Power stage troubles...

Gtrjunki66

Member
Messages
1
Hey all,
This is my first post to The Gear Page, and I hope it will bring me luck...

I am having trouble with my weapon of mass distortion, the Peavey 6505+ amplifier head. I have had it for 3 years now almost, and it's treated me well up until the past few months, where I've had numerous problems with the output stage. The internal fuse blew in post, which I had replaced. After that, I kept getting high pitched squealing noises up around 10k at any volume. I brought it in, and was told it was a loose pre-amp tube. Shortly after this problem was solved, all four post tubes at once stopped working. I replaced all four, correct bias (the amp was modified for EL34s), and it still did not work - no light from the power tubes. The standby and power LEDs both illuminate, however. I fear that it may be an output transformer, though I'm hoping it's just another fuse. If anyone could help me out with any advice, past experiences, anything, I'd be greatly appreciative. Thanks guys!
 

Blue Strat

Member
Messages
30,183
If the power tubes aren't lighting up the problem has nothing to do with the output transformer.

Try the previous power tubes to see if they're doing the same thing.

Unless there's a special fuse for the power tube heaters (assuming that those are the only ones not lighting up) there's likely a bad connection from the power transformer to the heaters of those tubes.

Whatever it is, it's not something that can be assessed from a distance. Possibly try another amp tech.
 

passfan

Member
Messages
73
Hey all,
This is my first post to The Gear Page, and I hope it will bring me luck...

I am having trouble with my weapon of mass distortion, the Peavey 6505+ amplifier head. I have had it for 3 years now almost, and it's treated me well up until the past few months, where I've had numerous problems with the output stage. The internal fuse blew in post, which I had replaced. After that, I kept getting high pitched squealing noises up around 10k at any volume. I brought it in, and was told it was a loose pre-amp tube. Shortly after this problem was solved, all four post tubes at once stopped working. I replaced all four, correct bias (the amp was modified for EL34s), and it still did not work - no light from the power tubes. The standby and power LEDs both illuminate, however. I fear that it may be an output transformer, though I'm hoping it's just another fuse. If anyone could help me out with any advice, past experiences, anything, I'd be greatly appreciative. Thanks guys!
Hard to diagnose anything electronic over the internet. Did your troubles start after the output tube modification ? If so , undo the modification. The squealing sounds like oscillation which could have been the result of an improper modification. The four output tubes not lighting up sounds like a filament supply problem. The fact that your pilot light still works could be a good sign if Peavey used 6.3 volts to light it. Take it to a better tech.
 

SatelliteAmps

Member
Messages
6,185
If the tubes aren't lighting, then it is most likely NOT the output transformer. Check for an extra internal fuse for the filaments. Most likely blown.
 

donnyjaguar

Member
Messages
4,199
I'm thinking moving to EL34 tubes from (presumably) 6L6GC would've created much higher current draw on the filament circuit, possibly enough to blow the secondary winding open.
 

Structo

Member
Messages
9,558
Yes unless the tech added an additional filament transformer how did he mod it to take EL34's?

Unless my math is way off, El34's draw .6 more amps each than a 6L6, so with four you are drawing 2.4 more amps on the filament tap.

Not sure any power transformer would be able to handle that.
 

Ronsonic

Member
Messages
3,305
Almost all recent Peavey production has a fuse in the heater circuit. You won't see the preamp tubes in a 6505 so that won't tell you. IIRC the early stages have their own DC supply that won't be affected by the same fuse.

The heater fuse has been an occasional cause of nuisance fuse blows in Peavey amps. For awhile the Classic 30 was really bad for that.

EL34 do draw more heater current than 6L6 so you are more likely to blow that fuse. You are also more likely to take out the power transformer.
 




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