Audio and Video Talk > Valves / Vacuum Tubes

E80CF and a new phase-splitter

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fredeb:
I recently bought a batch of tubes from @V4lve Lover , our friend in Holland . 13x 6080 , 10x E180f , 2x NOS Svetlana EL34 ( to go with the 2 lonely ones I had already ) and a single Phillips E80CF .

The E80CF was more thrown in with the rest , than something I wanted , but the more I research it , the more intrigued I get . A 9 pin minature triode/pentode

     


The E80CF is a special quality version of the ECF80 and has the same pinout , which is also the same pinout as an ECF82/6U8/6U8A . The ECF82 is becoming a popular substitute for the 7199 , in boards redesigned to drive the output tubes of Dynaco ST70 . Yes , ECF82 has a different pinout , and slightly different characteristics to 7199 , so it cannot be substituted directly .
 
This article found on r-type.org : http://www.r-type.org/articles/art-097.htm



Arthur Bailey released this design in Wireless World, September, 1962 .

It seems this design was used in some Radford amplifiers . STA25 below



Here is the ST70 circuit for comparison



Seems like a good circuit to try . Comments appreciated .









Moonraker:
Probably not the  greatest circuit in terms of symmetry of drive impedances.

fredeb:

--- Quote from: Moonraker on January 04, 2022, 08:38:13 AM ---Probably not the  greatest circuit in terms of symmetry of drive impedances.

--- End quote ---

Which one ? The Dynaco or Arthur Bailey circuit ?

The Bailey circuit , with ECF82 , is meant to deal with this issue , with ECF80/E80CF anode and cathode resistor values will need to adjusted .



Moonraker:
Radford use the Bailey circuit.  Their way of indicating capacitor values is really odd, but anyway the operation is clear from the Bailey schematic.

C6 is a decoupling cap and R8 is bias.  The circuit is therefore a paraphase type, but with a pentode amplifier stage which introduces an asymmetry.  The high overall NFB used in such a phase splitter (to ensure unity gain of the inverting stage) will tend to minimize any HF response advantages inherent in the pentode.

Maybe they got a stock of ECF80's cheaply.

The Dynaco circuit is simply a pentode amplifier followed by a 'concertina' type splitter.  Not nearly the same thing, but using a similar tube type.

handsome:
Not to split hairs but itís not a paraphase but a Schmitt splitter. And if i remember correctly (which is highly doubtful) that particular configuration was discussed at length on this forum. The pentode eliminates a triodeís Miller capacitance and the resultant increase in bandwidth then allows for more feedback to be used - provided the output transformer has equally good HF performance of course. Even when Schmittís use similar tubes you still need to compensate for the differences in gain (anode resistors), so they never have been the most accurate splitters. Concertinas on the other hand can have excellent balance given matched resistors and that never drifts despite tube aging.

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