Second Express build startup issues

[Ron Worley]

Hey all you Masters of the wreck, I've got a problem with a new express build that I can't figure out.

It's standard Express with a dual voltage PT that I installed with a Marshall voltage selector (the amp is for a mate in the UK). It also has the modified pilot light running off heater Voltage because I couldn't find a suitable 240V unit. (I installed a 6.3 bulb into the housing of a real TW indicator). I also has Moose's new "Vintage" OT with the different color wires than usual.

Everything went fine on the start up routine- all the voltages and such checked out OK with the bulb limiter, and then without it. Here are the final voltages:

Secondaries: 588.4VAC
B+1: 399.2 VDC
B+2: 390.1 VDC
B+3: 310.9 VDC
B+4: 293.2 VDC
B+5: 278.0 VDC

Heater voltages are all good- 5.54-6.62 (V1-V5). No redplating on the Power tubes. Everything measured with max negative bias V prior to biasing.

Plate Voltages ( don't know if these are good or bad..):

V1a: 209.4
V1b: 183.6
V2a: 263.4
V3a: 201.2
V3b: 207.4
V4: 400.1
V5: 400.6

Here's the real kicker, when I thought all was well, I got out the Les Paul for a quick sound / tone check..... absolutely nothing out of the speakers....

No hiss, nothing. Tried a different speaker cab and a different cable to make sure it wasn't the original setup.

I wired the OT with the connections set per the colors ascribed to me by Alden at Heyboer: blue- CT to the Standby switch, and green and purple to the plates of V4 and V5 respectively.

I am totally stumped...... I'm going to recheck my wiring on the impedance switch to make sure there's not a short there, otherwise, I am clueless...

I would appreciate any help you guys can render, I have to get this amp done this week to hand deliver to the UK on a business trip....

Ron

[jjman]

Heater voltages are a typo, yes? ("5.54-6.62")

When you check the voltage on the plates and screens of the output tubes, do you hear a short, little pop/squeal noise from the speaker? (You should.) If you don't, I would suspect a bad OPT or wiring problem on it's secondary.

[Wayne]

I wired the OT with the connections set per the colors ascribed to me by Alden at Heyboer: blue- CT to the Standby switch, and green and purple to the plates of V4 and V5 respectively.

Ron

ummmm... could this be the problem?

W

[Ron Worley]

Sorry, yes a typo on the heaters- they're all 6.52-6.62V

The colors are as described by the manufacturer and confirmed By Strato17- he had the same unit.

I checked the resistance across the OT secondaries- CT to each lead on the plates was 45 Ohms and then 90ohms across the leads to the plates. That tells me that the blue wire is indeed the CT.

I don't hear anything at all from the amp when it's powered up- zero, Nada...

I have the same horrible suspicion that it's a bad OT.... I am screwed....

Ron

[guitarsnguns04]

what impedance slector switch did you use? any pics?

[Lonely Raven]

Why would you be screwed if it's a bad OT? Did you get it used?

[Trigger]

This may be an obvious question but did you ground the cathodes on your power tubes. That got me once, quietest amp I had ever built until I found the problem.

[bnwitt]

Check all of your ground points to the chassis with an ohm meter. Speaker ground from OT secondary, all preamp board grounds to buss ground on pots. Input jack ground to pot buss. What does the pot ground buss to chassis read in ohms?

[rooster]

Well, OK, you didn't mention the bias voltage, Ron? Do you have a reading there?

[Ron Worley]

I will check the grounds as you noted. I am getting good bias voltage (~-35V at max setting).

The cathodes for the power tubes are grounded.... so I'm still clueless....

I will report back with the grounding findings.....

Ron

[Allynmey]

Ron, Post some detailed pics. Check the tail of the PI to ground. Happens all the time.

[Ron Worley]

The Impedance switch is a real NOS Stackpole, and it's working fine.

I checked all the grounds, and they all checked fine. Then for the hell of it, I rechecked the continuity from the impedance switch to the farthest speaker jack positive terminal......very high impedance.

Turns out that I had a bad / cold solder joint on the wire from the impedance switch to the first speaker jack...

Fixed that, and magically, I have hiss coming out of the speaker.... Don't have time to run an axe through it until lunch time, but I'm pretty sure I have found the culprit.

I checked every connection run with the meter prior to power up, but apparently missed this not-so-minor bit of circuitry!!

Thanks for all the help, you guys rock as usual!!

Ron

[guitarsnguns04]

I am glad to hear you have it under control! You going to post some pics for us to see anyhow?