About the Staccato controller in a VTTC
Philcogrump, Tue Jul 11 2006, 03:26AMI have been looking at many VTTC designs that uses really high-power tubes (beyond 811As) and pretty much all of them use the staccato controller. I understand that it is useful for pulsing the VTTC at a much lower duty cycle to minimize the stress on tubes.
If I recall correctly, wouldn't increasing the grid feedback capacitor also slow down the duty cycle without needing the staccato controller?
The reason I bring this up is because the staccato is solid-state. I figure if a VTTC is ... a VTTC, it shouldn't have any solid-state in it. Steve Ward's staccato outputs really low bps to about 30bps. I don't know if this is wise, but could the triac be replaced with a mechanical relay and use a low power thyratron to drive the relay. A simple tube multivibrator using a dual-triode like 6J6 could be used to produce the low frequency signal to drive the thyratron.
The only shortcoming I can see in this approach is the relay. I figure that a mechanical relay probably can only switch up to about 10bps maximum without great losses. I don't know how a VTTC looks at 10bps or less. Also, there is the possibility of an arc across the relay contacts, or worse, the relay will weld itself shut.
Any comments?
Re: About the Staccato controller in a VTTC
Steve Ward, Tue Jul 11 2006, 04:04AM
Provided you use half-wave input to the tank circuit (and not filtered DC), then the relay would have a good amount of time to open and close. You would have to be careful though, as im not sure how "fast" relay's are. You would have to find something that could close maybe in <1mS. Opening is less of a concern, you basically have a full AC half-cycle (8.33mS or 10mS for 50hz) to open it. But, its possible that relays cant even meet this speed requirement.
Running the coil in grid-blocking mode (aka "sputter mode") can increase the chances of tube arc-over from what i hear. Im not sure what the deal is with that, but this is what im told. Sputter mode usually produces an annoying sounding spark, but perhaps you could use a really big cap there and slow things down a lot.
Steve Ward, Tue Jul 11 2006, 04:04AM
Provided you use half-wave input to the tank circuit (and not filtered DC), then the relay would have a good amount of time to open and close. You would have to be careful though, as im not sure how "fast" relay's are. You would have to find something that could close maybe in <1mS. Opening is less of a concern, you basically have a full AC half-cycle (8.33mS or 10mS for 50hz) to open it. But, its possible that relays cant even meet this speed requirement.
Running the coil in grid-blocking mode (aka "sputter mode") can increase the chances of tube arc-over from what i hear. Im not sure what the deal is with that, but this is what im told. Sputter mode usually produces an annoying sounding spark, but perhaps you could use a really big cap there and slow things down a lot.
Re: About the Staccato controller in a VTTC
Steve Conner, Tue Jul 11 2006, 10:02AM
You could just use the multivibrator circuit to pulse the grid bias of the main power tube between a couple of hundred volts negative and zero. That way the power tube acts as its own staccato switch.
Steve Conner, Tue Jul 11 2006, 10:02AM
You could just use the multivibrator circuit to pulse the grid bias of the main power tube between a couple of hundred volts negative and zero. That way the power tube acts as its own staccato switch.
Re: About the Staccato controller in a VTTC
HV Enthusiast, Tue Jul 11 2006, 11:24AM
Use a triode tube as a switch and drive with some sort of low frequency oscillator. This can then in turn drive the grid.
HV Enthusiast, Tue Jul 11 2006, 11:24AM
Use a triode tube as a switch and drive with some sort of low frequency oscillator. This can then in turn drive the grid.
Re: About the Staccato controller in a VTTC
Philcogrump, Wed Jul 12 2006, 01:23AM
EVR, are you suggesting to use a triode on the end of the grid feedback coil and drive the grid of that triode with the multivibrator output? This way the grid feedback can be turned on/off and therefore make a staccato-like pulse on the power tube?
Philcogrump, Wed Jul 12 2006, 01:23AM
EVR, are you suggesting to use a triode on the end of the grid feedback coil and drive the grid of that triode with the multivibrator output? This way the grid feedback can be turned on/off and therefore make a staccato-like pulse on the power tube?
