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Old 31st Dec 2020, 4:19 pm   #1
David Simpson
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Default SPL802 semiconductor valve replacement.

Just wondering, does anyone have the pinout for this solid state option, made by LEDCO, to the PL802 TV valve?
The PL802's AVO VCM Code is 141 235 651. Thought I would try some comparison tests (Ia & Gm) against a PL802(if I can get one), and others in the family(I've got a PL82 & an EL822).
Me suspects that my MK3 wont like testing Fetrodes, so would power up slowly on my DC tester( which also uses an AVO VCM Th./Wheel switch assembly). I reckon the code should be 140 230 600, as this fetrode I have has Pin6((PL's screen) not connected to anything. Or even just 140 000 600, as pins 4 & 5 just go across a high wattage load resistor.
I see via "Search" there is some info about PL802T's, but those Fetrodes seem to involve different circuitry. But then, perhaps this one has been "got-at"

Regards, David
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Old 31st Dec 2020, 4:39 pm   #2
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Default Re: Spl802 (fetrode)

Radiomuseum.
https://www.radiomuseum.org/tubes/tube_pl802t.html

https://mullard.org/products/spl802-...pl802-nos-bnib
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Old 31st Dec 2020, 5:00 pm   #3
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Default Re: Spl802 (fetrode)

It's possible the FETrodes might not like the reverse bias time of the AVO's AC excitation.

To be on the safe side, I wouldn't put them anywhere near it, because it might not like how they react to it.

David
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Old 31st Dec 2020, 5:20 pm   #4
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Default Re: Spl802 (fetrode)

I thought these items used standard transistors, BF459 and BF259 not FETs but yes bias could damage them.
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Old 31st Dec 2020, 5:34 pm   #5
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Default Re: Spl802 (fetrode)

Thanks Frank for the links. Yep David, that was my thoughts re an AVO VCM. The R/M's "circular" circuit diagram shows a fixed 6Mohm bleed off from the Screen's supply, so will just look to see what mA the fetrode draws in my DC V/T.
Not being a TV guy, I wonder how reliable they were back in the day? Had I not found it in a box of gash valves several years back, I'd never had known such S/St. items were used to replace valves. Anyway, 'twas just a thought for a wee New Year project. Just found it again whilst sorting through an old box of assorted Si & Ga transistors which have yet to be tested.

Regards, David
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Old 31st Dec 2020, 5:42 pm   #6
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Default Re: Spl802 (fetrode)

Not absolutely sure of the make:

https://www.radios-tv.co.uk/wp-conte...02T_schema.jpg

Lawrence.
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Old 31st Dec 2020, 6:16 pm   #7
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Default Re: Spl802 (fetrode)

I don’t remember them being unreliable although I only used a few. The PL802 standard valve gave a better picture so where ever possible I used a valve.
I didn’t need any after about 1980 having left the trade, perhaps with the PL802 becoming unavailable they were used more in the 80’s although sets would likely been past their service life by then.
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Old 31st Dec 2020, 9:16 pm   #8
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Default Re: Spl802 (fetrode)

And another one:

https://frank.pocnet.net/sheets/084/p/PL802S.pdf

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Old 3rd Jan 2021, 6:46 pm   #9
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Default Re: Spl802 (fetrode)

Well, I've made up a comparison between the LEDCO & the other three diagrams. The Ledco just uses the Anode's 170V HT, whereas the other three use the Screen's 170V for the first FET's HT. Very simplistic.

Regards, David

Last edited by David Simpson; 3rd Jan 2021 at 6:54 pm. Reason: Duplication
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Old 3rd Jan 2021, 6:53 pm   #10
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Default Re: Spl802 (fetrode)

Well, have made up a comparison between the LEDCO SPL802's circuit diagram, and the other three.
The Ledco is very simplistic, just using the Anode's 170V HT for both Fet's.

Regards, David
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Old 3rd Jan 2021, 7:20 pm   #11
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Default Re: Spl802 (fetrode)

If you're going to test this in a DC valve tester don't forget a load resistor.

No FETs in these.

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Old 3rd Jan 2021, 8:23 pm   #12
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Default Re: Spl802 (fetrode)

Was the LEDCO schematic reverse engineered or was it copied from somewhere? Certain aspects of it don't look right to me, I would have expected the base of the output transistor to be connected to the Emitter of the driver transistor and the Emitter of the output transistor to go to pin 1 via a low value resistor so as to enable max drive voltage to the CRT.

Lawrence.

