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

Quad IIs are always a good option too. I’ve no idea if people take the same liberties with them they do with the poor old Stereo 20, but IIRC Quad will still service them!
 
I'm the exact opposite to Tony on this.... I'm not that bothered about physical condition, scratches, dents etc etc as it's the sound that matters to me (obviously what I would pay would go down if it is in poor physical/aesthetic nick but ultimately the potential sound quality and technical merit would decide it for me) .
I would still be put off by these though.

If you want something that is both vintage and sounds amazing it has to be Radford. Radford is in a completely different league from any of the other UK valve amp manufacturers and something like an STA25 will make any Leak or Quad valve amp seem like a toy. They will in fact beat most modern valve power amps. The price does reflect their capability though so you would pay around £2K+ for a decent STA25 MkIII.
 
Really! Well......it is one option of course.

Whilst the STA's are quite lovely sounding amplification I have a preference for the additional texture and gravitas derived from the Partridge C core OPT as sported on the Audiomaster 11A.

Other very high quality EL34 based contenders...Beam Echo DL7-35, Lowther LL26 and the Armstrong A10 MKII with its almost EL34/EL84 Hybrid presentation.
 
Those are all amps I’d love to spend time with. I doubt I will though as good NOS EL34s are just so crazy expensive these days! I’m pretty sure I’ll be sticking with EL84s as hopefully I’ll never need more power and I have a good stash of them that should see me out!
 
TL12.1s are legendary, considered by a fair few in the know as the finest tube amp period. Very, very hard to find a really good close pair though, and that puts me off. I really like my soundstage so buying a random pair is a real risk as the transformers were changed as few times as I understand it. A really tidy identical pair with close serial numbers would make many multiples of that!
 
Really! Well......it is one option of course.

Whilst the STA's are quite lovely sounding amplification I have a preference for the additional texture and gravitas derived from the Partridge C core OPT as sported on the Audiomaster 11A.

Other very high quality EL34 based contenders...Beam Echo DL7-35, Lowther LL26 and the Armstrong A10 MKII with its almost EL34/EL84 Hybrid presentation.

It's relatively unimportant what the output valves are. I stand by the Radford being vastly better than any other contender. I didn't like the Beam Echo.
Radfords had the best transformers and the best circuit design of all the vintage UK makes. The Bailey phase splitter allowed much better HF response and by reducing phase shifts it allowed considerably more negative feedback to be used.
 
TL12.1s are legendary, considered by a fair few in the know as the finest tube amp period. Very, very hard to find a really good close pair though, and that puts me off. I really like my soundstage so buying a random pair is a real risk as the transformers were changed as few times as I understand it. A really tidy identical pair with close serial numbers would make many multiples of that!

I don't particularly rate the TL12. Many more would rate the Williamson amplifier above it.... For best ever old valve amp my contender would have to be the Radford STA100.
 
Tony L: I hadn't looked at the enlarged photos of the TL 12.1,so I hadn't seen what condition it was in. If I had I wouldn't have suggested that you take a look.
 
Well....Opinions and Arseholes Mr Arkless....Opinions and Arseholes.

I don't recall basing my illustrative list of amplifiers on output valve type alone!

On papar specification perhaps the BPS can be regarded as an evolution of the older Radford model sans BPS, personally I prefer the overall musicality and tone of the earlier MK without this technical 'improvment'

And whilst pondering upon that last point I enjoy listening via PYE PF91 or say Rogers Williamson over 'Any' model of Radford that I have owned.
 
Well....Opinions and Arseholes Mr Arkless....Opinions and Arseholes.

I don't recall basing my illustrative list of amplifiers on output valve type alone!

On papar specification perhaps the BPS can be regarded as an evolution of the older Radford model sans BPS, personally I prefer the overall musicality and tone of the earlier MK without this technical 'improvment'

And whilst pondering upon that last point I enjoy listening via PYE PF91 or say Rogers Williamson over 'Any' model of Radford that I have owned.

It would depend on if one wants a valve amp to sound like a valve amp... I don't. I want uncoloured, undistorted, neutrality from my High Fidelity system;) The last thing I want is tone!!!
 
Curious....Playimg Devils advocate and To quote the Engineering mantra, should the veritable Old 12.1 be operating under the accepted level of audible distortion Viz 0.1, what more does the Radford/Bailey Phase Splitter offer other than an increased level of feedback employed within the circuit.
 
Curious....Playimg Devils advocate and To quote the Engineering mantra, should the veritable Old 12.1 be operating under the accepted level of audible distortion Viz 0.1, what more does the Radford/Bailey Phase Splitter offer other than an increased level of feedback employed within the circuit.

It is the combination of Radford's output transformer design and the much higher bandwidth of the Bailey phase splitter which allows more feedback to be used. The extra feedback then allows Radford amps to have less distortion, greater damping factor and a wider, flatter frequency response than most other valve amps. The way the whole of the output transformer secondary is used in all output impedance settings also helps. I have personally measured 0.03% THD from an STA25! It also sounds bloody marvellous and made even my extensively modded Stereo 20 sound old fashioned and generally rather lacking in comparison.... The leak does sound good but going over to the Radford, even at volumes the Leak's output can easily manage, shows the Radford to be in another league! Transparency, bass grip, dynamics, sound staging, treble purity, the lot are so much better than the Stereo 20 as to make comparison a joke really. If only it didn't belong to a customer and had to go back to its owner a week or so after I had rebuilt it...:(
 
Thank you for the comprehensive reply Jez, I do know the theory well, in that the on paper a Radford valve amplifier
Displaying the Fundimental and Harmonic profile of a Thermionic design married with sub 0.1 characteristics should...on paper be unmatched, however whilst exceptional For my part I prefer the 'musicality' of other amplification without the Bailey PS, in terms of amplifying a recording I just do not see it as a necessary or requirement to faithful HI fidelity.
 
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 there any information about the BBC's use of BTH amplifiers in those years?
 


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