Re: About the Staccato controller in a VTTC
HV Enthusiast, Wed Jul 12 2006, 03:20AM
Sure why not, but i don't see any reason the controller can't be solid state IMHO. Typically, when any type of equipment is "tube" based, it merely refers to the power component of the device. For example, TWT or magnetron radar transmitters are considered "tube" systems, but still utilize a wide array of solid state components. Even in tube based systems going back 50 years in the 1950's. Same for tube audio amps, tube RF transmitters, etc..., all of which contain a SUBSTANTIAL amount of solid state components.
I would go with the solid state interrupter. It by no means will belittle the title of VTTC.
Even the grand daddy tube audio amplifier of them all, the $350,000 Wavac SH-883 which features a single 833A 150W tube for its main power stage contains a fair amount of solid state components. However, you will still consider that a tube amp, and not a solid state amplifer.
HV Enthusiast, Wed Jul 12 2006, 03:20AM
Sure why not, but i don't see any reason the controller can't be solid state IMHO. Typically, when any type of equipment is "tube" based, it merely refers to the power component of the device. For example, TWT or magnetron radar transmitters are considered "tube" systems, but still utilize a wide array of solid state components. Even in tube based systems going back 50 years in the 1950's. Same for tube audio amps, tube RF transmitters, etc..., all of which contain a SUBSTANTIAL amount of solid state components.
I would go with the solid state interrupter. It by no means will belittle the title of VTTC.
Even the grand daddy tube audio amplifier of them all, the $350,000 Wavac SH-883 which features a single 833A 150W tube for its main power stage contains a fair amount of solid state components. However, you will still consider that a tube amp, and not a solid state amplifer.
Re: About the Staccato controller in a VTTC
Philcogrump, Wed Jul 12 2006, 03:50AM
I understand your point, EVR. However, I enjoy making devices literally all-tube. This shows how much effort and work was put in just to succeed in building something using simple vacuum tube technology even in areas where solid-state works just fine.
Back to the tube staccato controller for the VTTC...
How would a such triode be oriented in the grid feedback circuit? If the grid needs a negative feedback voltage, then would the cathode of the triode go to the other end of the feedback coil and the plate to ground? If so, then that would be problematic to drive the triode's grid in respect to cathode... unless the tube multivibrator circuit was isolated from the rest so its local ground can be connected to the cathode of the driving triode, and the plate of the triode goes to the high voltage ground.
On the other hand, let say I do not want to use a staccato controller. Instead, I run the VTTC with an undoubled MOT and a power tube that normally could withstand a doubled MOT with a staccato. I assume a such tube could handle the 50% duty cycle at that power level without a problem, right?
Philcogrump, Wed Jul 12 2006, 03:50AM
I understand your point, EVR. However, I enjoy making devices literally all-tube. This shows how much effort and work was put in just to succeed in building something using simple vacuum tube technology even in areas where solid-state works just fine.
Back to the tube staccato controller for the VTTC...
How would a such triode be oriented in the grid feedback circuit? If the grid needs a negative feedback voltage, then would the cathode of the triode go to the other end of the feedback coil and the plate to ground? If so, then that would be problematic to drive the triode's grid in respect to cathode... unless the tube multivibrator circuit was isolated from the rest so its local ground can be connected to the cathode of the driving triode, and the plate of the triode goes to the high voltage ground.
On the other hand, let say I do not want to use a staccato controller. Instead, I run the VTTC with an undoubled MOT and a power tube that normally could withstand a doubled MOT with a staccato. I assume a such tube could handle the 50% duty cycle at that power level without a problem, right?
Re: About the Staccato controller in a VTTC
Sulaiman, Wed Jul 12 2006, 06:12AM
If you google for "one tube transmitter" you will find a couple of 'keying' techniques
replace the Key with your interruptir relay.
Sulaiman, Wed Jul 12 2006, 06:12AM
If you google for "one tube transmitter" you will find a couple of 'keying' techniques
replace the Key with your interruptir relay.
Re: About the Staccato controller in a VTTC
Steve Conner, Wed Jul 12 2006, 09:41AM
I agree that Philcogrump should go all-tube for a x5 geek point multiplier.
