Tweed Deluxe issue

[SleepLess]

Hi.
A guy left his 5E3 at my place yesterday for a repair. It's the first time I see this: I get a buzz on the low E string around the 5th to higher frets. Note rings then a kind of high buzz. The amp doesn't sound as good as it should and I think it gets toi crunchy territory too soon. SO far I have:
- Checked all tubes.
- Checked the speaker (plugged the chassis into my 1X12 speaker cab)
- Replaced all the 5 coupling caps.
To no avail... I'd like to know your thoughts as I doubt this could be a bad wiring somewhere... What are the symptoms of a bad OT?
Thanks!

[phsyconoodler]

Quote:"I doubt this could be a bad wiring somewhere"

 That's the first thing to check.A cold solder joint will do exactly what you are describing.Why on earth did you change the coupling caps?

[SleepLess]

Quote:"I doubt this could be a bad wiring somewhere"

 That's the first thing to check.A cold solder joint will do exactly what you are describing.Why on earth did you change the coupling caps?

OK. I'll check the wiring and soldering. I changed the coupling caps because I thought that a failing one could cause these issues... 

[jojokeo]

A cold solder joint will do exactly what you are describing.

agreed, chop stick or just reflow everything you can w/ a HOT iron & touch of solder to each joint everywhere.

[SleepLess]

Hi!
So here are the symptoms:

1.   It is noisy. More than usual. I did the exact same grounding scheme as on my previous builds which were always silent.
2.   I have very farty bass notes. When I say farty I mean it’s really ugly. Far from being as good as they should, they lack clarity even with the amp only on 5. On 10 it’s ugly as hell. The medium and high notes sound ok/good and I would even say that the amp sounds glorious if you don't play the lower notes.
3.   I also hear some kind of a rattle that seems to be amplified by the speaker and I don’t know if this is linked to point 2 or not.
4.   I think that the amp gets into crunchy territory earlier than it should, and I’ve always used my same strat to test my amps and of course no pedal.
5.   The amp seems pretty sensitive to external interferences, like radio or phone or whatever external signal.

So here’s what I have done but NOTHING changed.
1.   Tried the amp in my external 1X12 speaker cab with an EVM12L (didn’t use the amp’s cabinet) in order to rule out the speaker.
2.   Swapped all tubes 1 by one for known-to-work tubes in order to rule out the tubes.
3.   Swapped all coupling caps and tone cap and silver mica cap.
4.   Measured all three pots they all go from 0 to 900+ Kohms.
5.   Measured DC voltage on all three pots to see if I had a leaking cap.
6.   Reflowed most solder joints.
7.   Checked that all transformers and sockets were securely fastened. Everything is.

So right now I’m totally stumped. This amp is noisy, sounds bad and farty on the bass notes and I don’t know why...

[jojokeo]

Is this totally a stock 5E3? If so, no need to post a schem. But, pictures would be a big help now if you can. It may be that the main resevoir and/or filter caps are going bad? How old are they, original?

[SleepLess]

Hold on, I think I have fixed it. The amp is brand new from July 2012...

I have found that the heater wires were reversed between the two 6V6s. That is green wire from V4 pin 2 was going to pin 7 of V3 instead of pin 2 and vice versa. Do you think this could have been the culprit? The amp seems to have cleaned up a lot and the notes are less farty, especially in the high inputs, not so much in the low inputs.

But I'm still wondering if I have 100% fixed it: the normal channel still buzzes/farts somewhat on the 6th string frets 9 and higher. Other than there it sounds good, really good glassiness on mids and highs. One strange thing is that if I plug the amp in bright low with bright volume on 0 and turn the normal volume up the guitar rings... Shouldn't it be silent???? I have read about 5E3 pots' interactivity but if this is normal they really ARE interactive!!! 

Thanks!

[jojokeo]

if I plug the amp in bright low with bright volume on 0 and turn the normal volume up the guitar rings... Shouldn't it be silent???? I have read about 5E3 pots' interactivity but if this is normal they really ARE interactive!!!

Yeah they're interactive controls but you may want to try looking at your wiring (why pics would help). You may have OT wires or others too close to sensitive ones causing parasitic osciallation. Maybe you don't have the power tube's grid resistors mounted to their sockets also w/ these wires too close to the OT wires? Maybe the plate wires need to be reversed too? It could be that you're not getting so much positive feedback that it's not howling but they need to be reversed anyway? That chassis is very compact so you need to be as careful or watchful as you can with this stuff. Hard to troubleshoot something that's not there. Same the with heater wiring - we would've never known it w/out seeing things. Shooting darts in the dark isn't the easiest thing to do. Usually out of phase heater wiring on power tubes gives you humm issues. We don't know if there's a center tap, artificial one, or nothing and if they're raised or not for more unknown examples. They all could have different symptoms for something. I got a new 5E3 chassis built & complete w/ new tubes for under $250 because the guy didn't know what was wrong w/ his before. That was the only main problem and that amp worked great after that.

[SleepLess]

Problem solved, it was indeed the out of phase filament wiring that was causing these problems. The amp sounds like it should now.
Thanks!

[HotBluePlates]

Hold on, I think I have fixed it. ...

I have found that the heater wires were reversed between the two 6V6s. That is green wire from V4 pin 2 was going to pin 7 of V3 instead of pin 2 and vice versa. Do you think this could have been the culprit? The amp seems to have cleaned up a lot and the notes are less farty, especially in the high inputs, not so much in the low inputs. ...

I highly doubt the "phasing" was the issue.

PERSONAL OPINION ALERT: I think "heater phasing" is a tremendous load of crap. I've built amps both ways (obsessing over heater wiring, and also doing "wherever the wire lands" and each way worked the same for me). I can't hear a difference between them.

I'd bet big money you repaired a cold solder joint in the heater wiring when you made the swap. The cold joint may have reduced the heater voltage, and impacted the amp's operation. You didn't happen to measure heater voltage in the beginning, did you?

Reduced heater voltage (like ~4vac instead of 6.3vac) can cause odd problems in output tubes, reduced power output and may cause strangeness in preamp tubes. In general, gain and Gm lowers, rp probably rises, emission is low, and there's a chance the tube could distort early depending on exactly where the voltage lands and how strong the tubes were to start. Kind of like cutting the power on an amp and continuing to play while the caps drain.

I think you did everything right, and I wouldn't have thought to check heater wiring early, so maybe we all learned a lesson.

[SleepLess]

You are absolutely right! I happened to measure the AC voltage on the heaters before rewiring the output tubes and I had 6.3V on pins 4/5 and 0.6V on pins 9!!!! Forgot to say so!!!

But here's what Bruce at Mission Amps told me about the out-of-phase heater wiring, I think it's interesting:

"If there is a goof on the filament wiring with respect to the 100 ohm resistors (which are DC biased by the cathode resistor on the power tubes) there is the remote possibility that the two power tubes become biased on with one of the 100 ohm resistors being in parallel with the 270 cathode biasing resistor.
That can do all kinds of weird things and make the amp noisy and flubby because the power tubes are running super high in current and overheating."

[jojokeo]

I also had something similar happen a long time ago only the tube/amp didn't work at all from one of the preamp tubes not lighting up. Afterwards, I ALWAYS check the heater joints along the entire chain before installing any tubes upon first power up on a new amp build. It's a fast, easy, and simple check. I like to apply the dc voltage when appropriate so it's checked too at the same time.

*my 5E3 variant has oversized trannies which I'm running w/ NOS Tung-Sol 5881s for a festival gig coming up this weekend and it sounds awesome with the bigger tubes.