THE PHILIPS 22AH708

[east electronics]

ΟΚ ...here is a joke

the schematic attached is the main section amplifier of the philips 22AH708... its an amplifier rated 80Wpc at 8R 52+52 rails and seems to me a japanese design implemented by the european .... so its bootstrap... BC5XX all over but VAS DRIVERS and OUTPUTS are B668-9 2SB 2SD family .... funny i think ...

havent finished repairing it since a f**** open trimmer blown pretty much everything arround the VBE area so i have no listening impressions but there is a thing that got my eye arround the driver area there is a network like a zobel or filter next to the driver supply formed by 10R +47nf film capacitor ...

any comments ????

 

[DuncanV]

This looks like a very typical Philips design.

The R/C network provides improved EMC performance. It suppresses external interference on power rails quite well.

 

[east electronics]

i dont really think that looks like a philips design

the attachment down under is a philps design ...these are the parts normally used in philips designs of te time

 

[homemodder]

Sakis most amps have such networks, sometimes only a cap is used, duncanV explains it well. I think what looks more strange to you might be the 15 ohm resistors instead, now that you dont see much. Those help to maintain stability of the output section although I dont see why they would be required in a EF, in a triple outputstage those resistors help quite a bit.

 

[east electronics]

corect so far ...seen capacitors here and there seen similar topology in hafler amplifiers
but the philips is a bit more than that and need to see it to understand ...it features piggy boards with ltp vas drivers and vi limiter placed in sort of a mother board to accomodate the output section only ...

There is no other bypass or decoupling elsewhere .... so this network located on the piggy boards next and close to the drivers does all the job

kind regards

 

[DuncanV]

Philips's use of Japanese transistors was not that uncommon those days. Also Motorola's MJ's can be found in their 70's and 80's amplifiers. Just have a look at some MFB systems for example.

The 15R tackles the potential risk of resonance, caused by the PSU wire inductance.

 

[DuncanV]

Oops, I ment the 10R resistors!
The 15R collector resistors are fusibles, maybe they are there only for safety reasons.