The oddest valve? KLL32

[Boater Sam]

Has anyone seen a set using the KLL32 valve? 2 v battery double pentode.

McMichael 484 & 486 and Pye 67A are the only ones listed in the Radiomuseum and I have never seen either.

Surprising, there are 2 available for sale currently. wonder if they will sell?

[M0FYA Andy]

They probably will sell now you've got people interested!
Andy

[kalee20]

I've got a Pye 67a although it uses a QP25 output valve (dual pentode). All valves are MO based, rather then IO based like the KLL32.

Was there a KLL31 and KLL30, by any chance?

Synchrodyne is good at answering questions like these!

Incidentally, I'd take exception to the title - the oddest valve to me is the EFM31 combined AF amplifier and tuning indicator (never seen one).

[barrymagrec]

Originally Posted by kalee20

Was there a KLL31 and KLL30, by any chance?

Not according to the Mullard Maintenance Manual.

[G6Tanuki]

The nearest I've ever seen to one of them was the ATP4 transmitting valve [used in WWII-era 18- and 38-sets] which was essentially one of the 1930s double-pentodes with the two electrode-sets strapped in parallel and with the anode connection brought out to a top-cap.

I guess it was a quick way for Mazda to produce a 'powerful' battery-filament RF output valve.

Wackiest valve I've actually got is an ECLL800: two output-pentodes *and* a triode all shoved into a B9A base.

[Herald1360]

Rare but not particularly odd. Putting both valves of the (low dissipation compared to similarly sized mains operated types) push pull output stage of a battery set in one envelope probably saved a shilling or two- one less bottle and one less socket.

The same series KCF30 is maybe odder- a triode pentode frequency changer, used in even fewer sets!

[Boater Sam]

How many sets Chris? I make it 2 but one is the Bush BA91 and that is fairly common.
The Pye 67A gets in on the act again, it must be a very odd set.

[turretslug]

In the "odd" stakes, the 28D7 double tetrode ranks quite high for me, supposedly originally orientated around "farm radios" intended for nominal 32VDC wind-generator systems (in the way that "28V" is a 24V battery in a charging system). There are a couple here, random strays amongst loctal pulls. I'd heard of them used in the BC1206 beacon receiver with its 28V HT, but in this case, the tetrodes are paralleled for single-ended Class A output simplicity. It would seem a waste and missing the point to build them into anything other than a push-pull circuit as a new design. Unfortunately, there's 11W of heater power needed for circuits typically capable of a few hundred mW of audio power, at least if one sticks to 28VHT.... Can't see the audio-phools going ape over them anytime soon, but who can tell!

[turretslug]

Originally Posted by G6Tanuki

The nearest I've ever seen to one of them was the ATP4 transmitting valve [used in WWII-era 18- and 38-sets] which was essentially one of the 1930s double-pentodes with the two electrode-sets strapped in parallel and with the anode connection brought out to a top-cap.

I guess it was a quick way for Mazda to produce a 'powerful' battery-filament RF output valve.

The US 6B4G does a similar thing with two off-the-shelf medium power triode assemblies strapped together in one envelope- again, it smacks of expediency.

[Refugee]

The 6CD6G is another internally wired double pentode but this time with a common anode and two full sets of grids and cathodes.
I initially thought I had spotted two rectifiers and quickly consulted the manual to find out what was going on.
http://www.r-type.org/exhib/aaa0321.htm
It is used as a series regulator in my Marconi signal generator and it is staying there as the instrument is so stable that it will beat several times per minute with Radio 4 LW as a frequency standard as well as being a very good sine wave generator all be it a little large.

[Trifocaltrev]

Both my Pye67A and my KB DR31 use a KLL 32 and both perform very well. The McMichael 484 uses a similar KLL 35. My Bush BA91 uses a KL35 as per the Bush Service Sheet. The Trader Sheet for the McMichael states that a KLL 35 is used as above.

Trevor.

[Boater Sam]

So far Trevor you are the only person to have a set or sets even that use these, have a cigar.
Is the Pye 67A a really odd set?
The KB DR31 is not listed as using KLL32 at all and the McMichael is listed in Radiomuseum as using KLL32 rather than KLL35

[G6Tanuki]

I wonder if the 'odd' construction of the 6CD6G could be because there would have been insufficient available emission from a single heater/cathode assembly?

