The amp i am working on now has 16 6AS7G output tubes all wired in series with a large resistor and connected directly to the incoming 120V AC line.
the 6AS7G draws 2.5amps at 6.3V mulitply that by 16 and that = 40amps! I see now why they wired them all in series. BUT i just have to think that Noise from the AC line could get into the audio....couldnt it?????
Wouldnt DC filaments be better?
Zc
the 6AS7G draws 2.5amps at 6.3V mulitply that by 16 and that = 40amps! I see now why they wired them all in series. BUT i just have to think that Noise from the AC line could get into the audio....couldnt it?????
Wouldnt DC filaments be better?
Zc
I just got a copy of a schematic for the Atma-Sphere amps my prototype ended up as, and i see that they are using a large trafo for the filaments. so the series connection in this amp must have just been for prototyping. When i rebuild this amp i am going to change that however.
Anybody have a 6.3V 40-50 amp trafo for sale???
Zc
Anybody have a 6.3V 40-50 amp trafo for sale???
Zc
Hopefully not considered a thread-hijack (or needless "resurrection"); here's a serial-filament/substitution question: I just had a 12av6 fail - and a replacement is long off - could I consider this...
I have some 6av6 <essentially the same tube, half voltage heaters>, so to regain operation in my serial string amp, swap the 12' for the 6', and serial-in a second 6av6's heater only? I would ground out the other connections on the dormant tube, with just its heater lit to satisfy the voltage-drop string on the line (iso'-tranny, of course) string?
I'd expect to have to tweak the one in-series-resistor to account for the increased current draw, but otherwise is that a stopgap tactic that anyone has employed? Heck, I suppose I could add a gain-stage, and make that redundant 6av6 "functional" for extra grunt.
'Thoughts?
I have some 6av6 <essentially the same tube, half voltage heaters>, so to regain operation in my serial string amp, swap the 12' for the 6', and serial-in a second 6av6's heater only? I would ground out the other connections on the dormant tube, with just its heater lit to satisfy the voltage-drop string on the line (iso'-tranny, of course) string?
I'd expect to have to tweak the one in-series-resistor to account for the increased current draw, but otherwise is that a stopgap tactic that anyone has employed? Heck, I suppose I could add a gain-stage, and make that redundant 6av6 "functional" for extra grunt.
'Thoughts?
@Alan4411 - Good catch; I shouldn't have presumed they had identical I-h...they don't: The 6's have the same heater 'power' consumption as the 12's - e.g. half the volts, but twice the current. Thus, I'd have to rework the filament string anyway <sigh>.
If the 12' replacement doesn't come, I will then likely just drop that socket from the heater string (adjusting the upstream resistor accordingly), and bodge a quick 6.3v for that socket's interim 6av6. Thx again for the "re-read-the-datasheet" nudge!
If the 12' replacement doesn't come, I will then likely just drop that socket from the heater string (adjusting the upstream resistor accordingly), and bodge a quick 6.3v for that socket's interim 6av6. Thx again for the "re-read-the-datasheet" nudge!
What is the heater arrangement? 12V or some serial solution.
I don't see why the following is not possible:
Use some diodes to rectify the 12V then use a regulator, resistor voltage divider or zener to create the 6.3V for the 6SN7. There would be a greater current draw, but should be within the tolerance of the transformer.
Should be easier going from greater volts to lesser.
I don't see why the following is not possible:
Use some diodes to rectify the 12V then use a regulator, resistor voltage divider or zener to create the 6.3V for the 6SN7. There would be a greater current draw, but should be within the tolerance of the transformer.
Should be easier going from greater volts to lesser.
@OldHector - serial; one dropping resistor then the chain of four tubes. As it is AA5-like, and features the odd-ball p-p/50C5 finals, it drops 100v worth of heater voltage at the 2x50 outputs, with the preamp/ph-s getting the rest.
The "rub", as Alan noted, is the expectation of the original filaments all to draw 150mA... I can yank an altered preamp out of that string and compensate with resistance, but then that differing (300mA) tube gets its own V(h) - - becoming more trouble than it's worth ;-)
The "rub", as Alan noted, is the expectation of the original filaments all to draw 150mA... I can yank an altered preamp out of that string and compensate with resistance, but then that differing (300mA) tube gets its own V(h) - - becoming more trouble than it's worth ;-)
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