp. After about 3 to 4 secs, both the relays turned on and the green power LEDs are on. I tried switching the amp ON and OFF a few times, connected the signal and speakers and both channels work fine. The next day, when I turned on the amp, it refuse to turn on, the fan is working, but both the relays and the green power LEDs are OFF. After about 5mins, the right relay and power LED turned on, but it took about 15mins for the left relay and power LED to turn ON. Once both channels have turned ON, then switching the amp ON and OFF repeatedly at time intervals is not a problem .Both channels turn ON within 2secs. Then the same problem repeats, when turning the amp ON the next day. After the 10 to 15 mins delay, the amp comes back to normal operation. Is the problem on the power amp board, preamp board or the power supply board. Please assist.
Thanks
Please do not start multiple threads on the same topic, your threads have been merged.
If you're a newbie, be sure to touch metal with only one hand at a time. Electricity that crosses your heart can stop it. Also, wear no jewelry on hands fingers or neck. Voltages and currents in the amp can burn your flesh to charcoal if it shorts through metal. The capacitors can be dangerous even with the unit unplugged, as they store energy.
The schematic shows a power Neon bulb and two clipping LED's. So I'm not sure if there are two power LED's or not.
Do this with the unit unplugged. I would start by removing and reseating the jumper plugs that set up the transformer for western or eastern hemisphere power.
After this using two alligator clip leads, check across the power switch that there is 120 vac (or 240 in the east) with the unit turned off. Plug in after connecting the two meter leads. Make sure AC voltage goes to zero with the switch on. If no AC with the unit off, possibly the high temp switch has failed. The contacts can drop in and out. With the unit unplugged, you can short across the temp limit switch with a clip lead, temporarily while a new part is on order.
IF that is okay, put clip leads with power off on each big filter cap in turn. Then with AC on check the DC voltage across . Should be 81 v on each, in turn.
The schematic shows a power Neon bulb and two clipping LED's. So I'm not sure if there are two power LED's or not.
Do this with the unit unplugged. I would start by removing and reseating the jumper plugs that set up the transformer for western or eastern hemisphere power.
After this using two alligator clip leads, check across the power switch that there is 120 vac (or 240 in the east) with the unit turned off. Plug in after connecting the two meter leads. Make sure AC voltage goes to zero with the switch on. If no AC with the unit off, possibly the high temp switch has failed. The contacts can drop in and out. With the unit unplugged, you can short across the temp limit switch with a clip lead, temporarily while a new part is on order.
IF that is okay, put clip leads with power off on each big filter cap in turn. Then with AC on check the DC voltage across . Should be 81 v on each, in turn.
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