SPL802 semiconductor valve replacement. - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

David Simpson · 11th Jan 2021, 3:41 pm

More Data. DS

ms660 · 11th Jan 2021, 3:47 pm

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.

ms660 · 11th Jan 2021, 4:08 pm

Quote:

Originally Posted by David Simpson

More Data. DS

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.

David Simpson · 11th Jan 2021, 5:27 pm

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

Nuvistor · 12th Jan 2021, 12:05 am

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

David Simpson · 14th Jan 2021, 3:33 pm

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

11th Jan 2021, 3:41 pm	#21
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	Re: Spl802 (fetrode) More Data. DS Attached Thumbnails

11th Jan 2021, 3:47 pm	#22
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	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, 5:27 pm	#24
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	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
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	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
David Simpson Nonode Join Date: Mar 2008 Location: Aberdeen, UK. Posts: 2,853	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 Attached Thumbnails