Does anyone know of any lowish power tubes capable of 50Mhz? Say in the 200-600V range? I'm asking as a last chance before I settle on a mosfet output stage for any power use. The tube itself would only be used at 24Mhz but more tubes are available into the 50Mhz band.
I'm aware that switching at this rate has been the reason for high voltages. Plus to be honest I would not be comfortable attempting a 1kV+ device, even if it was in a fully closed shielded case with separate compartments for the kV components.
GU-81M is 1.2KV
6HV5 is 5KV
GU-46 (60MHz) could be possible - more modest B+.
I've read the GU-81M threads for the audio amps made using these. Given the B+ values these would need a large voltage swing depending on the mu which then means needing a drivers stage capable of 50Mhz - so my thinking here is that there must be a driver tube that fits the bill?
e88cc is an option for line output (this is used in MarcelG's DAC) However I was wondering if there's an option to make a tube power section using the same.
Just research for my next tube amp at this stage.
I'm aware that switching at this rate has been the reason for high voltages. Plus to be honest I would not be comfortable attempting a 1kV+ device, even if it was in a fully closed shielded case with separate compartments for the kV components.
GU-81M is 1.2KV
6HV5 is 5KV
GU-46 (60MHz) could be possible - more modest B+.
I've read the GU-81M threads for the audio amps made using these. Given the B+ values these would need a large voltage swing depending on the mu which then means needing a drivers stage capable of 50Mhz - so my thinking here is that there must be a driver tube that fits the bill?
e88cc is an option for line output (this is used in MarcelG's DAC) However I was wondering if there's an option to make a tube power section using the same.
Just research for my next tube amp at this stage.
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Thanks for your trust but I guess asking at an RF Forum would bring more/better answers than an Audio one.
Unless 50MHz is a typo.
Unless 50MHz is a typo.
No problem I'll take the conversation elsewhere.
Essentially doing the same job as MarcelG's e88cc in switching the final DSD512 stream (so a 30-50MHz tube can keep up). So it's final audio output but the guts are operating digital. Hence being a little blurred in to which forum it would sit.
The 6BG6G, specifically the 'G' variant, and possibly the 30MHz 'A' variant, seems to fit the bill. Used in TVs but also in radio driver sections for the large tubes. 110mA operating current and up to 700V with a 0.34pF grid.
The question is insufficient.
Which type of RF amplifier would be the target?
A, AB, B, C ?
Modulated or linear?
Required power?
Try to read this:
https://www.google.hu/url?sa=t&rct=...g-Tuibes.pdf&usg=AOvVaw2aClwDF4EwdwJZw2DvpJwE
Which type of RF amplifier would be the target?
A, AB, B, C ?
Modulated or linear?
Required power?
Try to read this:
https://www.google.hu/url?sa=t&rct=...g-Tuibes.pdf&usg=AOvVaw2aClwDF4EwdwJZw2DvpJwE
Try color TV sweep tubes like 6KD6 or PL509.
My ham radio transmitter uses 2*6KD6 and here in Germany
5 pcs. of PL509 were very common because we had a limit of 150W
total nominal plate dissipation. it was not impossible to generate 1KW
with that setup because of their low residual plate voltage when fully on.
Gerhard
My ham radio transmitter uses 2*6KD6 and here in Germany
5 pcs. of PL509 were very common because we had a limit of 150W
total nominal plate dissipation. it was not impossible to generate 1KW
with that setup because of their low residual plate voltage when fully on.
Gerhard
My Drake TR-6 used 6GK6 as the driver. It drove a triplet of 6JB6A on 6 meters. I presume 6BQ5 would also work unless there is something peculiar to the 6GK6 pin out that made it more suitable for VHF.
There are plenty of options....in fact nearly all of the tubes we use today will work fine at 24 MHz, but as stated there is insufficient information given to propose a decent suggestion.
I am a ham radio operator, and was a transmitter design engineer at Motorola. I have used tubes in RF amps up to 50 MHz as far back as my teenage years. As in audio, the desired application is more important than the exact frequency of operation, especially below 50 MHz.
