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In Reply to: RE: BEZ T3A-3 amp 2A3 posted by mah on July 27, 2017 at 21:20:31
When I look up info on the EF37A it comes up as a high gain tube with a nice straight curve. Sounds like it should be a good tube for it's current usage. Have you had experience other wise?
BillWojo
Follow Ups:
The 6K7 is supposed to be directly interchangeable with the EF37A tube. I believe that when new this amp shipped with 6K7 tubes and someone upgraded the tubes.
If the high's were rolled off than I might suspect transformers but it's not "roll off" I'm hearing. It's the inability to play anything complex at the mid high range. It just smears together.
Since 6K7 tubes are dirt cheap, I might get a pair to test with. I'll also look into testing the 2A3 tubes.
Thanks
BillWojo
When you describe it like that, it sounds a bit to me like what I hear when a tube is worn out. This is odd, however, as you say you have it on both channels.
The other possibility is that the amp is just running out of gas and distorting.
One of the things I don't like about this amp is the lack of a bottom plate to easily access the wiring. Once the top cover is off the tube sockets and wiring are mounted to another plate that lifts up but not much due to the short wires going to the RCA jacks on the side of the chassis near the front. I need to get back into it and see how this thing comes apart.
In the meantime, I can easily measure any voltage going to the tubes. I have a complete set of tube socket test adapters that fit between the tube and the socket with a ring of test points.
Looking at the schematics above, it looks like filament is simply to both filament pins and the other voltages are referenced to ground? Let me know if this would be of help.
Thank you.
BillWojo
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