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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 27th Oct 2003, 11:15 pm   #1
Sideband
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Default Ferguson 391TRG by Tim Pullin

Elsewhere on this website, Tim wrote a very interesting account of his repair to a table radiogram.

http://www.vintage-radio.com/recent-...n-391trg.shtml

The use of a PCF80 as a phase splitter is interesting. Old 'uns like me will remember these valves being used as frequency changers in 405 TV's. My theory is that the heater/cathode insulation is better than that of an ECF80 because of its original use in series heater chains in AC/DC sets of the time. Therefore if it is directly coupled to the EL84 as in this present application, it's cathode is running at a much higher voltage than normal. It was probably felt that the greater heater/cathode insulation would be more reliable.

I remember a record player being manufactured by Philips that used an EL84 and a UL84 in cascade. The UL84 cathode was directly coupled to the anode of the EL84. The UL84 was chosen because the cathode was running at about 100V and the heater/cathode insulation was able to withstand this.

Rich

Last edited by Paul Stenning; 27th Dec 2004 at 12:53 pm. Reason: Fix link or code for vBulletin
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Old 28th Oct 2003, 12:11 am   #2
Tim
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Default Re: Ferguson 391TRG by Tim Pullin

That makes sense. Now I look at the circuit, the cathode must be at about half HT (approx 150V).

Thanks, I never thought of that.............

Last edited by Paul Stenning; 27th Dec 2004 at 12:53 pm. Reason: Fix link or code for vBulletin
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