UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Pye 1004 (Transistor Black Box) amp faults, help wanted please

Nickthedentist · 27th Aug 2019, 1:53 pm

Thank you everyone for your helpful suggestions.

I've pulled the two NKT452 output transistors, and both measure leaky (though definitely not s/c) in all directions. With them removed, the current consumption drops to 15mA.

All the electrolytic capacitors seem dubious; they all measure very high on my Peak tester (which implies they're leaky), or are open circuit. I plan to replace them all.

In view of Michael's wise words in post 5, can I ask the following, please:

(1) Should the voltages on T1-T5 all be normal, if run in its present state (i.e. with the output pair removed)? If so, and the voltages do indeed measure correctly, should it be safe to fit replacement output transistors with some degree of confidence?

(2) Cricklewood list the NKT453 @ £12 each. Has anybody actually had any success with this model fitting anything cheaper or more readily available? Will these Cricklewood ones be of reasonable quality, or will they be dubious re-labelled modern devices? Or will they be originals, and possibly doomed to early failure because of tin whiskers etc? I don't mind spending that kind of money to get it working reliably, but I can't afford to gamble too much!

Thank you again,

Nick.

27th Aug 2019, 1:53 pm	#6
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,864	Re: Pye 1004 (Transistor Black Box) amp faults, help wanted please Thank you everyone for your helpful suggestions. I've pulled the two NKT452 output transistors, and both measure leaky (though definitely not s/c) in all directions. With them removed, the current consumption drops to 15mA. All the electrolytic capacitors seem dubious; they all measure very high on my Peak tester (which implies they're leaky), or are open circuit. I plan to replace them all. In view of Michael's wise words in post 5, can I ask the following, please: (1) Should the voltages on T1-T5 all be normal, if run in its present state (i.e. with the output pair removed)? If so, and the voltages do indeed measure correctly, should it be safe to fit replacement output transistors with some degree of confidence? (2) Cricklewood list the NKT453 @ £12 each. Has anybody actually had any success with this model fitting anything cheaper or more readily available? Will these Cricklewood ones be of reasonable quality, or will they be dubious re-labelled modern devices? Or will they be originals, and possibly doomed to early failure because of tin whiskers etc? I don't mind spending that kind of money to get it working reliably, but I can't afford to gamble too much! Thank you again, Nick.