EVH Marshall preamp tubes?

[Carbia]

Gain is easy to measure with a scope.

For instance:
You put a tube in V1 and plug a signal generator.
set and measure the input voltage, usually 200-300mv AC peak o peak (like a guitar)
then measure the Vac from the plate of the tube, for instace 20v.

Then is easy to mesure the gain factor.
If the input voltage is 200mV AC and the output 20vAC the gain factor is 100. (20v is 100*200mV)

To measure the current you can place your multimeter in series with the tube plate and measure current or, at least in my tester it's possible to do.

I guess that if your tester only say good/bad is a very basic tube tester, and doesn't measure transconductance, only emission. My Precise111 has a function in which you can send the plate output to two banana jacks in which you can plug the multimeter to measure current easly.

[bobtec]

The only way is to just try out a lot of different tubes in your amp and see what is Best for That amp.. Not what someone used 40 yrs ago in theres,I use a RCA in V-1 a Sylvania in V-2 and a 161 mullard in 3.. and I have a shoebox full of tubes that I tried out..These work the Best for My amp...Ed now just gets boxes of tubes from ARS,and changes these out every few shows..some guy was selling his old ones on ebay a few yrs ago..I use to go to them back in the 1980's..Great deals

[rgorke]

The only way is to just try out a lot of different tubes in your amp and see what is Best for That amp.. Not what someone used 40 yrs ago in theres,I use a RCA in V-1 a Sylvania in V-2 and a 161 mullard in 3.. and I have a shoebox full of tubes that I tried out..These work the Best for My amp...Ed now just gets boxes of tubes from ARS,and changes these out every few shows..some guy was selling his old ones on ebay a few yrs ago..I use to go to them back in the 1980's..Great deals

really?!?!?! You like the Mullard I61 in V3? I never tried it....I will now!!!!

[Carbia]

After trying a lot, I like i63 in V1 and V2 and Sylvania 12ax7 in V3.

[rgorke]

Oh, yeah. I tried the I61 or I63 (can't remember which I have) in V3. Really seemed to make it punchier running a stock 12xxx spec with 100k NFB. I have Sylvania 12AX7WA in V1 and a short plate Sylvania in V2.

Thanks for the tip!!!

[sixpakldp]

I believe I asked the same question about EVH's preamp tubes a few years ago and was told Sylvania 12AX7WA. I instantly bought three of them and ran them for about two years. Very noticeable difference going to NOS tubes. A few years later I purchased, restored and blackfaced a 74 twin. When I brought it home and opened it up I was elated to find it had all NOS pre amp tubes. One day curiosity got the best of me and I took two of the RCA 7025's out of the fender and put them inV1 and V3. My Marshall has remained that way since. The Sylvanias are a great tune but to some extent the distortion is a little on the grainy side. The 7025's are super smooth and tend to really make the amp play fluidly under the fingers. The V2 Sylvania seems to add just the right amount of rawness to the overall sound. I also have a Millard that I run in V1, which is not as hot as the 7025. However if you look at the plate structure of the Mullard and the 7025, they are very similar. Anyway, if you going through tube swapping do your self a favor and try the 7025. It's a good one to have in the arsenal.

[SQUAREHEAD]

V1 - I61
V2 - I63 (STRONG)
V3 - Bejing 12ax7 (1980's) - not a new Chinese 12AX7!

I agree, Carbia... the nos Mullard tubes just can't be beat…
They just do it 'right'