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I have a Sun Audio 2A3 SET amp, it sound great. I took the tubes out to clean the dust on the amp, when I put the tubes back, (I think I made a mistake, the 2A3 tube has 4 pins, and I forgot it can goes into the sucket any which way, well at least mine is)
I turn the power on...no sound at all, I checked all connection, it take about three minutes before I notice the 2A3 tubes wasn't lite up, and still cold. I turned it off, correct the 2A3 insert into the sucket, then power it on again. But this time I can hear a borkened and distored sound, it plays soft, also the 2A3 tubes are still not lited and still cold.
Did I burned my power transformer or power supply? The 5U4 and 2 6SN7 are all fire up and glowing. I open the bottom plate, I didn't see any burned component, wire or smell any burn...
Can you guys help me? Your experience feedback will be highly appreciated.
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.
Do you have access to a tube tester? Or a set of known-good 2A3 that you can substitute into the unit? Sounds like you could have damaged the tubes. As for other damage, do a voltage check and see if these match or are close to product's data. Hopefully you have this information or a schematic with voltage marked at certain points. If none of the above, maybe best to take the unit to a tech & have things checked out.
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!
With the cost of good triodes these days... Consider this one of your 9 lives.
;^)
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