The "Jones" Super Gainer

[pwdrive]

Here is a link for the Jones Supergainer:

http://home.comcast.net/~btse1/vintrad/hb/dr.htm

Lawrence.

[Skywave]

Is that not, in effect, merely a 'short-superhet' - one without an R.F. stage ? However, I don't understand what L5 does - or why it's there.
Someone enlighten me, please.

Al.

[pwdrive]

Hi Al, not looked at the circuit since I posted it, not sure what a defacto definition of a short superhet is either (it seems to vary) so bear with me.
I think the Jones supergainer can be traced back to the late20's/early 30's.
As you can see the mixer is regenerative as is the detector, the regen in the mixer stage employs a Hartley arrangement ie: tapped cathode feedback which you will be familiar with.
The cathode tapped feedback would be difficult to homebrew for the detector (450 Khz transformer) ie: you would have to unwind, tap, and rewind the secondary, for most constructors, this would be a hit and miss affair, so a seperate cathode feedback winding is used (L5) so you can use a standard unmodified IF transformer.
Electrically it's the same as a tapped cathode coil in a Hartley arrangement so far as I am aware.
Any IF frequency can be used within reason, if the IF transformer has a wide bandwidth then it can be tuned across that bandwidth, that's the same as my Regenerodyne receiver, but you will know that anyway. The forunner to the R1155 receiver (forget the model number off hand) used a regen RF as well as a regen detector (No IF) they were quite sensitive apparently in the hands of an experienced operator, safe crackers fingers being a pre requisite.

Lawrence.

[Skywave]

Thanks Lawrence: I am starting to understand its operation now.

By making the mixer regenerative, it enables a sharp increase in the selectivity of the mixer's tuned grid cct. At the same time, it also acts as a conventional freq. changer by virtue of the separate local oscillator, the tuning of which is ganged to the tuning of the mixer grid cct. to produce a constant freq. for the I.F. The (second) detector is also regenerative by virtue of the inductance in its cathode, the Q of that inductance being variable by the variable resistance across it. Thus the degree and threshold of the regenerative action is controllable; the bias for that detector being obtained by auto-bias: the 1 k-ohm resistor in the cathode, suitably by-passed to R.F. by a capacitor.

Anyway, that's my 'first-off' analysis: can you fault it ? If so, then please do so. ; I'm always prepared to learn


Going off on a related tangent, I wonder if the Mr. Jones (as in this cct.) is the same Mr. Jones whose name is associated with the Jones noise-balancing cct., a derivation of which features in the Collins 136-series of 'noise blankers', intended to be fitted into receivers like the 75A4, 75S1 and the KWM-1 ?

Al.

[pwdrive]

Hi Al, yes, that's as I see it too, however I subscribe to the Regenrx forum (Yahoo groups) and there was a debate on that forum as to how that regen det can work without mutual inductive coupling, the debate seemed a bit inconclusive.
According to a Wiki article the Hartley does not need mutual coupling between the two inductors to work, however the Wiki article does not give any source ref. for that claim.
I might submit that question to the regenrx group again and see what comes up.
I would guess that the circuit has been built by many and as such I presume it works.
As to your question about Mr Jones of super gainer fame: all I know is that his first name was Frank.

Lawrence.

[pwdrive]

"Is that not, in effect, merely a 'short-superhet' - one without an R.F. stage ?"

Hi Al, after doing a bit of searching the consensus seems to be that a short superhet is a receiver where the hetrodyning has taken place in the mixer but no additional amplification of the resultant frequency has occured by an active device before detection, I think the term "short superhet" is one that has just caught on for want of a better description.
As regards say the Regenerodyne receiver then this would be a short superhet with the regen backed off but when brought into regeneration then it wouldn't.
A direct conversion receiver could be regarded as a short superhet but would not fit the definition above as there is no envelope detector, however the process of hetrodyning has taken place, the resultant of which is AF, if the resulting AF could be heard without further amplification then it would fit the definition....maybe?

Lawrence.

[Skywave]

My use of that term 'short superhet' is, in retrospect, annoying, since I do try to avoid that phrase, simply because it is open to so many different interpretations - as you observe. Now not wishing to be pedantic, the term 'short superhet' implies that there is a 'normal' superhet - or even a 'long' one! There are many configurations of a 'superhet', so even the introduction of three adjectives (short, normal and long), doesn't really help towards a clear classification or description. We can even take such an adjectival qualification from the sublime to the ridiculous - 'wide', 'tall', 'deep', 'shallow', etc.: all of which are open to individual definitions and interpretations; pointless.

A few years ago, this question of what defines a 'short superhet' arose on another forum: there was no consensual agreement amongst the members. Someone did refer to the TRF 'notation': e.g. 1-V-2. In response, I suggested a similar notation for a s/het.: 1-M-2-D-2; one RF - mixer - 2 IF - detector - 2 AF, but it did not receive even an informal approbation!

However, I feel that the word 'heterodyne' (as in 'superheterodyne') is not open to such a wide interpretation. 'Super' means more than or greater than, and we all know the meaning of the word 'heterodyne'. So a 'superheterodyne' means a process where the incoming signal freq. is converted to another freq. which is above audibility. That rules out a regenerative detector, since the result of the heterodyning action is an audio frequency: so that becomes an 'ordinary heterodyne' (or possibly an 'audioheterodyne') receiver.

Anyway, all of that is merely a few thoughts from me - which, therefore, are not going to have slightest impact on the use and meaning of the word 'superheterodyne' in radio & electronics engineering circles. But it's pleasant to swap notes on such things with like-minded individuals: like your good self.

Al.

[pwdrive]

Hi Al, yes I read some of those posts on the other forum, as you say various views on it, in my own mind I am taking it to be no IF amp for the sake of simplicity.
I have been doing a bit of searching about Armstrongs early work, all very interesting stuff.

Lawrence.

[pwdrive]

Hi Al, superhet, yes, forgot about that! I remember when I first got interested in radio that we referred to is as the "supersonic hetrodyne" rather than superhet, so yes the DCR cannot be classed as a superhet. How easy it is to forget.
Not got very far with the question of the two seperate coils in that supergainer regen, one chap I have been in touch with reckons it was a bit of a fudge by Mr Jones, there are a couple of mentions on the web about the Hartley osc. using two seperate coils (not mutually coupled) but no specific description.

Lawrence.

Lawrence.

[Skywave]

Hartley osc.: my understanding is that it must feature a tapped coil - usually arranged with the cathode of the valve to the tap. That puts part of the coil in the cathode cct., part in the anode cct. - in terms of the R.F. cct.; the tap of the coil being the reference point for the R.F. cct. Consequently, there is a mutual inductive coupling between anode and cathode, and since the R.F. currents in cathode and anode are 180° out of phase, oscillation is enabled. The amount of mutual coupling is critical: enough is required to overcome the R.F. cct. losses; too much gives an over-drive situation, resulting in squegging. It is the position of the tap on the coil that determines the amount of positive feedback: ideally just enough and a bit more.

So, on that basis, L5 in Mr. Jones' cct. doesn't - at first - seem to appear as the inductance in a Hartley osc.: there is no tap on the coil. However, if the tap is considered to be at the 'top' of the coil, producing maximum +ve feedback then that might just work if the -ve bias on the grid is large enough (considering the gm of the valve); that bias being provided by the auto-bias by-passed resistor in the cathode.

Al.