You're right, the switch tube will need its plate grounded and its cathode connected to the power tube grid circuit, since the grid has to be negative to cut it off. So you'll need a negative HT rail as well as a positive one. I've seen plenty worse in tube circuits, though. >_<
Another possibility would be to use a tetrode as the main tube instead of a triode. Bring the screen supply in through a dropping resistor, and when you don't want the coil to fire, suck the screen supply away by switching it to ground with another tube.
Or, key the cathode current of the main tube the same way as the usual staccato circuit does, but use a thyratron instead of a SCR.
Steve Conner, Wed Jul 12 2006, 09:41AM
I agree that Philcogrump should go all-tube for a x5 geek point multiplier.
You're right, the switch tube will need its plate grounded and its cathode connected to the power tube grid circuit, since the grid has to be negative to cut it off. So you'll need a negative HT rail as well as a positive one. I've seen plenty worse in tube circuits, though. >_<
Another possibility would be to use a tetrode as the main tube instead of a triode. Bring the screen supply in through a dropping resistor, and when you don't want the coil to fire, suck the screen supply away by switching it to ground with another tube.
Or, key the cathode current of the main tube the same way as the usual staccato circuit does, but use a thyratron instead of a SCR.
Re: About the Staccato controller in a VTTC
HV Enthusiast, Wed Jul 12 2006, 01:52PM
I sure hope you don't plan on using a solid state diode to rectify the input HV then.
HV Enthusiast, Wed Jul 12 2006, 01:52PM
wrote ...
I agree that Philcogrump should go all-tube for a x5 geek point multiplier.
I agree that Philcogrump should go all-tube for a x5 geek point multiplier.
I sure hope you don't plan on using a solid state diode to rectify the input HV then.
Re: About the Staccato controller in a VTTC
ragnar, Wed Jul 12 2006, 10:16PM
Yes, EVR, he'll have vacuum-tube rectifiers, vacuum tube transformers, a vacuum tube camera to capture the results with, and he'll just upload the pics to the site with his vacuum tube PC and vacuum tube internet.
ragnar, Wed Jul 12 2006, 10:16PM
Yes, EVR, he'll have vacuum-tube rectifiers, vacuum tube transformers, a vacuum tube camera to capture the results with, and he'll just upload the pics to the site with his vacuum tube PC and vacuum tube internet.
Re: About the Staccato controller in a VTTC
..., Thu Jul 13 2006, 12:32AM
Um, you don't need a diode to rectify the B+ considering the main triode is a diode with an extra element
..., Thu Jul 13 2006, 12:32AM
Um, you don't need a diode to rectify the B+ considering the main triode is a diode with an extra element
Re: About the Staccato controller in a VTTC
Philcogrump, Thu Jul 13 2006, 05:06AM
Of course, I do not even plan to use a diode for the doubler on the MOT. As I mentioned earlier, I was planning to do it without the doubler and run the VTTC on AC power. If the time comes where I might need a doubler, I can always try my 1616 rectifier.
I think I may have a tube that could work for experimentation, a 4-400A. The driving power is under 10 watts, so a TV output tube could be used to switch the grid feedback easily. The 4-400A is a tetrode, so I could also try the idea of pulling down the grid to ground to shut off the tube, but this method may lead to arc-overs, which worries me a bit.
Below is a schematic of the preliminary idea. Also thought about maybe adding a time delay relay (yes, a tube-based one of course) in series with the MOT to allow the rest of the circuits to warm up before the HV is activated.
Philcogrump, Thu Jul 13 2006, 05:06AM
Of course, I do not even plan to use a diode for the doubler on the MOT. As I mentioned earlier, I was planning to do it without the doubler and run the VTTC on AC power. If the time comes where I might need a doubler, I can always try my 1616 rectifier.
I think I may have a tube that could work for experimentation, a 4-400A. The driving power is under 10 watts, so a TV output tube could be used to switch the grid feedback easily. The 4-400A is a tetrode, so I could also try the idea of pulling down the grid to ground to shut off the tube, but this method may lead to arc-overs, which worries me a bit.
Below is a schematic of the preliminary idea. Also thought about maybe adding a time delay relay (yes, a tube-based one of course) in series with the MOT to allow the rest of the circuits to warm up before the HV is activated.
Print this page