Peavey heritage VTX series 130w - 6L6EH electro Harmonix - UK Vintage Radio Repair and Restoration Discussion Forum

SeanStevens · 11th Oct 2023, 2:36 pm

Hello

asking for a friend in London (Finsbury Park)

I've just sold the valve tester I had access to - so the story so far . . .

The amp is a beast, worked well, then developed a hum. New valves and off it went again for a while. After some years out of use, has had crackly pots lubed and it works fine on one channel, hums badly on the other.

User is going to be come a Forum member I hope so she can read the responses . . .

Has anybody the capability to test the valves to see if they are at fault? I'm guessing it could easily be a capacitor issue surrounding the offending channel, but it would be good to eliminate the valves being duff.

Amp has all valves installed + 3 old spares (6L6GC).

SEAN

JonSnell · 11th Oct 2023, 9:23 pm

The VTX uses a novel idea in the output stage, fixed voltage on the grids with a solid state driver on the cathodes. I have had the transistors suffer from thermal runnaway in the past.
The output stage is of an Ultra Linear design but as these valves are running with 525volts on their anodes, a standard valve tester will probably not show up many if any defects.

I am in Weymouth and would be happy to service the amplifier for you or even just test the 6L6s but as I say, testing might not show up any isues in the valves.

11th Oct 2023, 2:36 pm	#1
SeanStevens Octode Join Date: Sep 2009 Location: Bath, Somerset, UK. Posts: 1,028	Peavey heritage VTX series 130w - 6L6EH electro Harmonix Hello asking for a friend in London (Finsbury Park) I've just sold the valve tester I had access to - so the story so far . . . The amp is a beast, worked well, then developed a hum. New valves and off it went again for a while. After some years out of use, has had crackly pots lubed and it works fine on one channel, hums badly on the other. User is going to be come a Forum member I hope so she can read the responses . . . Has anybody the capability to test the valves to see if they are at fault? I'm guessing it could easily be a capacitor issue surrounding the offending channel, but it would be good to eliminate the valves being duff. Amp has all valves installed + 3 old spares (6L6GC). SEAN __________________ There are only 10 types of people, those who understand the binary system, and those who don't.

11th Oct 2023, 9:23 pm	#2
JonSnell Hexode Join Date: Oct 2019 Location: Weymouth, Dorset, UK. Posts: 442	Re: Peavey heritage VTX series 130w - 6L6EH electro Harmonix The VTX uses a novel idea in the output stage, fixed voltage on the grids with a solid state driver on the cathodes. I have had the transistors suffer from thermal runnaway in the past. The output stage is of an Ultra Linear design but as these valves are running with 525volts on their anodes, a standard valve tester will probably not show up many if any defects. I am in Weymouth and would be happy to service the amplifier for you or even just test the 6L6s but as I say, testing might not show up any isues in the valves. __________________ Valve equipment repairs since 1968 https://jonsnell.co.uk