A Quart in a pint pot?

[Tractorfan]

Hi,
Maybe it was an AF pentode Kalee20 (post 14). That makes more sense.
I have a couple of Grundig tape recorders where the motor is also the mains transformer and thus has extra windings to supply the heaters & HT.
Cheers, Pete.

[ParcGwyn]

Not a commercial design, but what about Sir Douglas Hall's Spontaflex design. Coupling components not even required.

Dave
GW7ONS

[Bryan M]

I remember in an early Radcom a circuit for a grid-dip oscillator using a magic eye as both oscillator and indicator.

Bryan

[Maarten]

Originally Posted by G6Tanuki

And I recall a number of early hybrid TV receivers where "free" low-voltage DC for the small-signal transistor stages was obtained from the cathode resistor of the audio output valve.

Or in some cases from the ground-end of the series heater chain.

[Synchrodyne]

How about the regenerative demodulator described in this thread:

https://www.vintage-radio.net/forum/...ad.php?t=82422

Cheers,

[ScopeMonkey]

Originally Posted by Bryan M

I remember in an early Radcom a circuit for a grid-dip oscillator using a magic eye as both oscillator and indicator.

It isn't from Radcom (PW in this case) but such a circuit has been discussed on this very forum:

Thread link

My runner-up vote goes to the (US? Can't remember make/model offhand, but Dynaco rings a bell?) valve audio power amp where the cathode bias resistors for the output valves were... none other than the heaters of the input stage valves

However, the outright winner for me has to be the superhet receiver discussed here: an entire superhet radio, in one valve.

Circuit pic (from the linked thread) here (too big for the forum).

Ed.

[G6Tanuki]

Also, the "Fremodyne" VHF-FM receiver built using a single double-triode valve. It's essentially a superregen-superhet [downconverting the FM broadcast band to something around 20MHz where the superregen detector operates].

See http://oldradios.co.za/projects/39-r...-receiver.html

[ParcGwyn]

Lots of info on building Fremodyne receivers here:

http://members.iinet.net.au/~cool386/

Dave
Gw7ONS

[Synchrodyne]

The American 6BU8 valve, variously described as a double, dual-control pentode and a split-anode pentode, handled both noise-gated sync separation and line-gated and noise-gated agc voltage generation in TV receivers. The two pentodes has shared a common cathode, a common control grid and a common screen grid, but had separate suppressor grids and anodes. It was less two valves in one envelope than a single, special purpose valve with an unusual electrode structure, and which was capable of handling two separate tasks.

Actually, commonplace though it was, the single pentode (or triode) agc circuit much used in negative modulation TV receivers, was an example of compact multifunctional design. This simultaneously provided gating (black level or sync tip), gain and rectification for the agc system, and the line flyback pulses provided both timing for the gating and the energy for the gain. There have been various descriptions as to how it functions, but its multiplicity may be seen by considering it to be a grid-controlled shunt rectifier. As such it is rectifying incoming line flyback pulses (“AC”) to provide a DC output. The magnitude of the DC output is determined by the grid potential, so it is effectively acting as a DC amplifier. But this grid control happens only at the time that the valve actually conducts, i.e. during the line flyback pulse, which coincides with the sync tip or back porch, the grid being fed with negative-going video. The “smart” part, as it were, was using the line flyback pulses as the means to obtain adequate agc gain. Its inherent simplicity may be seen if one attempts to map out a high-gain agc system for a valve TV tuner (by which I mean one whose outputs are baseband video and audio, such as might have been used by the relay companies) in which line flyback pulses are not available.

So the 6BU8 built upon was was already an example of compact design.

And now for something completely different in terms of multifunctionality, the domestic TV aerials in which the mast and array were also used as the basis for an antistatic radio aerial, as per the attached.

Cheers,

[Herald1360]

Originally Posted by ScopeMonkey

My runner-up vote goes to the (US? Can't remember make/model offhand, but Dynaco rings a bell?) valve audio power amp where the cathode bias resistors for the output valves were... none other than the heaters of the input stage valves

I like that idea. Not only does it save a few watts of heat but it conveniently provides a nice DC supply for the preamp heaters.

[G6Tanuki]

Another offering: the 1B8GT/1D8GT octal valves. A battery-heater Diode-Triode-Output-Pentode.

Detector, first-audio and 'power' amp all in a single bottle!

http://www.radiomuseum.org/tubes/tube_1d8gt.html
http://www.radiomuseum.org/tubes/tube_1b8gt.html

In a similar way I'm morbidly fascinated by the US approach of combining an output-pentode and a half-wave power-rectifier in the same bottle: 117L7GT - 117M7GT - 117N7GT - 117P7GT style: while I appreciate the 'economy' packaging which was appropriate for low-budget 'midget' bedside radios they must have run horridly hot!

[Herald1360]

117 volt heater rectifier pentodes seem to have been used in some interesting mains/battery sets like this Emerson 505:

http://www.nostalgiaair.org/Resources/607/M0004607.htm

where there were two output valves(!) one battery and one the pentode of the 117V valve. On mains, the series heaters of the battery valve front end are fed from the mains output valve cathode current

Single valve record players also feature.

[llama]

Another clever old trick: the synchronous vibrator. One set of contacts to create AC from DC in order to get it through a step-up transformer, and another set of contacts to "unchop" it.

I seem to remember the associated capacitor provided tuning and quenching but I'm vague on that issue.
Graham

['LIVEWIRE?']

Somewhere I have a U.S. Radio magazine from the early '70s, which features a 'one tube' superhet radio. The valve in question was, IIRC, described as a 'unicorn' type (or maybe that was the name of the receiver!) which combined frequency changer and (IF)amplifier in one 'bottle'. Such valves were never sold on the UK market so - in those pre-internet days, would have been difficult to obtain in the UK

[Herald1360]

There was a general discussion on these at:

https://www.vintage-radio.net/forum/...ad.php?t=56561

[Synchrodyne]

Mention of the orthogonal stereo amplifier in this thread: https://www.vintage-radio.net/forum/...d.php?t=111640 reminded me that it might qualify for inclusion here. With just two output valves one obtained a push-pull output for the sum (L+R) channel that typically contained the majority of the signal, although the difference channel (L-R) was amplified on a parallel single-ended basis. It was used for example in the Murphy A674SR. I wonder if anyone ever used it with the output valves in ultra-linear connection.

Cheers,