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27th Oct 2003, 11:15 pm | #1 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,572
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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 |
28th Oct 2003, 12:11 am | #2 |
Dekatron
Join Date: Jan 2003
Location: Bradford on Avon, Wiltshire, UK.
Posts: 3,310
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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 |