definition of a 'short' superhet.

[Sideband]

Now I always thought a short superhet was one that dispensed with the IF stage like the Champion 851. This little set has a UCH81, a UCL83 and a UY85. The UCH81 functions as a normal frequency changer and there is a single IF transformer. The triode of the UCL83 functions as detector and the output is then fed to the pentode section. It's very basic and is classed as a local station receiver. Probably selectivity is not good but then it doesn't have to be.

However as in the thread linked above, the Pye 15a listed there has been referred to as a short superhet but has a normal frequency changer and IF amp. It lacks an AF amp so the output from the detector is fed straight to the output pentode. This will certainly restrict the output but otherwise the radio will function as a normal superhet. Apart from restricted output, I would expect this set to perform quite well

One radio that I have (Philips 470A) uses a PEN4DD and dispenses with an AF amplifier but it's performance could hardly be described as mediochre. In fact it not only performs superbly with regards to sensitivity and selectivity but also produces several watts of audio at good quality.

So out of interest, is the term 'short superhet' applied to any circuit that does away with either an IF stage or an AF stage or does it signify a particular type of circuit .


Rich.

[paulsherwin]

Originally Posted by Richard_Newman

So out of interest, is the term 'short superhet' applied to any circuit that does away with either an IF stage or an AF stage or does it signify a particular type of circuit .

That's my understanding of the term - a superhet lacking one of the standard stages, either an IF or AF amplifier.

My experience has been that a missing AF stage is by far the commonest variant. Pye seemed to make little else in the 40s and 50s, including some quite expensive models and radiograms. They *are* less sensitive than a standard superhet like-for-like, as you'd expect, though they can perform reasonably well.

The AGC performance tends to be poor because the IF amp is left running at maximum gain all the time, so it's necessary to turn up the volume with weaker stations.

Paul

[PJL]

Just working on a Philips 170A which makes this a short superhet with RF stage?...Peter

[Sean Williams]

A Short superhet is a set that is bereft of an IF amplifier stage........

Cheers
Sean

[Aerodyne]

Like Paul, I've always taken it to mean either an IF or an AF amplifier stage is missing, though I suppose because the term of superhet is used, it should really only mean an IF stage...
-Tony

[ukcol]

I think Tony has hit the nail on the head.

It is what's between the aerial and the detector that defines a set as a superhet' (or a TRF or direct conversion) receiver. What happens after the detector has no bearing on that definition.

It follows, in my view, that it is only how many stages there are between the aerial and the detector, that defines a superhet as short, long or otherwise.

Are superhets with 2 or more IF stages after the FC "long superhets"?

[Heatercathodeshort]

Hello,
I have always considered a 'domestic superhet' to contain four valves and a rectifier i.e. five stages including detector taking into account double valves etc.
My view is that any receiver using less than five stages must be considered a short superhet. I think it would be fair to say that very few receivers were produced minus an I.F. stage and the lack of such resulted in a very poor receiver. If the I.F. stage could have been omitted, believe me the makers would have done it! [ as the normal] The true definition of a short superhet is probably one minus an i.f. amplifier but in my view you need this stage to qualify as a true mark of the design. Its probably more a personal view than maybe the technically correct. For some time now I have been considering producing a very short superhet using the PFL200 valve on its own....Time will tell. Regards John.

[Sean Williams]

From what I can recall, all of the superhet midget radios I have owned, and still own are all shorn an IF amplifier stage - None of them perform below the level of the DAC90.

All of these sets are referred to as "short superhets"

Typical line up as follows

35z4gt - Rectifier
50L6gt - output bottle
12sq7 - detector and AF amp
12sa7 - mixer bottle

the missing stage would be something like a 12sk7, used as an IF amplifier (if one was ever needed)

So, I stand by the claim that a "short superhet" is a radio missing an IF amplification stage.

Cheers
Sean

[FERNSEH]

A typical pre-war short superhet employed three valves plus the HT rectifier.
The frequency changer could be a triode-pentode, a triode-hexode or an octode. Valve types of those times were the AC/TP, TH4 or the FC4.
A vari-mu pentode served as the IF amplifier. For the detector,AVC and output, typical valves would be the Mazda AC2PenDD or the Mullard PEN4DD double-diode pentodes.
These specialised output valves had a very high slope, (gm) of 9.5mA/V and therefore were very sensitive so it was possible to drive the control grid direct from the detector diode. The audio amplifier could be dispensed with.

A post-war short superhet would employ the EBL31, the octal base version of the side contact EBL1. Other valves in the set would be the ECH35 and EF39.

A valve holder tax was in force in those times so if the valve count could be reduced, all the better.

DFWB.

[FERNSEH]

Here are two examples of pre-war short superhets. They are the Philco "Peoples Set" and the McMichael model 361.

The Philco is the really interesting one. In response to a request from the Government to produce an affordable radio set Philco rose to the challenge with the model 444.
The receiver employs three valves plus the type 80 HT rectifier.
The frequency changer is the pentagrid 6A7, the IF amplifier is a type 78E and the double-diode output pentode is a special type made by Mazda, the Pen61DD.
The Pen61DD is really a AC2PenDD fitted with a 6.3 volt heater in order that the valve can operate with the other two signal valves which are of American origin.

The other set is the McMichael 361. The three signal valves in this receiver are all Mazda, AC/TP, AC/VP1 and the AC2PenDD.

Both receivers give more than adequate sound output dispite having no AF amplifier stage.

DFWB.

[KB-KR20]

Witts - The Superheterodyne Receiver 6th edition published 1944 lists '"Short" superhet' in its index. The relevant page discusses the practice of adding a frequency converter to a straight set in order to pick up high frequency (Short Wave) signals and convert them to about 300kc/s (IF) so that they could be heard on long wave.
Mick

[wireful3]

Hi, I rember reading somewhere a definition of the short superhet that implied the essence was a frequency changer and then the minimum stages following. It makes the Sobelette mentioned by Fernesh a good example.
It is worth remembering that not having an IF stage means there is only one tuned IF transformer so loses some of the selectivity advantage of the superhet.
As the main thing is to reduce cost then for a local station receiver selectivity might not be so important.

[FERNSEH]

Some time ago an article appeared in Chas E Miller's magazine, "The Radiophile" featuring an Italian superhet receiver which employed only two signal valves plus the HT rectifier.
The frequency changer was a 6A8, an octal base pentagrid valve and an octal double-diode pentode of which was of American origin.
The clever thing about the set was that the output pentode also served as the IF amplifier in a reflex circuit. The two diodes in the output valve served as the detector and AVC rectifier. The AVC voltage was supplied to the frequency changer signal grid.

In an earlier post HKshort mentioned an idea of constructing a superhet receiver which would employ one PFL200 double pentode. I'd think that the project is feasible. The "F" section will be the frequency changer and the "L" section will operate as the reflex IF amplifier and output valve. The detector will be an OA79 germaium diode.

DFWB.