Mystery suitcase & unknown chassis

[Croozer]

Following an auction, I have been gifted the contents of a mystery suitcase. Therewithin are the chassis of five ac/dc radios of various vintages, mainly octal valves, several missing, the obligatory dac90 (complete with ul41) - a car radio (with one valve missing) - and a mystery chassis.

It (mystery first photo) has two pairs of PL36s, an ecc82 and a mains (?) transformer. Each pair of PL36s has anodes in series with TX, all four cathodes are in series and there are no passive components on the board except a 4mFd smoothing condenser. Some sort of power supply?? I have no idea.

Beyond that, I now have an interesting collection of bits. None of the chassis are complete. The best of the output valves are gone although there are a couple of interesting examples:

-A 50L6gt which I assume is a 50v version of a 6L6
-A CBL31 which claims to be a double diode pentode (why?)
-A couple of CY31 rectifiers(steam punk full wave PSU?)
-A number of EF39 RF pentodes (could these be used at AF as drivers?)
-A couple of double diode triodes (which could be used at AF)
-Various frequency changers (add a tuning condenser and an Osc coil - does that give the guts of a pantry TX?)
-All those PL36s. (TV line output valve?? probably hardy beasts? Do they behave like ordinary high slope pentodes? Are they linear enough to be used as class A amplifiers? Or are they more intended to be heavy duty switches?)

No cabinets and nothing (as far as I can see) that is unique enough to merit a restoration - but plenty of useful bits - output transformers, mains droppers, ul41s .... (drop me a pm if there is anything specific you see and need and i can send for postage).

I've got so many bits and so little knowledge. How creative can I be with this collection of components - what novelties in construction? Unconventional AF amp? FM slope detector? Pantry TX?
Answers on the back of a 10/- note....

[G6Tanuki]

I remember seeing some PL36s used with a hunky transformer as a DC-to-AC inverter (for those people who still had DC mains but needed to run AC-only radios/tape-recorders/tellies) They're beefy and work well as output-valves. Not seen them used single-ended, push-pull AB2 is definitely an option though! I've also seen them used as RF linear-amplifiers.

50L6 is a power-output bottle but nowhere near as beefy as a 6L6; it's probably closer to a 6V6. Commonly used in US 'midget' radios with series heater-strings.

CBL31 was intended for cheap superhets: the diodes are for detector/AVC and the pentode-bit is a relatively-high-slope one so it can be driven directly from the detector.

[Croozer]

Apologies. This time with photos. Unknown chassis is the first pic. Car radio the last one.

Thanks for the explanation about the double diode Pentode CBL31 - I suppose this would be an economy measure to save a valve - sort of early integrated circuit!

An inverter for getting an AC supply would seem a likely suggestion for the mystery chassis. I will trace out what remains of the circuit when I get a chance.

Meantime here are pics of some of the chassis

[Croozer]

And the remaining two radio pics

[Boater Sam]

CBL31 is the 0.2A heater version of the 6.3V EBL31 for series heater chains along with the CY31 rectifier. Becoming a bit expensive now.

[joebog1]

First pic with 4 X PL36 looks to me like a big PA amplifier by Phillips !!.
In Australia they loved their PL36, a 6CM5 in aussie speak. Origionally horizontal output bottle in TV sets, but a pair can fetch around 50 watts RMS, a quad will easily make 100 watts
and I have seen ( still have the chassis) of 6X 6CM5 in PA amp service.
Output transformer I would bet is generic Philips made, as it,s exactly the same "colour/design/build" as I have seen in Australian PA amps.

Joe

[Herald1360]

An EL36 might be a 6CM5, but a PL36 has 300mA series heater needing 25v.

[Refugee]

24 volt transformers are pretty easy to find these days.

[HamishBoxer]

I wonder if the car radio is D.R.H. (My initials by the way!) Will check the one I have.

[Maarten]

A Philips (output) transformer will have code numbers on it, or traces thereof.

[Silicon]

The chassis in the second photo looks like a Bush DAC90.

The box around the dropper resistor is lined with Asbestos.

The CBL31 may have been used in a 'short' superhet for the reasons given above.

