Who is interested in vintage PA equipment (Public Address)

[Hartley118]

Originally Posted by GrimJosef

Quite a few years ago now I picked up a 19" rack-mount module marked ELETTRA AMPLIFIER TYPE 2275A. The output stage had four DA42s wired in parallel push-pull with the drive coming from two EL37s. The valve museum says of the DA42 that "It was designed for use as a push-pull pair in Class B to give 175W out with 1kV on the anodes". So presumably four valves would deliver 350W or so.

The story was that there were three identical modules which, between them, made up the PA system for one of the Magnox power plants, possibly Sizewell A. Apparently they were taken out of commission when they could no longer find anyone in the electronics crew there who was brave enough to service them (yup, in a nuclear power station !). How much of this is true or not I don't know.

Mine's very nicely made with tidy looming and every wire numbered at each end. But there are a lot of electrolytics to sort out and the thing weighs the thick end of 60kg if I remember rightly. So it's going to be a while before I get the lump back onto the bench.

Cheers,

GJ

Elettra was a Marconi brand, so I’m guessing that this is a GEC amplifier. GEC were big in PA systems in the 1950s. I recall working in the electronics side of a massive Sheffield steelworks back in 1962. It had many GEC PA systems, typically 500W rack mounted amplifiers feeding 4-foot straight horns.

Martin

[Reelman]

Originally Posted by barrymagrec

T633B? I have the Electrical and Radio Trading service chart manual March 1951 - August 1951 with the service information for that Trix amplifier.

Quite probably! Unfortunately it is hidden in the garage at the moment and encased in a home made box the previous owner made for it. When I’m next in the jungle there I’ll have a look.

Thanks Barry,

Peter

[stevehertz]

When I joined my first band 'Pentagon' in 1973 all the members bought and owned their own instrument and amplification. And so it was that our vocalist Eddie (RIP god bless him) owned a truncated cone shaped microphone that appeared to have been dipped in tiny ball bearings, and an Impact PA system. The latter comprised - as I recall - a 40w valve amp in a distinctively shaped black leatherette covered cabinet and two rather small - about 4ft - column speakers that I think housed about four 8" speakers. On reflection, the amp box was mildly 'V' fronted with the control panel at the top, angled upwards. I think it had four sets of inputs and because there were five of us in the group, two of us had to share a channel for backing vocals. In use it barely coped with what was asked of it and not surprisingly often went into distortion with us lot shouting down five mics, not to mention the pickup from the backline amps. Once, the amp got pulled off the top of a piano it was sitting on and crashed down onto the stage. Eddie was down on the dance floor singing and dancing with ladies, the mic lead running off the stage to him. Oh, BTW the gig was at Winson Green prison, Birmingham, and a recently promoted prison officer who clearly didn't like Eddie dancing with the ladies decided to pass between the stage and Eddie, snagging the mic lead in the process and pulling the amp to the floor. All hell let loose and Eddie was eventually prised off the prison officer. But the amp still worked! The amp and the columns had stylised 'Impact' chrome badges on them. Anyway, it was eventually upgraded to a similar format Selmer PA of slightly more power as I recall. Happy days. Well, sometimes..

[Kyri]

I have an Eagle International PA amp, I have had it for some time. It works perfectly without any changes, and has some valves which date it to 1970 or so - at least the mullard date codes are 1970. 50W claimed from 4 EL84, well maybe 30-35. In any case it is very loud.

I did buy a 2nd one more recently which likely works but I haven't fired it up yet as it had a break in the mains lead which needs sorting but partly why it was cheap. The other reason is people don't tend to value them. This is depite the build quality, which is outstanding. Check out the transformers, and the nice quad of (tungsram labelled) mullard EL84's:

[Valvepower]

Wow! this is turning out to be a good ‘ole rabbit hole, anyway more rambling from myself…

Quite a few years ago now I picked up a 19" rack-mount module marked ELETTRA AMPLIFIER TYPE 2275A. The output stage had four DA42s wired in parallel push-pull with the drive coming from two EL37s. The valve museum says of the DA42 that "It was designed for use as a push-pull pair in Class B to give 175W out with 1kV on the anodes". So presumably four valves would deliver 350W or so.

I figure this is based on one of the circuits in the GEC Approach to Audio Frequency Amplifier Design book, which I encountered first in the guise of the Babani Hi-fi, PA, and Disco Amplifier Design book.

