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Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Ah, I meant the DC parts like the plate supply and the screen supply. I want to measure it so that won't damage either of them. My 39K resistor from grid to ground just burned up after a couple seconds after the plate supply was turned on... Never did that before even with runs longer than one minute. Anybody have any idea why it would do that?
EDIT: The resistor is ok. It still mesures 39K and now the VTTC is working again...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Hi all
6KG6 is just the American name for the EL509. There's also a 40KG6 which is the American PL509. This may be cheaper because hams and audio guys buy up the EL509, but they can't use the PL509 because of its oddball 40V heater voltage.
You also get an EL519 and a PL519 that you could try, and those Russian 6P45s tubes are beam tetrodes, listed as a substitute for the EL509. Heck, the EL509 is probably a beam tetrode too (the "third grid" is a beam forming plate)
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Dr. Conner wrote ...
Hi all
6KG6 is just the American name for the EL509. There's also a 40KG6 which is the American PL509. This may be cheaper because hams and audio guys buy up the EL509, but they can't use the PL509 because of its oddball 40V heater voltage.
You also get an EL519 and a PL519 that you could try, and those Russian 6P45s tubes are beam tetrodes, listed as a substitute for the EL509. Heck, the EL509 is probably a beam tetrode too (the "third grid" is a beam forming plate)
Well so far i have tried with a 6dq6 and 811a and a pentode from tv that started with a 1. None of these oscillated, i dont believe they had feedback. Does it have to be a beam tube?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Arcstarter wrote ...
Dr. Conner wrote ...
Hi all
6KG6 is just the American name for the EL509. There's also a 40KG6 which is the American PL509. This may be cheaper because hams and audio guys buy up the EL509, but they can't use the PL509 because of its oddball 40V heater voltage.
You also get an EL519 and a PL519 that you could try, and those Russian 6P45s tubes are beam tetrodes, listed as a substitute for the EL509. Heck, the EL509 is probably a beam tetrode too (the "third grid" is a beam forming plate)
Well so far i have tried with a 6dq6 and 811a and a pentode from tv that started with a 1. None of these oscillated, i dont believe they had feedback. Does it have to be a beam tube?
As I have suggested in a post above, the degree of positive feedback coupling outlined in the original German apparatus looks rather inadequate, and I suggest adding a few well insulated turns of overwinding - perhaps on a former of its own - to the anode resonator to improve coupling.
The value of the anode choke also looks rather on the low side, and I would suggest increasing it to at least 1mH, and perhaps more, if it can be insulated adequately from flashing over.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
As far as I know the anode choke should be identical to your secondary coil. That way it has a 1/4 wave resonance at the operating frequency, which would make it block RF completely, which is good.
The feedback in this circuit is by capacitive pickup from the high voltage output. It's basically identical to a Vackar oscillator. Marko and I have argued for days over the phase shifts in this circuit, I think the tube's input capacitance is needed for proper operation, since the Vackar uses a capacitive divider for feedback, whereas he thinks the grid resistor should be chosen to swamp it.
Whatever, the 10nF capacitor in series with the antenna is redundant, since the antenna is a capacitive pickup with a capacitance much less than 10nF.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Yeah, I tried removing the 10nF cap and it didn't do anything. About the grid to ground resistor, can I replace it with a RF choke that would have a reactance that is a couple Kohms? I have a 90uH choke and it would have ~8.4K of reactance at 15MHz (which is about where the VTTC is oscillating).
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Simple VTTC questions
