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A valve amp question.

 
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frankus



Joined: 13 Sep 2004
Posts: 1100
Location: Chelmsford/Arachnipus

PostPosted: Thu Dec 10, 2009 9:46 am    Post subject: A valve amp question. Reply with quote

I play a Peavey Classic 30. I like it's tone, size and appearance - I've found plugging in a Marshall Solid State preamp into the amp's effects return gets me a really great response and articulation, which I much prefer for clean playing.

This is great as I can put the preamp on the pedal board and use the fx loop on the preamp for the time based effects. I get another channel for lead and I guess with some AB/Y wiring I could have a blend of preamps.

My concern is (the Peavey being an A class amp): are the amp's preamp valves suffering when they're not receiving input?

Does anyone know if this practice is okay?

Many thanks Smile
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PGA n00b



Joined: 21 Mar 2009
Posts: 55

PostPosted: Thu Dec 10, 2009 11:28 am    Post subject: Reply with quote

the class A just specifies how the power amp tubes are used

it's ok for the preamp to not get any input, actually I think they wear out faster if they receive input
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frankus



Joined: 13 Sep 2004
Posts: 1100
Location: Chelmsford/Arachnipus

PostPosted: Thu Dec 10, 2009 12:46 pm    Post subject: Reply with quote

Hi thanks for getting back,

In checking your comments (using duncanamp's and Torres' websites) I discovered most valve preamps are class A. So, as you say, with respect to the preamp, the combo's classification is irrelevant.

Class A - Current runs across the valves at all times.
Class B - A little current crosses the valves until a bias point is crossed.
Class AB - a bit of both.

Since the pre-amp is class A, there's always some current running across the valve's cathode - just no signal from the grid and so no electrons collected at the anode.

This wouldn't be the same as having the valve on standby where only the valves' heater is left on; and whilst valves wear out faster if they're driven, these valves wouldn't be receiving a signal - not a natural state.

If a preamp valve goes - I wouldn't be aware of it and left unchecked it might damage the rest of the preamp circuit - not great for resale.

So I'm thinking checks, procedures, working within tolerances, (removing the preamp valves - perhaps) or if it's really a non-starter - looking for another amp. I hope you understand why I'm still not wholly assured it's a safe thing to do.
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