am transmitter - vlsi project

Hallo Anno

That's the challenge. If the tube is really unobtanium which it most likely is for us here in the US I'd have to figure out how to get another tube in there or, ideally, come up with a semiconductor solution. Since the socket is so odd one would have to cut off a tube to make a plug. This is hard to do in a safe manner. But compared to when we were youngsters at least now we have access to stuff like diamond blades and wet saws.

Try asking in news:rec.antiques.radio+phono There are a lot of people there that collect and restore antique test equipment, and someone may have the tube you need.

That's a toughie-- you could use an Australian 6G7, or a USA 6SF7, they're both remote cutoff pentodes and two diodes. A bit high on transconductance, so you might need a 100 ohm resistor in the cathode lead. Ugh.

You will have to make an adapter socket- those funny german p-base sockets are mighty rare.

Hello Michael,

Good idea. Although I don't see this thing as a valuable antique, more like an old tractor that I'd like to put to use again. So maybe I just scrape all the tube stuff out and build a nice solid state oscillator around the rather elaborate and top notch LC circuitry in there. That would probably leave 95% of the enclosure unoccupied and reduce the power consumption by 95% :-)

That would be no problem. An Aussie tube would restore the balance out here. Had to replace the IF tube in my old Astor BPJ with a German tube about 15 years ago. It hasn't developed an accent yet :-)

Might be better to tear the tube stuff out of there, keep the nice LC circuitry and build something modern around that. I mean, it's just a level-controlled oscillator and amp. Although I'd like to maintain its whisper quiet phase noise behavior.

Cheers! Rich

Hello Rich,

That's the ones. But instead of ultra-high efficiency they should be gold-plated with some outrageous claim as to how many dBs they will be better than anything else on the planet and the whole galaxy.

That's not as crazy an item for some of those high-power tubes-- the datasheets suggest you keep the metal to glass seals at under 200C if you want them to continue to hold vacuum.

Now those "Stereo imaging cones" to put under your equipment.....

Has anyone who's been following up on this thread said anything practical about generating this on VLSI?

Because I was just now sort of musing - the Xilinx XC9500 CPLD can be clocked at fantastically high frequencies (well, fantastic to a guy who grew up with inductors wound on a toilet paper tube), like "system frequency up to 178 MHz."

With that kind of speed, writing a PWM to modulate a class 'D' 1 MHz with

I'm actually not sure if I've said that right.

I'd have a 128 MHz internal clock, and a programmable divider down to 1 MHZ (for example), and PWM that: 50% duty cycle with no modulation input, and so on.

If you have an analog input, you'd have to digitize it, but if you're making it up, you can generate whatever you want.

Have Fun! Rich

On the digital modulation described: Unless i really missed my guess, it is a lot like old class B, C linear rf amplifiers. One amplifier running class B taking care of the power dips and a class C amplifier doing all the plus work. Something like 57 percent efficient, and broad band capable. Of course if the step size is about 1.20 to 1 it could give you a fairly linear 60 db modulation range. Also the on-off switching seems to be at least at carrier frequency, making this some kind of modified class S amplifier.

how to fabricate plugs:

stick a layer (or two) of polyethelene sheet (from a plastic bag) over the socket through the sheet poke suitabley sized pins into the socket so that they go suffiiciently deep into the socket, and protrude atbout 10mm. apply 6mm thickness of automotive body filler (or similar two-part putty)

when it's almost set trim the edges with a knife.

I can't vouch for the delectric strength of the putty, but if it's an issue apply heatshrink to the pins before the putty.

Bye. Jasen

Hello Jasen,

Cool! That might also be a nice method to make other connectors that have gone obsolete. Then someone pulls it some day and see a Walmart logo from the bag on the bottom. Ah, that's where I can buy these... :-)

Dielectric strength shouldn't be an issue. I bet that Bondo and stuff like that would be quite good but I'd have to throttle the "plate" voltages anyhow when changing over to FETs. Most dual-gate RF FETs can't stand more than about 12V on the drain.

Hello Rich,

The OP eventually wants to integrate this into a tiny bare chip. Keep in mind that FPGA at high clock rates almost need a direct link to the next electricity plant.

Where is the challenge in that?