R1355 GEE Receiver
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Above is a 1949 Clydesdale
ad for the R1355 with RF units. These were sold for conversion
into Band I TV receivers, often with the Type 62A display unit
shown below. I recently rejected an offer to sell me a pair of
these equipments for £695, but I did buy an example of
the R1355 receiver not too long ago for a lot less. To my surprise
it had been completely rewired and fitted with brand new components.
Clearly someone had spent a lot of effort but for what end result?
See the pictures below. The blue/yellow example is mine whilst
the plain one is just a basic unpainted modified example.
Note the orientation of the
upper (unwired) 6-way connectors. The front panel was also painted
in yellow before being roughly painted in blue.... all part of
its history. |
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Above, the transformer
has been renewed and the choke removed, but both examples shown
here appear to have been modified for a similar purpose. Note
the unwired upper connector. That white cable is the mains lead,
and two blanking covers are fitted over holes drilled for an
earlier modification. The blue receiver is fitted with a lower
4-pin plug for its mains supply, some examples like the example
below fitted with an RF26 had a 6-pin plug which is missing one
of its VR65 valves.. now maybe a 6V6 for driving a loudspeaker
carrying TV sound? |
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Below... note that pot
fitted to the PSU chassis isn't wired. |
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Above.. note the new components. |
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Above.. 5 stages of amplification
at 7.5MHz followed by an AM envelope detector whose output
is filtered and passed to 2 stages of AC amplification. Click
the circuit to see an alternative version.
All is slowly being revealed...
I managed to unplug the RF24 with some difficulty because the
thick blue paint was jamming the metalwork. Much to my surprise,
although the three valveholders were wired up and various wires
extended towards the upper side of the chssis, the coils, behive
trimmers and valve caps were unwired. All three valves are new
SP61's and checking those in the main receiver revealed, not
VR65's but again, brand new SP61's. The valveholders look new
as do the front panel connectors and Pye plugs. The restorer
never did finish the job. I should probably do this but after
getting rid of that blue paint.... done! The front panel doesn't
come off because its welded to the chassis. First coat of matt
black. |
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G019445 is the serial
number of the blue RF24.whose chassis is yellow just like that
of the R1355.
It certainly looks like original
yellow paint, but could the previous owner have stripped both
equipments down to basic metalwork and had them sprayed? I reckon
nearly all the components are new. That includes the valves their
holders, plus all the resistors and capacitors (even tagstrips
which are all labelled with their RAF numbers). For some reason
the project was never completed. If you examine the second picture
above you may notice the beehive trimmers are not wired up and
the coils have just unsoldered wire ends poking out. The switch
isn't wired up either (in fact it's never been wired up), neither
are the valve top cap leads. If you examine the tuned circuits
in the schematic above you may also note several damping resistors
and fixed capacitors are not fitted. Whoever was responsible
for the work didn't complete the job.
Oddly the blue paint was wet
when the RF24 was fitted because its case had well and truly
stuck in place, leaving the outer case behind when extracted
from the R1355. |
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The label cleaned up nicely
rubbing fine emery paper on the lettering.
Click the
plate on the top right to see an untouched example of an RF24B
Those securing screws were a
right pain as finding correct size screws was virtually impossible
so I ended up drilling the plate for slightly larger self-tapping
screws and after drilling the front panel I fitted the alternatives.
The last owner didn't have decent screws either so he used the
original rusty ones. |
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The RF24 front panel came off
easily and where the yellow paint has flaked off is revealed
clean bare metal with no sign of any original black coating.
Removing the panel entailed loosening of the front of the ceramic
switch carrying the ident mechanics and the long operating lever.
Because the switch wasn't wired the front section just dropped
out.
An odd modification was found
that must have been made during reassembly viz. the bakelite
knob, secured by a set screw, was drilled for a split pin as
if a loose knob was a stock fault in the RF24/RF25. In fact,
checking other examples I found all had a cotter pin securing
the knob and one of these RF units had an extremely stiff switch.
Ideally I should fit a proper pin as the split pin makes operation
incomfrtable. |
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Another puzzle is the pair of
Pye plugs. The one on the RF24 was very loose and failed to tighten
up. I discovered the mating threads were different sizes allowing
only a couple of turns before seizing up. As the material is
brass I was able to secure the front carrying the thread into
a vise and turn the other part using a 16mm spanner creating
a matching thread allowing the two halves to be tightened. Both
were stamped on the front "943-9142". Either the parts
are faulty or someone mixed up the two mating parts.
A suggestion which I believe answers
the puzzle is those numbers are part of a "modern"
NATO stock code for a metric-threaded connector whilst early
WW2 examples used a British thread. Parts from the two types
must have got mixed up.
A big improvement over the blue
version.. The switch needs some channel lettering and the turnscrews
need refitting once their fresh paint has dried. The handle now
stripped of blue and yellow paint was fairly rusty (now rubbed
down to remove the worst) which probably suggests the condition
of the original RF24 was much the same before painting yellow. |
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Just waiting for the blanking
plugs. Oops.. I put the two multi-way connectors on upside down
just like they were fitted in the blue panel...
I suspect the rotary switch
below the connectors should be fitted with a grub screw not a
4BA bolt and that split pin on the RF24 knob is horrible. |
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To proceed further is
quite daunting. Although both the R1355 and the RF24 appear substantially
complete the wiring between tagstrips and major components other
than valveholders was never completed. The majority of work is
around the two rotary switches. I could use an old RF unit, which
would mean finishing off the receiver, if I decide to see if
the whole thing works. To do this I'd need to reverse engineer
the circuit diagram and investigate the yaxley switch to determine
how to tackle the anti-jamming wiring. I imagine the power supply
is OK. The mains lead extends to the front of the R1355 where
it's been cut, but has it ever been tested and fired up? I didn't
notice the EA50 diode rectifier but hopefully it's lurking under
the chassis and what's under the IF cans... are the coils and
other components present? It goes without saying that the original
high-cycle power unit has been stripped out and a 50Hz one fitted.
Does this mean the R1355 was once converted for TV used and hence
RF/AF wiring/component changes made for this purpose or did the
"restorer" revert to the original R1355 design? Clearly
lots of detective work is required.... |
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Below.. a schematic of
the original hi-cycle power supply for aircraft use. A previous
owner of the R1355 has removed many of the components and fitted
a 50Hz mains transformer to supply AC LT of 6.3 volts and a DC
HT supply, keeping V5 the voltage regulator, and deriving the
negative bias supply from the HT supply rather than the EHT supply
which is no longer fitted. To re-constitute the negative bias
rail is tricky as the original circuit was part of the EHT system
and as such was very variable in voltage with respect to loading.
Advisory figures are quoted of -150 volts with R41 (75Kohm) load
and -230 volts with R41 switched out [see the wiring details
for this condition]. To understand the new power supply in respect
of the bias voltage I'll need to check its wiring and carry out
some tests. The circuit digram will be supplied later...
A quick check revealed no bias
supply but the Partridge mains transformer has loads of terminals
and may include a winding suitable for a bias supply, or an elevated
voltage range suitable for deriving a bias voltage from the HT
negative feed. |
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Below is the content of
the last, larger screening can (opposite V7 and V8) in which
you can see the elusive V6, a VR92 or EA50 rectifier. I opened
each of the 6 cans and all had been refurbished with new resistors
and capacitors. |
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To segregate from the main descriptive material
the wiring details are here...
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