Superheterodyne receivers
with an AM r.f. pre-amplifier stage
and / or
improved selection.

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Online since 12/18/2003. Last update 05/20/2009.
(C) Copyright Rainer Steinfuehr 2003-2009 Berlin.

In the early days of radio, after the introduction of the superheterodyne receiver, top of the line sets were equipped with an r.f. stage. This was to make sure they were highly sensitive with a good noise factor on the a-m bands. At the same time the selectivity was also improved. But this incrase in selectivity was only achieved with a tuned r.f. stage.

There were manufacturers who used an aperiodic (untuned) broadcast band r.f. stage. A good quality was a tuned band pass filter in front of preamplifier and aperiodic coupling to mixer. Technically somewhat better is this concept: tuned circuit - preamplifier- tuned circuit - mixer (Why? because this principle works well up to the short wave bands). The response courve of a tuned band filter against coupling from tuned circuit via an amplifier stage to tuned circuit differ in the way of skirt steepnes but also with regard to far-off response and neighbouring channel selectivity.

Till 1945 there were more sets with an r.f. stage because the tubes of the time amplified less and also the tube noise was somewhat greater and additional r.f. amplification had a positive effect, the sensitivity could not increased with this method. An other benefit is an lower emission of the oscillator frequency via the antenna.

After 1945 r.f. stages in receivers became the exception, top receivers had instead an additional i.f. stage, because this way the needed amplification was easier to realize. I own a re-aligned Grundig 4010 with r.f. stage and it offers very good sensitivity on the a-m bands.

Receivers with a tuned r.f. stage can be recognized in most cases by the 3-gang variable capacitor when you look inside the set. (But don't confuse with a 3-stage trf receiver or a receiver with only a tuned band filter in front of mixer except rf stage).

In the middle of the 1950 decade there was no more a great interest of the industry for constructing radio sets with AM preamp. Only some models came on the market.

I have today no information about sets with a modern preamp tube like EF91 (low noise level). In the Lorenz Goldsuper W45 is a EF93 integrated, but this set was not double tuned. So I think a set with EF85 is a good choice. Also the EF41 will work not so bad.

Certainly the r.f. preamp radio sets are a raritiy today, also from technical viewpoint. An interesting field for collectors. Do not inform other collectors about these facts in order the keep prices down (no pun intended).

Keep in high regard in these vintage sets. Even today (better tonight) they catch weak stations out of the full occupied b.c. band. In combination with a well constructed i.f. band-width selection (like the mhg circuit by saba ) it is a pleasure for the in technology interested broadcast listener.

A special model series was constructed by Kaiser. The double mixer (double conversion) models W1151 and W1156 was export models and unknown inside Germany. Except the model Kaiser Contest DX1151 (a model for ham radio use) is well known here. (Who has a schematic for Kaiser W1151 or W1156? Please send email)

The different construction variants of radio sets with / without AM r.f. preamplifier:

Abbreviations: 1=tuned circuit, P=preamplifier, M=mixer, F=only ferrite antenna preamp, 0=aperiodic.
Example 1: (11P0M) means 2 tuned circuits in front of preamplifier, aperiodic coupling to mixer.
Example 2: (0P1M) means aperiodic coupling to the preamplifier, between preamp and mixer 1 tuned circuit.

The noise resistance of the pre-amplifier tube or (when no rf-preamp stage is in use) the mixer tube define the reception sensitivity too. The lower the noise resistance the better the sensitivity.

Interesting are the radio sets 302 and Wegaphon 502 made by Wega. Here is the tuning indicator tube EM84 also as rf-pre-amplifier in use !!!

The following example list shows a selection of radio sets with r.f. stage. You will find also some samples of schematics of r.f. stages. Take notice that not all models use the preamp or two tuned circuits for shortwave.

Koerting

Koerting

Do you have also information about radio sets with AM r.f. preamplifier or tuned band filter AM r.f. stage? I have currently no time for searching for data in my data bases. wumpus@oldradioworld.de
You have information about the with '?' marked data-fields? wumpus@oldradioworld.de

Thanks for support to

• Berthold Bosch (Many detailed information and noise resistance of EF11 and CF3 and AF3 and 1294 and ECH81. Radio sets: AEG 70WU, Blaupunkt L498W, Blaupunkt Riviera, Continental Imperial 711W, Dominus 51 W, Siemens Schatulle SB 700W, EAK Gross-Super 97/51W, Philips 990X, Blaupunkt 5W77, Blaupunkt 8W78, Mende Super 365, Saba 581WK, Imperial 98W, Blaupunkt 7W77, Telefunken D860WK, Olympia 381W, Philips D57, Grundig 5010, Kaiser W1151 and W1156, Koerting Amata, Braun Commodore, Krefft Pasha, Lorenz 395, Saba 980WLK, VEB Rochlitz 9R81, Telefunken T8001WK, Koerting AS 7340, Schaub Korsar, Blaupunkt 5A649, Lorenz Autolor, Stradivari 2, Stradivari 11E91, Imperial 5W, Imperial 6W, Imperial 53W, Imperial 64W, Telefunken 650 WL, Nora W500, Loewe Super 32, Sachsenwerk ESWE 335, Lumophon W76, AEG 3WS, AEG G97W, AEG 107W, Schaleco BS9W, Owin F96W, Blaupunkt 4A75, Blaupunkt 9W78, Blaupunkt 9W79, Schaub SG42 alt und neu, Siemens P48, DeTeWe 865, Kaiser Danzig).
• Hans Langer (Philips D56)
• Jürgen from Rödermark (Radione R2)
• N. Kanne (Blaupunkt 7W78, Telefunken D860WK)
• Sven Henkerle (Koerting Ultramar W)
• Anton Rosecke (Telefunken T586WLK)
• Reinhard Exner (Wega 302, Wegaphon 502)
• Wolle from the Wumpus-Gollum-Forum WGF , only in German, VEB Elektroakustik Hartmannsdorf-Geräte