[Croozer]

There is indeed a Dac90, minus its case. It's in fairly miserable condition but it still has its o/p transformer and valve and mains dropper.

The car radio is indeed badged DRH - couple if additional pics attached. It has three of its four valves present, but looks like someone has had a go at the front end. The tuning (three presets) is missing its mechanism.

Interesting and surprising to learn that the mystery chassis is likely a Philips PL36 amplifier. I can't see any markings on what (I now assume) will be a push pull output transformer. Last two pics show above and below decks. Assuming four valves, two parallel push pulls that must have been one scary powerful beast.

Last year I built a modest stereo amp around a pair of UL84s, which has created a demand for a repeat from various people including my sister-in-law who liked the steam punk novelty. I was hoping to pull enough components from what remains in the case, but the only pair of o/p valves are ul41, which don't seem to have a great reputation - the case will, however, provide the elusive speaker transformers.

I had a quick look at the PL36 datasets. The graphs show scary high anode currents (over 1000mA!) so I guess this would rule out their single ended use with a conventional SE transformer robbed from one of the other sets. I'm not good at the maths, (so this is from interpretation of the graphs) by under-running the anodes at say 50-70V (I also have a great big toroidal mains TX with a 50V o/p), or by holding down the g2 voltage again to 50 V and biasing g1 high (-30V) or some combination of the above, i wonder if it would be possible to get the anode current down to a suitable range for those little SE output transformers? (and at the same time be on a straight enough bit of the graph to sound ok) It would also have the benefit of keeping the top caps of the anodes down to something safe (ish).
3
This isn't intended to be a 'disposals' type thread, but if anyone should see anything they need to maintain the originality of a better example, complete a project etc, send me a PM and I'll send on the bits for postage.

[Refugee]

It looks like some air has sneaked into one of the PL36 valves on the amp chassis.
I thought so on an earlier photo but this later photo looks even worse.

[Radio Wrangler]

That 1000mA anode current figure is just a peak rating. It means that you can run them at any current up to that and the power ratings for anode dissipation and G2 dissipation will tell you that you can't have it handling this sort of current for much of the time. Running these valves with enough negative bias on G1, or a suitable value of cathode resistor will let you set any lower current you want.

Such valves, though, when run up to their power capabilities in an audio amp, and especially when run as pairs makes me expect that the turns ratio of the output transformer will be unusually low which will be a limitation if used with more usual audio output valves.

Similarly, the anode voltage ratings will be a lot higher than the HT these valves would be used with. It'll be a pulse rating for use in TV line output stages.

David

[Herald1360]

Here's an Oz take on a PL36 amp:

http://www.vk6fh.com/vk6fh/2009ampli...uversion_1.htm

[joebog1]

Thanks Herald1360
Joe

[GEC 1972]

Hi Croozer,
The chassis in the third photo is an Ekco U29 (originally in brown and cream Bakelite cabinet) and the last is an Ultra U7961 "Troubador" (available in either brown or cream Bakelite cabinet).

[AC/HL]

That amplifier is a bit sparse. Series connected heaters, 110V? Could it be an inverter or a stabilised PSU?

[mark_in_manc]

Is the Ekco U29 missing its wave change switch (appears it might be)? I have a more-or-less complete one on the roundtuit pile whose wafer switch is all smashed up - think I'm missing one knob too. I don't know what else I'm going to need for it, but if you decide you want to shift your one on...

cheers
Mark

[Croozer]

Mark, yes, the wave change switch is missing (I assume it should be next to the tuning coil?) if you want the rest of the chassis, drop me a pm.
Many thanks for the pointers on PL36 used for audio - complete with circuit diagram and 55v grid bias. One of them has indeed gone to air. While there are strong arguments that this could be an amplifier, I have sympathy for ac/hl's argument on sparse components. I will take the transformer off the chassis to try to work out whether it is a meaty PP output transformer (for which I have no use and would need to rehome) or a mains transformer (which would be useful to me)...

I'd like to try to use the PL36s SE, the graphs seem to suggest that strapped triode and with lowish anode volts there is a usably straight part of slope.... But it will be down to experiment rather than calculated design