6g3 'deux' - lux build(s)

[StrummersOfThunder]

Pots and jacks all in place.
Tonight ill wire up the power section and pre-wire the boards. Might get them in.
Two at a time doesnt take twice as long but it does add up

[StrummersOfThunder]

Got the power rails done, under-board wiring and started the of board connections to these two 6g3 amps last night. Aiming to complete them this weekend and prepare for testing

[StrummersOfThunder]

Need a little help from the gurus...

I powered up amp one today.
Had the trusty current limiter in place and im glad I did.
Wihtout tubes in it powered fine. With a 5ar4 in place I got 340v AC to the rectifier and 450v to the first node, dropping to 300v by the third node. A little high but not bad.

Testing the amp with tubes I found I had very low signal thru with the guitar and amp up on full. There was audible NO signal passing thru the bright channel .....Then I noticed Mr current limiter heating up!
Removing the power tubes resolved the current limiter.

I quickly had a look at the voltages/current. The current across the 1 ohm resistor on pin 8 was 105mV (mA) !!!! on both tubes. They were piping hot.
Plate voltages 450v.

Ive checked and checked my schematic but to no avail. Im leaving it for today and will put fresh eyes on it tomorrow.

What would be the likely cause of such massive current draw at the output tubes?

Yes it was plugged into a load.
Also the bias voltage seems spot on at -25v.

The rest of the board seems on the high side voltage wise, but from what I read this isnt surprising with the hammond iron when comparing to the older schematic voltages.

[StrummersOfThunder]

I’m only getting -170mv on pin 5 of each output tube socket with the tubes out. So no negative bias ?

[StrummersOfThunder]

Stand down! I’m an idiot

[jeremyb]

Stand down! I’m an idiot

Flat batteries for the EMGs in your 8 string ESP?

[StrummersOfThunder]

Stand down! I’m an idiot

Flat batteries for the EMGs in your 8 string ESP?

Man I wish it was that metal.
The rectifier that went up in flames was pretty bad ass tho

[StrummersOfThunder]

It’s alive !
Sounds pretty cool too
Compared to the 6g2 it’s definitely much cleaner / louder and woodier

[MikeC]

Strange that you got any appreciable voltage drop at the nodes without tubes. No/low current should = no/low voltage drop. Me suspicious right there.
But glad she's now up and running.
What actually was the issue?

[StrummersOfThunder]

Strange that you got any appreciable voltage drop at the nodes without tubes. No/low current should = no/low voltage drop. Me suspicious right there.
But glad she's now up and running.
What actually was the issue?

Yeh good point
There was some drop tho. I did leave the preamp tubes in
The issue was 1k5 resistors between on 5 and 1

[MikeC]

Grid stoppers?

[StrummersOfThunder]

Grid stoppers?

Yep
Issue went a meat when I removed them

[StrummersOfThunder]

Strange that you got any appreciable voltage drop at the nodes without tubes. No/low current should = no/low voltage drop. Me suspicious right there.
But glad she's now up and running.
What actually was the issue?

you are right,. there was no voltage drop sans toobs

[StrummersOfThunder]

Still I have to sort the bias I think
With the -25 from the schematic and plates at 410v my tube current is way too hot.
I guess ill revert to the deluxe reverb bias set up with the bias pot / 50v centre tap.
Mike do you use a 10k bias pot with a 10k resistor on it? What would be your move if you need to get a little more sweep out of it to get more -ve bias voltage?

[MikeC]

Yes I'm using 10K pot on BFstyle amps. Reduce the series resistor (the one between the AC tap and the diode) to get more negative voltage.