Amp problem, any ideas?

[Vol. Knob]

I have a Peavey Windsor, I swapped out the preamp tubes for lower gain 12au7 and 12at7s.  Its been a great amp ever since.  However, recently I plugged in and got no sound.  I did, however, notice that when I plug straight into the effects return I do get sound.  Mind you, the eq knobs, preamp knob, power amp knob all do nothing. 

Hmm... fuse is still good. 

Ideas?

 

[MUYFUE]

sounds like something is wrong in the pre-amp...I'm saying that becasue the power section still works.
:icon_scratch:
Try to inspect the pre-amp tubes for damage. maybe you just got a busted "t00b"

 

[jimh]

If you take the fx loop out/send into another amp, do you get sound?
Similarly, if you jumper the fx loop send straight to rtn with a short cable, does sound return?

From what you describe the power section must be ok.  

 

[Death by Uberschall]

Change out the pre-amp tubes one at a time until you find the bad one.  :icon_thumright:

 

[Vol. Knob]

Already tried swapping out tubes and jumpering the effects loop.  As well as try running the effects send to another amp.  And noting.  Odd.  Looks like its a trip to the shop.

 

[MUYFUE]

D'oh...Sorry, man.
I hope it's not a big deal!
:glasses9:

 

[mayfly]

if the preamp is completely dead (i.e. no sound - not even hiss), then it's usually something mechanical.  I suspect that a solder joint somewhere has become loose - or here's another thought - there could be another internal power supply fuse for just the preamp that's blown.

hmmm...

 

[DangerousR6]

I had a similar situation with my Blue VooDoo, it just went silent while playing. Checked all the preamp and power tubes, no problem there, checked all fuses. Turned out to be a 5amp 600w resistor on the board... :dontknow:

 

[Death by Uberschall]

If you find an internal fuse blown, check the pre-amp tubes.

 

[mayfly]

I had a similar situation with my Blue VooDoo, it just went silent while playing. Checked all the preamp and power tubes, no problem there, checked all fuses. Turned out to be a 5amp 600w resistor on the board... :dontknow:

Hmmm - that's possible as well.  I've seen these go open when running funny 12a variants  :icon_jokercolor:

 

[Superlizard]

Do all the preamp t00bs light up?

(regardless of lighting up or not - heaters could be fine):

If the preamp t00b sockets are PCB mounted, there could be a loose/cold solder joint on one... your swapping
may have been enough physical force to be the "straw that broke the t00b socket's back" so to speak.

 

[MUYFUE]

They raise a good point. A few years ago my Trace didn't work all of a sudden, I took it to a guy who diagnosed it with bad AC filament.
He "repaired" it...but it broke again...
I opened up the amp and the connection on the board was a plastic adapter clip that failed. in other words it was cracked. I had the clip removed and had the connections soldered directly...simple problem. easy fix. Amp has never failed again. I hope its soemthign mechanical like that.

 

[Vol. Knob]

I opened it up, there are internal fuses, but none are blown.  And in fact, the two preamp tubes do not light up...

 

[jimh]

DOnt suppose you know if the Power tubes have AC heaters and the Pre tubes are DC heaters.  Maybe heater rectifiers are gone?
Its the heaters that make the tubes glow, as they quite literally heat the element to release teh electrons.

You've tried known working tubes in the sockets?

 

[mayfly]

DOnt suppose you know if the Power tubes have AC heaters and the Pre tubes are DC heaters.  Maybe heater rectifiers are gone?
Its the heaters that make the tubes glow, as they quite literally heat the element to release teh electrons.

You've tried known working tubes in the sockets?

+1 if the heaters are not working, that would cause the symptoms you describe.  The DC heater suggestion is a good one.  Do you have access to a multimeter?  You could measure the voltage on the pre tube heaters to see if it's AC or DC, and if you have any voltage at all.

With a photo, we can go from there.

one thing - how do you know the fuses are not blown? Did you measure them, or are you just looking at them?  Sometimes they can look fine but be blown all the same.

 

[jackthehack]

I opened it up, there are internal fuses, but none are blown.  And in fact, the two preamp tubes do not light up...

WhT about the V3 tube in the pre-amp circuit?

 

[mayfly]

DOnt suppose you know if the Power tubes have AC heaters and the Pre tubes are DC heaters.  Maybe heater rectifiers are gone?
Its the heaters that make the tubes glow, as they quite literally heat the element to release teh electrons.

You've tried known working tubes in the sockets?

+1 if the heaters are not working, that would cause the symptoms you describe.  The DC heater suggestion is a good one.  Do you have access to a multimeter?  You could measure the voltage on the pre tube heaters to see if it's AC or DC, and if you have any voltage at all.

With a photo, we can go from there.

one thing - how do you know the fuses are not blown? Did you measure them, or are you just looking at them?  Sometimes they can look fine but be blown all the same.

forgot to add - be careful in there!  Hold the meter probe with your right hand, and hold your left hand behind your back.  Connect the -ve probe using an alligator clip - again with your left hand behind your back.  Don't ask questions - just do it that way!

 

[Vol. Knob]

I have swapped out the tubes with others and they don't light up either.  The phase inverter tube (located over by the power tubes) does light up..  Also noticed that the pilot light does not light up.  I didn't use a multimeter on the fuse, just looked at it.

 

[mayfly]

I have swapped out the tubes with others and they don't light up either.  The phase inverter tube (located over by the power tubes) does light up..  Also noticed that the pilot light does not light up.  I didn't use a multimeter on the fuse, just looked at it.

no pilot - yea, I really suspect the heaters.  I think Jim is right about the DC heater circuit failing

 

[jimh]

+1 on the multimeter to check the fuse. And the single-handed usage  :icon_thumright:

By the way, dont think anyone has mentioned, but if you do use a meter to measure the heater voltage (across pins 4 and 5 on the socket), you want to be looking for around 6.3V wether they are ac OR dc.
The heaters are usually (not familiar with this amp so cant say for definite...) just parallelled / looped from one tube to the next to the next to the next, so you may simply have a broken pcb track or wire part way down the circuit, hence why half of your tubes are glowing and half not glowing.  Also, in most VIntage style amps that I've seen the pilot light uses the heater circuit for it's power, and is usually last in the chain.

Some amps use dc heaters as they tend to be less noisy than ac heaters, although in a well designed circuit with good chassis layout there is actually little difference.
As far as I'm aware its not common to split the heater section, ac for Power, dc for Pre, but its not out of the question.  Look for a small bridge recitfier or a set of 4 diodes which may be burned up.