new Express build problems

[Randy Magee]

I am getting a very low volume extremely distorted sound out of this new Express build. I've checked it over a number of times for wiring errors and can see none. Some are a little low, some are a little high, but nothing seems off the chart. My voltages are as follows:

Mains: 119.7 VAC
Secondaries: 590 VAC
B+1: 401
B+2: 388
B+3: 311
B+4: 294
B+5: 280

V1
pin1: 215
pin3: 1.7
pin4: 6.6VAC
pin6: 192
pin8: 1.3
pin9: 6.6VAC

V2
pin1: 264
pin3: 2.8
pin4: 6.6VAC
pin9: 6.6VAC

V3
pin1: 196
pin2: 25
pin3: 36
pin4: 6.6VAC
pin6: 206
pin7: 24
pin8: 36
pin9: 6.6VAC

V4
pin2: 6.6VAC
pin3: 400
pin4: 384
pin5: -34
pin7: 6.6VAC

V5
pin2: 6.6VAC
pin3: 400
pin4: 382
pin5: -34
pin7: 6.6VAC

I will have to post pictures of the internals later... anything obvious from the voltages or suggestions as to what to check next? Edit: I am using a known good set of tubes, so a tube is not the problem...

[Randy Magee]

Here are some pictures of the internals... not the neatest of builds...

[dartanion]

Mains of 199.7V looks really suspicious.

[Randy Magee]

Sorry, that's a typo... mains are 119.7

[T Wilcox]

I cant see the ground jumper over to the main speaker jack!
Hope you haven't been playing plugged in there too long!

Todd

[T Wilcox]

Confirmed
I see no ground at all! on speakers
Edit: Maybe I am wrong I forget that Switchcrafts are grounded at chassis, but I would definitely check continuity!

[Randy Magee]

The Switchcrafts are grounded through the chassis... I checked continuity with my meter... the pictures of the originals that use Switchcrafts don't have a wire lead to ground either...

[T Wilcox]

Good, yeah I ran wire to ground on my build just in case jacks come loose or something.

Well sorry I dont see anything else jumping out at me.

Although this may not be the problem
Noticed some connections ie V1 pin 3 look to be just ran through hole and then soldered. I strongly suggest making good mechanical connection by crimping wire at all points before soldering.

Todd

[don280z]

Sounds like a bad pre-amp tube socket.....Have you wiggled the 12aX7's to see if there is a loose/poor connection?

[Randy Magee]

It's not a bad socket... I've poked, prodded and wiggled all the tube sockets while it's been running... I'd think the voltages would be way off if there was a socket problem...

[Gibsonman63]

I can't really tell from the pics. Do you have shorting output jacks, non-shorting or one of each? A lot of times the main output jack will be shorted and the extension cabinet will be non shorted. If you plug into the wrong one, your output will still be shorted.

It looks like you have done all the reasonable tests. If you have another head, you may want to test your guitar, instrument cable, speaker cable and speaker just eliminate the silly stuff. I had a jack problem on one of my guitars recently and I was convinced for a while that my amp was cutting out.

[fishy]

So, what else have you tried to this point?

Checked you guitar cable, guitar and speaker.......

I can't really make out the input jack connector and wiring very well but I would revisit that.

Recheck all grounds relative to the safety ground. You don't necessarily need an open to make things go South....

If you have some other tubes to try it is worthwhile. Might just be a bad one.

Chopsticked?
Might come up with a cold solder joint but I recommend a thorough review of the amp and the various voltages etc before you entertain this since it requires poking around a live amp.

[Randy Magee]

I can't really tell from the pics. Do you have shorting output jacks, non-shorting or one of each? A lot of times the main output jack will be shorted and the extension cabinet will be non shorted. If you plug into the wrong one, your output will still be shorted.

It looks like you have done all the reasonable tests. If you have another head, you may want to test your guitar, instrument cable, speaker cable and speaker just eliminate the silly stuff. I had a jack problem on one of my guitars recently and I was convinced for a while that my amp was cutting out.

Both output jacks are the non-shorting type... I've tried the same guitar and cord through an 18 watt I built a while back and neither are the problem... I've tried different tubes, but all these tubes work fine in a JPM45... I'm stumped on this... I've been through the layout several times and highlighted every connection on the layout as I proceeded and couldn't find a mis-wire anywhere...

[Randy Magee]

So, what else have you tried to this point?

Checked you guitar cable, guitar and speaker.......

I can't really make out the input jack connector and wiring very well but I would revisit that.

Recheck all grounds relative to the safety ground. You don't necessarily need an open to make things go South....

If you have some other tubes to try it is worthwhile. Might just be a bad one.

Chopsticked?
Might come up with a cold solder joint but I recommend a thorough review of the amp and the various voltages etc before you entertain this since it requires poking around a live amp.

I'm comfortable working inside the amp live... I know the basic safety rules and have built some several amps in the past without a hitch. I don't, however, have a signal generator and oscilloscope to trace the signal path through the amp...

[Colossal]

With a basic multimeter, you can do AC analysis on each gain stage. If something is shorting, you should see the AC output drop dramatically at the offending stage. Prior to getting an oscilloscope I used this technique to see how the AC signal at each stage built on the preceding. On one build that I had made a layout error, I found it by seeing that the AC signal was much lower than it should have been at a particular point. That might not be the case in your build, but it's a good trick and will at least help rule out shorts or other connection/signal path irregularities.

Hope you sort it out.