That was quick! Pamphonic Car PA System

[Pamphonica]

Spurred on by Lucien's excellent thread about who loves old PA systems, I hauled this system down off the top shelf in the "museum".
(Lucien's thread: https://www.vintage-radio.net/forum/...public+address)

Coming from 1954, it rejoices under the title of the Model 599 Loudhailer System, with the Model 733D 8 ohm horn and a Pamphonic-badged Lustraphone (dynamic?) hand microphone.

It was used as a car-mounted electioneering Public Address system by the Chipping Norton Labour Party until probably the early 1970s. It runs from the 12V car battery, using a small dynamotor to generate the HT. The huge (18") horn is mounted on a plank with webbing straps, to go on the car roof. The "inside" unit containing the amplifier is also mounted on a wooden support with a handle slot, along with the hand microphone. The amp unit did have rubber vibration mounts but all four of these have perished.

It was donated to me about 10 years ago and I had not done more than peek inside.

This time, I decided to get it going. Given the 50 years' "rest" I started with the dynamotor. One brush was mis-seated, but that was a quick job to rectify. With the output valves removed to avoid run-away currents, I pushed the microphone switch and the dynamotor immediately spun up and sounded lovely, generating an HT of a whopping 340V.

Next was a quick test with the output valves (6BW6) in place but monitoring the voltage across the cathode resistors. 14V on both sides - bang on the money. So the dodgy Hunts brown coupling caps were still probably doing their job.

Finally, with speaker attached, I ventured to produce sound. Perfect first time. Nice and crisp. Given that this is election day, I had to gave out a smart mock election call to voters (but only in the workshop!).

After 50 years dormant, to have this system running perfectly first time is amazing, and almost certainly on its original set of valves. It draws 1A on standby (heaters only) and 6A on speak, from a 13.8V supply.

Hence the title - one of the fastest "restorations" I have ever had. Big grin!

[GrimJosef]

Nice job Jeremy !

You'll have to bring it to RetroTech and use it to entertain and inform the queue and/or keep us up to date with the latest arrivals on the Bring and Buy .

Cheers,

GJ

[Lucien Nunes]

Excellent!

In the context of a vehicle with likely a 22A dynamo at most and possibly even one with only 3rd brush regulation, it makes sense to save current by starting the dynamotor with the PTT switch. But it means that every time you go to open your mouth you get an audible reminder of the hoops that had to be jumped through to make valves work on ELV battery supplies. Does it do the little overspeed thing at startup due to the inductance of the shunt field?

Is there an official output power rating? At that HT I'm guessing it gets 15W from a 31W or similar dynamotor.

[Radio Wrangler]

That would fit well with a pair of 6BW6 which behave like 6V6 but in a smaller bottle. With intermittent speech use, they should keep their cool quite well.

You aren't leaving those little brown Hunts jobbies still in position, sitting, waiting to pounce are you?

I remember a cream table top Lustraphone mike, like an overfat pepper pot, from my junior school days, but I can't remember what recorder was used with it.

David

[Herald1360]

That's a dinky little dynamotor!

I did expect the "huge 18" horn" to be about 4 feet long, though, rather than the re-entrant variety

Mind you, you could get four re-entrant ones on the roof for all round shouting without needing to cross over all the trumpets

[joebog1]

The days of real engineering!!!!. Today it would be a few hundred transistors, a whackin great big inverter with + & - supplies, a current draw of 100 amps, require a couple of 3 Farad capacitors to "buffer" the 6" long 0 Guage power supply cables.

One double triode, two 6BW6's, a tiny Genemotor, a few caps and resistors and it STILL works !!!!.
Real engineering!!!!. I love it.
Good story Jeremy.

[Herald1360]

Or more likely a 4"*3"*2" little Chinese 12V 15W chip amplifier taking about 2A on peaks.

You'd still need the "huge horn" though......

[Outrun_uk]

Nice bit of kit, has The Blues Brothers written all over it!

[joebog1]

Chris,

Oh how I love to be alone in the country,
But Im with you dear,
Oh how I love to be alone in the country.

Thats is exactly how it works.
quote:
Or more likely a 4"*3"*2" little Chinese 12V 15W chip amplifier taking about 2A on peaks.
unquote.

WILL those skungy little chips still work in 50 or 60 years?, OR will it be scrapped in two years and another one purchased to top off the land fill?.

Joe

[Uncle Bulgaria]

Originally Posted by GrimJosef

Nice job Jeremy !

You'll have to bring it to RetroTech and use it to entertain and inform the queue and/or keep us up to date with the latest arrivals on the Bring and Buy .

Cheers,

GJ

Excellent idea!

Well done, Jeremy. I expect you were imagining a long-drawn-out process when you took it off the shelf. I expect the most difficult part was the lifting it down!

[Nickthedentist]

Very nice and probably almost unique.

I wonder how it survived so well for 50+ years after being decomissioned? Was it in the hands of another enthusiast?