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ECF801 any good for audio

ilimzn

Member
2005-02-11 1:25 pm
Zagreb
Doesn't the ECF801 have a common cathode for the triode and pentode?
The ECF802 is a great tube, so is the ECF80. The latter works great as first stage and phase splitter, it was used for many years by Klein + Hummel in their studio amps and active monitors, also in 'civilian' guise as Saba. They used very low currents through the pentode to get the maximum possible gain, but IMHO it works far better with a more substantial current and gains around 100. Also works great as a driver for Schade pentode outputs, either SE or PP. ECF802 differs mainly in the triode gain. ECF82 sadly is not as linear. In all cases there are a few tricks to get around tube tolerances, as proper choice of operating point is crucial to get low (actually very low) distortion. One of the trick is not to use active G2 regulation, rather a simple resistor to drop voltage, and a capacitor to cathode (also to ground will work for high gain even when NFB is applied to the cathode because of very small swing WRT G2 voltage).
 

Willleung

Member
2007-05-08 7:48 am
Doesn't the ECF801 have a common cathode for the triode and pentode?
The ECF802 is a great tube, so is the ECF80. The latter works great as first stage and phase splitter, it was used for many years by Klein + Hummel in their studio amps and active monitors, also in 'civilian' guise as Saba. They used very low currents through the pentode to get the maximum possible gain, but IMHO it works far better with a more substantial current and gains around 100. Also works great as a driver for Schade pentode outputs, either SE or PP. ECF802 differs mainly in the triode gain. ECF82 sadly is not as linear. In all cases there are a few tricks to get around tube tolerances, as proper choice of operating point is crucial to get low (actually very low) distortion. One of the trick is not to use active G2 regulation, rather a simple resistor to drop voltage, and a capacitor to cathode (also to ground will work for high gain even when NFB is applied to the cathode because of very small swing WRT G2 voltage).

Thanks ilimzn, just checked and you are right.. I got 10 PCF803 coming in, was using ECF801 data sheet they seems to have a seperate cathode (was thinking i brought a load of junks...)

http://www.tubebbs.com/tubedata/sheets/124/p/PCF801.pdf

[IMGDEAD]http://www.radiomuseum.org/images/tubeenvdiag_klein/pcf803.gif[/IMGDEAD]

Thanks for the head up on the ECF82 and the 802, will draw a load line later this week.
 
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Miniwatt

Member
2004-11-01 5:46 pm
Got here after a search:

In all cases there are a few tricks to get around tube tolerances, as proper choice of operating point is crucial to get low (actually very low) distortion. One of the trick is not to use active G2 regulation, rather a simple resistor to drop voltage, and a capacitor to cathode (also to ground will work for high gain even when NFB is applied to the cathode because of very small swing WRT G2 voltage).

How does that work?? I'm also curious to hear what the other tricks are.
I'm designing a stage with ECF80 and I was looking at ECF802 as well.
Thanks.