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replace ECC85 with ECC83?


 
10/28/2003 9:58 AM
per
email
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  
Per.  
DK.
 
10/28/2003 9:32 AM
6 10
email

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
per
email

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?  
Thanks.  
Per.
 
10/28/2003 3:08 PM
Andy
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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 )
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Per  
 
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 .  
 
Chris
 
10/28/2003 4:04 PM
Chris ( CMW amps )
email
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 !  
 
Chris
 
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