First Time Build Problems

[ThermionicScott]

Actually, I am in the US. I am using this power transformer.
https://d1sjrnpi226dnf.cloudfront.ne...pdf?1382030387

Gotcha. Much harder to miswire that one without it being painfully obvious.

I'm curious now if your voltmeter might be off, or your wall voltage really low. What does a brand-new 9V battery read on your meter?

[dwilliamsaudio]

A brand new 9V measures 9.26V. It is pretty much in line with two other voltmeters I used at work today to test the same battery.

[dwilliamsaudio]

OK, I've looked at my DC voltages on the test points from the schematic that Jazz P Bass posted. I will do the all the AC test points after I can figure out how to generate a 100mVAC 1khz sine wave. I have a tone generator that will do about 300mVAC, but not 100. Maybe I'll run something out of Pro Tools. Or maybe there's an app for that.

My readings are on the left, the correct voltages from the schematic are on the right in ().
TP1: 360 (370)
TP2: 320 (320)
TP5: 250 (250)
TP6: 17.48 (21.2)
TP7: 207 (204)
TP8: 45.6 (46)
TP9: 166.5 (165)
TP10: 1.25 (1.25)
TP11: 1.168 (1.33)

I don't know if any of these look alarming to anybody, but I was hoping for a more obvious discrepancy. I also should probably have pointed out that I did change out the .022ufd coupling cap for a .01 as recommended by TubeDepot's manual. I don't know what, if anything, this would effect on my meter for any specific test points.

[nosaj]

Oh another question what kind of guitar are you using and pickups?

Thanks,
nosaj

[eschertron]

Make sure Tube Depot didn't accidentally send you 10 Ohm resistors for the heater's artificial center tap instead of 100 Ohm. Just thinking out loud as to what may cause the lower heater voltages. Does your build have a fuse on the heaters? Can you verify that you're not dropping voltage across that?

[dwilliamsaudio]

I am using 2 different guitars. I have a couple more I could try. 1 is a telecaster with Dimarzio Area T pickups. The other a Dot with Seth Lover PAF style pickups. Neither of those guitars are especially high output. But I am turning up the amp most of the way and it's clear like a PA system.

[nosaj]

Any chance you can measure the output of the guitars?
What is the vol control on the guitars set to?

nosaj

[dwilliamsaudio]

They are both 100 Ohm resistors. I really wanted that to be it. It would have been an easy fix. The only fuse is the main fuse on the control panel. I'm not exactly sure how to check my guitar output, but I always play everything all the way up. Could I somehow be losing Input signal before it gets to V1?

[ThermionicScott]

Just for kicks -- and I willfully admit this is kind of a tangent -- have you measured the unloaded filament voltage (all signal tubes and the light bulb pulled)? If it's not at least 6.3V, I'd wonder if the transformer was miswired or something. What voltage do you have at the wall?

The HT secondary voltages can be expected to sag a little with tubes drawing current, but shouldn't be down to 307V. For comparison, I'm using a similar unit (Weber W025130) in a cathode-biased 2x6L6 amp which taxes the HT and filament windings more than a Deluxe, and the secondaries still read about 330V with 120V at the wall.

[dwilliamsaudio]

If I understand your test I am only getting 3.4V AC. I removed the bulb and all tubes other than the rectifier tube. Do I want to remove the rectifier as well? I have 123.6V at the wall.

[ThermionicScott]

If I understand your test I am only getting 3.4V AC. I removed the bulb and all tubes other than the rectifier tube. Do I want to remove the rectifier as well? I have 123.6V at the wall.

Okay, since the rectifier tube is on a different winding (as you know), that's fine for these tests.

So, that'd be 6.8V unloaded for the filaments if you measured from one side to the other instead of ground -- I'm feeling better about the filament wiring. What do the HT secondaries measure without the signal tubes in place? That corresponds to pins 4 and 6 on the rectifier tube.

Since I tend to imagine everybody has as much time to kill as I do , I'm curious if plugging in the signal tubes one by one, starting with the output tubes, would reveal any that are drawing abnormal amounts of heater current (heater voltage suddenly drops).

It's seeming like you've got things wired up correctly, but the secondary voltages just all droop a bunch with tubes in place, even with healthy wall voltage. Does the PT get hot to the touch after playing a while? If not, the amp is probably fine, and just has idiopathically low voltages.

[ThermionicScott]

Oh, another dumb question -- red/blue bias tap wire is taped off and NOT grounded or touching anything else, right? It must sound condescending to ask things like this, but I'm trying to eliminate whatever I can think of.

[dwilliamsaudio]

Not condescending at all. I am a first time builder asking for help. Red/Blue is definitely taped off and not touching anything else.
Measuring filaments one to the other instead of to ground gave me 6.77. So, as you said, basically 3.4x2.
The secondaries without signal tubes measured 703V. Fully loaded, the secondaries measure 617V, and the heater voltage measures 5.78 at the lamp. It was a nearly equal 2.9 at each tube pin to ground. I do not believe the transformer is getting hot to the touch, but I suppose I haven't actually touched it.

[g1]

Just for the heck of it, I'd disconnect the lamp socket and see if it has any effect on the heater voltage.

[ThermionicScott]

Not condescending at all. I am a first time builder asking for help. Red/Blue is definitely taped off and not touching anything else.
Measuring filaments one to the other instead of to ground gave me 6.77. So, as you said, basically 3.4x2.
The secondaries without signal tubes measured 703V. Fully loaded, the secondaries measure 617V, and the heater voltage measures 5.78 at the lamp. It was a nearly equal 2.9 at each tube pin to ground. I do not believe the transformer is getting hot to the touch, but I suppose I haven't actually touched it.

Okay, it's behaving like one would expect when unloaded: all of the voltages drift up, and I imagine your rectifier heater voltage also drifts above the nominal 5V when one isn't plugged in, but I'm not worried about it in particular.

In addition to g1's idea, you might try double-checking your soldering and grounding for the power cable and fuseholder. If you haven't soldered the three gray-themed wires together that are shown connected with a wire nut, that would be worth doing. If there is resistance on the primary wiring, that could explain an abnormal voltage droop on the secondaries under load.

P.S. After everything else has been eliminated, there is the possibility that the transformer itself is underspec'd for the job, but I do not want to besmirch anybody prematurely.