1Ж42А. As a mixer/Frequency changer????

[Mike Watterson]

Just add a second diode, ground is anode, cathode to existing anode.
Or try it with capacitor direct to g1 with a 10M or 18M grid leak.

You can't sensibly have a wide band (entire MW) high impedance RF transformer. It won't work if a 10 mH choke from 0V to diode input doesn't work.

Alternative DC path solution: Wire like a valve detector. Diode across the 18M or 10M grid leak, fed with capacitor from RF amp, thus cathode to 0V. Also try it the "wrong" way round, where it drives g1 positive instead of negative.

[Amie]

Hello Mike.

From an earlier post....

Thanks for the exposition, I hadn't realized that there was a restriction on the number of valves.

Now that you have said common mode choke, I understand. But to get that to work at AF for a cathode follower wouldn't be easier than other methods of demodulation.

My interest in the more commonly available rod pentodes, or other subminiature filamentary cathodes valves is their possible use as substitutes for the rarer battery valves. Dads Vidor was so equipped for the output stage with a little plug in module using a rod pentode running only half its filament, don't know the details, but one day bravery will allow me to investigate. I recall Dad saying that it was a better performance than the original valve.

You mentioned that there was a vhf superregen one valve pocket set, Dad had a collection of 'vest pocket' sets from the US that he collected when working over there, he had a set like that, but it had two valves, called the 'Hastings FM junior'. There is a similar circuit diagram on the radio museum site.

Amie.

[Murphyv310]

Just add a second diode, ground is anode, cathode to existing anode.
Or try it with capacitor direct to g1 with a 10M or 18M grid leak.

You can't sensibly have a wide band (entire MW) high impedance RF transformer. It won't work if a 10 mH choke from 0V to diode input doesn't work.

Alternative DC path solution: Wire like a valve detector. Diode across the 18M or 10M grid leak, fed with capacitor from RF amp, thus cathode to 0V. Also try it the "wrong" way round, where it drives g1 positive instead of negative.

In fact the best performance has been placing the diode between the G1's and ground, cathode connected to ground and the RF coupled to the diode/G1 via a 180pf cap, my original YouTube clip had the diode connected that way. Even looking at the RF output on a scope with an X10 probe severely damps the signal and my X20 was never returned after loaning it a few years back.
I'll revert back to the original way once I get the new diodes.

I've actually tried every possible configuration of diode placement over the last week, some increase distortion with better resolution of weak stations but are hopeless on my local others distortion free with lower sensitivity, the above way gives the best overall results.

[Murphyv310]

One thing I did also try was to make the AF amp a second stage of RF amplification and then detect the resultant RF. I had then to screen both valves as it was unstable. You'll see in the photo how I resolved that issue. It then was far better on weak stations but grossly distorted on strong stations.

[Mike Watterson]

I've run an entire radio with Rod Tubes on B7G adaptors:
The 1j24b will replace all types except the DL94. Not sure about DF97 & DC90 at VHF.
Using one filament of a 1j29b replaces a DL91, DL92, DL96 and two filaments replaces a DL96

Two off 1j24b wired as a triode oscillator driving g2 of a Pentode mixer will replace a DK91, DK92 or DK96. Anode of triodised oscillator direct to g2 of the input valve. The original g4 or whatever screen grid HT isn't used. You can't use a single Rod Tube, not even the 1j42a or 1j37a. In general assuming heater/filament and HT voltages are compatible, a Pentode-Triode (or Hexode-Triode) and Pentagrid family(Heptode, Octode) are interchangeable with an adaptor. LO leakage is worst with Heptodes/Octode as the g1 and g2 are a kind of triode oscillator driving a "virtual cathode" of a pentode or hexode, thus the g3, or what ever pin in is RF in, has a lot of the LO on it. A real triode-pentode or triode-hexode feeds the oscillator (usually from the grid, but can be anode) into a grid AFTER the RF in, g1 on the Pentode or Hexode.

I did try a single 1J24b as a replacement for a DK96, it's poor though works.
https://www.radiomuseum.org/forum/dk96_d...37b.html#4
and https://www.radiomuseum.org/forum/1j24b_1j24b.html#6
Two work better even than the DK96.

Though I haven't found the post.

DL91, DL92, DL94, DL96: The DL94 replacement needs both filaments
https://www.radiomuseum.org/forum/1j29b_1j29b2.html#3



There is almost no AGC action, though some battery sets only have AGC on the mixer and run IF at full gain. Gain on the Rod Tubes is by varying g2, for the 1j24b with 85V HT, max gain is about 55V and almost no gain is about 20V.

For the DAF series or 1U5 etc, simply add a 1N60 to the B7G adaptor.

The IF amp and AF preamp  will need a 2nd resistor from g2 to f- or f+ as the gain is unstable with certain ranges of series resistor to g2. The Russian radios used either a pair of resistors as a potential divider or a another HT rail.

If you don't at least do it on the IF amp, the set may "motorboat".

