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The Frank Jones supergainer

In the 1940s, Frank Jones was a prolific writer on anything radio related and published many books and designs.

One was the Supergainer, and later, the Ultragainer

Years ago I had a crack at making one, and was suprised at its lively performance, especially considering its low parts count. Using modern high slope TV valves in my case made for a very compact and nice performing radio.

The original did have some quirks, I think caused by the choice of components back in the 40s. The Ultragainer used not only the regenerative IF, but also a regenerative mixer stage, I would say a nightmare to tune and to remain in tune.

The regenerative IF was also dodgy by design, the feedback obtained by "lifting" the cathode from RF ground and relying on Anode to Grid, and Grid to Cathode spurious valve capacitances to make an artificial tap on the IF coil.

This is VERY poor design practice, usually capacitances are added to swamp these random and variable unknowns. I do wonder how many of the original designs that were built actually worked correctly in the day. Just changing the valve, or using a valve from a different manufacturer would likely have failed the project.

A quick video on my version supergainer in action, and compared to the JRC, same aerial..... the difference is..... um.... quite suprising I thought.

Using an ECH84 gated synch separator valve for the HF Oscillator and mixer, and the ECF80 , the pentode section being the regenerated IF/detector, and the triode section being the audio output stage.

It works very well on SW AM, but leaves much to be desired on CW/SSB.

After some thought and experimenting, the answer seems to be CIO injection via the screen grid of the detector.

The screen grid is used as the regeneration control, the DC voltage here is varied from around 20 to 30 volts to increase/decrease the pentode gain. By injecting an external oscillator signal at the 1700kc IF frequency,and superimposing it on the DC voltage, the detector doubles as a regenerative product detector.

By doing this, the detector can remain in its most sensitive spot, giving maximum selectivity, not being required to go into oscillation.

Also, the detector locks on to the stronger BFO signal, and if this is crystal controlled, will keep the receiver exactly on frequency.

Why this is so is a little unclear, there must be some slight interaction between the detector and first oscillator, even with the BFO offset frequency required for SSB reception.

Although I hope to use the audio output triode to double as a crystal controlled BFO to save adding another valve, I dont fancy my chances of this working correctly, being in the same envelope as the high gain IF. Changing from a ECF80, or 6BL8 to a ECF82/6U8 may help, I think that one has an internal shield?

Anyways, thats my next move.

8 comments

8 Comments

Triode

Jan 26

'regenerative product detector' ... um ... I had the same idea a while ago, but I aimed to achieve the same by using a 2nd ECH84, and in the following way: 1) signal from 1st mixer, fed to 1st control grid, 2) regeneration control by setting the DC voltage on the screen, and 3) injecting the 'CIO' (i.e. the 'gating signal' from the Crystal Osc.) on the 2nd control grid.

I suspect the 'poor performance' as SSB detector in your experimental setup being cause by instability of 'CIO' induced by current variations on the screen grid, that's working as the plate of the regenerative detector. The easy 'locking' you mention is perhaps in support of my explanation.

The use of a 5 grid converter tube (ECH84 can be seen as such, imho), with separate grids for separate inputs, should keep the interactions against the CIO a bit lower.

Currently I have a few of such ideas I would like to experiment with, but unfortunately I'm occupied into a big campaign of components recovery from broken radios and pieces of old electronic stuff. Once I finish ... I'ill start joyfully using all the saved goodies ....

Cris

dayleedwards

Jan 26

Replying to

Actually, thats a very good idea. After all, SSB detection is only another mixing process, and all the gain advance is in the prior stage, so separated from any influence. I would be even more interested to phase lock this stage to get synch AM detection, again without needing to run the regenerative stage into oscillation. Like, doing that gets a similar result but is not totally reliable with deep fades, the regen stage is not then working at its full potential. I am studying some of these more "esoteric" TV valves after reading your post, I am sure there is something with another control grid that may just save another valve envelope and heater current. Valve TVs had almost disappeared here in the late 60s, so we are going back in time here. I vaguely remember something with 2 pentode like sections with a common anode. Synch detection and SSB demodulation have much in common, so both can easily be accommodated.

