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Old 21st Apr 2017, 12:57 pm   #1
IanG3XYV
Triode
 
Join Date: Sep 2014
Location: Bedford, Beds. UK.
Posts: 26
Default Bush BP10 IF transformer

I am in the process of renovating my portable BP10. I've changed the usual capacitors and am tracking signals with a signal generator and scope. Local oscillator is fine and audio output seems ok but there is a lack of gain in the IF area. There seems to be a fair amount of signal at the first IF stage but not at the detector after the second IF transformer. The IF valve (DAF91) tests ok and I am suspecting the second transformer. The Trader Sheet 960 gives the dc winding resistance for both windings for both transformers as 12.5 ohms. I am measuring a little higher than that for the first but 39 and 25 ohms for the second transformer which seems high. Is there some kind of copper corrosion going on here which affects performance?

Anyway, on the off chance that someone might have a spare I thought I'd ask here. All costs covered of course. I am prepared to attempt to remove and rewind so any advice on this would be appreciated. I do have lots of enamelled copper wire and instruments to measure inductance.

Ian
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Old 21st Apr 2017, 3:41 pm   #2
Ed_Dinning
Dekatron
 
Join Date: Jan 2004
Location: Newcastle on Tyne, Tyne & Wear, UK.
Posts: 4,328
Default Re: Bush BP10 IF transformer

Hi Ian, strip it out of its can first and examine carefully. If you are lucky it will be green spot on the winding connections.
I believe these coils were wave wound, difficult to do without the right equipment, but if another one does not show up you can carefully layer wind the dead winding to a similar inductance and should not suffer too much loss of gain.

Possibly also worth drying the coil out in a hot cupboard.

Ed
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Old 21st Apr 2017, 8:19 pm   #3
IanG3XYV
Triode
 
Join Date: Sep 2014
Location: Bedford, Beds. UK.
Posts: 26
Default Re: Bush BP10 IF transformer

Thanks for the advice Ed, I'll give it ago.

By the way, I hail from the same part of the country as you. I shall be in Alnwick in May for a school reunion.

Ian
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Old 21st Apr 2017, 9:51 pm   #4
ronbryan
Octode
 
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,325
Default Re: Bush BP10 IF transformer

AM IF transformers are often wound with multi-strand (Litz) wire to give a higher Q than single stranded wire. Higher than normal winding resistances can be caused by some of the strands going open circuit. If you are lucky, re-soldering, or shortening and re-soldering the terminations may yield an improvement.

Ron
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Old 22nd Apr 2017, 9:00 am   #5
Ed_Dinning
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Join Date: Jan 2004
Location: Newcastle on Tyne, Tyne & Wear, UK.
Posts: 4,328
Default Re: Bush BP10 IF transformer

Hi Ian, yes I forgot to mention about Litz. I have some here if you need it.

PM me when you are coming up and you can call over if we are about.

Ed
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