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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

ECC85

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#21
oshifis said:
The basic reason is that the ECC85 is a variable transconductance tube. This means its transconductance is dependent of the grid bias, and this behavior is used for AGC circuit in VHF/UHF tuners. For audio we need (relatively) constant transconductance for minimizing the distortion of the stage.
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http://www.r-type.org/pdfs/ecc85.pdf
http://www.elektronky.sk/images/stories/elektronky-pdf/6386LGP.pdf
sorry i do not see the ecc85 is remote cutoff tube, curves look standard to me
 
#22
The ECC85 was used in Luxman amps because they were designed by Tim de Paravicini and he also uses them in some of his current production. As I recall they were also used in some iterations of the Leak Troughline tuner. This is probably why they are a bit pricey on eBay.
I also recall there were some designs in Wireless World about 10-15 years ago for direct-coupled valve amps which used the ECC85 as the phase splitter.
 
#23
ECC85 is essentially an ECC81 with an internal screen and normal B9A pins 4,5 heater. It is expensive because nobody makes it any more, yet it was widely used in FM front-ends in Europe.

New audio designs should use ECC81 instead, unless the screen really is needed. Then we can keep our old FM receivers working for a little longer.
 
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