Perdio PR73 - very poorly (dead) - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

GeoffK · 23rd Jul 2019, 12:45 pm

Quote:

Originally Posted by Tully Bascombe

Quote:

Originally Posted by GeoffK

Check the quiescent battery current (in one battery lead with minimum volume. If the current is over 10 to 15mA remove the output transistors and test it again, if the current drops then it is the output transistors that have failed, they can still carry on working but the sound gets less and the battery current goes up as the transistors get warmer and warmer. The black finish on the output transformer is just the tape it just finished with.

I haven't dared measure quiescent current yet. It's enough to bake the transformer and melt the wax insulation. Any guesses?

If this was done first it would have led to a quicker diagnosis instead of this somewhat protracted post just to find faulty output transistors. Measuring quiescent current would only take a few seconds to establish if it was too high, long before overheating the output transformer occurring. Faulty output transistors would have been the prime suspects when the output transformer is overheating but it shouldn't be left switched on long enough to overheat the transformer. Make sure the replacements are correctly orientated.

Mike. Watterson · 23rd Jul 2019, 4:44 pm

Very often true about dot colour. It's on some data sheets.
Later it was more common to use A, B, C, D.

Tully Bascombe · 26th Jul 2019, 12:15 pm

Just to quickly finalise this somewhat protracted post, I've now installed AC128 output transistors and all is good. Working very nicely, good sensitivity with excellent sound quality.
As a newcomer to this hobby and prone to having the odd senior moment, I would like to thank everyone for their helpful comments and generally pointing me in the right direction.
Regards,
Tully

Boulevardier · 26th Jul 2019, 1:08 pm

Excellent news - well done! I've been getting "senior moments" since I was about 13 years old...
Per ardua ad astra!

Mike

23rd Jul 2019, 4:44 pm	#22
Mike. Watterson Heptode Join Date: Dec 2014 Location: Limerick, Ireland. Posts: 901	Re: Perdio PR73 - very poorly (dead) Very often true about dot colour. It's on some data sheets. Later it was more common to use A, B, C, D.

26th Jul 2019, 12:15 pm	#23
Tully Bascombe Triode Join Date: Mar 2019 Location: Chesterfield, Derbyshire, UK. Posts: 24	Re: Perdio PR73 - very poorly (dead) Just to quickly finalise this somewhat protracted post, I've now installed AC128 output transistors and all is good. Working very nicely, good sensitivity with excellent sound quality. As a newcomer to this hobby and prone to having the odd senior moment, I would like to thank everyone for their helpful comments and generally pointing me in the right direction. Regards, Tully

26th Jul 2019, 1:08 pm	#24
Boulevardier Octode Join Date: Sep 2017 Location: Bristol, UK. Posts: 1,658	Re: Perdio PR73 - very poorly (dead) Excellent news - well done! I've been getting "senior moments" since I was about 13 years old... Per ardua ad astra! Mike