More acquisitions
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Voxon bass fifty amplifier
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This old amplifier was donated
by Alan Phillips, a visitor to the Radio Museum carrying duff
lift circuit boards needing attention. I'd previously shown
Alan my rebuilt Moreton
Cheyney amplifier when he said he'd got something similar.
It was only later I lifted it onto the workbench when I realised
it was indeed similar because of its immense weight and having
removed the rear cover and noticed the two hefty transformers..
Those output valves are Pinnacle-branded EL34s, and the name
"fifty" maybe implies 50 watts output? |
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The valves are a mixed bunch.
The EL34s are Pinnacle and a Mullard with the two smaller audio
valves both ECC83, again a Pinnacle and a Mullard. The rectifier
valve is an EZ80, presumably for the EL34 anodes and on the right,
under the chassis, is a selenium rectifier for the ECC83s. There's
also a pair of silicon rectifier diodes.. maybe for the EL34
bias supply? Or the other way round as I haven't checked the
circuit details.
As you can see below, from the printing
on the mains selector panel (missing its shorting plug), the
amplifier post dates the Radiospares change to "RS"
in 1971 but my Hi-Fi year books are silent on the Voxon name..
at least in 1972/76/ 79. |
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Below a view under the
amplifier chassis and then a view from the top. Most of the parts
seem to have been sourced from RS. The mains transformer appears
to have a date in November 1966 and the output transformer is
marked 15 ohms and "785-80" (possibly an RS stock number?). |
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Audition Instruments Pre-amp/Reverb unit
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Above...this preamp which
came with the Voxon, at first looked like it came from the same
manufacturer but when I looked inside it was completely different.
It uses a couple of printed circuit boards marked "CDK TP-15A
and TP-15B" and Toshiba transistors. From the crude build
quality it looks British***. The badge states "Audition
Instruments" but I can find no record of this nor the Voxon
amplifier, although "Voxson" does appear mis-spelled
as "Voxon" in a few places.. |
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*** You can see the construction
in the pictures below. When I attempted to detach the chassis
from the case after removing securing screws it wouldn't budge.
I used a screwdiver as a lever and forced it out. The self-tapping
screws holding the lower circuit board were far too long and
prevented the chassis sliding into the case so it had been jammed
in place. Wiring conforms to the "scrambled" spec and
anyone that's handled Roberts
radios from the same era as this pre-amp will recognise the
general design and be aware of excellent performance coupled
with incredibly poor mechanical design with little thought for
a repairman. I'm reminded of a comment by a Plessey mechanical
engineer (concerning some satellite ground station equipment)
back in the late 60s... "the string is NATO approved string
not just any old string". |
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Inside the pre-amp case
are two early printed circuit boards with the mains transformer
on the right.
All the transistors seem to
be PNP devices and are germanium rather than silicon based. The
pair in the centre, mounted on heatsinks screwed to the lower
of the two circuit boards, are Toshiba 2SB462 with the "B"
standing for PNP. The case style is TO66 dating back to the 1960s.
Maybe the marking "CDK
TP15" means something to somebody? |
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BC221M
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Another item from Dave
G3SUL is this BC221 which is a different model to my
previous BC-221-AF example seen here. The availability of
these equipments back in the 50s, 60s and 70s provided a convenient
way of meeting the terms of ones amateur radio license although
actually having one to show a GPO inspector didn't always mean
it had ever been used. |
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Dave also gave me this
wooden box. It contained a rather nice 550-0-550V transformer,
not the original Type 2 Crystal Monitor, whatever that was? |
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HP Spectrum Analyser
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Dave, G3SUL kindly donated
this equipment which comprises the HP141T, HP8552B, HP8553B,
HP8554B and HP8556B (together with a few very nice 1930s radios
which are pictured below, together with a nice clean RA17). As
you can see the spectrum analyser is in immaculate condition
unlike my usual Hewlett
Packard acquisitions. Timing is amazing because I was just
about to go searching for a low frequency spectrum analyser with
which to investigate my
current amplifier rebuild. The 8556 works from 20Hz to 300KHz
and includes a tracking generator and I'm hoping this will let
me measure the quality of the amplifier in terms of linearity
and distortion. Below some radios donated by Dave, G3SUL. |
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This generation of radios from
1936 often used a fashionable shiny brass grille over the speaker.
I removed the speaker assembly and found the grille was really
badly tarnished but turning it over revealed the other side was
in fair condition. I glued the cloth in place and fitted the
grille which restores the radio's looks.
I use a brushing wax to restore
cabinets and once applied looks OK.
Below its unusual audio output
valve, an MPT4. |
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Ultra Lynx
From 1931
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A very clean example of
the RA17 with S/No. N2866. |
This has a few faults
that need clearing up.
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Skanti
TRP8255
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This is the Plessey-badged
transceiver fitted in the HDRS, later NCRS, cabins that were
supposed to carry army radio traffic to attempt to bring order
back to the UK, devastated by nuclear war.
Thankfully the possibility of
this ever happening caught MoD off guard leaving the project
high and dry.
All advanced projects go wrong
because of software problems and HDRS was no different. MoD were
more to blame than Plessey because sensible timescales and costs
were always secondary to available time and cash.
The more a project is starved
of timescale and finance the worse things can get. HDRS wasn't
really required but Plessey managed to get the thing delivered
under the guise of a sort of plaything for the Army.
Later the whole thing was sold
off at bargain basement prices and here's one of the radios I
bought from a fellow radio ham...
Read more
about the Project.. which for
a period I had the dubious pleasure of managing. |
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