Valve for Marshall AVT275 amp

eyrepm · 4th January 2010, 07:04 PM

I have this transistor amplifier, Marshall AVT275, with a valve pre-amp. I bought it used over 5 years ago, and I think it's time to sell the amp, and to replace the valve. But, I'm having trouble getting info about it. What I do know is that it is a 12ax7, dual triode. The valve itself says "Marshall VLVE-00041 WK14". Can I get just any 12ax7?

Amp with power on. Not much glow. Lit room.

Amp with power on. Un-lit room.

Thanks in advance

llwhtt · 4th January 2010, 07:13 PM

Any 12AX7, 7025, ECC83 will do. The number on the Marshall tube is their stock or part number. Is the original one bad?

Craig

eyrepm · 07:37 PM

I think the amp sounds bad... It's tiresome to play on. And it's hard to get any satisfying sounds on it. Which is why I'm selling it, but if a new tube is cheap enough, it will hopefully be easier to sell

I am green as can be with these things, but I've read pre-amp valves last for about 4 years. Other places say just one. They have almost no glow, either. As you can see.

Rod Coleman · 4th January 2010, 07:39 PM

The AVT275 runs these gently, and I never found one that sounded better with a new 12AX7 (=ECC83). But they are cheap enough to be worth trying.

More important, there is a frequent failure on AVTs that has turned up here regularly. Two resistors R202 & R223 (both 2.2 Ohm, 1 Watt parts) are given to failing high value, or open. This happens a lot if the fans get obstructed (like parking the amp on a pub seat with the backrest blocking the vents).

The heater goes dim or even out when this happens. check for 12v across valve pins 4 to 5.

It's a 15-minute fix if this happens to yours, and the parts cost less than a drink. Take it to a tech, though - it may take a while just to find the parts on the back-PCB, if you don't know where to start.

If you do know, follow the wires from the transformer to the back PCB. The two that go to W106 & W107 will lead you to the resistors, which can be checked in situ for value, or just changed anyhow.

eyrepm · 4th January 2010, 07:44 PM

Thank you for the answers! It might just be a bad amp in general. I will take it to a tech, though.

4th January 2010, 07:04 PM	#1
eyrepm diyAudio Member Join Date: Jan 2010	Valve for Marshall AVT275 amp I have this transistor amplifier, Marshall AVT275, with a valve pre-amp. I bought it used over 5 years ago, and I think it's time to sell the amp, and to replace the valve. But, I'm having trouble getting info about it. What I do know is that it is a 12ax7, dual triode. The valve itself says "Marshall VLVE-00041 WK14". Can I get just any 12ax7? Amp with power on. Not much glow. Lit room. Amp with power on. Un-lit room. Thanks in advance

4th January 2010, 07:17 PM	#3
eyrepm diyAudio Member Join Date: Jan 2010	I think the amp sounds bad... It's tiresome to play on. And it's hard to get any satisfying sounds on it. Which is why I'm selling it, but if a new tube is cheap enough, it will hopefully be easier to sell I am green as can be with these things, but I've read pre-amp valves last for about 4 years. Other places say just one. They have almost no glow, either. As you can see. Last edited by eyrepm; 4th January 2010 at 07:37 PM.

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4th January 2010, 07:13 PM	#2
llwhtt diyAudio Member Join Date: Jun 2008	Any 12AX7, 7025, ECC83 will do. The number on the Marshall tube is their stock or part number. Is the original one bad? Craig

4th January 2010, 07:39 PM	#4
Rod Coleman работник diyAudio Member Join Date: Jul 2004 Location: Warwickshire UK	The AVT275 runs these gently, and I never found one that sounded better with a new 12AX7 (=ECC83). But they are cheap enough to be worth trying. More important, there is a frequent failure on AVTs that has turned up here regularly. Two resistors R202 & R223 (both 2.2 Ohm, 1 Watt parts) are given to failing high value, or open. This happens a lot if the fans get obstructed (like parking the amp on a pub seat with the backrest blocking the vents). The heater goes dim or even out when this happens. check for 12v across valve pins 4 to 5. It's a 15-minute fix if this happens to yours, and the parts cost less than a drink. Take it to a tech, though - it may take a while just to find the parts on the back-PCB, if you don't know where to start. If you do know, follow the wires from the transformer to the back PCB. The two that go to W106 & W107 will lead you to the resistors, which can be checked in situ for value, or just changed anyhow.

4th January 2010, 07:44 PM	#5
eyrepm diyAudio Member Join Date: Jan 2010	Thank you for the answers! It might just be a bad amp in general. I will take it to a tech, though.

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