Do you know just what the difference is between the ECH81/83 and the 84? I may have already asked you, forgive me if I have. I am suspecting the ECH81 has a remote cutoff, the 84 being a sharp cutoff? The 84 certainly has more conversion gain, the triode section also seems far more active.

Valve data books seem to be of limited value when we are playing with unusual circuits and applications, and pressing them into a service they are not designed for.

One instance was my amazement just how much juice a 6AQ5 output bottle drags, and the excessive heat, when a 6AU6 in a similar configuration runs unfazed , giving a similar power output with just a biasing change. Even the lowly 6BA6 makes quite a good power output tube needing only a sniff of G2 voltage..

I too salvage components, they are of much better quality, and, oh the variety.....

Triode

Jan 27

Replying to

ECH83 is basically a selected 81, for low anode voltage. In fact the max ratings are the same. I have estimated from 25 to 35 dB conversion gain for the 84, with average 'Q' tank coils. Could be a bit higher too, though. The 84 is very cheap: less than 1 $ each. The Russian version of the 81 is cheap too and I suspect it's better in all respects vs the European brands. I also tried the CCCP version, successfully. The 83, though, seems to have slightly higher gain when used with same voltages as the 81. The 84 allows same gain of 81/83 but at lower voltages.

Triode

Jan 27

Replying to

And yes, 81/83 are remote cutoff while 84 is sharp. What about considering the 7360/6ME8/6JH8 family for our 'extreme multipurpose' applications? :-) Also, the '200' TV tubes series worth being investigated. For example, the E/PCH200 has separate cathodes but 10 pin base. Ebay sellers from China have these sockets, new and cheap. The E/PFL200 is a double pentode (both suppressors connected to the respective cathode, though ..).

The 'P' tubes series is attracting because of their prices, lower than the correspondent 'E' devices. The '200' series is attracting for the additional pin on the base, thus allowing 1 possible degree of freedom more to experiment with.

But, for the reason that it's dirty cheap and dirty available and almost none wants it, the ECH84 is my preferred. The E/PCH200 following immediately after.

LarryDee

Jan 23

Very cool. The performance is crazy good. Nice writing too !

dayleedwards

Jan 24

Replying to

Thanks Larry.

The controls are left to right, RF attenuator, main tuning, with fine tune underneath, and regeneration on the right. Perhaps the most useful improvement of the supergainer concept over the straight regen that I could mention is there is no need to adjust the regeneration over a wide frequency span. My set covers 4.5 to 13 megs, the regeneration control only needs a very small tweak occasionally to bring up weak signals, or to narrow the passband for any adjacent power stations. The RF attenuator is vital, the high mixer gain can easily overload the regen IF.

As someone has said, valves are cool.

Triode

Jan 27

Replying to

Well, in my regenerodyne I have 1.5 Mhz wide bands x crystal, being L.O. rock bound and I.F. tuneable. The advantage of a fixed IF is that you mention, on the other hand is not easy to have stable VFOs up to several mhz, as in your setup. Do you have the VFO beating up or below the IF? What's the drift rate? In mine, IF tunes from 1.7 to 3.5 and can be left on a frequency for 12hrs without need of corrections

dayleedwards

Jan 27

Replying to

You are correct, certainly better stability with low freq oscillators, but to cover large frequency ranges, the tuneable IF approach becomes problematic in simple designs. I have always thought that given the effort is not much greater to build in a large coverage as a small coverage, lets go large.... there is more to listen to.

Having the VFO high generally improves and makes tracking easier , so, mine is above the IF. My supergainer on AM signals, at 12 megs being the worst case scenario, no tuning is needed for an hour or more, but if you are talking SSB , my long term stability will not be anywhere as good as you have, the VFO covers 5500 to 15500, almost a 3:1 ratio. Your VFO can be more of a high C design, giving less drift.

My listening is shortwave broadcast, any SSB is mainly the aeronautical HF. On 8867 ssb , the supergainer will sit there for maybe 20 to 30 minutes without retuning after a warmup, but most amateur band listening would involve constant retuning anyway as operators come and go. In that regard, my short term stability would probably be OK.

Its all a compromise........but fun. I also enjoy the simple one knob tuning......