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I'm really getting a sense of how dirty the power is in my house, how much things sag and draw, etc.
Last night I went to confirm the plate voltages and found things 7 to 10 volts lower than I remembered. I went and turned off a space heater and my readings were back to normal. Yikes.
I tried running a 470ohm resistor at the cathode and I got 23v (for 49ma), with 370-something on the plates but that only came out around 9 wattts of dissipation per tube.
I don't quite understand how things all interact, but it seems that a change one place means big changes elsewhere. I'm guessing that my plates are now only at 330-something because the (massive) change in current being pulled by the tubes is loading everything down.
So here's where its running now
I get 17v across the cathode resistor (seems way low, but bear with me)
its a 220 ohm resistor
so 17/220 -- .077 and change, so 77ma -- sound about right?
figure about 4 less for the screens, so 73ma (I didn't actually measure this)
Ive got 333 and 336 on the 6v6 plates respectively (depending on space heaters, lamps, etc)
so lets just go with 334 as a conservative average.
334v*.073ma = something like 24 watts dissipation between the two tubes.
So assuming the tubes I've got in there now are reasonably matched (I don't really know how to test this, I don't have a tube tester -- is there any way to figure it from measurements in the amp? are the reasonably similar voltages an indication that they draw similarly?) I'm getting something like 12 watts dissipation -- which is good.
I'm not sure why that cathode voltage is so low (17v when I'd expected 20 to 23), but the current draw and dissipation numbers seem to be pretty much perfect, unless of course I'm misunderstanding how to figure this stuff.
Last night I went to confirm the plate voltages and found things 7 to 10 volts lower than I remembered. I went and turned off a space heater and my readings were back to normal. Yikes.
I tried running a 470ohm resistor at the cathode and I got 23v (for 49ma), with 370-something on the plates but that only came out around 9 wattts of dissipation per tube.
I don't quite understand how things all interact, but it seems that a change one place means big changes elsewhere. I'm guessing that my plates are now only at 330-something because the (massive) change in current being pulled by the tubes is loading everything down.
So here's where its running now
I get 17v across the cathode resistor (seems way low, but bear with me)
its a 220 ohm resistor
so 17/220 -- .077 and change, so 77ma -- sound about right?
figure about 4 less for the screens, so 73ma (I didn't actually measure this)
Ive got 333 and 336 on the 6v6 plates respectively (depending on space heaters, lamps, etc)
so lets just go with 334 as a conservative average.
334v*.073ma = something like 24 watts dissipation between the two tubes.
So assuming the tubes I've got in there now are reasonably matched (I don't really know how to test this, I don't have a tube tester -- is there any way to figure it from measurements in the amp? are the reasonably similar voltages an indication that they draw similarly?) I'm getting something like 12 watts dissipation -- which is good.
I'm not sure why that cathode voltage is so low (17v when I'd expected 20 to 23), but the current draw and dissipation numbers seem to be pretty much perfect, unless of course I'm misunderstanding how to figure this stuff.
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