I recently acquired an EICO HF-30 in reasonable condition. It is the eight tube version. The only thing missing when I got it was one of the EZ-81 rectifiers. With a new EZ-81 installed, the amp sounded pretty good, however, there was noticeable hum when the amp powered up, that did not increase with volume increase. I do not own equipment to test the frequency of the hum, but with a cell phone app I measured it to be around 240 Hz. I am not sure how accurate that measurement is...
Since then, I have restuffed the canned capacitor. My amp came with the 2 x 20 uF and 2 x 10 uF canned capacitor, and that is what I used to redo the capacitor. C5, the 300 uF electrolytic capacitor was also replaced. I have replaced all of the resistors that were of the +/-10 % and 1/2 watt rating with +/- 5 % and 1 watt rating resistors. All of the stock +/- 5 % resistors that I did not replace have been tested to still have the proper resistance. I have also replaced the "molded" capacitors with new polypropylene capacitors. The RCA plug has also been replaced.
Based on another thread (http://audiokarma.org/forums/index.php?threads/eico-hf-30-rebuild-hums-like-crazy.694508/), I grounded the filaments of the output tubes, but this had no effect on the hum.
If there is anyone that has some advice on what I can do to reduce/eliminate this hum would be greatly appreciated.
I rate myself as a new hobbyist, so please keep that in mind with you advice.
Thanks
Since then, I have restuffed the canned capacitor. My amp came with the 2 x 20 uF and 2 x 10 uF canned capacitor, and that is what I used to redo the capacitor. C5, the 300 uF electrolytic capacitor was also replaced. I have replaced all of the resistors that were of the +/-10 % and 1/2 watt rating with +/- 5 % and 1 watt rating resistors. All of the stock +/- 5 % resistors that I did not replace have been tested to still have the proper resistance. I have also replaced the "molded" capacitors with new polypropylene capacitors. The RCA plug has also been replaced.
Based on another thread (http://audiokarma.org/forums/index.php?threads/eico-hf-30-rebuild-hums-like-crazy.694508/), I grounded the filaments of the output tubes, but this had no effect on the hum.
If there is anyone that has some advice on what I can do to reduce/eliminate this hum would be greatly appreciated.
I rate myself as a new hobbyist, so please keep that in mind with you advice.
Thanks
