German one-valve superhet FM tuner

[regenfreak]

Hi
I have got these two unknown German ECC85 all-in-one FM tuners. I am going to bring them back alive and study its design. The ECC85 acts as RF, oscillator and mixer (autodyne convertor) but I am not sure if it uses elaborate and complex regeneration feedback and an adjustable neutralisation network for the first RF triode section.

The German design philosophy was: less the number of valve, the more complicated the design would be. Some designs have horrendously complicated impedance matching transformers, capacitor bridge, regen control and phase shift reactive LC elements that blew my mind away.
Hope to ID this and look up the schematic. It could be Saba

[kalee20]

I can't wait for the circuit!

[Synchrodyne]

BBC RD Report 1951/07 (http://downloads.bbc.co.uk/rd/pubs/reports/1951-07.pdf) covered some early German FM adaptors, a couple with two valves and one with a single valve. Possibly the single-valve ECC85-based units are later versions of the same idea.


Cheers,

[regenfreak]

BBC RD Report 1951/07 (http://downloads.bbc.co.uk/rd/pubs/reports/1951-07.pdf) covered some early German FM adaptors, a couple with two valves and one with a single valve. Possibly the single-valve ECC85-based units are later versions of the same idea.


Cheers,

I did a forum search and found your reference to the BBC report a few days ago, credited to your old posts. I read the report and other articles you posted. Cheers.

I have a closer look, both primary and second coils of the internal IF transformer have no capacitor in parallel. For the secondary coil, I would have to connect an appropriate value of external capacitor making it to resonance at 10.7MHz. The primary coil uses the distributed capacitance of the ECC85 valve to form LC resonator. There are a AFC input and double balanced 300 ohm input to an antenna coupling transformer.
There is a 3 turns tickler coil for regeneration. I don't see any regeneration throttle capacitor trimmer, neutralisation inductive or capacitive trimmer at all. It looks like a relatively "less complicated" design.

[Mr 1936]

Hi regenfreak

The adaptors studied in the BBC report appear to be rather crude FM to AM slope detectors, with regeneration or superregeneration used to sharpen up the response. The output is at audio.

The examples you have look like a more conventional tuner head with RF, Mixer and Oscillator, which would have been followed by a separate 10.7 MHz IF amplifier and discriminator. The construction looks quite similar the Schaub adaptors

FM (and TV) tuners were often bought in by smaller manufacturers who would have found them too daunting a prospect to design. It's not hard to see why they fought shy !

[Nuvistor]

The ECC85 FM tuners I saw used a grounded grid RF amp, so neutralising wouldn’t be required.

[FERNSEH]

From the GFGF bulletin Funk Geschichte No. 124.
Cover picture shows the Schaub UE52/II FM adaptor.
The circuit diagram of a single-valve FM tuner.

DFWB.

[G6Tanuki]

I wonder to what extent these German efforts inspired and borrowed from the Australian / Hazeltine Corporation Fremodyne, which was a weird self oscillating converter and superregen demodulator using a dual triode.

[orbanp1]

Here is a good discussion about German tube based FM-tuner design issues:
https://www.radiomuseum.org/forum/gr..._analysis.html

While the thread uses a capacitor used circuit as an example, the analysis is equally valid for inductively tuned tuners.

Regards, Peter

[ms660]

Stern:

https://www.radiomuseum.org/r/stern_..._156000_e.html

Lawrence.

[FERNSEH]

Title of the article is: "UKW-Entpfang mit Pendelruckkopplung"
VHF reception with swinging back-coupling.

The patent for this concept was registered by Edwin Howard Armstrong in 1921.
First attachment shows a 1935 circuit proposal for a such a receiver.

DFWB.

[ms660]

This could be the circuit for the OP's tuner in this manual:

https://nvhrbiblio.nl/schema/RFT_5170.pdf

The tuner layout picture in the manual looks very similar.

Lawrence.

[ms660]

Another one in here (Stern 156000 UKW Tuner):

https://nvhrbiblio.nl/schema/RFT_5040.pdf

Lawrence.

[regenfreak]

Originally Posted by ms660

This could be the circuit for the OP's tuner in this manual:

https://nvhrbiblio.nl/schema/RFT_5170.pdf

The tuner layout picture in the manual looks very similar.

Lawrence.

Brilliant! Thanks!!! I believe you are right! The second IF coil is untuned and is fed directly to grid of ECH-81

The patent for this concept was registered by Edwin Howard Armstrong in 1921.
First attachment shows a 1935 circuit proposal for a such a receiver.

DFWB.

It looks like a single tuned permeability autodyne.

Here is a good discussion about German tube based FM-tuner design issues:
https://www.radiomuseum.org/forum/gr..._analysis.html

While the thread uses a capacitor used circuit as an example, the analysis is equally valid for inductively tuned tuners.

