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Old 6th May 2021, 11:42 am   #22
matspar's Avatar
Join Date: Aug 2009
Location: Portsmouth, Hampshire, UK.
Posts: 210
Default Re: Philips 663A combined radio/television 1948

Hi Andy, yes she does indeed have a 5:4 ratio rubber mask, which appears to have survived very well. Gorgeous HMV 1804, bet you wished you'd kept hold of that one!

The cabinet on the 663A will require a lot of work but I'm confident I can retain much of the original finish when the time comes.

I've got a short update on the 663A and a small bit of progress.

I'm still waiting for 4 new ECH35's to arrive to try in the line and frame osc, and the sound and vision freq changers. Postage seems incredibly slow down South lately!

In the meantime having had a bit of a play around I've discovered the timing issue of severe line foldover can be improved by experimenting with the values of R91 (3k) and C120 (0.005) across the line coils and eht flyback transformer. Halving both values to 1.5K and 0.0025 provides the best compromise as shown. Any increase in values will damp the EHT and focus is lost. I'm thinking this issue may be being caused in the first instance by a poor line oscillator ECH35 having an effect on the drive/frequency. Substituting the EL38 produces identical results.
The width control R138 will not behave as expected and instead tends to move the entire image to the left and begin to reintroduce the foldover.

There is still no audio but massive noise and disturbance on screen causing jitter, line pulling and instability. Definition is poor and focus is fully advanced and could be better. The 663A is also suffering from velocity modulation as the picture brightness will vary along the scan, however this was improved somewhat by giving the EF50 in the first RF stage a good wiggle in its socket. I'm undecided if a lot of these problems are being caused by the reciever end or the line limebase (or a combination of the two) hopefully I can start ruling things out once those new valves arrive.

There are a few circuit differences, most notably R43, which instead of being returned to deck is actually connected to the plus side of C119, which is a polarised capacitor (8uf electrolytic) in my set. This all looked totally original and wiring it to circuit causes total loss of sync.

Resistors are all within spec and all capacitors have been restuffed/replaced in the area of the circuit shown, except for three low value items C121(220pf) C99(180pf) & C101(12pf) which I've left alone for the time being.

Still a great deal to do!! as always any thoughts on these fault conditions most welcome and appreciated.
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Last edited by matspar; 6th May 2021 at 11:55 am.
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