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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 20th Nov 2023, 6:50 am   #1
Martin G7MRV
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Default 6CW4 Nuvistor as HF oscillator?

I appreciate that this tube was designed for VHF use, but would there be any major pitfalls to using one in a little HF oscillator/one valve Tx?

The 8056 would be much easier to power having a much lower anode voltage but I can get a 6CW4 with socket included.

This is just for fun really, I just fancy playing with one. I suppose I could create some form of socket if needed from something like a strip of turned pin connectors
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Old 20th Nov 2023, 10:35 am   #2
Radio Wrangler
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Default Re: 6CW4 Nuvistor as HF oscillator?

As there is gain well up into UHF, you might have trouble with spurious oscillations if lead lengths aren't very short. You may need a grid stopper resistor close to the thing if the rest of your circuit is the usual sort of HF construction. Some scope plug-ins using nuvistors had problems.

David.
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Old 20th Nov 2023, 10:51 am   #3
G6Tanuki
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Default Re: 6CW4 Nuvistor as HF oscillator?

There's no reason why a Nuvistor shouldn't be used for HF, though you may need some stopper resistors and ferrite beads to control any VHF/UHF oscillational aspirations.

In one of the early Sixties ARRL handbooks there is a design that used a Nuvistor as a superregen receiver on 50MHz and self oscillating modulated stage on transmit.

Shades of the old WS19 B-set!!
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Old 20th Nov 2023, 1:09 pm   #4
Martin G7MRV
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Default Re: 6CW4 Nuvistor as HF oscillator?

Interesting. I've picked up an 8056 triode. No socket, I'll have to think of something to connect it up, but the very low 'HT' is appealing. I might try a little regenerative receiver with it, or a simple one tube cw tx, depending what circuits I can find that would suit

I'm guessing designs intended for similar spec normal size valves will adapt?

I've some sub miniature wire ended valves somewhere as well to try the same with. The diddy little tubes just appeal to me
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Old 20th Nov 2023, 2:10 pm   #5
Martin G7MRV
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Default Re: 6CW4 Nuvistor as HF oscillator?

Well, turns out my low ball offer on a 6cw4 with socket has been accepted, quite a surprise, so I can play about with both
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Old 20th Nov 2023, 5:55 pm   #6
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Default Re: 6CW4 Nuvistor as HF oscillator?

There's at least one design for a grid dip oscillator on the net (6CW4) which I'm sure covered SW and VHF frequencies.

B
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Old 20th Nov 2023, 6:39 pm   #7
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Default Re: 6CW4 Nuvistor as HF oscillator?

Yes, I remember a GDO based on a "low HT voltage" Nuvistor so the entire thing could run off a 12V car battery without needing vibrators or inverters or other bulky stuff..

It included a single transistor as a DC amplifier so you could use a 1mA meter rather than the fragile 50uA one you'd have needed otherwise.

A Nuvistor would, IMHO, make a good valve for use in a VFO; the electrode construction's rigidity would minimise microphonic effects and the low heater power combined with compactness would promote stability. In times-past I built a number of rather successful VFOs using the 6AK5/EF95, which in a way could be seen as the precursor of the Nuvistor on account of its smallness and good VHF performance.
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Old 21st Nov 2023, 3:58 am   #8
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Default Re: 6CW4 Nuvistor as HF oscillator?

This is the one I was thinking of http://www.w4cwg.com/ngdip.html.

30V on to a 7586.

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