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Old 24th May 2021, 12:22 pm   #21
Restoration73
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Default Re: Masteradio D517/VHF Skymaster

The Callins were also used by Thorn - if in doubt change on sight. Fot the RF/IF transistors
the AF114-117 were replaced bt the smaller AF124-127 which are still around.
The AC127 audio NPN has equivalents AC176 and AC187. The PNP complement for
those is AC188. Audio output transistors fail if the quiescent current is too high or
thermal runaway occurs so check the current with the volume set to zero.
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Old 24th May 2021, 1:19 pm   #22
blackaddler
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Default Re: Masteradio D517/VHF Skymaster

OK, thanks.

If I need to replace AC127/AC128, I'm wondering whether a pair of GT332Bs would be suitable? I'll probably be ordering them anyway, so would just get extra.
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Old 24th May 2021, 1:27 pm   #23
Cobaltblue
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Default Re: Masteradio D517/VHF Skymaster

AC127 and AC128 are a complimentary pair one NPN and the other PNP.

GT332B are PNP I thought and used to replace RF transistors such AF117 rather than output transistors

Cheers

Mike T
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Old 24th May 2021, 2:34 pm   #24
blackaddler
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Default Re: Masteradio D517/VHF Skymaster

Ah OK. I thought I'd cross referred it somewhere - probably my mistake. I've got so many tabs open that it's getting difficult to keep track of what I've seen where.
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Old 27th May 2021, 2:47 pm   #25
blackaddler
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Default Re: Masteradio D517/VHF Skymaster

Going back to my original Skymaster, I've started checking the capacitors. A bit of a mixture, as Volstatic replaced a couple for me, back in the early 70's.

Pic 1 shows the 4 caps, 2 of which are the original 10v 400uf Elkomold B1s.

One replacement is the large grey 25v 500uf cap marked RS. I tested this at 600uf.

The other is a Sprague 25V 500uf, which tests at 597uf.

When I checked the board, I realised that the Sprague had been installed the wrong way round!

Should it matter with this particular cap?
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