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replace ECC85 with ECC83?

10/28/2003 9:58 AM
replace ECC85 with ECC83?
Hey there.  
I`ve just bought an russian built 100w tube head, with 4 6L6 and 3 ECC 85 (its named "heavy duty", anybody heard of this one?). Can I replace the ECC85 with ECC83 without any further mods? I think it "cranks up" a little to early, any advice how to get it a little "cleaner" I have no schematics or anything, but I have worked a little with tubes etc. before.  
Thanks in advance  
10/28/2003 9:32 AM
6 10

Hi Per.  
Sorry, ECC83 and ECC85 don't have the same pinout, so it doesn't work. You'll have to rewire the tube sockets first.  
Is it really ECC85's in it? It's very odd I think. The only amps I've seen ECC85's in, are old Philips PA-amps, but only as a phase inverter.  
ECC85 is really a HF radio tube, usually found as the first tube in an FM-reciever.
10/28/2003 10:25 AM

Hi 6 10  
I was pretty much surprised myself, when I saw this tubes, but they are ecc85` maybe somebody have replaced them, the amp was bought secondhand. I must try to figure out how to rewire the sockets. As far as I can find out the difference is pin 9, is that right?  
10/28/2003 3:08 PM

that's right. the only difference is that there is no center tapped filament, and the whole thing runs on 6v. so the mod shouldn't be too difficult to go to a 12A*7 type. tie pins 4&5 together and run one filament wire to pin 9. no big deal. the other difference between the two tubes is that the ecc85/6aq8 has less gain. the 12AX7 is about 100, while the '85 is around 57.
10/28/2003 3:36 PM
Chris ( CMW amps )

I've got probably ( gotto look :) ) some ECC85s over here , if you can't find any specs I can snailmail you a copy , just let me know and I'll try to help you .  
10/28/2003 4:04 PM
Chris ( CMW amps )
ECC85 specs
except for the filament-wiring ( 6.3 Volts to pin 4 and 5 , pin 9 is an internal shield ) the layout is the same as an ECC83 .  
Here are some specs :  
S = 5.9 mA/V  
u = 57  
Ri = 9.7 k  
Wa = max. 2 x 2.5 W  
Kinda like an ECC81 .  
Good luck !  
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