Valve frequency multipliers

I'm afraid that doesn't sound very promising. A triode could be anything from a water-cooled UHF transmitting valve to a PX4 to a

For me to find a version of Spice that works on my computer under OS8.6, then learn to use it well enough to get any useable results would take years - with almost no chance of the outcome working any better than if I had guessed at the component values to start with.

Tubes have model files, and you can adjust various parameters.

I don't know the parameters that I need for this job, the valve manuals only publish static figures and some basic curves. Finding out things like the gm of an EF91 when the signal is applied to G2 or G3 is almost impossible as an academic exercise, it is quicker to solder up a test rig and get the answer by experiment.

Then create your own Spice model from it. That's what the late great Jim Thompson used to do very frequently. He was our go-to guy here for anything to do with constructing models. Sadly missed <sigh...>

Last February would have been his 21st birthday.

Cheers

Phil Hobbs

Leap year baby, was he? I always thought it was rotten luck to be born on the 29th of Feb!

Liz: You should not attempt to transmit anything around 150 MHz. It is on a frequency band reserved for satellite communication, and any unlicensed transmission is strongly frowned at.

I am being very careful to avoid transmitting any spurious signals at

The block diagram (referred to above) shows that the 150 Mc/s output of the multiplier chain is mixed with the output of a variable frequency oscillator to give a signal in the 144 - 146 Mc/s band. A balanced mixer should attenuate the 150 Mc/s signal and further filtering removes any remaining residual 150 Mc/s and the image freqency (164 - 166 Mc/s).

In an earlier design I proposed a low-side input to the mixer at 135 Mc/s but abandoned this when I realise that the image would be 124 - 126 Mc/s:. This is in the band allocated to aircraft and I live undeneath the flight path to Bristol Airport.

You're starting with a too low IF. The standard method for 2 meter transverters is to start with a 28 MHz band signal, to get the images far enough to use less complicated filters after mixing. You have to be careful about oscillator signal leaking through the mixing process anyway.

The 160 MHz bands are for maritime mobile services.

Megacycles / second have been buried even in the US for over half a century. The current radios use MHz or GHz. </nag>

My first 2 metre receiving setup had a crystal-controlled down-converter and a CR100 communications receiver running at 28 Mc/s. The CR100 was so unstable that it would shift several Kc/s if a gnat landed on the front panel. I improved the mechanical design, which was very poor, and made it useable but it was never particularly stable.

Using a VFO on the transmit side requires an even better degree of stability, which is why I chose to keep the crystal-controlled frequency high and use a more stable lower frequency VFO to generate the transmitting frequency. The VFO coil is wound on a ceramic former and bonded with epoxy resin to reduce expansion of the copper wire. I have made provision for temperature compensation and checked that the frequency drift with changes in the H.T. voltage are negligible.

On the receive side, the first down-conversion ratio is 145 to 5 Mc/s i.e. 29:1, the second ratio is 5 Mc/s to 100 Kc/s i.e.50:1. If these were stupidly different I would be very worried, but they aren't too far off the ideal of both being 38:1 and the greater ratio is at the lower frequency, where filtering is easier.

Luckily I live far enough from the sea that my transmissions will never get to the coast. If I go portable, the highest land is still some way inland and my maximum output is less than 10 Watts, so I don't think there is likely to be much of a problem.

Yes, I know ...but I am well over half a century old and I prefer Mc/s.

So am I, and I succeeded to abandon megacycles in favour of SI units

Yikes! (to quote JL) I'm 83+. Guess I Should start eating healthily.

Jim was always talking about wine. And his pancreas got him.

If Spice was of any use in RF ham gear, the amateur radio guys would have been all over it three decades ago.

I've modeled known-good valve power cctry only as a curiosity, to see if spice could come anywhere close to practical results. Curiously the nowhere-near-common valves used already had models, so I'm pretty sure somebody else had already made a run at the identical application. (Tek HV oscillator).

RL

That should have been 6CX8 (6CM8)from the article.

There are functioning models for 6BL8 (ECF80), which has a pentode/triode combination.

I expect just as big a problem in modeling would be in coupling/filter magnetic components.

Oscillators never do . . . .

RL

Some fraction of my income comes from an instant-start TCXO-accurate triggered 50 MHz LC oscillator. That was developed with Spice (and a PowerBasic program.)

Amplifiers oscillate . . . Oscillators don't.

I used, but well over half a century after the target device was built.

I designed and built a novice class CW transmitter in spring 1969. It was used by several novices to get their required experience, and stored after the novice class requirements were changed decades later. The transmitter was found when the attic of my parents was cleaned.

The cleaning was done in 2020, at the worst COVID block-out time. To do something useful, I created a description of the transmitter in LaTeX, as an exercise. I used LTspice to draw the schematics, and as a side product, a working model of the transmitter got born.

I had to create plenty of components, e.g. all tubes (EF94/6AU6, EL83/6CK6, EL500/6GB5 and OA2/150C2). With extensive Internet search, the matching Spice models were found, mostly from HiFi enthusiast pages.

When running the models, I noticed that a real-world crystal model is too slow to start, so I had to change it to lower Q, so that the solver did not grow tired to start up. The simulated results matched quite well with the built device, despite that in a transmitter, the tubes are working well outside of the normal HiFi biasing range.

RF design is still in the ancient days of load pulls and Smith charts and slide rules. I expect that Qspice may change that. Everything interesting is nonlinear.

Spice is great for modeling mosfets and phemts. Why not tubes?

Probably because few people use tubes any more.