The 4CX150 and 4CX250 were used extensively by the US Navy in the pacific.
AM, AME, FSK RTTY, Single Sideband Voice, etc.
They were linear enough to use there.
Not very pretty.
4CX150 is good for UHF, so needed to be built in a double box, with the screen connection right at the wall between one box to the other box.
Needs an odd socket.
4CX150 uses a glass window.
4CX250 uses ceramic (with beryllium oxide for heat transfer?) instead of the glass window.
Linearity is a function of the circuit configuration, including whether it is broadband or narrowband (audio is broadband, does not use pi filters, etc.).
The difference between a UHF oscillator or a UHF amplifier is the former has positive feedback (whether intentional or un-intentional).
I'm just sayin'
AM, AME, FSK RTTY, Single Sideband Voice, etc.
They were linear enough to use there.
Not very pretty.
4CX150 is good for UHF, so needed to be built in a double box, with the screen connection right at the wall between one box to the other box.
Needs an odd socket.
4CX150 uses a glass window.
4CX250 uses ceramic (with beryllium oxide for heat transfer?) instead of the glass window.
Linearity is a function of the circuit configuration, including whether it is broadband or narrowband (audio is broadband, does not use pi filters, etc.).
The difference between a UHF oscillator or a UHF amplifier is the former has positive feedback (whether intentional or un-intentional).
I'm just sayin'
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The KWS-1 used a pair of 4X150 for a kilowatt. The 30S-1 used the 4CX1000A, with inverse RF feedback. It was ( is ) considered a pretty good linear amplifier. Maybe one of the best.
There was an explosion of surplus 4CX250 stuff around here about twenty years ago, tubes, sockets, chimneys, were all over the hamfests for a pittance. I suspect they were FAA surplus from the Mike Monroney aeronautical center over at OKC. TONS of Raytheon 6293 as well, also dirt cheap.
4CX250 were popular for amateur amplifiers because you can make a compact, low profile amp with them. I can think of at least one or two commercial manufacturers that used them.
I thought I had given all of my 4CX250 stuff away, but a year or so ago I found some Johnson silver sockets ( with the integral bypass caps ), and some 4X150's ( glass ) in the back of a drawer. No chimneys though, but I think RF Parts still has them. I've heard the glass tubes are prone to leaking vacuum.
2C39 variants are generally a freebie at hamfests around here; it's common to see boxes of them.
There was an explosion of surplus 4CX250 stuff around here about twenty years ago, tubes, sockets, chimneys, were all over the hamfests for a pittance. I suspect they were FAA surplus from the Mike Monroney aeronautical center over at OKC. TONS of Raytheon 6293 as well, also dirt cheap.
4CX250 were popular for amateur amplifiers because you can make a compact, low profile amp with them. I can think of at least one or two commercial manufacturers that used them.
I thought I had given all of my 4CX250 stuff away, but a year or so ago I found some Johnson silver sockets ( with the integral bypass caps ), and some 4X150's ( glass ) in the back of a drawer. No chimneys though, but I think RF Parts still has them. I've heard the glass tubes are prone to leaking vacuum.
2C39 variants are generally a freebie at hamfests around here; it's common to see boxes of them.
7203/4CX250B and 8167/4CX300A have been designed for class AB1 AF amplification and have a 300V 12W screen dissipation rating, same as EL84 anode dissipation. It may be possible to use this tube as triode, with screen as anode. The anode would work as shield, connected to ground, removing the hazard of a big metal part connected to B+. A readily available EL84/6V6 output transformer should be OK for this circuit. Some common tubes such as EL519 can be connected this way. Total dissipation would be less than 30w (15W heater + 12W G2): no special chassis or cooling will be required. I wonder if anyone already tried this arrangement with 8167/7203.
Not sure about the 4CX250B, but some transmitting tubes need forced-air cooling just to light the filament.
The reason they aren't real popular for amateurs these days is that the grid is a little too anemic to handle "grounded grid" operation.
The reason they aren't real popular for amateurs these days is that the grid is a little too anemic to handle "grounded grid" operation.
The need for cooling air for just the filament is a pretty across-the-board requirement for ceramic external anode tubes, if you look in the manufacturer's specifications, at least of the "CX" families.I looked into this pretty extensively a couple of years ago because I was in fact interested in possibly running some external anode tubes at reduced voltages and power outputs with minimalist cooling.
Regarding linearity/ distortion, and analogies to RF, consider that an RF application has a tuned tank circuit, centered on a narrow bandwidth (giving a flywheel effect to waveform form), which, especially with grounded grid, allows RF amps to typically run in single-ended Class AB or even Class B and still have acceptable levels of linearity. Audio output has no tuned tank circuit, and needs to cover a bandwith of (or approaching) 10 octaves..
Not trying to quash anyone from using external anode ceramic transmitting tubes in audio applications - if you want to go there (with appropriate caution for the exposed B+ surfaces) more power to you (literally) - just trying to be candid that there are some limitations specific to the context of these particular devices.
In an RF amplifier, the 'narrow band' tuned tank circuit gets rid of two things:
1. Harmonic Distortion
2. The second order Intermodulation Distortion (sum of 2 in-band frequencies, and difference of 2 in-band frequencies).
That means that for RF applications, such as SSB (Single Side Band), only the 3rd order Intermodulation distortion remains.
All Generalizations Have Exceptions.
Yes, Audio is a completely different thing than a narrowband RF application.
The same principles hold true for Power MOSFETs and Power Bipolar transistors that are designed for RF, versus tubes designed for RF.
1. Harmonic Distortion
2. The second order Intermodulation Distortion (sum of 2 in-band frequencies, and difference of 2 in-band frequencies).
That means that for RF applications, such as SSB (Single Side Band), only the 3rd order Intermodulation distortion remains.
All Generalizations Have Exceptions.
Yes, Audio is a completely different thing than a narrowband RF application.
The same principles hold true for Power MOSFETs and Power Bipolar transistors that are designed for RF, versus tubes designed for RF.
I guess I just struggle to see a point to using this type of tube for audio... the limiting factor always seems to be the output transformer. I would love to build a 200W tube amp, if only I could find good 300W output transformers without spending a crapload of money. I can work out a power supply without trouble, but I feel like I'd be stuck winding my own transformers if I didn't want to pay an insane price for them.
There are lots of excellent glass tubes (that look nicer and don't need forced air cooling) that can make stupid power.
For RF I see a point. They work well and big power using RF transistors is still pretty expensive. Tube amps also a lot more fun for RF.
There are lots of excellent glass tubes (that look nicer and don't need forced air cooling) that can make stupid power.
For RF I see a point. They work well and big power using RF transistors is still pretty expensive. Tube amps also a lot more fun for RF.
Monolith Magnetics 12K SE OT SA-833 $2125 !! (1914.7 Euro)
product & prices | MONOLITH MAGNETICS
or you can do it (13K or 20K 50 Watts SE) for 1/10 price
N. Crowhurst Twin Coupled works for SE too!
200 Watt P-P too, off the shelf OT.
product & prices | MONOLITH MAGNETICS
or you can do it (13K or 20K 50 Watts SE) for 1/10 price
N. Crowhurst Twin Coupled works for SE too!
200 Watt P-P too, off the shelf OT.
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Woah...
Why are they so expensive? It's just copper and iron with a little bit of engineering. It's a transformer, not a rocket.
Amorphous metal core, essentially custom made, high Z, high V, and they probably had to do a number of attempts before they got a design to work well. (high bandwidth claimed, although the low freq. and primary inductance don't add up)