Nostalgic EF50 TRF

[Doodlebug]

When I was a young teenager I built my first short wave receiver using the valves
that helped win the war, namely the EF50.  It was a 1-v-1 circuit.
That was some 70 years ago !!

Recently, for old time sake, I have rebuilt the same receiver using some old
components and some new.
Using the same type of Muirhead dials I used then for bandset and spread.

Testing it out, the o/p stage is OK but I have a most odd fault, driving me nuts.
The coils are plug in, home made from PVC pipe.
The reaction feedback coil winding is at HT potential but when I plug in the coil it shorts out the HT.
No faults on the coil or the circuit, but the short persists.

It's as though the ghost of the original set I built is haunting me. 
I shall exorcise the ghost and clear the fault me hopes.

   
   

[Panrock]

Nice job.

Happy fault tracing!

Steve

[Amie]

Did you get the detector working Albert?

Tidy workmanship sir!

Is that an Eddystone diecast box you've used as a chassis?

Thanks,
Ami.

[Doodlebug]

Yes, sorted out. An extra wire that shouldn't have been there.
It is a diecast box, but doubt if it's Eddystone. From eBay :-)

When I built the first one I bought an aluminium chassis from Smiths of Edgeware Road, London, for 2/6d !
Some very old 'uns here will remember Smiths.

[Doodlebug]

A word of warning using old valve holders.....

Having sorted out the detector stage I found that the RF stage was dead.
HT on valve OK but not drawing any current.
Then I noticed that the valve was not getting slightly warm as it should,
in drawing 6,3v at .3 amps, nearly 2 watts.

Checked heater volts at pin connections. All OK.
Took out valve and checked for 6.3v at valve holder. All OK !

I'm sure the ghost of the first one I built 70 years ago was playing tricks again.

Then I tumbled to it. I was using old valve holders from way back and
there was slight oxidation right inside the valve pin connections in the valve holder.

A tiny scrape inside the two heater connectors and set sprung to life.

Beware using old valve bases. The ghosts of past circuitry will get you !

[Panrock]

Beware using old valve bases.  The ghosts of past circuitry will get you !

Yes, particularly when using what were called (I think) B9G bases as needed for the EF50, copious amounts of which are also found in the 'Argus' televisor (attached) and which I was too lazy to clean properly before photographing.

Steve

[Doodlebug]

Steve, do you where one can obtain the clamping screw rings that were used to
hold the EF50's firmly in their holders?
I don't see any on your Argus TV.

The Ef50's can easily loosen if one has any receiver etc upside down for servicing
without those clamps........none on eBay.

[Panrock]

Hi Albert,

I used to hate the bl**dy things. They seemed to make valve removal such a fiddle, especially in confined spaces.

I've just checked to see if there were any in my stores I could send you, but sadly there were not.

Steve

[Amie]

....do you where one can obtain the clamping screw rings that were used to
hold the EF50's firmly in their holders?

If you have no luck with finding the base clamps I've seen suitably sized metal caps from glass jars or similar with expansion springs used to hold them in place. Dad had a three valve TRF with a vertical chassis that had been modified thus.

Thanks,
Amie.