........

[JimiJames]

Looks like a basic bias setup with the 1ohm resistors on the ground from the power sockets. The forumula is 17.5 devided by plate voltage = target between 1ohm resistor and pin 1 and 8 of power socket (17.5 /380 = .046 or 46ma between resistor and socket). The instructions are in George's 100w plexi kit somewhere in this forum.

Good call as usual...
http://www.metroamp.com/downloads/100_W ... MP_KIT.pdf" onclick="window.open(this.href);return false;
Section: 18-G

[bognermatchless]

Will I need to bias differently if I plan to use a variac?

[Strat78]

The variac will change the voltage on the plates, so again your plugging the plate number into the formula whether it is 450v from the wall or 350v with a variac. At that point the variac will be married to the amp. If you plug directly into the wall by a mistake with the bias set for 350v with a variac, you will melt your tubes at full wall voltage, so be mindful of that.

[bognermatchless]

Thanks for the help.

I am currently in the market for some new power tubes, do any of you have a suggestion for what you like best? I was thinking the EH6CA7 but doing a search hear on the forum resulted in words such as "hard" sounding, which is not what I think of when I think Van Halen, I think of chewy and sag and looseness.

[Tone Slinger]

With your amp/spec (or really any other for that matter) I'd get the regular EH el-34's or The Eh 'Mullard' el34's. These tubes 'give it up' a little better and are used alot by both George M. and David Bray. Keep in mind that Bray also uses a PPIMV (like Marks Mod5 builds). You will get alot of 'haters', concerning EH tubes, but hey, try them for yourself. Cheap price and readily available. Get them from 'Lord Valve', cause he not only matches, but burns them in under REAL circumstances before shipping. To just match them is kinda stupid, since they will drift like a MoFo upon burning them in, leaving you with more descrepency between tubes.

[jerrydyer]

I love EH el34's

[mightymike]

Nice Amp Detective work. What a fun read!

[bognermatchless]

Can anyone chime in on this?

I LOVE the tone setting the master low and putting everything to 10 except the bass and playing like that, sounds unbelievable.....however I am curious about the tone at higher volumes. If I cranked the master wide open, is there something in the tone that otherwise would be missing with the master set low? With this Mod5 spec?

I don't have a proper cab to blast a 100 watt amp open like that at the moment, or else I'd def try it and see what happens, but I am curious.