Thanks for that.

From the GFGF bulletin Funk Geschichte No. 124.
Cover picture shows the Schaub UE52/II FM adaptor.
The circuit diagram of a single-valve FM tuner.

Again single permeability tuning. It wuld have poor selectivity.

FM (and TV) tuners were often bought in by smaller manufacturers who would have found them too daunting a prospect to design. It's not hard to see why they fought shy !

The Americans stayed away from the complex design philosophy in most cases except a few exceptions. I have a Zenith H722 that uses a single 12DT8 for the autodyne design. The Americans tend to use double tuned first IF but the Europeans like to omit the first IF resonator caps and the Germans love quirky designs.

I wonder to what extent these German efforts inspired and borrowed from the Australian / Hazeltine Corporation Fremodyne, which was a weird self oscillating converter and superregen demodulator using a dual triode.

I am not sure they were inspired as they work in different principles.

The ECC85 FM tuners I saw used a grounded grid RF amp, so neutralising wouldn’t be required.

Based on the schematic in the link from Lawrence, i guess C5 = 2.5p across the anode and cathode of the first Triode is a fixed neutralising cap.

[Synchrodyne]

Originally Posted by regenfreak

The Americans stayed away from the complex design philosophy in most cases except a few exceptions. I have a Zenith H722 that uses a single 12DT8 for the autodyne design. The Americans tend to use double tuned first IF but the Europeans like to omit the first IF resonator caps and the Germans love quirky designs.

The single-valve FM front end did not enter American practice until quite late, 1959-60, when Standard Coil and others started producing ready-made double triode-based units. But it was further developed beyond the original German conception. Variations included triple triode, either RF/autodyne/AFC or RF/MX/oscillator; double tetrode; frame grid triode RF with regular triode autodyne (used by Zenith for stereo receivers); and pentode RF/triode autodyne (e.g. by GE, who favoured the pentode for RF).


Cheers,

[Synchrodyne]

Originally Posted by Nuvistor

The ECC85 FM tuners I saw used a grounded grid RF amp, so neutralising wouldn’t be required.

I think grounded grid was probably the modal choice, but neutralized grounded cathode was used by some, also a combination with push-pull feed to grid and cathode, as in the Radford FMT1, which I think used a D&W unit.


Cheers,

[regenfreak]

he single-valve FM front end did not enter American practice until quite late, 1959-60, when Standard Coil and others started producing ready-made double triode-based units. But it was further developed beyond the original German conception. Variations included triple triode, either RF/autodyne/AFC or RF/MX/oscillator; double tetrode; frame grid triode RF with regular triode autodyne (used by Zenith for stereo receivers); and pentode RF/triode autodyne (e.g. by GE, who favoured the pentode for RF).


Cheers,

There is something about using pentode in the RF amp front end. Have they got higher equivalent noise resistance than triodes? I have seen the pentode of ECF80 was used in the mixer (Leak Troughline) or front RF amp of FM receivers. The Germans preferred to use pentodes in early FM designs and in some battery sets.

Yes the americans used frame grid trides; included double triode 6DJ8 ( = ECC88 ) in cascode and single triode 6DL4 EC88 in Marantz 10B in 6-gang "pi" bandpass RF amp stages. EC88 is not half of ECC88 They invent similar names to confuse people!

I have seen triple triode 6GY8, I am yet to see any FM domestic receivers use triple triodes or dual tetrodes...maybe they were used in TV tuners?

[G6Tanuki]

Pentode RF amps struggle at VHF frequencies because 'partition noise' [the noise created by the randomness associated with a particular electron emitted from the cathode either heading for the anode or the screen-grid] becomes an issue,.

A similar effect afflicts multigrid mixers once you get much above 50MHz.

See http://www.r-type.org/articles/art-011.htm

[FERNSEH]

From the GFGF article.
The response curve of the FM demodulator.
The choice of the received swing frequency recommended by R.Cantz was 20 to 50Khz.

DFWB.

[regenfreak]

Originally Posted by G6Tanuki

Pentode RF amps struggle at VHF frequencies because 'partition noise' [the noise created by the randomness associated with a particular electron emitted from the cathode either heading for the anode or the screen-grid] becomes an issue,.

A similar effect afflicts multigrid mixers once you get much above 50MHz.

See http://www.r-type.org/articles/art-011.htm

I see thanks. From the datasheet the equivalent resistance of the pentode section for ECF80 is 1.5k ohms versus 500 ohms for ECC85, three times bigger.

Electron travel in vaccum is a rather interesting subject. I have read about the effect of electron transit time in UHF planar triodes up to 7.5GHz...