Voltage Problems w/ Modded BF Bandmaster Clone.

[Thisismyname]

New build using a Fender Blues Dlx power transformer and power circuit, excluding the relay switching circuit that branches off of the bias supply.

I created my own layout. The amp is a single channel with no FX. It has a switchable T-Wreck style 3rd pre stage, 3-way NFB switch, cathode/fixed bias switch, Valve Wizard bus ground, more localized filter cap placement.

Wall outlet>variac>current limiter>amp.

At first power yesterday, voltages seemed fine with no tubes installed. With pre tubes, voltages seemed fine, although AC voltage at PT primary was at 110vac instead of 120vac at line voltage position.
 
After installing power tubes, where my current limiter should be at line voltage, it's now at 95.7vac for 5-10 or so seconds. Then it drops down to 90.8vac(measured at fuse post-switch.) When switching to cathode bias, it goes down to 75.5vac. Limiter brightens.

Touching the turret between the top phase inverter grid and input cap with my multimeter causes my limiter to briefly brighten. Taking the probe off causes the same effect. This issue is not present with tube removed.

With fixed bias, the power tubes pass very little current, around 9-12ma, although low AC voltage may contribute? Cathode bias is a little higher, all other amp voltages drop at least 10v.
Coldest bias voltage is -36.9vdc, hottest is -29.9vdc.

Voltages measured at 90.8vac with fixed bias:

                      V1-12AX7
P1-170.4
P2-0
P3-1.3
P6-173
P7-0
P8-1.3

                   V2-12AX7
P1-238.9
P2-0
P3-2.3

                    V3-12AX7
P1-209.8
P2-27.2
P3-45.9
P6-206.9
P7-28.7
P8-46.1

                       V4 and V5-6L6
P3-312.1
P4-310.8
P5- -34.8

B+ -311.7
Screen-310.9
PI Plates-285.2
Pre Plates-264.3

I suspect a short somewhere, but I haven't found it yet. I've swapped all the tubes too. I'm not sure what's going on.

Any and all help is greatly appreciated!

Pictures in next post.

[Thisismyname]

Problems uploading some of the pictures, working on it.

[sluckey]

Get rid of the light bulb limiter. Adjust the variac for 120VAC output. Plug in amp to variac. Turn on and recheck voltages.

[Thisismyname]

Get rid of the light bulb limiter. Adjust the variac for 120VAC output. Plug in amp to variac. Turn on and recheck voltages.

Did that, didn't blow a fuse like I thought I might. Got 120v at the fuse. I've only worked with 6V6s and EL84s, I guess I didn't expect the normal voltage drop through the limiter to be THAT much more with 6L6s.

Some voltages still seem off. Measuring with fixed bias;

                    V1
P1/P6-- 226/228
Grids 0v
P3/P8-- 2.0/1.9

                     V2
P1--324 (seems way too high)
Grid--0v
P3--3.3

                V3
P1/P6--277/271
P2/P7--42.1/44.4
P3 & P8--70.1

                V4 & V5
P3--430
P4--429
P5  -43.2

          At 120vac input;
B+ is 5v higher than Blues Dlx spec
Screen Node is 5v higher
PI Node is 21v higher
Pre Node is 39v higher

I also can't get the bias hot enough. Should I reduce the reduce the 15K resistor in between the 25K bias pot and ground?

Any suggestions about the other voltages?     

[sluckey]

V2-1 should be high since you used a 10K cathode resistor. Don't worry.

All other voltages look fine to me.

I also can't get the bias hot enough. Should I reduce the reduce the 15K resistor in between the 25K bias pot and ground?

Reducing that 15K will make the tubes run hotter. But I'm not convinced that's your issue. You may have some weak tubes. My Bandmaster has the bias set to provide -44v on pins 5 and that caused the tubes to idle at 48ma (20W).

Here's my Bandmaster with voltages. Could come in handy...

     http://sluckeyamps.com/misc/bandmaster.pdf

[Thisismyname]

At the hottest bias, I got 33ma of current at 14-15 watts dissipation. And that's with -43.2 on the grids. 430 on the plates.
I was using new JJ 6L6GC.

I tried a pair of Sovtek 6L6WGC just now and, with hottest bias, got 43ma of current at 18 watts dissipation. Same grid bias, plate voltage down to 421v.

So probably weaker tubes. I'd rather use the JJs. Should I change that resistor or do something else?

[sluckey]

Reducing that 15K will make the tubes run hotter.

[Thisismyname]

Reducing that 15K will make the tubes run hotter.

Thanks, Sluckey. I'm always irrationally nervous and doubtful when powering up new builds. The concept of "what I don't know I don't know" really freaks me out, even with things I actually do know.

I appreciate the help, thanks 👍

[sluckey]

Hey, you already knew it. Just needed a little nudge.