Color TV sweep tubes do come in all sizes, and have been used successfully as an RF output tube in frequencies to 30 MHz and beyond. The 6BG6 was mentioned. The 6BG6 is a 6L6GB with the plate brought out to a top cap so that it could withstand the high voltages seen in TV sweep duty, where the peak plate voltage reaches several kilovolts. The 807 is also a 6L6GB with a different base and a top cap to optimize it for RF transmitter use.
TV sweep tubes can be operated at low voltages, even in the 100 volts and less range where they work quite well, just don't expect 100+ watts at these voltages.
If big power is NOT part of the application (you have only discussed a voltage range) then any of the TV video or IF amplifier tubes will do well depending on the desired power level.
In the 5 watt range there is the venerable 12BY7. It has been seen in audio amps like the Citations, and ham radios like many Kenwoods where it is the driver for a TV sweep tube or a 6146A. That's why they are getting scarce today, but there are dozens of other video amp tubes. The 6CL6 is anther that often sees audio amp and RF duty. There are dozens more.
Below that power level are all the IF amplifier tubes which are all designed for 39 or 45 MHz. The venerable 6EJ7/EF184 comes to mind but there are many.
If high frequency switching is desired, then you need is a tube that can be saturated or cutoff cleanly and quickly. Triodes can be used but what ever is driving them must be able to quickly charge and discharge Mr. Miller.
I would use a pentode with a large cathode to get a low saturation voltage. Again small TV sweep tube come to mind, but there is another alternative if the power levels are low. The 6W6 was originally developed for TV vertical (frame output) sweep. It was adapted for use as the output stage in line powered radios. The 50L6, 25L6, 12L6 and several others are just 6W6's with a different heater voltage. There are smaller versions in 7 and 9 pin sizes, the 50C5 is a miniaturized 6W6, and the 6CU5 is the 6 volt flavor. The 6DB5 is the 9 pin flavor. All of these will operate at 24 MHz.
There are possibly better choices, including all the old computer tubes, but more information is needed to determine one.
One thing to consider is that you'll basically be building a fairly capable rf amplifier. I'm not familiar with the British radio spectrum but it's possible you could interfere with vital radio communications such as aircraft etc. You could have your version of our FCC knocking on your door. I'd keep it fully enclosed in a grounded metal enclosure and put ferrite chokes on all cabling to be safe. That's just me. Good Luck!
How about the currently produced 4X250 ?
A tetrod but in the right circuit it might be a good candidate ( it was not mentioned what the tube should be used as )
A tetrod but in the right circuit it might be a good candidate ( it was not mentioned what the tube should be used as )
Thank you, that seems like a good starting list.
I was thinking about class A or AB (although digital can be done class B), although I tend to stick with triodes, my initial plan was to use 6BQ7As and EF91 for one of the logic gates with a mosfet final switch for driving speakers. However if one of these fits, I can tube & RF transformer before the output filter. Other options here are 12AX7 for high gain for example.
The ideal would be something that could drive 89dB and in terms of wattage I'd be happy to start with something low powered for near field listening. I have some 8ohm Castle Harlechs but I was thinking of a near field small full range bookshelf design ~2-5W.
Previous research has come up with 6BQ7A etc capable of running ~300Mhz due to the small input capacitance and a compromise I'd already made the decision that the entire amp has to run enclosed/shielded.
I'll have a look through availability, cost and what fits.
I was thinking about class A or AB (although digital can be done class B), although I tend to stick with triodes, my initial plan was to use 6BQ7As and EF91 for one of the logic gates with a mosfet final switch for driving speakers. However if one of these fits, I can tube & RF transformer before the output filter. Other options here are 12AX7 for high gain for example.
The ideal would be something that could drive 89dB and in terms of wattage I'd be happy to start with something low powered for near field listening. I have some 8ohm Castle Harlechs but I was thinking of a near field small full range bookshelf design ~2-5W.
