Low clean output (Dynacord Twen)

[SelmaSedlak]

Hello,

I am trying to diagnose low clean output in my recently acquired Dynacord Twen.
It is a german guitar combo model from late 60s and is rated 17 Watts.
However with my scope I measure only a little bellow 10V into an 8 ohm load resistor before the sine signal begins to clip. This amounts to about 12 watts.
I also own another amp of this model, and in comparison the one on my bench actually has lower headroom. It starts to overdrive at around 4/10 of volume pot rotation while the other at around 7/10. Also the overdrive seems to me less pleasant. Unfortunately the other good working combo is borrowed to my friend, so i cannot currently do a side by side comparison of sound and measurements.

I bought this amp in almost original condition (other than exchanged speaker wire) and i have so far done these changes:
- installed a new 3 prong power cable
- bypassed the original multi-section cap-can and installed a set of discrete F&Ts and new dropping resistor.
- installed new pair of 6V6s
- exchanged the shared cathode resistor + bypass cap on the 6V6s - I'm using a 220r, as the original 180r biased too hot.
- tried exchanging the coupling caps between PI and output tubes (even though the originals measured quite low leakage).

When i scope throughout the amp the preamp signal seems clean, when i pull the 6V6 the outputs of the PI is also reasonable clean but whit the output tubes in, I can scope the distortion on their grids as well.

My voltages are:
B+ 341V
B+1 329V
B+2 326V

PI:
Plate: 232
Grid: 25
Cathode: 89

6V6s:
Plate: 336
Screen: 327
Cathode: 20.1

I have tried switching different EZ81 a ECC83s and also putting the original 6V6s and cathode resistor back in but with no substantial change.
Components measure close to spec.

I am looking for hints what could cause the lowered clean output and what should i check next.

Thanks for any advice!

Amp details: https://www.smemmusic.ch/en/dynacord-twen-tube-amplifier
Schematic and gut-shot attached.

[AlNewman]

Personally, I'd replace all those wax caps as well.  They are almost certainly leaking some amount of DC, and the capacitance is likely not where it should be.

[acheld]

Personally, I'd replace all those wax caps as well.  They are almost certainly leaking some amount of DC, and the capacitance is likely not where it should be.

Although I've become much more conservative in replacing caps, those puppies would not survive my shop.   

The actual correct thing to do, if you want to maintain originality as best you can, would be to test the caps out of circuit and replace the suspect ones.  Nahh, just replace 'em.

[AlNewman]

I'm looking at the schematic, and there's 4 wax caps tied to the screens through the trem circuit.  There's a coupling cap between V1a and V1b.  There's another to ground off the V1 supply.  And there's another between the feedback loop for the tone circuit.  I wouldn't call all of these critical caps, but if I was getting nasty signal or low output voltage, those areas may definitely be worth a look.

[Helmholtz]

I don't see any wax caps.
But those Wima epoxy caps can get leaky.

[AlNewman]

My bad.  They look very similar to wax caps.  I wonder, are they still paper and foil caps, or a different dielectric?

[Helmholtz]

Wima made different types.
Here's some info on those used in early Vox amps:
https://www.voxac30.org.uk/vox_ac30_wima_capacitors.html