1П24Б 1p24b

[Amie]

Hi Peter.

That's a really well thought out project, I'm impressed with the method of NFB that you've devised, I will be looking forward to seeing the signal stages when you have them ready for us!

I'm hoping to translate some of my current experiments to filamentary cathode valves too, as a good friend has donated some rod pentodes to the cause

Thanks,
Amie.

[Murphyv310]

Nice amp with some interesting features.
I particularly like the phase splitter. How is the response from the second valve in the splitter, out of interest?

[Kalee20]

Like this (photo from my notes!):
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Square waves from the two antiphase outputs - loaded by two x10 scope probes, which (see another recent thread) have a capacitance of about 15pF. Timebase here is 50μsec/div.

[Murphyv310]

Excellent indeed.

[Amie]

Hi all

I've recently been doing some experiments with superhet circuits, and have been sent some of the 1j24b by a good friend. One of the test bed chassis I've been using is from an old EverReady Sky Captain that uses the DK mixer valve. As these are now a fairly rare comodity I thought I'd try using two Russian rods to replace it. Basically the arrangement is as per the attachment shown without band switching for simplicity.

Thanks to Kalee20 and Michael Watterson for material and intellectual help....



Amie.

[Kalee20]

Looks a useful circuit, good work

The 4k7 resistor in series with the oscillator feedback winding, was that arrived at empirically, and if so, how?

Operation of the mixer valve is different from the conventional DK96 changer, as it has RF applied to the first grid whereas the pentagrid puts the incoming RF on its 3rd grid. Might even be more sensitive, do you have any comparative data, such as, most distant station received for original and for Russian replacement?

Finally, did the IFT primary need any twiddle to bring on-tune with the 1j24b?

These little rod pentodes are addictive...

[Murphyv310]

The basis of the circuit is around Michael's DK96 Rod pentode substitution using two 1J24b
Michael's original circuit attached
The 4 7k seems high I'd have thought 100r but rod pentodes oscillate easily.

[Amie]

Indeed it is based on Mr Watterson's ideas it does work well.

The 4k7 is what was in the chassis originally feeding g3 through the oscillator coil primary, I guess its there to stop the windings from having their own peaks of resonance, in the ER it was taken from the feed to the IF valve screen supply...

The mod did work very well, though that chassis is pretty fair anyway, for a cheap and simple set up.

The first IF did need peaking a bit, the whole alignment would need doing if it were to be left, seemed to favour the extremes of the MW... Not miles out though.

Amie.

[Mike Watterson]

Glad to see people getting some value. I've a plan to substitute an 1L6, obviously adding a parallel ballast to have 50 mA. I've found that the 1j24 has much lower anode capacitance than the DK96, DK92 and DF96. Possibly other electrodes are also lower capacitance. I did my last DK96 and DF96 ersatz with a small trimmer and fixed capacitor on the anode and then was able to swap without re-alignment on a simple MW/LW 125mA set. The DK92 has the wrong capacitances to replace the 1L6 on the higher frequency bands, otherwise despite the different design and pin names it's pin compatible.
So I've wired up a pair of 1j24b to replace the DK92 and I'll try it on a Pye "world band" set before the RCA, Zenith & Halicrafters I have that uses the 1L6.

However I've been busy writing & editing fiction.