12-30-2013, 07:30 AM
morzh;
It was rated for 300VDC and was just not adequate for what the rectifier was delivering to it before all the rest of the tubes warmed up. The original electrolytic was rated at 250VDC. I was having trouble finding a 25mFd at the voltage that I was looking for from my usual sources. I finally realized that electrolytics have such broad tolerances for capacitance that finding a 25mFd was really not so important. The main thing is to find one that has plenty of voltage handling capability. When I started looking at 20mFd electrolytics there were many available at much higher voltages and I chose one of those. Physically it was no larger than the lesser rated one I had used. It appears that tubesandmore.com has lots of units to choose from at very good prices. I plan to continue ordering from them unless something prevents.
The fact that the B+ voltage is high there before the other tubes warm up may be an indication that the audio tubes in particular need to be checked for adequate emission. If they are weak and do not have normal current, that could contribute to the voltage being high. I need to check the nominal B+ again and see how much it is after warm-up. If it is still too high compared to the voltages indicated on the schematic, then more checking needs to be done.
Joe
It was rated for 300VDC and was just not adequate for what the rectifier was delivering to it before all the rest of the tubes warmed up. The original electrolytic was rated at 250VDC. I was having trouble finding a 25mFd at the voltage that I was looking for from my usual sources. I finally realized that electrolytics have such broad tolerances for capacitance that finding a 25mFd was really not so important. The main thing is to find one that has plenty of voltage handling capability. When I started looking at 20mFd electrolytics there were many available at much higher voltages and I chose one of those. Physically it was no larger than the lesser rated one I had used. It appears that tubesandmore.com has lots of units to choose from at very good prices. I plan to continue ordering from them unless something prevents.
The fact that the B+ voltage is high there before the other tubes warm up may be an indication that the audio tubes in particular need to be checked for adequate emission. If they are weak and do not have normal current, that could contribute to the voltage being high. I need to check the nominal B+ again and see how much it is after warm-up. If it is still too high compared to the voltages indicated on the schematic, then more checking needs to be done.
Joe
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