Pin Diodes used in MB8719 chassis old and new

[ExitThirteen]

LC,

The reason I don't think the BA479's will be a viable replacement is because the capacitance difference between those and the MC301's. There's quite a bit of a gap in capacitance between the two diodes.

~Cheers~

 

[loosecannon]

thanks for the reply xit13,

This may be a question with no answer, but can you think of anything in particular i should be looking for when i try some of the BA479's?

Like, which aspect of their performance do you think will be adversely affected by the difference in capacitance?
LC

 

[ExitThirteen]

LC,

I'd have to specifically look into the MB8719 AGC circuit and see how it's designed, but generally, more capacitance will create a slower response or "attack" when strong signals are present, so the AGC circuit may potentially respond a touch slower when attenuating really strong signals.

~Cheers~

 

[Onelasttime]

BA479 are pin diodes! http://www.vishay.com/product?docid=85527

 

[loosecannon]

just did my usual re-up on electrolytic caps from mouser, and bought some BA-479's to play with.

they just arrived yesterday, and i have to put a 148GTL back together to use as a test bed.

I'm not really sure how i'm going to test them, aside from having a local that is very close to me key up and peg the needle, then unkey and see how fast the gain recovers.

does anyone have any other tests that i should do?
LC

 

[Onelasttime]

Truck Stop! LOL.....If the front end can survive that it can survive anything. You could use a trigger on your scope to capture the recovery time and use that as your standard. You would have to have either the original parts or an original radio to use as a reference though.

 

[loosecannon]

just to put a cap on this, as it seems i forgot all about this thread, the BA479's seemed to work just fine and i couldn't really tell any difference in the radio's performance as compared to a 2000GTL that had the stock PIN diodes in it.

it's been over four years and i haven't heard anything from the radios' owners since returning the radios to them, so i'll call that a success i guess.

This was a good discussion.
LC