Marshall Amp Forum - View Single Post - Preamp Tubes?

solarburnDSL50 · 07-03-2009, 12:09 AM

Quote:

Originally Posted by RiverRatt

I like new production tubes in V3 and V4 - the Mullard and Raytheon 12AT7's I have sound great there as well, but the new tubes seem to have a bit more presence or maybe they are a little more aggressive. It's hard to explain. I'm mainly just worried about Marty's info about Tung-Sols failing in V3.

There's a guy on the Les Paul forum who knows his stuff who insists that the PI tube can't have any affect on the tone of the amp. My experience seems to say otherwise. I can hear a difference and feel a different response from the amp with phase inverters that have different gain factors, or even between different makes of the same value.

Josh, I hear what you're saying about the bias setting. I've always thought that the JCM 2000 EL34 amps are biased way too hot at Marshall's recommended setting. Like I said, My DSL50 likes to be around 36-37mV instead of the 45mV that Marshall uses. One of these days I've got to open up my amp and measure the plate voltage. I suspect that 45mV is going to read somewhere between 80-90%.

In order to get a bias of 45mv the PV would have to be at 380 running at 70% dissipation which is hot. My DSL has varied from 450 to 475 PV depending on the power tubes. I run my bias the same as you and even at the higher PV's there is only one number difference in bias. Its between 36 and 38 at 70%. Definitely under the 45mv recommended. If guys like to run em' that hot, burn em' up. I don't.

V1 and V2 have the most effect on tone. I don't hear much of a change from V3 on. On my Night Train you can definitely hear the effect on tone the PI has when changing tubes there.