Although not strictly PA, however back in the very early 1970’s I used to read the Designing and Building Sound Mixer book in the local library, and thanks to a kind Forum member I was able to get a copy of this book a few years ago. I just remember being fascinated by the the mixer built in the brown face Leak preamplifier case. Mind you it would have been only 5 years or so later I would be actually building group PA amps as job!

I have in the round-tuit pile a Geloso G-227A PA amplifier. This uses two EL34's giving roughly 35 watts… one day It’ll get around to getting it restored!

Terry

[Kyri]

Terry, have you seen this? http://www.chambonino.com/geloso.html

[Valvepower]

Originally Posted by Kyri

Terry, have you seen this? http://www.chambonino.com/geloso.html

Many thanks for the link, although I have seen it. I used to correspond with John Chambers before he retired, although I’ve not heard anything from John since he called it day quite a few years ago.

John has one of the Beck PA amps on his site and remember one of these coming into Roost for a service. This from memory this amplifier was only 40 to 50 or ‘so’ watts as it used the Radiospares Deluxe output transformer, or had this been fitted as repair in the past. They were popular as 'repair' output transformer for this type of amp? As this was back in 1975, I’ll never know!

http://www.chambonino.com/work/beck/...4ch-pa-60.html

…Ah, and I forgot our ‘stylish’ WEM Band Mixer telephone table in the hallway… Or should that be… using the modern parlance ‘upcycled’ telephone table, anyway, it makes an interesting talking point!

Terry

[GrimJosef]

Originally Posted by Valvepower

... I figure this is based on one of the circuits in the GEC Approach to Audio Frequency Amplifier Design book ...

It might be, although 'loosely based' might be a better way of putting it.

I did start tracing the circuit out (years ago). One unusual feature is that the final stage HT (not much change out of a kilovolt) is balanced, +/-500V, either side of chassis ground, presumably for insulation reasons. I'm ABSOLUTELY going to have to remember that if/when, say, I ever have to work live on things like the heater wiring.

Cheers,

GJ

[stevehertz]

Here's a link to the Impact amplifier(s) I referred to in post 43. I got a few details wrong after nearly 50 years.

https://www.edgaraudio.se/tubes/impact.htm

[Valvepower]

Great stuff Stevehertz as I’ve not seen that site… and down another rabbit hole! Crikey, the second one today, what with going a down rabbit hole looking into Beck Amplification.

Back in the 1970’s and 80’s I remember the Impact amplifiers and fixing couple of them. It says they were sold to Dallas Arbiter and seeing they (Sound City) were only just across town (Southend) and there was flow of people and parts between Roost and Sound City in the mid 70’s, and I vaguely remember something about Impact in the Dallas Arbiter era…, however the 'ole brain maybe playing tricks on me!

Terry

Originally Posted by stevehertz

Here's a link to the Impact amplifier(s) I referred to in post 43. I got a few details wrong after nearly 50 years.

https://www.edgaraudio.se/tubes/impact.htm

[Techman]

Originally Posted by Kyri

I have an Eagle International PA amp, I have had it for some time. It works perfectly without any changes, and has some valves which date it to 1970 or so - at least the mullard date codes are 1970. 50W claimed from 4 EL84, well maybe 30-35. In any case it is very loud.

The one I bought for a quid at the junk sale last weekend and that I mentioned back in post #12 is an Eagle. The only information I could find on the 'net for it was an old advert dating it to 1973. It uses 2SD217s for the outputs and is apparently rated at 35 watts. Unusually for me I've not powered it up yet, although the word at the auction was that it was working and used to be used at various outside events, which was exactly what was said about the last one I bought at the same sale several years before. Looking inside, it looks like a resistor has been completely cut out somewhere back in the signal stages with just a wire end stuck up out of the board, so a possible historical modification, but there's no circuit diagrams available anywhere. This is now the second Eagle amplifier I've got, as I already have another very small one dating from sometime in the 60s that I've had for years - I've got the paperwork and circuit diagram for that one!

[stevehertz]

Terry, did you ever work on a Sola Sound amplifier? A mate of mine has one and it has stood him in good stead for over 50 years!

[Kyri]

Originally Posted by Techman

The one I bought for a quid at the junk sale last weekend and that I mentioned back in post #12 is an Eagle.

