Peavey 6505+ won't come out of Standby

[jc986]

Hello,

I turned my 6505+ on today and as soon as I switched it off of standby there was a pop and a bit of smoke. I flipped the amp back into standby and noticed that one of the power tubes was not lit, so I turned the amp off. I had a spare set of tubes so I swapped the new set in, powered on, and they all light up, but when trying to take the amp out of standby, the standby light doesn't illuminate and there's no sound. The main fuse accessible from the back of the amp must be alright, or there wouldn't be any power to the amp at all, right?

I popped the chassis out of the headshell and looked at the other fuses and none of them look to be blown visibly (I've only experienced 2 blown fuses in the past with other amps and it was pretty apparent in those cases). I've got some new fuses on the way since the ones I have on hand aren't the same value needed for a 6505+. Any ideas?

[alexradium]

internal fuse gone on B+,it should be F1.

[Enzo]

And probable cause was the failed power tube. Smoke? Power tubes often take out a screen resistor when they fail.

[alexradium]

And probable cause was the failed power tube. Smoke? Power tubes often take out a screen resistor when they fail.

yes,those 100 ohm tend to open for nothing,bad quality,i would change them all with 1K 5 watt from a reputable company.

[jc986]

Here's a pic of the fuses. I've only experienced a couple blown fuses in the past and in both cases the fuse was visibly blown. These look alright to me, but I'm not an expert. I have some 1A fuses on hand, and should get some 2A fuses in the mail tomorrow that I can try in F1.

[alexradium]

1A sloblo are ok,2A is for fast type.

[jc986]

Hard to tell from that picture, but the F1 location is marked for a 2A fuse. Here's a pic with the fuse removed, which was a 2A fuse.

[Enzo]

It doesn't matter what the fuse looks like. Yes, many are obviously blown, but not always. ALWAYS check the fuses. And we do that by removing them from the clips and testing them with an ohm meter.

Of course other things are possible, the big 400 ohm resistor could have picked this moment to fail. That would keep your status light dark too.

[jc986]

Ok, I tested all the fuses with my multimeter and they all test fine. Where is this 400k resistor?

[Enzo]

Well, we are drifting into just testing parts. The real deal is to trace the problem to its source. SO is ther good B+ voltage on pins 3 and 4 of EVERY power tube socket?

And I said 400 ohm, not 400k. R64, left center of schematic, in B+ supply. COnnects to standby switch.

[tboy]

Here's a pic of the fuses.

Where are these photos being hosted? I'm not able to view them, and I've heard from other members that they can't see them either.

[jc986]

They are being hosted in my Google Photos, but I didn't have them in a shared album. I believe it is fixed now.

I tested for B+ voltage on sockets 3 & 4, and socket three is reading around 490 on all sockets, but socket 4 is not reading anything.

[Enzo]

Do you mean pin 3 and 4 of each socket?

Assuming pin 4 has no voltage, look for that 10 watt 400 ohm resistor and see if it is open.

[jc986]

Yes, sorry I meant pins 3 & 4 on each socket. I’ll check the resistor tomorrow. Thanks for all the help so far.

[jc986]

Do you mean pin 3 and 4 of each socket?

Assuming pin 4 has no voltage, look for that 10 watt 400 ohm resistor and see if it is open.

Sorry for the delay, just had a chance to work on this again, and it was the 10w 400 ohm resistor. Once this was replaced, amp fired up and sounds good as new. Thanks again!!