Parmeko System 22 - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Trevor · 21st May 2007, 8:17 pm

Hello Percival
After looking at the circuit,s it seams to me to be quite a simple unit
To get things clear is the live side of the output capcitor standing at half the supply volts, when you disconnect all the output transistors If not is it high /low
Check the driver transistors I would in the matter of course change them all any way You can use 2n3055 for the output devices and bc142/143 or bd139/140 for drivers
Check the bias diodes and bias resistor please let me know how you get on
regards trev

percival007 · 27th Jun 2007, 5:54 pm

Hello Trevor,
i have today got the output stage working.
I used 2N3055's for the output transistors, the diodes and bias resistors all checked out ok. However, i replaced all the electrolytics as some of them were a little bit worse for wear. I also replaced the small variable resistors for setting the idle current. I have been caught out on more modern sets than this by not changing these pots!
I now have to re-furbish one of the speakers as one of the tweeters has failed and the binding posts need replacing.
Thanks for your help, regards, Percy.

21st May 2007, 8:17 pm	#21
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: Parmeko System 22 Hello Percival After looking at the circuit,s it seams to me to be quite a simple unit To get things clear is the live side of the output capcitor standing at half the supply volts, when you disconnect all the output transistors If not is it high /low Check the driver transistors I would in the matter of course change them all any way You can use 2n3055 for the output devices and bc142/143 or bd139/140 for drivers Check the bias diodes and bias resistor please let me know how you get on regards trev

27th Jun 2007, 5:54 pm	#22
percival007 Heptode Join Date: May 2005 Location: Oxfordshire, UK. Posts: 852	Re: Parmeko System 22 Hello Trevor, i have today got the output stage working. I used 2N3055's for the output transistors, the diodes and bias resistors all checked out ok. However, i replaced all the electrolytics as some of them were a little bit worse for wear. I also replaced the small variable resistors for setting the idle current. I have been caught out on more modern sets than this by not changing these pots! I now have to re-furbish one of the speakers as one of the tweeters has failed and the binding posts need replacing. Thanks for your help, regards, Percy.