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Marshal guitar amp valvestate 40v model 8040 stops working after 10 minutes.

Posted by Anonymous on

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Posted on Jan 02, 2017

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robotek
  • 1512 Answers

SOURCE: Marshall valvestate 8040 - how to change the valve?

Hi chagzuki, you are right, but only when the valves are used as outputs, You amp has transistorised outputs, and a single tube used for distortion/gain. You will get a very long life out of this tube also because its supply voltage that is is used in the valvestate preamps is really quite low. Just enough for it to work really, so the tubes life can be expected to be much longer than normal. It is also a preamp tube, not an output tube, so they rarely need changing. If you ever did want to change it(dont bother), it is located on the PCB inside the unit. You have to slide the sleeve off to get at it. Get yourself a JCM800=the best guitar amp ever built(imho), then yo got pure Marshall tone, and output tubes that need changing every 6 months or so. Now go RIFF OUT and dont worry about your valvestates' "valve"

regards
Graeme

Posted on Mar 22, 2008

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SOURCE: marshall 8080 valvestate amplifier

There could be a short in the rectifier diodes or in the transformer itself. Can you take some measurements inside the unit?

Let me know.
Dan

Posted on May 29, 2008

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Hi Andy

The problem you face is most probably the same that stops most all valve state amps from working. They suffer terribly from fry/cracked solder joints. You will have to remove the main circuit board from the chassis, and resolder any suspect joints you can see, particularly about the rear loop in out jacks, control pots on the front panel, and power supply. There is a large power resistor and zener diode that cause problems in this model from memory. The valve never fails in these amps. Due to the lower supply voltages they are run at, they are not under alot of pressure, and as such give good reliable service. Go over the amp for dry joints first, and see how you get on. I have repaired so many of these with that problem.

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Guitar amplifier


Hi thecross

I have fixed so many of these amps over the years... Marshall Valvestate series of amps are notorious for dry solder joints developing on the main PCB. If you have the skills(or an old mate that does)Remove the PCB from the chassis and resolder any suspect dry joints and you will fix the problem. Check particularly about any components there the PB has changed colour. This is an indication of heat in that area, and heating and cooling is a major cause dry joints.
I am more than happy to answer any other questions you may have about it, just give me a hoy :) If you are still unsure, or have problems, then before you give a rating for this advice, please get back to me and we can try some more things.
Thanks for using FixYa, If you consider the advice I have given you as sound, a FixYa rating is a great reward for my efforts to help you. Cheers.

regards
robotek

Jun 16, 2008 | Audio Players & Recorders

1 Answer

Marshall 8080 valvestate amplifier


There could be a short in the rectifier diodes or in the transformer itself. Can you take some measurements inside the unit?

Let me know.
Dan

May 29, 2008 | Audio Players & Recorders

1 Answer

Marshall valvestate 8040 - how to change the valve?


Hi chagzuki, you are right, but only when the valves are used as outputs, You amp has transistorised outputs, and a single tube used for distortion/gain. You will get a very long life out of this tube also because its supply voltage that is is used in the valvestate preamps is really quite low. Just enough for it to work really, so the tubes life can be expected to be much longer than normal. It is also a preamp tube, not an output tube, so they rarely need changing. If you ever did want to change it(dont bother), it is located on the PCB inside the unit. You have to slide the sleeve off to get at it. Get yourself a JCM800=the best guitar amp ever built(imho), then yo got pure Marshall tone, and output tubes that need changing every 6 months or so. Now go RIFF OUT and dont worry about your valvestates' "valve"

regards
Graeme

Mar 22, 2008 | Audio Players & Recorders

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