Previous research has come up with 6BQ7A etc capable of running ~300Mhz due to the small input capacitance and a compromise I'd already made the decision that the entire amp has to run enclosed/shielded.
I'll have a look through availability, cost and what fits.
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You have asked several questions about vacuum tubes for RF applications without telling us what it is that you want to build, except that it needs a "lowish power tube" and you mention "switching" at a 24 MHz rate.
I guessed that you might be attempting a vacuum tube DAC in my first reply, hence my list of tubes. Now you talk of driving a speaker.
Are we discussing a class D vacuum tube amp? If so, is this with or without an OPT? In either case making square waves (needed for optimum "switching") at 24 MHz will result in harmonics well into the radio and TV spectrum. Applying them to any wiring leading to a speaker is the basic definition of a transmitter, thus asking for trouble. Even mosfet based class D amps run in the below 1 MHz range and filter the signals leading to the speaker.
Again, what is it you are trying to accomplish?
I guessed that you might be attempting a vacuum tube DAC in my first reply, hence my list of tubes. Now you talk of driving a speaker.
Are we discussing a class D vacuum tube amp? If so, is this with or without an OPT? In either case making square waves (needed for optimum "switching") at 24 MHz will result in harmonics well into the radio and TV spectrum. Applying them to any wiring leading to a speaker is the basic definition of a transmitter, thus asking for trouble. Even mosfet based class D amps run in the below 1 MHz range and filter the signals leading to the speaker.
Again, what is it you are trying to accomplish?
Looking through all the data sheets, there's a fair selection.
What I may do is start with something simple - no need for water cooled 4X250. Something like the 12BY7(a) or 6EJ7/EF184 are simple given they're B9A packages. Seems the 12BY7 was used as a driver for the 6146b. Increasing power would be easier with the EL84 or EL34.
Something that hadn't occurred to me initially is which class? I'd stuck with class A given that's my favoured approach however digital, by it's nature' is on or off, which lends itself to Class B with better energy efficiency. Why I'd not thought of that before! :facepalm:
What I may do is start with something simple - no need for water cooled 4X250. Something like the 12BY7(a) or 6EJ7/EF184 are simple given they're B9A packages. Seems the 12BY7 was used as a driver for the 6146b. Increasing power would be easier with the EL84 or EL34.
Something that hadn't occurred to me initially is which class? I'd stuck with class A given that's my favoured approach however digital, by it's nature' is on or off, which lends itself to Class B with better energy efficiency. Why I'd not thought of that before! :facepalm:
To answer that - you've pretty much described it. A digital stream causing the final tube as an amplified digital signal, reconstructed on the output filter as analogue before being passed to the speaker.
Misunderstanding : 4X250 is aircooled. If loaded fully it needs forced air cooling, typically
by a fan charging the airtight chassie and holes in the sockets for 4x250 that channels the air through the tubes cooling fins.
by a fan charging the airtight chassie and holes in the sockets for 4x250 that channels the air through the tubes cooling fins.
OK, now that I understand, you definitely do not want to run a tube in class A for a digital circuit. An optimum digital circuit should consume little or no power, the device is either off, passing no current and leaving its output at one rail. Then it switches to full conduction (saturation) as quickly as possible passing a lot of current, but having a very low voltage across it.
This is why I talked about big cathodes and sweep tubes, as they can pull their plates to within a few volts of its cathode (low saturation voltage, like VCEsat). The penalty for this is a hungry heater, so a tradeoff may be needed.
If I was to go down this path I would use something like the 6W6, or 6GF5 but I have a bunch of them. The EL84 or EL86 / 6CW5 (lower voltage) would also be a good choice.
The output impedance of a tube is usually too high for direct connection to a speaker, so an OPT is used. Whether or not it is possible to perform this impedance transformation at RF, then apply the reconstruction filter at 8 ohms is yet to be seen. I have discussed this on these forums many years ago, and saw many reasonable and convincing arguments as to why it could, or could not be done. I have never tried it.
I know that at least one vacuum tube digital audio amp has been seen on this forum, and I think there was another. I'll post the link if I can find one.