How do I adjust plate voltages?

[cdc3jj]

I took apart my ceriatone HRM BM today (finally) to sheck the plates voltages of v1,2 &3... v1 is good. v2 is about 5 low and v3 is about 40 low. How do I go about getting those up? FWIW v1~200 v2~195 v3~249.
The OD kind of sounds like fuzz more than OD to me. Could this have something to do with it? Thanks

[David Root]

Are you measuring from plate to ground ie chassis? V3 cathode normally has an appreciable voltage on it.

[cdc3jj]

I think so. I measured from pin 1 of each tube to the chassis.

[David Root]

V3 sounds low unless you have a 12AT7 in there instead of 12AX7. I would measure pin 6 also on each tube, and pin 3 or 8 on V3, the PI cathodes.

[cdc3jj]

It's an ax7. Actually.... jj ecc 83s but that's the same thing right?

I hooked up the kleinulaton and v1 went up... here's the readings

v1, pin1~200.8
v1, pin6~205.2

v2, pin1~196
v2, pin6~204.2

v3, pin1~251
v3, pin3~41.7
v3, pin6~244.7
v3, pin8~41.7

pin 3 and 8 of v3 are connected. Would an at7 be better as the PI?

[JD0x0]

correct me if im wrong but doesnt the BluesMaster have lower PI voltages than a "normal" ODS

[dogears]

250 is normal for a Bluesmaster PI.

Make sure your OD trimemr is set very low. Try 20k to ground.

Also, the mid trimmer needs to be really low. Try 4K as a median. Tweak from there.

[David Root]

My mistake. I was thinking of a normal ODS.

[Structo]

Just to clarify, with the amp off and unplugged, caps discharged.
Measure the middle lug or wiper of the OD trimmer to ground.
20K - 30K is usually where it sounds best.

Your voltages aren't too bad.
In fact I think if you were to try different tubes in V1 and V2 you might find that the voltages will vary by as much as 10v sometimes between tubes.
Generally you want V2 a little higher than V1.

Also, do you know where your power tubes are biased at?
I don't know much about the Bluesmaster amps but most ODS amps sound best with the bias on the cool side.

I don't know what your power tube plate voltages are like but if they are in the neighborhood of 440-455v then try 34-36ma.

With 34ma being for the higher plate voltage.

I attached a 6L6 bias chart if you don't feel like doing the math for the bias numbers.
You will notice as the voltage goes up, the bias current goes down.

Try settings between the 50 and 60%. 60% is pretty high for these amps.

The bonus is that with a cooler bias setting, your power tubes will last longer.

[cdc3jj]

Which pin do I measure the plate voltages from on the power tubes?

[sergio]

from pin3 to ground

[heisthl]

Which pin do I measure the plate voltages from on the power tubes?

from pin3 to ground

This is a backpocket measurement - put one of you hands in your back pocket and be very steady with the hand that touches the meter probe to pin 3.

[cdc3jj]

Looks like I need a different meter. Mine just blinks OL when I touch pin 3. I'll have to hit up my dad tomorrow when I head down to my hometown.

I'm either getting used to the way this amp sounds or I'm bonding with it. I don't know. I put in some sovtek 6l6's that were matched and biased around 35. Then redid the RF mod. I found a nice spongey OD sound.

I'll post my findings on the power tube voltage tomorrow or thursday. Thanks for all the help so far.

[Structo]

OK, Please learn how to safely work on that amp before you go digging inside where there is over 400 volts direct current.

Not only is that many times over what can kill you inside the amp, just catching a bit of a charge is enough to throw you across the room.

What Henry was eluding to was if you keep one hand in your pocket it won't be possible for you to get a charge in one hand and exit out the other one. With your heart being in the middle of things.
Never have two hands inside a live amp!

Did you know that in certain amps it can still hold hundreds of volts in the capacitors, even when the amp is turned off and unplugged?

Is your meter an auto ranging meter?

If you plan on working on your own amps or perhaps get into modding and building them, my advice is to buy a good meter.
The holy grail many will tell you is a Fluke but there are other good meters out there as well.
I would suggest you get one that is auto ranging, measures capacitance as well and reads RMS voltage.
Buy a book or two on tube amps and how to safely discharge filter caps and how to measure voltages correctly.
There is a list of amp books in the technical section I believe.
This is a great forum but it's on you to learn the safety aspects and at least some basic theory.

Good luck.

[mcinku]

The OD kind of sounds like fuzz more than OD to me.

One more thing you can try... it really helps if you set your OD level at 5 and use your Klein Recovery pot to bring the volume down to acceptable volume.

... and like others said OD trimmer should be set very low.