philips 22rh580 germanium amp

[om kalsoum]

a few years ago i owned a philips 22rh580 2x5 watt germanium transistor amp.
but it run hot and got thermal runaway and destroyed itself.
now my plan was to rebuild the power amplifier section af this amp but this is a dutch amplifier and beleave me that good for the sound but bad for the electronic hobbyist ( philips does this for its uniqueness ).
this is the fact it is interly build opun a negative power supply
( look at the power supply in the schematic ) so ground is the most positive point in the amp ( look at the schematic below ).

can somebody help me turn this schematic around so that it is based upon a positive supply again.

thanks alot
ps the amp should stay as original as posible, i have all the components.

[teemuk]

The obvious question is why do you want to reverse the polarity?In my opinion, your biggest trouble is finding suitable transistors, not worrying about supply polarity.

By a quick look it seems like all you need to do is replace NPNs with proper PNPs and vice versa, then reverse the capacitors so that they have the correct polarity. The rectifier and that diode in the vbe-multiplier circuit (bias servo) have to be reversed as well.

If you want to use silicon devices that bias circuit will definitely need some adjustments.

[darkfenriz]

It is as simple as swapping ground to positive and negative to ground.
C623 should be connected to ground anyway.
To avoid thermal runaway you can use a Vbe multplier or two germanium diodes (1n34 or 1n60 not sure) in series with low value trimmer in the place of a pot.
Adam

[Zen Mod]

...........

[om kalsoum]

well i have all the transistors and to fix the thermal runaway i have a 130 ohm thermal resistor (just like in the schematic ) the parts arrent my biggest problems and the output transistors are on a original heatsink (salvidged them from a other little philips device ).

and thanks for the replies

[jaycee]

blimey... i have some of these AD161/162 transistors I pulled from an old tape player in my pre-teens

They've been in my parts collection for quite a while, does any one know if they would be static sensitive? They're probably well toasted if they are.

edit: I just checked and I have two pairs of AD161/162 (in TO-3 style packages, smaller) and an AC187. These all definitely came from the tape player. I do remember it also having some stud-mounted thermistors but these got used (and broken) in other "experiments"

[XEAGLEKEEPER]

If it is designed to operate with pos. ground why change it? Just to see if you can

[poynton]

Originally posted by jaycee
blimey... i have some of these AD161/162 transistors

So do I !!

does any one know if they would be static sensitive?

I built several amps similar to this design many years ago. I do not think they were static sensitive ..too leaky. Anyway, static was never the cause of failure - inadequate heatsinking, overloading, shorted output - yes!!!!

Andy

EDIT - PNP emitter to ground was the norm. NPN devices were rarer and so more expensive. I mainly used OC71/81, OC72/82 and OC35/OC28

[Nigel Goodwin]

Originally posted by om kalsoum
a few years ago i owned a philips 22rh580 2x5 watt germanium transistor amp.
but it run hot and got thermal runaway and destroyed itself.
now my plan was to rebuild the power amplifier section af this amp but this is a dutch amplifier and beleave me that good for the sound but bad for the electronic hobbyist ( philips does this for its uniqueness ).
this is the fact it is interly build opun a negative power supply
( look at the power supply in the schematic ) so ground is the most positive point in the amp ( look at the schematic below ).

Nothing 'Philips' or 'unique' about it, transistor circuits were usually -ve supply with +ve chassis back then - it made more sense that way. As already mentioned, PNP transistors were FAR more common (and cheaper) than NPN ones.

can somebody help me turn this schematic around so that it is based upon a positive supply again.

As others have said, why would you want to? - you want to keep it 'original', but them one to change it completely - I'm also somewhat bemused by wanting to recreate a crappy old amplifier?.

[poynton]

Originally posted by Nigel Goodwin


I'm also somewhat bemused by wanting to recreate a crappy old amplifier?.

Because it's there............