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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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11th Jan 2021, 3:41 pm | #21 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,858
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Re: Spl802 (fetrode)
More Data. DS
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11th Jan 2021, 3:47 pm | #22 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Spl802 (fetrode)
The transistor job only has to amplify enough to swing the CRT cathode enough and to be able to work at the PL's supply voltage.
PL802 curves here, short grid base as you would expect: https://frank.pocnet.net/sheets/010/p/PL802.pdf Lawrence. |
11th Jan 2021, 4:08 pm | #23 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Spl802 (fetrode)
That schematics not too clear but you can make out the PL802, the line and field blanking transistor is in the cathode circuit, the other transistor to the left is a luminance amplifier, its input is taken from the luminance delay line, the brightness control controls the voltage on the grid and thus the CRT cathodes, the DC restoration is up round that circuit as well, also there's probably a beam limiter input there too from the line output stage.
Lawrence. |
11th Jan 2021, 5:27 pm | #24 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,858
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Re: Spl802 (fetrode)
Thanks Lawrence for the link & extra info. The Frank P link shows a conventional exponential Gm graph, but mine are unfortunately a lot different. Must get to the bottom of that. The MK3's is more like a soft ladder Ia profile, but then perhaps PL802's don't respond well to AVO VCM's 20mS pulsed half-waves. The DC Tester's profile looks more like an effing voltage regulator's. Me thinks I'll do a repeat with whopping big ferrites in external leads, just in case severe PO is an issue.
Has anyone else had a go at testing/curve tracing a PL802, I wonder ? Regards, David |
12th Jan 2021, 12:05 am | #25 |
Dekatron
Join Date: Aug 2013
Location: Wigan, Greater Manchester, UK.
Posts: 9,433
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Re: SPL802 semiconductor valve replacement.
An excellent circuit description in WW page 501 of a PL802 video amplifier. It expands on Lawrence’s description.
https://worldradiohistory.com/UK/Wir...7-10-S-OCR.pdf
__________________
Frank |
14th Jan 2021, 3:33 pm | #26 |
Nonode
Join Date: Mar 2008
Location: Aberdeen, UK.
Posts: 2,858
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Re: SPL802 semiconductor valve replacement.
Right enough, PO is certainly a problem with testing PL802 valves. Had to make a Ferrite beaded B9 to B9A Adaptor for testing this valve, over & above other PO avoidance measures. Now have more exponential results which I've transposed on to the curves kindly supplied by Lawrence. A wee bit smaller than my A4 metric graph paper, being old imperial size from 1969, but clear enough. Wonder if it was obtained from a super-dooper TEK 576 or similar.
The Frank P graph gives approx. Gm of 40 & my DC tester gives approx. 45 in the -1.3Vg region. The MK3 comes in at approx.37. Me thinks there is a challenge for Colour TV experts to build the wee circuit on page 3(fig.1) & supply the appropriate video signal, for testing these semi-conductor variants. As obviously they cannot be tested in normal valve testers or even homebrew ones. Guess my simple efforts are over. But if there are keen RoeTest or Sussex or Curve Tracer guys out there, who want to delve further into PL802 valve's characteristics, please do. I'm sure it'll be of interest to TV buffs. Regards, David |