Telefunken Spez. 801 Kurzwellen Empfänger

17t. Telefunken Spez. 801
Kurzwellen-Empfänger (year 1937).

Telefunken Spez 801 HF-receiver (valve RE094 should read RES094).
It is an interesting receiver, it has some circuits you usually don't find in comparable receivers, it uses ACH1 as detector for CW, but uses the same stage as detector for AM. It also has a sort of Q-multiplier. Most valves are directly heated 4V-types, with indirectly heated 4v-type for the first RF amplifier, mixer and detector. But most valves are odd types (7 out of 9 are: RES094, RENS1284, RE134, and ACH1 is also a somewhat strange valve - it exists according to LA9DL Just Qvigstad three different versions with different sockets, one is very rare, and two have same type number, but different socket). It also has sort of semiconductor diodes in AGC detector, but as quite common before the war - they are drawn the opposite way around. R. Helsper wrote in his book (KW-Empf. Type Spez. 801 Gr 2/37) in April 1998: In dem Buch "Die Empfangsanlagen der Reichsflugsicherung" von Otto Koch (1938) ist der Empfänger bescrhrieben und in zwei Versionen abgebildet (see www.qsl.net/dl6vw ). The receiver is also mentioned (with circuit diagram) in Fritz Trenkle: Die deutschen Funkführungsverfahren bis 1945 pg56. For later German receivers it was emphasized on using only one type, and in few cases two types of valves.
Frequency coverage 1,46-23MHz, Intermediate Frequency = 600kHz

This receiver is also mentioned by G3VA in Radcom, Technical topics, Januar 2005

AGC circuit (note that signal diodes are incorrectly drawn on the original circuit diagram).
The receiver has an extra IF amplifier (RES094) to drive the AGC detector, the bias network seems
somewhat obscure with likely some positive voltage going into the agc-line. It is not any
delay (voltage) on the diodes, but forward voltage drop may help for this, see the similar
AGC circuit for Kw.E.a. Such extra IF amplifiers are quite rare at this stage of development;
I know only the two German receivers which have such - and Collins 51-S, and the Drake 1-A
to 2-B, possibly a lot more post-war receivers.

Telefunken Spez 801 receiver has ACH1 as "product detector",
and the second version has Q-multiplier to improve selectivity, but
RF-gain was abandomed in order to keep the same amount of controls
on the front, so it might be a problem to adjust the IF level for
proper SSB reception

Q-Mulitiplier.
For historical reasons it might be interesting to show the circuit for the Q-multiplier, it was added to improve the lack of selectivity, but one might wonder if the idea could have been found in ARRL handbook because a similar circuit is also shown there.

A similar Q multiplier is shown in ARRL handbook 1939 and may have been wellknown several years ahead.
Read more about Q-multipliers on page q2

Find data for rare valves like ACH1 and RES094 and other.

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Last update: 2004.12.30