Invective 120 tube bias runaway

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lownoma44
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Invective 120 tube bias runaway

Post by lownoma44 » Wed Mar 25, 2020 10:58 am

The power tube in V10 seems to have a runaway issue. The tubes in all other sockets are sitting pretty healthy at 27 mV. The one in V10 however it's going nuts. With the standby switch still in the down position it fluctuates around the 70-90 millivolt range and goes beyond the millivolt range of the meter once the switch is flicked up. With the amp off and unplugged I also probed the bias test points on the ohm setting of my DMM. The 3 other sockets have no resistance and the V10 has no continuity at all. I haven't seen the amp schematic so I am unsure if each socket has it's own screen/grid resistors. Could this be just a bad solder joint on the socket to PCB or an issue with the resistors.

lownoma44
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Re: Invective 120 tube bias runaway

Post by lownoma44 » Wed Mar 25, 2020 11:24 am

Also I swapped tubes around so it stays on just that V10 socket.

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JamesPaul
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Re: Invective 120 tube bias runaway

Post by JamesPaul » Wed Mar 25, 2020 3:26 pm

Welcome to the forum.

That definitely looks like an issue with the V10 socket or bias as the issue follows that socket. Possibly the grid resistor.

i would expect Peavey Customer Service to still be answering the phones. Give them a call (877-732-8391 between 8 a.m. and 5 p.m. Central Time, Monday-Friday) and they should be able to email you the schematic. I should be easy sort out once you have the schematic.
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
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lownoma44
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Re: Invective 120 tube bias runaway

Post by lownoma44 » Wed Mar 25, 2020 9:23 pm

Still waiting on a schematic from Peavey. But if anyone has it can you tell me what resistors on the pcb are labeled R170, R171, R172, R173? It looks like the resistor is cracked and wondering if this could be my issue.

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JamesPaul
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Re: Invective 120 tube bias runaway

Post by JamesPaul » Thu Mar 26, 2020 12:27 pm

I had to call Peavey today, so I checked on the Invective schematic. It is currently only available to authorized service centers. That makes sense as the Invective is still relatively new and there are a lot of features on it which are likely proprietary.

Either take it for service, or if you have experience working on tube amplifiers assume V7 thru V9 are good and start comparing/contrasting their circuit measurements with V10's.
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
James Paul's Peaveys
Decade, Classics, Ecoustic, Windsors, VYPYR, Triple XXX, XXL, VKs, Bandit, JSXs, VIP, Piranha and a Penta.

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