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My deluxe started to get progressively crunchy and finally the volume dropped to near zero. Does this sound like a power tube failure?

Could be a bunch of different things, including that. You need to measure voltages at key points in the circuit to find clues.

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Great tones come in small glass jars!

Are the key points and desired voltages posted somewhere?

On both the layout and the schematic in the resources section

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Fantasy Noise is what my shop of dreams is called and was the only way to beat my addiction, like many here I suffer from G.A.S.


Tele's make the best noise

Here's what I measure:

Mains 120.1 VAC

On standby, B+ at first cap 542.6 VDC

With VRM on max:
First cap : 393.2
Rectifier pin 8 : 395
Rectifier pin 6 : 0
Rectifier pin 4 : 0
Rectifier pin 2 : 20.5 VAC
Pilot light : 3.1 VAC

Any ideas?

That's only for the rectifier. What about the rest of the tubes?

Does this volume loss happen every time a little while after you switch on, or is it permanent? If it's not permanent, then you need to take readings before and after the volume loss.

_________________
Great tones come in small glass jars!

Today there was no loss of volume, but some other unusual symptoms:
Normal channel
- tone on 1, vol on 11 : loud hum
- tone on 1, vol on 12 : loud squeal
- tone on 5, vol on 10 : quiet squeal starting
- tone on 6, vol on 10 : loud crackling
- tone on 12, vol on 10+ : loud squeal and crackling

Bright channel
- tone on 1, vol on 10+ : loud hum
- tone on 6, vol on 11 : squeal
- tone on 6, vol on 12 : crackling
- tone on 12, vol on 3 : squeal
- tone on 12, vol on 4+ : loud pop and crackling

Here are all the voltages (VRM on max)
* Loud hum when test probe applied to pin
** Voltage jumping around
All measurements VDC except where noted

Pin V1
1 189
2 0
3 1.6
4 3.1VAC
5
6 191.3
7 336
8 1.5
9 0.3VAC

Pin V2
1 189.7
2 0.1*
3 1.3
4 3.1VAC
5
6 233.1
7 16
8 47.9
9 3.1VAC

Pin V3
1 -
2 0
3 381.5
4 0.3VAC
5 45 – 50**
6 67 – 69**
7 3.1VAC
8 21.7

Pin V4
1 -
2 0
3 383.5
4 0.3VAC
5 15 – 18**
6 15 – 20**
7 3.1VAC
8 21.7

Pin V5
1
2 20.5VAC
3
4 347.5VAC
5
6 348.3VAC
7
8 395

Tube swap time.
Start with the preamp tubes then move to the output tubes.

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http://pdfelectronics.com

Plate voltages on V1 and V2 are to high.
Grid voltage on V3 and V4 is not there it should be about 338vdc.
Check your connection at the board between R22,R21 and C12 should be about 338vdc.
If you have the correct voltage on the board but not the tube, suspect a cold solder joint or broken wire.
Its hard to have high plate voltages on V1 or V2 if anything was wrong at the board connection R22,R21 and C12. As V1 and V2 plates are fed through that point.
You show an AC signal on Pin 4 V3 and V4 where there should be a grid voltage of about 338vdc.
Your B+ is correct so its not the problem, its the grid voltage thats the problem. check your connections on V3 pin 4, if you are wired according to the layout..

Or at least thats the way I see it.

_________________
Fantasy Noise is what my shop of dreams is called and was the only way to beat my addiction, like many here I suffer from G.A.S.


Tele's make the best noise

Grid voltage or screen voltage?

_________________
Great tones come in small glass jars!

Screen grid it would seem.
Sure hope you don't have that HV on the control grid.

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http://pdfelectronics.com

I measure 353.4 at that point.

Tried this (preamp and power tubes only as I didn't have a spare rectifier tube) - no change.

If you have voltage there but not at pin 4 V3&4
then I would think either a cold solder joint or broken wire.



Ok How about 6V6 Pin 4 Grid Number 2 (screen) voltage should be about 338 vdc.
It was a long day of commisioning and no tubes in those ccts. I agree I should have said screen

_________________
Fantasy Noise is what my shop of dreams is called and was the only way to beat my addiction, like many here I suffer from G.A.S.


Tele's make the best noise

I don't know what I was smoking when I took the earlier measurements. Now I'm getting 353 VDC at pin 4 of V3 and V4.

Can any of the squealing/crackling at high tone/volume settings be related to the VRM?

Taken from a tramp posting. This was Zaphods suggestion.

Thats for the Tramp, for the Tweed it will be slightly different. What is being done is, you are jumpering the input of the VRM to the output of the VRM. Then you have a normal B+. If your problem goes away, it was the VRM, if it doesn't it is something else.

_________________
Fantasy Noise is what my shop of dreams is called and was the only way to beat my addiction, like many here I suffer from G.A.S.


Tele's make the best noise

Shorted out the VRM - no change.

The other change I had made was installing the DC blocking caps on the inputs. Could these be the culprit?

Jumper them out and see what happens.
And maybe its time to order a new rectifier tube.

_________________
Fantasy Noise is what my shop of dreams is called and was the only way to beat my addiction, like many here I suffer from G.A.S.


Tele's make the best noise

Finally getting back to this. Volume is very low.

Installed new rectifier, new power tubes and swapped in some other preamp tubes (V1=7025, V2=12AY7)

Here's what I get:
V1
Pin 1 : 175
Pin 3 : 1.45
Pin 6 : 179.8
Pin 8 : 1.45

V2
Pin 1 : 125.8
Pin 3 : 2.0
Pin 6 : 190.6
Pin 8 : 70.8

V3
Pin 3 : 380.4
Pin 4 : 350.7
Pin 8 : 22.1

V4
Pin 3 : 393.9
Pin 4 : 350.7
Pin 8 : 22.1

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<-- This way to the unquestioned answers

Pin 8 v2 seems really high for a cathode. Could it be open? That resistor might need replacing.
This is off the top of my head though.