A faulty pot maybe?

Shielding the cabinet is not nessasary. If you paly a singlecoil guitar, its probably better to use the schielding there instead 

Great rock playin' !

(In order to facilitate a Les Paul, you mighy consider trimming off some bass in the OD section)

I would use a 1M pot, which is similar to the input impedance of both the Dumblator and the Klein.
(A 250K pot might roll off some of the high frequences in the signal). Remember not to use too use long connection cables, which might also roll off highs.

Tip: If you have a small booster pedal, you can put this after the reverbpedal in order to get the signal up to the same level as before the pot. Your signal path would look like this:

Overtone preamp (send) => 1M pot => reverb pedal => boost pedal => (return) Overtone poweramp

This way you get the essence of a Klein/dumblator, even though a klein or dumblator would be superior.

Your pedal receives too much input signal, which is why it overdrives nasty.

Adding a pot at the loop input to reduce the signal is the solution.

And that is exactly what the klein is capable of. It lowers the signal to the pedal, so it wont distort (your pot idea), AND amplify the signal after the pedal back to 'the initial' level, so you don't loose signal.

I fully respect that you are making a 'showcase' amp, which pictured alongside your custom products, will help boosting your custom guitar knob business.

Personally, I think you are overdoing the wood finish thing.

However, I come from the land of Bang & Olufsen, which is probably why I prefer more subtle, somewhat  cooler, Bauhaus like designs. 

The most omportant mod you can make to facilitate both lespauls and strats is a switch, that swhtches between a 10n and 47 n 'mid' capacitor. Simple but effectfull!

Thanks 

Tony, Which tube brand and type have you installed in V1 ?? Please share

Good question.....although, Tony cannot possibly provide us with an answer on that one, since he didnt swap the tubes between the two amps respectively nor reverse engineer the Dumble on the celestion demo stand.

We could also ask him, if the differences between the two amps could be due to

- the transformers used or
- the values of the powerstring used and thereof voltages
- the capacitor make or
- the construction differences between a ODS and a S&M
- etc

He cannot possibly answer any of it 

Tony, you're a great player !!!
Both the Dumble and the SM sound great. 

I'm a little curious about the feel of the amps.
How would you describe the difference in 'feel' between the two amps, if any?

...even if its two very different situations - playin at a show and playing in a more quiet studio setting.

I wouldn't do a free float....

You can always 'mismatch' a tube amp 100%.

E.g. If your amp has an 4 ohm tap only, you can run it with both a 2 ohm cabinet or an 8 ohm cab.
I've run an old bassman top, which has a 4 ohm tap, for many years. No problem.