Felix.
Hope english is ok.
Having fooled around with a number of Suprem amps i can for a fact tell you that your Piccolo is of later vintage and altho i´ve never been into a Piccolo of that age i have when it comes to the Luxor 40´s and what not.
It IS stock. They look like that. Period.
The earlier Piccolos,of which i own two myself to this day,indeed are different creatures. (Also own a GZ-34 rectified Club DL aso...)
Having read the thread.. As far as anode voltage any EL-84 of quality will take them 400+VDC. The screen (schirmgitter/g2) is another matter,and one way of making sure the tubes will survive is to install highpower zener diodes vs the g2´s. I do it all the time when working on older amps,where B+ voltage often soars as a function of higher mains voltage these days,and when doing so for an EL-84 amp i normally run 47V/5w ones,which are followed by 100 Ohm/2w resistors before hitting the actual pins of the tubesockets. (the latter mainly to combat RFI/EMI)
The whole thing works and works very very well and from a practical point of view will hand you an amp that doesn´t stonewall powerwise in the same manner an amp will with a more conventional setup vs the screens. In fact the entire amp will become way more "snappy" to the response.
Be aware that your bias will have to be readjusted though and one way of handling that is to reverse engineer your bias circuit and localize the resistor heading for ground..and replacing that with a trimpot of similar value (use the closest higher value trimpot) that you install as a reostat. Use a common 1/4w trimpot..
This way you will have an adjustable fixed bias voltage for g1. Ergo this entails setting up some manner of actually measuring anode loss in idle with at least SOME sort of precision.
In turn on a more general note. These smaller Suprem amps can be turned into real screamers with rather minimum effort. That said they in my opinion lack out a bit when it comes to safety precautions.
The way they´re built (hardwired) make for a rather...shaky proposition IMO. Simple 7 lug solder supports that are bolted/screwed to the chassis with M3 fasteners is a WAY better idea. Especially so if you intend to play around with the amp any as far as modifying it,now or down the line.
