Davoli Krundaal - Amplificatore D531T [schematic]

[modman]

It's cute and pink and it's probably a accordion amp, but got kind of intrigued by the tube setup:
1 x 12AX7 or ECC83
2 x ECL82 - which is a triode and pentode in one package!
3 tubes: 2 gain stages, tremolo, phase inverter and 10W output

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[modman]

I wasn't going to ... but I did. Paid too much, but what do you expect trying to wrestle a pink amp from a very nice lady...
it's very sensitive to high output humbuckers
the tremolo doesn't work.



Just a demo, no work done yet...

[modman]

In the first stage, I wanted to get it working again and not do any mods, just get the tremolo tremming again. This amp has been worked on before. One of the two can capacitors has been replaced and much of the power section was redone... This surprised me because there the chassis screws were still sealed with yellow paint.

The schematic contains an error: the first dropping resistor is 5k/4W, not 47k.
One of the 330k to ground before the output tube on the verge of breaking, and this pulled off the bias completely so basically running in class A, on one power tube.
Ressurection of the tremelo was just a matter of replacing all the tremolo capacitors. Nice Ducatis but they were all completely out of whack, the 100nF measured 550nF, the 47nFs about 80-100nF...
The Danish Peerless speaker seems to have been a replacement, and the baffle cutout is a bit too wide, so it is only attached by 2 screws for now. I may have to make a new one.

I would like to restore the amp the way it originally was, at least layoutwise, but I have not found any gutshots of this unit online. The circuit is very close to the Hagstrom 39, the only difference is the way the tremolo is connected and that is has a EZ81 rectifier while the Davoli has solid state rectification. Then again the Hagstrom was built on pcb, the Davoli seems to have been point-to-point.

[soulsonic]

[modman]

I cannot believe it myself, but I found another one. This is a greenie

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[DrNomis]

What a cool little amp, definitely worth fixing it so its working right.

[modman]

When I came across that first, pink one, I thought a lot of work had been done to the amp, considering the haphazard way in which the components were attached. There are capacitor holes in the chassis, but they were not used in this built. Anyway, looking into this second seafoamapplebluegreen unit, I know now everything in both units was 100% factory original.

Tremolo came alive by replacing the 47nF capacitors
Replaced filter caps and coupling caps and bypass caps
Replaced cathode bias resistor
Installed three prong

Has the original alnico (Krundaal) speaker which is nice, but small... which is not bad; but the more of these cute, well-intended European guitar (but is it really, or is it a converted accordion amp again) amp, the more I get curious about this question: who designed the cabinets for Leo Fender? Electronics schmelectronics, isn't the woodworking what really sets 50's Fender amps apart from all the rest?

Anyway, it's a great little compact pushpull 10W amp with tremolo - I really don't want to get into building more amps, but if I do, I would recreate this circuit with better shielding and grounding, in a 10" combo....

Would that be a waste of resources? Are there inherent problem with these triode/pentode tubes?
thanks for reading this far
J