A modded Cossor 54

[Geordie McBoyne]

Hi Frank, the Cossor CRT in the model 54 is type 3244.

Geordie McBoyne.

[`FRANK.C]

Thanks Geordie for the tube type.

I got a chance to remove it this evening and I removed the bottom from the chassis to get my first glimpse of the underside.

It appears that I have a stowaway in the form of a 4TSP valve. At least I haven't seen on there in any of the photos on the web.

Frank

[Geordie McBoyne]

An audio amplifier perhaps? These sets had only just enough audio output.

Info about the 4TSP: http://www.r-type.org/exhib/aaa0495.htm

Geordie McBoyne.

[`FRANK.C]

Hi Geordie
Quite possibility is an audio amp.
Going by The Valve Page the extra RF amp for this set has 3 valves so it cant be that.
There also appears to be an extra transformer or choke mounted on the speaker.
I will have to trace it out first chance I get.

Frank

[`FRANK.C]

I time to have a peek at the extra valve and scribble down the circuit. See below.
It is an RF amp inserted before the original aerial coil.
Two resistors are of unknown values to me.
The G2 resistor measures 36K it is all orange in colour with silver at one end. So maybe it is 33K?
The cathode resistor is open circuit. It has an orange body with one black band at one end the other band is very dark but I think it is either brown or red.

I also traced where the choke mounted on the was going. It turns out it is wired in parallel with the HT choke. So it is probably safe to assume the original HT choke is open circuit.

Frank

[Freya]

A fringe amplifier then, looks like its been there a very long time. I would have thought your resistor was 30k originally.

[`FRANK.C]

Hi Stephen
The G2 resistor probably is 30K I had forgotten that back then the values were more rounded.
The amplifier is there a long time. The valve is held in place with a bracket each side of it.
One bracket is bolted to the chassis the other one is soldered to the choke.

The choke on the speaker is soldered in place.
They had big soldering irons back then.

Frank

[Geordie McBoyne]

Circuit diagram of the three stage pre-amplifier for installation in the Cossor models 54 and 1210 and the post-war model 900.

Geordie McBoyne.

[`FRANK.C]

Hi Georgie
Thanks for digging out that diagram. It is very interesting.

Frank

[LENINGRAD T2]

Hello,
The additional valve I believe was designed to amplify the input signal. The question is whether it is needed in this TV to run it properly?
This is a very unique TV receiver. It is worth restoring it to its glory. I keep my fingers crossed.

Adam