What reasons would cause a flash over in a TV damper tube with 480VAC in a bridge configuration? It rarely happens, but I have seen it happen at least thrice. I turn the amplifier on then there is a flash, then I turn the amp off, then when I turn it on again everything goes fine.
The tubes I'm using are 6DE4.
Any answers are appreciated.
The tubes I'm using are 6DE4.
Any answers are appreciated.
Would you consider 270uf caps to be too large?
This is the power supply I'm using
480vac
6DE4 x 4 Bridge
40uf input cap (motor run)
100ohm resistor
235uf cap (2 x 470uf 450v stacked)
100 ohm resistor
235uf cap (2 x 470uf 450v stacked)
100 ohm resistor
235uf cap (2 x 470uf 450v stacked)
530vdc B+
330k breeders connected to caps
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Is it one particular tube that likes to flash over, or are they all equally likely to flash? If there +is+ an event, how many tubes tend to flash over - 1, 2, 3 or all 4?
IMO, at those voltages, those are BIG caps. And even with 100R separating the first two stages (40U / 235U), that 2nd stage is huge - call it 100R shorted to gnd at power-on. And that motor-run cap you have is ultra-low ESR and rated for high ripple current, so it's not going to be your friend in terms of current limiting.
Try this - change out that 1st 100R for 1K and see if you get any flash over. You don't need the B+ connected to the circuit, just test the PSU as a block. Let the bleeders pull the voltage down between tests.
If that prevents the flash over, then revert the 1K to 100R and try a 10uF in place of the 40uF cap at the input.
IMO, at those voltages, those are BIG caps. And even with 100R separating the first two stages (40U / 235U), that 2nd stage is huge - call it 100R shorted to gnd at power-on. And that motor-run cap you have is ultra-low ESR and rated for high ripple current, so it's not going to be your friend in terms of current limiting.
Try this - change out that 1st 100R for 1K and see if you get any flash over. You don't need the B+ connected to the circuit, just test the PSU as a block. Let the bleeders pull the voltage down between tests.
If that prevents the flash over, then revert the 1K to 100R and try a 10uF in place of the 40uF cap at the input.
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Is the flash immediately upon turn-on or about 5-10 seconds after?
If it's immediately it can't be capacitors since the DE4 takes a while to heat up and it's likely the heater just briefly incandesing on startup. This is especially true if you are running the 4 tubes in series across 24v which would be the preferred way in a bridge setup. It's not necessarily an indication of a bad tube btw. Some tubes just do that when they're cold. My series string AM/FM looks like it's going to catch fire the 17EW8 flashes so brightly on startup. Been that way for years and gets turned on about 5 times a week.
In my experience damper diodes do really well as power supply rectifiers and should be fine with the capacitance you have in the supply. Actually, you could get away with way more than the 40uF you have. If it was capacitance causing your issue the tube should flash any time it sees an empty supply capacitor. Could test this by turning the amp off, waiting a second or two for the sound to die, and then turning the amp back on while the tubes are hot.
If it's immediately it can't be capacitors since the DE4 takes a while to heat up and it's likely the heater just briefly incandesing on startup. This is especially true if you are running the 4 tubes in series across 24v which would be the preferred way in a bridge setup. It's not necessarily an indication of a bad tube btw. Some tubes just do that when they're cold. My series string AM/FM looks like it's going to catch fire the 17EW8 flashes so brightly on startup. Been that way for years and gets turned on about 5 times a week.
In my experience damper diodes do really well as power supply rectifiers and should be fine with the capacitance you have in the supply. Actually, you could get away with way more than the 40uF you have. If it was capacitance causing your issue the tube should flash any time it sees an empty supply capacitor. Could test this by turning the amp off, waiting a second or two for the sound to die, and then turning the amp back on while the tubes are hot.
It's the first time for this set.
Only one tube has done it.
Definitely flashed before 10sec...even 5sec.
Same tube is fine now.
All 4 tubes have their Heaters wired in series to a 24vct transformer.
The amp is single end 6L6GC triode strapped.
Both channels combined take 90-100mA
I'm building another amp, and plan on using smaller caps with more filter stages as I'm looking to do higher voltage...535VAC center tap transformer.
I really am considering transmitting rectifiers such as 836, 1616, 3B24, or even thyratrons rather than dampers. I'm thinking the dampers may not be rated high enough for higher voltages. 5000 volts for a damper does not equal 5000 volts for rectifier service. Though having top caps make using the transmitting rectifiers more difficult and potentially less safe...the cats...I guess it's all about tradeoffs offs. Safety first. I do have a way to be sure the anode caps cannot be removed without using a small hex wrench.
Only one tube has done it.
Definitely flashed before 10sec...even 5sec.
Same tube is fine now.
