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Conversin from ECC808

12/19/2000 2:05 AM
Conversin from ECC808
Is there an easy way to convert preamp from ECC808  
to use ECC83 or ECC88. ECC808 should be version of  
other two but premium (Imax = 350mA compared to  
300mA for ECC83). My problem is that tube sockets  
are mounted on the PCB (old Echolette M120 amp).
12/23/2000 11:30 PM

Hi Vlad.  
Unfortunately all these tubes have different pinouts! ECC83 also uses three pins for the heaters, the others two.  
The ECC88 takes lower plate voltage than ECC808, and it has much lower gain. It's more suited as a driver tube than a preamp tube.  
If it's possible to solve the connections on the PCB, I guess it would be best to convert it to ECC83.  
You can find data sheets for all these tubes at Duncans:  
I guess you have some problems finding ECC808's?  
Good luck!  
12/24/2000 4:31 AM

Vlad, It's me again.  
If I remember right, someone told me that the ECC808 was in the ECC83 family, not so the ECC88.  
So, being the ECC808 (Telefunken I guess) a very similar to an ECC83 tube, and very high quality low noise low microphonic tube... Why change them?  
And there are four of them... One for each input.  
Look for the tube datas Edgar recommended, but I think it would be too much work, maybe not for better.  
I've been thinking on this these days, and maybe with two sockets between the actual socket and the tube, you "could" make an adaptor.  
The real problem is that even being very similar tubes, they have completely different pinouts, and more, different heater voltages.  
Just my opinion, anyway.  
12/24/2000 11:03 AM

Hi Guys.  
There's no problem with the heater voltage, except for the rewiring. Just connect the heaters of the ECC83 in parallel, pin 4 and 5 together, the other end on pin 9, and it's 6.3 volts.  
I agree with JC, that it would be best to keep those fine ECC808's, but I guess they're getting hard to find for reasonable prices!?  
You would of course get a lot more to choose from with ECC83's!  
Vlad, do you have a shematic for that amp, and maybe a layout? It would be interesting to see it!  
12/25/2000 3:37 AM

Schematic? Layout?  
Wishful thinking...  
Well I did my research on conversion too and it seems  
that it would be the best to keep these Telefunken  
808's until they die. If it is measured by them,  
any replacement should last me a life time :).  
Another reason for conversion is that amp has 4  
channels and it could be modified to have different  
voicing on them. 808's are so clean that even when  
input pot(volume) is all the way up, amp is getting  
very little breakup from them. It is designed more  
as a HI-FI than guitar amp.  
My idea was to use two tube sockets and do cross  
pin wiring so that mod is easily reversible  
(plug in adapter).  
Edgar, as I understand you, pins 4,5 and 9 of ECC83  
should be shorted and connected inplace of pin 5  
of 808 (4 is not used)?  
Thanks and Merry Christmas Guys!  
P.S. Would it be safe to simply unplug three tubes  
and use just one channel (and save other three)?
12/25/2000 11:50 AM

Hi Vlad.  
I think you missunderstood me about the heaters!  
If you want to run ECC83 (or 81, 82 and a lot of others), on 6.3 V heater voltage, you connect one lead to pin 9, and the other lead to pins 4 and 5 connected together.  
There are separate 6.3V heaters for the two sections in the tube, but they have one end connected together at pin 9.  
So, you connect as above for 6.3 volts, and to pin 4 and 5 (leaving pin 9 free) for 12.6 volts.  
If you want more breakup, I guess you have to make more gain somewhere in the amp. How that should be done, is hard to say without the schematics.  
If you could draw it up, you should be able to get a lot of suggestions here at Ampage!  
I don't think there would be a problem to pull the preamp tubes not in use.  
Good luck!  
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