Interesting, they are indeed well made. The second one I bought was almost identical and relatively cheap, worth it for the valves alone. They were some matsushita japanese EL84's but I can't find the pictures. I really should fix that lead and power it up slowly.

I also noted your comment about sound city. I remember being a student at school and saved up for an old valve head which cost me £50 or maybe £55 in around 1990, it weighed a ton. I had to take it home on the bus, the bus stops were about a mile from the shop and from my house so I had to take rests, but it made a perfect seat whilst taking those rests.

Some of the EL34's (it had 6 of them) needed replacing which I got from a local radio shop which has long gone. It was so loud that we used it as a PA for the whole band and it was never at full power that would have blown the windows out. I never realised I could have removed some valve pairs. I'm sorry to say I sold it on not long after but I would have injured myself lugging it around if I had kept it. I have a photo somewhere but it was a Sound City 120 Head.

[Kyri]

Originally Posted by Valvepower

I used to correspond with John Chambers before he retired, although I’ve not heard anything from John since he called it day quite a few years ago.

I contacted John many years ago to make good an old amp I found. Today I would likely have had a go myself but back then I had no idea what to do. I was fortunate that he was so passionate about amp restoration that despite being very busy he would spend time on the phone talking through the progress at various stages, fascinating chats I remember.

http://www.chambonino.com/construct/const16.html

I still have that amp, I don't know when he retired but figured he must have since the web site has not been updated for a long time.

Cheers!
Kyri

[Lucien Nunes]

Wow! this is turning out to be a good ‘ole rabbit hole,

I was hoping it would be. At the moment we are not surprisingly quite focused on amplifiers. Who has examples of PA speakers - both horn and cabinet - and microphones?

[MikeCross]

I still have an interest in PA equipment and keep an eye open for bits that can be restored.
When I started my electronics training I was assigned to projects that had audio content. As part of these projects I used equipment supplied by companies such as Vortexion, Tannoy, Grampian, Reslo, Quad, Ferrograph, Nagra and Revox. Equipment that was built to last.
Now retired, I have collected a Vortexion 30/50, a Ferrograph test set and a Ferrograph recorder which are used in my workshop. However my real love was the Tannoy AP60, of which we used very few, these seem to have totally disappeared.

[wd40addict]

Originally Posted by Lucien Nunes

Who has examples of PA speakers - both horn and cabinet - and microphones?

I have a pair of WEM Songbirds to go with my PA120 and a Torque to go with my ST50.

[Hartley118]

Talking of microphones.....How about this pair of Grampian DP2 moving coil mikes from the 1940s?

Introduced I believe in 1939, The DP2 was rumoured to have been used by Winston Churchill to announce Victory in Europe.

Martin

[Valvepower]

No, I’ve not done any work on a Solar Sound amplifier, well that I can remember. I figure I would have seen one but given the mists of time I can’t remember anything about them though.

I have worked on, and seen many Solar Sound pedals – I’m not sure, but were Colorsound pedals made by Solar Sound?

Terry

Originally Posted by stevehertz

Terry, did you ever work on a Sola Sound amplifier? A mate of mine has one and it has stood him in good stead for over 50 years!

[Valvepower]

Speakers…

I was never directly worked for a speaker manufacturer, but I got well involved with PA speakers working at Roost, Canary, Adam Hall and doing Tec stuff in Music shops and fixing gear for local bands and PA companies.

When I was at Adam Hall in the mid 1980's A.S.S. Acoustic Sound Systems run by Tony Rossell were right next door. At that time A.S.S were making their own PA speakers and speakers for Turbosound. The were some pretty impressive speaker systems in the A.S.S works at this time, to say the least!

I remember Tony A.S.S using the Matamp MOSFET power amplifiers (amongst others), I must admit they were built like tanks and sounded rather nice.

Found this on the net (I remember John Entwhistle coming the A.S.S factory)...
https://app.photobucket.com/u/Jazomi...6-641e4d6df483

This was the time where power met the work of Linkwitz-Riley. The BSS crossover was an impressive beast with is plug-in cards with various crossover alignments, the Linkwitz-Riley being the most popular.

There was the Folded horn and the good ole 4560 speakers, just to name a couple of cabs.

Whilst down a rabbit hole I came upon a Roost PA amp, which I think could have well been wired by myself in the mid 70’s.

Finally, attached a rather silly Roost advert featuring speakers from 1977…

Terry