All 4 tubes have their Heaters wired in series to a 24vct transformer.
The amp is single end 6L6GC triode strapped.
Both channels combined take 90-100mA
I'm building another amp, and plan on using smaller caps with more filter stages as I'm looking to do higher voltage...535VAC center tap transformer.
I really am considering transmitting rectifiers such as 836, 1616, 3B24, or even thyratrons rather than dampers. I'm thinking the dampers may not be rated high enough for higher voltages. 5000 volts for a damper does not equal 5000 volts for rectifier service. Though having top caps make using the transmitting rectifiers more difficult and potentially less safe...the cats...I guess it's all about tradeoffs offs. Safety first. I do have a way to be sure the anode caps cannot be removed without using a small hex wrench.
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It definitely sounds like heater flash and nothing to worry about. You're running those tubes so easily I doubt you'll ever have to replace the rectifiers!
When it comes to these guys there is a lot of misinformation out there. They're rated for 175mA DC output, 5kV PIV, and 900V Heater-Cathode. Stay within those specifications and you'll be just fine. Assuming you are wanting to run them right on the edge but within specifications you could do a ~2600V supply at 175mA for half-wave or ~1500V supply at 350mA for full wave.
As for input capacitor size, my guess is as good as yours but the 6X4 does 70ma at 10uf capacitance and the 6CA4 does 150mA at 50uF so there is no easy multiplier there. I'd say 100uF is on the safe side for a 350mA supply.
When it comes to these guys there is a lot of misinformation out there. They're rated for 175mA DC output, 5kV PIV, and 900V Heater-Cathode. Stay within those specifications and you'll be just fine. Assuming you are wanting to run them right on the edge but within specifications you could do a ~2600V supply at 175mA for half-wave or ~1500V supply at 350mA for full wave.
As for input capacitor size, my guess is as good as yours but the 6X4 does 70ma at 10uf capacitance and the 6CA4 does 150mA at 50uF so there is no easy multiplier there. I'd say 100uF is on the safe side for a 350mA supply.
Yes they are... but it has an lnverse voltage rating of only 1050V.
May be a good candidate for a voltage doubler... I have a pair and a transformer with dual 3VAC secondaries for the heaters.
Kylej1050,
Thank you... I will take this information to heart. You are correct...There definitely a ton of misinformation... Its like eating a Snickers bar just to get to the peanuts.
I also read that less capacitors are better for the sound...
Sometime I think a battery supply is the best... and a capacitor is essentially a battery... then again, if it were that simple...
Thank you... I will take this information to heart. You are correct...There definitely a ton of misinformation... Its like eating a Snickers bar just to get to the peanuts.
I also read that less capacitors are better for the sound...
Sometime I think a battery supply is the best... and a capacitor is essentially a battery... then again, if it were that simple...
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My amplifier will use one of them, in choke input mode filter.
I have 3 of them, two new and one more used.
Note the hand-home-made toroidal transformer and 5.6Hy 40ΩDCR inductor.
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yes....been using that tube in a hybrid rectifier setup, at a dollar a pop, what is not to like?
i am using a 10ufd/600 volt film first cap, then choke, then 470ufd caps, 50ohm 10 watt, then another 470ufd, there are two other 470 caps, one for each channel....
two froward biased 3A diodes supply the two other caps....i know this may raised eyebrows
but this is what i do...
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the 6cd3 is also a dollar tube, has 250mA dc output, a 12 watt plate, 12pin compactron type...
http://www.nj7p.org/Tubes/PDFs/Frank/127/6CD3.pdf
if i were using dampers as rectifiers, i will tie the cathodes to the heaters,
some here in the forums recommend it for safety....
looking at the heater cathode specks,
we find this for the 6de4.
i would be more concerned with the lower specs...
http://www.nj7p.org/Tubes/PDFs/Frank/127/6CD3.pdf
if i were using dampers as rectifiers, i will tie the cathodes to the heaters,
some here in the forums recommend it for safety....
looking at the heater cathode specks,
we find this for the 6de4.
i would be more concerned with the lower specs...
Assuming that you are correct,
Why do you say that heater flash "nothing to worry about"? Not trying to argue, but I think we can all agree it's not an anticipated behavior - is it?
Why do you say that heater flash "nothing to worry about"? Not trying to argue, but I think we can all agree it's not an anticipated behavior - is it?
Good grief, filament 'flash' on power-up is another matter entirely - and it's quite common in certain Euro tubes, like Mullard / Tele / Brimar 12A_7 series. Some mfrs even added start-up delay circuits to their equipment, simply to avoid this precise issue.
So if that's what's happening here, I guess I must have extended too much credit to the OP.. assuming the OP knew a filament surge (undesirable, but typical) from an inter-element arc (not what you want at all).
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