View Single Post
Old 9th Feb 2023, 10:23 pm   #12
TheMightyMadman
Triode
 
Join Date: Aug 2022
Location: Stockton-on-Tees, Cleveland, UK.
Posts: 39
Default Re: Help Needed - Armstrong 626 Tuner Amplifier

Quote:
Originally Posted by cooperman View Post
The circuit diagram for the amplifier can be found here:-
https://www.audiomisc.co.uk/Armstrong/600/600faq.html

I think the transistors that have failed are the ones shown as items 623 and 624 - 2N5320 and 2N5322. You may have better luck trying to find those transistors rather than the RCA ones. The 2N ones are in a round can - unlike the flat package your existing transistors have.
Thank you very much I'd seen that page previously, and I wasn't sure whether the early schematic that it shows matched up to the A17 board layout that it shows. To cut a long story short, your suggestion worked - I'm very grateful!

Quote:
Originally Posted by Ted Kendall View Post
The usual comments about DC coupled power amplifiers apply here - satisfy yourself that all the semiconductors are in good shape before you power up, otherwise you may go round in circles, blowing up what you have just replaced.
Thank you I made sure to check the current adjustment potentiometer and the diodes before fitting replacement transistors.

Quote:
Originally Posted by Silicon View Post
I have no experience of this unit but blown transistors are sometimes caused by faults in the output stage bias components.

I would carefully check those yellow diodes and cheap potentiometers.
Thank you I made sure to check the current adjustment potentiometer and the diodes before fitting replacement transistors.

Quote:
Originally Posted by DrStrangelove View Post
Just had a quick browse of the RCA power transistor manual but there's nothing in there with that sort of part number.

It may well be one of those old favourites: the house coded transistor.

Oh how we love them.
Thank you

Quote:
Originally Posted by Trevor View Post
40636 is the output device basically a high voltage 2N3055
You could always use a 2N3773
I used to retail these amps back in the day
Trev
Thank you
TheMightyMadman is offline