In article ,
Iain Churches wrote:
"Dave Plowman (News)" wrote in message
...
In article i,
Iain Churches wrote:
Think you mean LSU/10. Cabinet by Lockwood - before they became
famous in their own right as speaker assemblers.
Yes. Sorry. Typo on my part. LSU/10 with the shelf at the bottom.
I *think* there's some more confusion here. The LSU/10 used a dual
concentric unit by Parmeko with a Lorenz super tweeter added
afterwards - and I don't think ever had any equalisation offered.
I'm pretty sure they were the normal 15 ohm.
The EQ was on the amp, in addition to the input level control.
The LSU/10 was 25 Ohm, according to two BBC people who
contacted me about this. This may also solve the puzzle of an
early Radford which I have seen with a BBC plate. It too has
a 25 Ohm OPT.
Was Radford current with the LSU/10?
No. That's the puzzle.
But I have a feeling that the Radford transmission line speaker
was 25 Ohms. So that may be the answer. An unsuspecting
buyer at auction who takes home such an amp which has been
separated from the speaker with which it was designed to work
will surely be disappointed.
Indeed.
I'm trying to rationalise why an LSU/10 would have been 25 ohm. When it
was designed actual drive units had settled down to the 'normal'
impedances, IIRC. Before the war they could be anything - my father made
an extension speaker for our HMV radiogram, and the Wharfdale speaker he
used was fitted with a multi-tap transformer with a list on the back of
which makers used which impedances.
But of course if you introduce a complex crossover the impedance can be
anything. And the LS5/1 certainly had a complex crossover which could have
required a 'special' valve amp. But I don't think this applied to the
LSU/10.
Doing a Google on LSU/10 produces all sorts of half truths - one saying
they were fitted with Tannoy dual concentric and a Lorenz tweeter. But the
Lorenz tweeter was added to the original with Parmeko unit which cut off
at about 8 kHz - fine for the AM broadcasting of the time it was
developed. When FM arrived some listeners complained of hearing odd things
the BBC engineers couldn't. Hence the obviously later addition of this
tweeter - just fixed to the grille. The Tannoy unit was certainly retro
fitted to some cabinets - IIRC for pop music balancing and higher SPL
output - but this certainly wasn't done to them all. And didn't need an
additional tweeter.
It produced an 'interesting' sound, the LSU/10. Effortless but coloured
would be how I describe it. And totally abuse proof with the original
built in amp. I'd be willing to bet Keith G would love the sound it
produced.
I've got piles of old BBC Engineering Monographs and my own 'Evesham' etc
notes. Perhaps I'll have a wade through them and try and find more
details. The mind plays tricks with the passage of time...
--
*Tell me to 'stuff it' - I'm a taxidermist.
Dave Plowman
London SW
To e-mail, change noise into sound.
Is there a value in QUAD II amplifiers?
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