1965 Hohner Orgaphon 50 MH (4xPL84)

[manolo]

hello everybody !
This amp eleven (11) inputs ! , reverb (reverb tank is missing) , super sounding optical tremolo , ef86 section and four PL84 .
I cant find a schematic on web no information available .
The closest thing i found is this schematic from a hohner orgaphon 45mh which has two PL84.Anyone have a schematic with 4 PL84?

http://music-electronics-forum.com/a...haltplaene.pdf

So , how to bias this thing with the output shunt method (as we do with fenders) ?
Also my amp has ECC83 but the schematic above has ECC808! Big difference?

Thanks for any help

[sumac]

Hi,

I've owned few old Hohner amps (18M, 30MH, 25MH). From what I understand your amp is very similar to 25MH except it has 4 output tubes instead of 2. Schematic for 25MH can be found on the web easily. If your amp has ecc83's it probably means it is an older model (1963, 1964). ECC808 are similar to ECC83 but have different pinout! Good thing is that you can easily replace old tubes in your amp. ECC808 are extremely expensive tubes. PL84s are super cheap NOS!

Not sure what is output shut method, but you can install 1Ohm resistors to cathodes of output tubes and bias by measuring voltage drop across these resistors.. Your amp should have trimpots for adjusting bias voltage..

Considering the age of your amp you should probably replace all elytes and reflow all solder joints - they are known to develop cracks over time. I had to do this on all my hohners. Also some resistors (those thin dark red ones and little grey ones) tend to drift in value and in my experience they are quite fragile - they break (split) very easily..

Its a pitty your amp doesnt have reverb tank - reverb on these amps sounds HUGE.

ALSO BE CAREFULL WITH THOSE TOWER ELYTES! One of them caries something like 180V on its outer shell! At least cover it with insulating tape or better replace with axial cap and move it inside the chassis. That tagstrip on the top of power transformer is also not the wisest thing.. I've replaced those with one of these: http://kutilska.poradna.net/file/vie...-41000-lrg-jpg

These amps are quite difficult to work on so prepare yourself many hours of tedious work..

martin