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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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19th Sep 2017, 10:12 pm | #1 |
Hexode
Join Date: May 2003
Location: Hertfordshire, UK
Posts: 258
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Rank A823 frame O/P transistors
Can anyone advise on suitable replacement frame output transistors for the Z968 scan drive panel please?
I have two of these panels, one has Texas R2354A and R2354B transistors, and the other has RCA 16029 and 16039, all TO-220 style packages. I have bits and pieces of service data copied from various R&TVS books over the years, but nothing on this version of the panel. Many thanks, Roy |
20th Sep 2017, 6:54 am | #2 |
Heptode
Join Date: Apr 2003
Location: Cornwall, UK.
Posts: 988
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Re: Rank A823 frame O/P transistors
Hi Roy.
I seem to remember using TIP31C & TIP32C transistors in this chassis. To be fair, I don't rember having to replace these often in the A823. These were one of my 'stock' range of transistors that got used for many other applications in my workshop in the mid '80's. I'm sure other members will suggest some other types too. SimonT.
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The honesty of imperfection.......... |
20th Sep 2017, 9:09 am | #3 |
Nonode
Join Date: Jan 2004
Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area.
Posts: 2,965
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Re: Rank A823 frame O/P transistors
As Simon says I am sure I have seen TIP31C and TIP32C transistors used as frame output transistors, and on the original sets the BD131/132 output transistors but I will have to check this out when I go home tonight.
The frame output transistors were reliable on the A823 chassis most of the problems were caused by the electrolytic smoothing cap on the 40v line from the line output stage drying out.
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20th Sep 2017, 2:38 pm | #4 |
Hexode
Join Date: May 2003
Location: Hertfordshire, UK
Posts: 258
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Re: Rank A823 frame O/P transistors
Thanks both.
I agree the ouptput transistors are generally reliable. Perhaps I should have mentioned that this is not a restoration of a long-disused set, but a repair to one that is in regular use. The frame height and linearity were becoming unstable due to dodgy presets, and the frame collapsed while attempting to adjust these. One transistor is now cold while the other overheats, and the "mid point" voltage will not set up correctly. The 40V supply is fine. Looking at the circuit of the original scan drive panel, the output pair are both NPN, type BD131, but the later Z968 panel has two different types of NPN transistor. Perhaps a pair of TIP31C would work here? The spare Z968 works fine but also has twitchy presets, so it could go the same way. The presets are fully enclosed "Piher" types, so not easy to clean. Roy |
20th Sep 2017, 3:50 pm | #5 |
Dekatron
Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 7,444
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Re: Rank A823 frame O/P transistors
The frame timebase of the Bush A823 is based upon a Mullard design which was also used in the BRC 2000 and Pye CT70 series. Also the Philips G8.
The original frame output transistors employed in the A823 FTB output stage was a pair of NPN BD131s. In the circuit diagram I have in front of me the output transistors are: 5VT9 RCA 16039 and 5VT10 is a RCA 16029. Both transistors are NPN types. The operation of the circuit is surprisingly complex and well worth study. Replacement transistors: Try TIP31 or TIP41s. Check all the electrolytic capacitors in the output stage as well as the ramp forming capacitors 5C24 (50mfd) and 5C25 (25mfd). Also the clamp diodes 5D8 and 5D10 (BA148 or BY206). DFWB. |
21st Sep 2017, 11:18 am | #6 |
Hexode
Join Date: May 2003
Location: Hertfordshire, UK
Posts: 258
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Re: Rank A823 frame O/P transistors
Thanks, I will check all those electrolytics and diodes, and try a pair of TIP31.
Roy |