Also if there are always fresh batteries, or a battery eliminator / mains adaptor, put 12 Ohm to 22 Ohms in series with each f- to LT- / OV.

You can't really replace valves in a series wired set unless maybe you have the 22 Ohm resistors and an overall parallel resistor to make up filament current to 24 mA or 48 mA. The value would be adjust on test with no HT for each valve. I'd sooner try it on a 50mA series set than a 25mA series set. The Rod Tubes were intended for parallel use only, though there were some Russian sets that seem to have used 12V LT and rod tubes, no doubt for a vehicle and with serious amounts of ballast resistors.

I did a set of drawings on the Radiomuseum years ago.
And photos:
https://www.radiomuseum.org/forum/invict...cki.html#3

he had a set like that, but it had two valves, called the 'Hastings FM junior'

I was thinking of it. My bad, it's two valves. One for RF and one for the headphone.
https://www.radiomuseum.org/r/hastings_fm_jr.html
I'm sure it could be duplicated at least with 1j24b. I don't know if the 1j42a can do VHF.
The fact it was allowed a patent is further proof that the USPTO is broken. Their concept is that companies should fight in court and they will not expend effort (money) on looking for Prior Art, considering if anyone expert in the Art could easily come up with the implementation or if it's actually novel. They make money approving Patents. They make almost none rejecting them.

I made a small matchbox transistor super-regen FM radio. The coil was tuned by a plastic straw with a brass slug, ferrite slug and space between them so it did about 80 MHz to 120MHz and could receive the local air traffic as well as FM radio.

Sputnick https://www.radiomuseum.org/forum/sputni...ter.html#4

Note you need earthed screens. The regular B7G valves have them internally, the Rod Tubes don't.

[BusyBee]

I have been away for a day or two so have missed a lot of this discussion. All interesting stuff!

It's probably missed the boat a bit but I have these test results for various diodes. All home tests so take as found but there are interesting comparisons between vacuum tubes, germanium and silicon diodes. Some of the older types were 'used'. The 1N60 is reckoned to be a good diode in crystal radio circles but beware of forgeries which are rife. Some of the Russian ones are very good (see D311 graph, I have found it useful).

Tracy    

[Mike Watterson]

What we tested was the actual DC mV on a dual diode peak detector vs RF mV in. I forget what the the frequency was. The 1N60 performed to lower signal levels than a 1N5819 HP Schottky signal diode, which is also seriously more expensive. It was a proper lab at work. We mostly tested currently available stocks so no valve based detectors of any kind. We did include some old Ge diodes I have and some freshly purchased OA47 (which was poor actually). It was for an actual product, so it was really a choice between the 1N60 (still made), 1N4148 and a small signal Schottky sold for RF and switching applications.
I think for general use the 1N4148 is best.
For low level RF, like RSSI, Forward & Reverse HF power meter, AM radio detector etc, the 1N60 wins.
The Schottky diodes more for high speed switching applications and some specialist RF, though for RF switches a PIN diode is better.

[Murphyv310]

Hi.
In fact I tried a 1N5819 in the set with not a sausage of output!!!
I have now reverted back to the diode between the G1's and ground, prior to that I tried the leaky grid again. It is really fussy as regard to grid leak value. No results with 1meg, open circuit it does work but very weak, 15meg gives an improvement and it works at its best at 10meg, with lower values it gradually fades to nothing at 3.3meg. Even at its best it is no where as good as with the ge diode. With the diode connected anode to grid the HT current on the AF amp drops with a strong signal, just what I expected it to do.

[Kalee20]

The 1N60 performed to lower signal levels than a 1N5819 HP Schottky signal diode, which is also seriously more expensive.

The 1N5819 is actually intended as a low power rectifier (1A) rather than a microamp signal diode. As such it'll have power-level capacitances, which might explain poor results. It does have a higher voltage drop (0.4V) than Ge point-contact, but not as high as PN silicon, like 1N4148.

(It does make a decent rectifier for power supplies - I know, I've used it!)

[Mike Watterson]

I'm confusing it with an HP Signal Schottky. I have the 1N5819 also for PSU applications. A full drawer of them. Memory playing tricks. Now that I'm reminded, I'd not even bother testing the 1N581x series

The actual HP/Aglient parts we tested as as Schottky signal diodes were probably the 5082-2835 and 5082-2800, certainly I still have some 5082-2800.
Definitely much poorer sensitivity than 1N60 for low level audio to 30MHz.

5082-2835 specs
PIV = 8
Vf = 340mV @ 1mA
Capacitance = 1pF

5082-2800 specs (similar to 1N5711)
PIV = 70
Vf= 410 @ 1mA
Capacitance=2pF
Unfortunately I recognised the number because I have that part.

The signal Shottkys will work to maybe 800MHz. The 5082-2800 is likely intended for UHF mixers as they come in matched pairs and quads (ring diode mixer needs four matched parts). The 5082-2835 as matched batches.

I may have a copy of the test data somewhere.