The Amp Garage

If you want to work out the details on a graph to understand electrically what's going on: Grab and print this data sheet. https://www.tube-data.com/sheets/019/e/EL84.pdf Use the graph on the top of page EL84-3 that says, "Vg2 = 300v". That's very close to the operating point voltages of your amp. ...

Do you have a tube tester that test for Gm of a tube ? A normally good AT7 can work better then a very weak AX7 . A easy way to prove out which tube is working better is to just set your meter for ac volts and you can then read the audio drive signal you have coming into the input of the PI . You c...

This can't be right, but it may be my ears. I tried a chinese 12AT7 in the drive channels tube and it seemed way louder. How can that be? Wouldn't a 12AX7 be just as loud or louder just by adjusting the gain pot for less drive? I mentioned my ears because i have trouble with my ears needing to pop q...

If cold biasing limits the output of your amplifier, you have a very weak phase inverter. It's a cathodyne by the way. Can the PI tube make a difference in clean headroom or volume from one model to the next? I tried a sovtek LPS long plate i had and i didn't try it in a band setting but at home it...

If cold biasing limits the output of your amplifier, you have a very weak phase inverter. It's a cathodyne by the way. Can the PI tube make a difference in clean headroom or volume from one model to the next? I tried a sovtek LPS long plate i had and i didn't try it in a band setting but at home it...

It's really not going to change "headroom". It's a class AB1 amplifier (I assume this is the Peavey Classic 30, 4x EL84). It will produce the cleanest tone when the bias is set around 65-80% of the output tube's plate dissipation. That's just baked into the circuit. Turning the bias "colder" (less ...

wattage ( IE power ) as ohms law states is a product of voltage x amps. If you monitor the amps output tube plate voltage as you adjust the bias you will clearly see that as you set the bias hotter the plate voltage will drop. The main thing that always takes place as you bias a output stage colder...

I usually have the master all the way up or close but the gain pot set as low as 1/3. So basically i'd get the same volume as when my bias was hotter by raising the gain pot a bit? That will only work as long as the amp stays clean. What i'm trying to get at is whether the amp will be the same as i...

Ok, 54% which I suppose should be good enough to keep it from going under 50% with any wall voltage. I swear it seems less loud tho, but then all i can do at home it turn it up and hit a chord. Low idle current means low power stage gain, requiring more drive for full output. I usually have the mas...

Ok, 54% which I suppose should be good enough to keep it from going under 50% with any wall voltage. I swear it seems less loud tho, but then all i can do at home it turn it up and hit a chord. crazy thin is, from the factory it was at 43%. (set resistor, i installed a bias pot) Whats that about?

Really? So basically the colder i go within reason, the cleaner it will be with the master cranked way up and no volume loss? I mean, if thats the case i'll defnitely lower it but i didn't realize that. I just figured people generally bias 70% minimum because it's supposed to sound better. I guess m...

I dn't disagree, tho i;d say 50% is too low especially given my amp isn't very loud and often is dimed to keep up with the band. Second, the voltage at hone is usually 123-125 while placed i go including rehearsal go as low as low teens and if i set it at home for 50% it'll go lower at some places. ...

I realize bias changes as an amp heats p, but which way does it typically go? I assume current goes up. My amp is a very hot running amp (not just mine, they are noted for this) and i can't bias i when its at it's peak heat because i need to play it at band volume for a set to get it there and i can...

Stevem wrote: ↑Sat Jun 20, 2026 10:38 pm No, what your assuming is not the case.

Ok, so no need to upgrade the PT too? Then what kind of improvement do you think i might get with say a 50w OT? I suppose i could get a peavey classic 50 OT

If the amp will drive external speakers and more of them, try hooking on an additional cab or two. You might get better acoustic efficiency that way. Or the external speakers may be more efficient. Well, thats what i've been looking at doing but it's anything but ideal for me on several levels. But...