Posted: Sun Nov 30, 2008 3:26 pmCan tube testers check for filament to cathode leakage?
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Posted: Sun Nov 30, 2008 3:26 pmPosted: Sun Nov 30, 2008 3:36 pmThe Eico 666 has a big "H-K leak" switch on it.
Posted: Sun Nov 30, 2008 5:25 pmEven the most basic emission tube testers can perform an inter-elements "shorts" test. The usual indicator is a neon bulb. These should have a "short" button or slide switch, and really egregious shorts will light it up without any operator input. Yellow_Light_Colorz_PDT_11 :o
If there is no tube tester available, just use an ohm meter, at least it will show "cold" shorts or high resistance "leakage" on any tube.
The better testers like the Eico "satan special" 666 and the Hickok testers can perform much more accurate and specific leakage testing.
/ed B
If there is no tube tester available, just use an ohm meter, at least it will show "cold" shorts or high resistance "leakage" on any tube.
The better testers like the Eico "satan special" 666 and the Hickok testers can perform much more accurate and specific leakage testing.
/ed B
Posted: Mon Dec 01, 2008 10:11 pmAre you sure it isn't merely tube microphonics from a vibrating mains transformer? That would change level depending on the tubes tried and how resistant each design is to vibration.
I mentioned this before, but it looks from your close up pic that the mains trannie is mounted directly to the chassis which would likely cause alot of vibration in the chassis, and quite possibly hum due to the valves vibrating. It did with mine and it lessoned considerably mounting the transformer on rubber washers.
- John
I mentioned this before, but it looks from your close up pic that the mains trannie is mounted directly to the chassis which would likely cause alot of vibration in the chassis, and quite possibly hum due to the valves vibrating. It did with mine and it lessoned considerably mounting the transformer on rubber washers.
- John
Posted: Wed Dec 03, 2008 8:02 pmThe other day I finished mounting my power transformer on rubber washers. To avoid them from being crushed from the torquing of the nuts, I mounted some thin metal washers over top of the rubbers. The rubber washers did not seem to help with the humming so I tried changing around some of my 6SN7s. Sure enough, the loudest hum followed one of the 6SN7's to the other channel. Then I tried one of my EH 6SN7s. That made the hum so loud it could be heard throughout my workshop! It has to be the tubes.
Posted: Sat Dec 06, 2008 11:30 amI'd try a couple of hum balance controls (1 for each channel). 100 ohm 5 watt pots. Wire them temporarorly with them hanging out the bottom to get at them. This might be the easiest fix..... I'm guessing is the input tube will be most important. So look to see which heater winding is powering the input tube and try a hum balance control on that first. Good luck.........