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In Reply to: RE: Need Help! I messed up my 2A3 SET amp posted by Shufumei on October 19, 2009 at 16:35:45
Are you SURE the 2A3s are inserted correctly. There are two pins that are larger than the others, these are the cathode filament pins, these pins go in the holes in the socket which are larger. You may want to check first before proceeding. It sound to me that they may still not in correctly.
The main problem is the cathode filament is a dead short if connected incorrectly. If you insert the tube rotated 90 degrees, the worst case situation is that cathode pin will be a B+ and the other will be connected to the heater. This will cause a short of B+ through the filament. This should cause excessive current through the B+ supply and blow a fuse. It also could expose the heater supply (if DC filaments are used) to sufficient voltage to blow the heater filter capacitors. This could explain why the filament no longer heats up. In addition, the cathode bypass capacitor could be blown if it is specified to a lower voltage than B+ (which is likely).
If the tube is rotated 180 degrees, then you have coupling of the B+ supply to the grid through the filament. If the voltage rating of the coupling capacitor (assuming capacitor coupled driver) is lower than the difference between the B+ voltage and the voltage at the top of the plate of the driver tube, you could blow the coupling cap. However, this is very unlikely, since it is typical that a coupling cap would be selected with sufficient voltage for possible failure scenarios.
So, I would recommend you check any fuses on the amp to start with, and make sure the tubes are correctly inserted into the sockets. If the filaments still do not light off, the amp will need to be serviced.
Be very careful the next time.
Thank you, it worked. I carefully insert the tubes back correctly. (thick pins to bigger holes) and the amp comes back alive! Many thanks!
I got no reply after I posted on amp/preamp section at least 6 hours. I got real helpful instruction in tube section right away! I think it tells a lot!
Thanks again!
You are welcome. Glad to see it is up and running. Too bad that many of today's UX4 sockets have oversized holes that allow the large pins to fit through the smaller holes.
I agree with your last statement. If offshore manufacturers would stick to original design specifications for sockets and tube pin sizes, this would not be possible.
Edits: 10/20/09
Thank you guys for the info, I will try and let you know.
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