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BTH power amplifier type A1A (1950s, the BBC?): any documentation

Rosewind

Lost in Translation
I have seen these old valve mono blocks advertised locally. They are supposedly from the BBC in the 1950s. I can't seem to find anything in the ususal places, so does anyone know anything about these mono blocks?

I have three photos that can be seen via this link:
https://drive.google.com/file/d/1eDdq7xdrDnmZrM2mmbNyX_Bor6xPMniI/view?usp=sharing
https://drive.google.com/file/d/1gE6iQphQvPIVvfdz4fTVJvUqOm7KxzVW/view?usp=sharing
https://drive.google.com/file/d/1pDhucrxf3BzGujimXMyFI5u6edsyegN4/view?usp=sharing


view

view
 
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Never heard a pair but they seem well regarded and the BBC did use them. As I understand it they were a competitor to the Leak TL-12.1 and they certainly look decent with hefty transformers etc. I suspect if they are a nice pair they’d eBay for good money so probably not a lot of risk.
 
Is this worth a punt - would they sound good driving ESL 57s?

Tony L: you already answered part of my question.
 
Assuming a sympathetic rebuild I imagine they would be great with Quads, EL34s will drive them easy (I’d expect the to be a good 30 Watts or so) and they look to have some serious transformers which is always a good sign. If they are as in your first post and different cosmetically that will knock the value a bit. Just make sure the transformers are the same type on each as if not you’ll likely not get a solid image out of them. The rest can be rebuilt (I’d go as period correct as possible e.g. paper in oils, good quality carbon etc).
 
I will try to go have a listen during the weekend, and I will snap a few photos of the innards.
 
Some time ago I serviced a stereo A1A with El84s.It uses a very early printed circuit board for the components, and the printed tracks fall off when you even look at them.
Don't know if the mono's have the same printed circuits but if they do then any work done should be with great care. Incidentally it worked very well and very much on a par with the Leak ST20.
 
Thanks. Good to know. I wonder how much a full service would be. Obviously I don't know whether they are fully working or not. This remains to be seen.
 
Fantastic - what nice pictures. I hope the ones I am looking at are in full working order and that they are as original as can be. I have just arranged a listen to them Saturday.
 
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Just an update. The seller just checked them and one of the monos has a fault which means that he will change all similar components (a total of 4).

He bought them in Aarhus 30 years ago from a shop that had some English contacts. They had been in storage for a long time at the BBC and had to have a complete overhaul. Being an electronics engineer he did this himself and also added a feature where, when not used for music replay, the valves are kept warm with a low current so as not to wear out the valves.
 
Just an update. The seller just checked them and one of the monos has a fault which means that he will change all similar components (a total of 4).

He bought them in Aarhus 30 years ago from a shop that had some English contacts. They had been in storage for a long time at the BBC and had to have a complete overhaul. Being an electronics engineer he did this himself and also added a feature where, when not used for music replay, the valves are kept warm with a low current so as not to wear out the valves.

That could have the opposite effect!!
 
How? Doesn't it depend on the solution?

I could have him reverse it.

I think I will buy the set, however I will need to listen to them and have a look at them internally and externally. I will take photos.
 
It depends how it's done yes. Reducing the heater voltage or running with heaters on but no HT can reduce valve life... Counter intuitive yes but it can cause a problem called cathode poisoning in some circumstances.
 
If the chassis has been altered, ie: a switch added, that needs to be reflected by a price reduction ;-)
Let's see the photos asap.
 


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