Ok, I have read a bunch of sites telling me how to bias amps. The problem is, they don't make it easy. I haven't seen one site that goes through it with pictures. Here's one I found:
Here's the Marshall Service Bulletin on biasing the JCM2000 series amps:
1. Make sure the amp is connected to a load with the proper impedance selected.
2. Power up amp on Standby, and let the circuit stabilize for a couple of minutes.
3. Locate the male three pin molex connector (CON2) with the two mini pots (PR1 and PR2) (located on each side of the molex connector) on both ends found at the bottom of tube bay.
4. Connect DMM (set to read mV) with alligator leads, reference common lead to center pin (pin2) on molex connector CON2 and positive lead to pin1 on CON2.
5. Take amp off Standby with no signal, adjust mini-pot (PR1) closest to pin that the positive lead from your DMM is connected to and set it to mV voltage that is listed below.
6. Repeat steps 4 & 5 for pin3 mV and until pin1 & pin3 mV readings are the same.
DSL50 45 mV TSL 601&602 80 mV
DSL100 90 mV DSL 401 1.375V
TSL100/122 90mV DSL201 .675V
Here's a quick bias lesson:
What you want to do is measure the plate voltage (B+) from pin3 of one of the power tubes. It should measure between 450-500V. Now the max plate dissapation (Pa Max) for EL34s is about 25W. To calculate the correct bias, you want to:
(Pa Max/B+)(.7) = 38-45mA depending on the exact plate voltage of your amp. Check and adjust via the molex connector and pots from above.
This is all giberish to me. I'm a visual learner. Reading how to do it, doesn't help me at all. I know I could do it, if it was just explained better. One question I have is:
1. When biasing, do you bias the power tubes or preamp tubes?
Also, I know it may be trouble, but if ANYONE can show me pictures of the process, it is greatly appreciated. I know that's asking a lot, but if anyone is bored and wants to do something that'd be awesome.
Epiphone Les Paul Standard
Fender Squier Stratocaster
Fender Bassmen Ten
Marshall JCM 2000 DSL 50
Peavey Blazer 158 (Practice)
Big Muff Pi
DanElectro Hashbrown Flang
Zoom 505 (sounds like crap, but it was free)