TV deflection-tubes are an interesting design-space: they generally need to be able to pass very high peak currents at relatively-low HT. Some of the later US "sweep tubes" intended for colour TV had peak cathode-emission of a couple of amps! This is part of the reason they make relatively-good RF linear-amplifiers when dealing with the relatively-peaky-but-low-average waveform of SSB voice-signals. They're not so good for 'continuous carrier' modes though.

[Trifocaltrev]

HI Sam,
The Trader Sheet 876 clearly shows the McMichael 484 as using a KLL 35 and the KB, DR31 R&TT Sheet shows a KLL37 both of which concur with my sets.

I have two Pye 67A sets, one of which uses Mazda Octals and the other the Mullard K Series.There is nothing special about the set, it is a standard 3 waveband battery table set.

Trevor.

[Mr Moose]

Hello,
Until the coming of the National Grid many homes needed battery radios as their main (as opposed to portable) radio set. These needed to have a reasonable output power but low battery consumption so push-pull pentodes like the KLL32 were used with a 2V accumulator for the LT. Once the National Grid appeared after the war, most homes had mains supplies so there was little demand for table battery sets and portable sets had moved to 1.5V dry battery valves, so the demand for a 2V double pentode like the KLL32 (which came out in 1946) disappeared hence its rarity in radios.
Unusual valves like the KLL32 would remain unsold on dealers shelves whilst the more common ones would sell out once production had ceased so you can sometimes find that 'rare' valves are more common now than 'common' ones.
Yours Richard

[Refugee]

Originally Posted by G6Tanuki

I wonder if the 'odd' construction of the 6CD6G could be because there would have been insufficient available emission from a single heater/cathode assembly?

TV deflection-tubes are an interesting design-space: they generally need to be able to pass very high peak currents at relatively-low HT. Some of the later US "sweep tubes" intended for colour TV had peak cathode-emission of a couple of amps! This is part of the reason they make relatively-good RF linear-amplifiers when dealing with the relatively-peaky-but-low-average waveform of SSB voice-signals. They're not so good for 'continuous carrier' modes though.

When I was finishing off a partial restoration of the sig gen I had a look on the web and found that in the US there was a tall version of the 6CD6 with a much longer cathode that looked more like a sodium lamp.
It looks like the design was to cut down on height.

[Marconi_MPT4]

Hi,
KLL32 was designed to operate in class B mode. With a standard 120v HT battery it was possible to obtain 1W with less than 2% distortion at a quiescent current of 3.3mA. Each grid would have been driven from one half of a transformer phase splitter winding.

Quite a few circuits were published in the 1930's to improve HT battery efficiency even further. One circuit I recall biased the valves to (almost) cut-off point with no signal. A Westector diode was used to rectify the incoming signal which generated enough bias for the output valves to operate within their normal range giving better audio quality when required.

Cheers
Rich

[G6Tanuki]

"Quiescent push-pull" was briefly the 'thing' in battery-portable radios in the 1930s, to save on HT consumption.

http://www.r-type.org/addtext/add019.htm

Of course push-pull class-B (with just a trickle of standing current to tame crossover-distortion) became the standard way to do it once transistors caught on in the 1950s.

the setup with the Westector to control bias sounds very much like a version of 'sliding bias' that was used in some applications: the "Reference-shift modulator" - http://ekladata.com/ddX2c-NG42DyDMPd..._cq_jun_56.pdf - shown here being an example. Turn the negative-bias up when the signal-amplitude is low, to reduce standing current.

[FERNSEH]

From the Continent: the DLL21 the 1.4volt double-pentode.
https://www.radiomuseum.org/tubes/tube_dll21.html
I believe that the KLL32 is unique to Mullard. I've searched for a KLL1, an electrically similar valve only with exception of the ct8 base, but it seems no such valve was ever produced.
However, there was a KDD1, a class B double-triode: https://www.radiomuseum.org/tubes/tube_kdd1.html
Mullard KCF30? believed to be a re-based Mazda TP25. IO instead of MO.

DFWB.

[Paul_RK]

This thread needs the Loewe 3NF: three triodes, two capacitors and four resistors.

http://www.electricstuff.co.uk/loewe.html

A good reminder to us not to complain too much when a resistor that's gone high is a bit tricky to get at.

Paul