Last edited by ms660; 3rd Jan 2021 at 8:40 pm. Reason: extra info
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Old 3rd Jan 2021, 11:12 pm   #13
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Default Re: Spl802 (fetrode)

The guy who gave it to me said that the original owner claimed it was a "Fetrode". Now that I've removed the big heat sink & heater substitute resistor, going by the soldering on the wee square pcb its possible its been got-at. I'd just rev/e'd the c/d from the pcb. Certainly, the top c/d looks the most substantial & better designed.
Think I'll bin this doubtful ledco & use some miniature veroboard to build another more decent substitute. Probably will just build a wee temp. test rig rather than put one of these solid state devices anywhere near a valve tester. Anyway, obviously the electronic formulae relating to transistor functions are totally different to Barkhausen's which govern testing valves.
Isn't electronicing fun ?

Regards, David

PS Had trouble downloading the diagram sheet in post 9.
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Old 4th Jan 2021, 11:33 am   #14
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Default Re: Spl802 (fetrode)

Typically, the anode load would be somewhere around 2.5k (ish) depending on the RGB drive settings, the cathode would be connected to deck via the blanking transistor.

The PL802 was a 40mA/V job.

Lawrence.
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Old 4th Jan 2021, 12:05 pm   #15
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Default Re: Spl802 (fetrode)

Right enough Lawrence, it was that heffing big Gm slope for the PL802 which inspired my (valve testing)interest. Not being a TV buff, I've no experience working with that family powerful wee TV pentodes. So it intrigued me as to how a semi-conductor device could replicate their performance.
I've worked with the likes of DTG1200's & 2400's, in the past, used in marine equipment's HT PSU's. Plus other transistorised PSU's. But two diddy black BF's replacing a PL802 is something else.

Regards, David
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Old 4th Jan 2021, 12:21 pm   #16
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Default Re: Spl802 (fetrode)

Some TV's used a PFL200 for the luminance output but most used the PL802, LEDCO did other SS replacement jobs too, they did a replacement CDA panel that replaced the three PCL84 jobs in one of the PYE TV's

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Old 4th Jan 2021, 1:28 pm   #17
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Default Re: Spl802 (fetrode)

I wonder why Ledco & Philips used the BF459 seeing that TITS (Towers International Transistor Selector.) designate it as "VLE" (VHF), & not "TLE" - - specifically for TV Line usage ? Further down the TITS page is the BF472 which seems more appropriate for TV usage & has an Ic of 100mA & an HFE of 50min. But then, what the heff do I know about TV circuitry requirements. My comfort zone is with valves & analogue circuitry for radios, R/T's & T/Eq. etc. I'll try & get my hands on an ordinary PL802 & do some Ia/Vg graphing. Should be fun with such low -ve Vg values & high Gm expectations.

Regards, David

Last edited by Cobaltblue; 4th Jan 2021 at 1:47 pm. Reason: Not everyone knows about Towers International Transistor Selector.
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Old 4th Jan 2021, 1:40 pm   #18
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Default Re: Spl802 (fetrode)

Luminance is to at least 5MHz.

Lawrence.
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Old 4th Jan 2021, 8:43 pm   #19
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Default Re: Spl802 (fetrode)

We had them on the shelf but we tended to fit a proper 802 if available. The s/s ones seemed a bit short of gain and also a little 'soft' on the video.
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Old 11th Jan 2021, 3:39 pm   #20
David Simpson
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Default Re: Spl802 (fetrode)

Perhaps just SPL802 as the title, please Moderators, as we're not talking FET's.
What a thumping wee pentode the PL802 is. A TV expert chum has just sent me an NOS one to test. Results were totally different between my DC Tester & my VCM MK3.
Re the MK3 - Ia readings were easy enough to read, but struggled to guess accurate -ve Vg on the dial in the decimal zone.
DC Tester - Uses external BSM 3/2A 3 channel modern bench DC PSU, therefore could get pretty accurate Vg source, plus accurate monitoring of Vh/Ih. Also monitored Vh with my Newlec DMM closer to the valve's holder. Belt & braces, eh. In addition, for PO avoidance, Grid supply was fed via a ferrite'd extension valve - holder box, plus also inserted another ferrite'd adaptor(UX7) for more "belt & braces".
The DC Tester uses a built-in Marconi TF1041C VVM for accurate VA & VS monitoring. And an external AVO8/3 for accurate Ia measurement.
This must be the most twotting graphing exercise I've ever undertaken.
Apologies for seperate A4 graph sheets, but since Covid I've lost my local source of A3/A4 scanner/printer.
As for the circuitry which the PL802 is expected to work in - baffles me as to how an SPL802 or PL802T can replicate a PL802's performance.
Does anyone have a Mullard Valve Data Book showing characteristic curves, please ? Wouldn't mind a scan copy.
Don't forget - as much as I enjoy testing & graphing valves - I'm a dummy where complicated Colour TV circuitry(or any TV circuitry for that matter) is concerned.

Regards, David
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