Masteradio D517/VHF Skymaster - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Restoration73 · 24th May 2021, 1:22 pm

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.

blackaddler · 24th May 2021, 2:19 pm

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.

Cobaltblue · 24th May 2021, 2:27 pm

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

blackaddler · 24th May 2021, 3:34 pm

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.

blackaddler · 27th May 2021, 3:47 pm

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?

24th May 2021, 1:22 pm	#21
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	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.

24th May 2021, 2:19 pm	#22
blackaddler Triode Join Date: Feb 2015 Location: Addlestone, Surrey, UK. Posts: 14	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.

24th May 2021, 2:27 pm	#23
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,865	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 __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk

24th May 2021, 3:34 pm	#24
blackaddler Triode Join Date: Feb 2015 Location: Addlestone, Surrey, UK. Posts: 14	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.

27th May 2021, 3:47 pm	#25
blackaddler Triode Join Date: Feb 2015 Location: Addlestone, Surrey, UK. Posts: 14	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? Attached Thumbnails