Cossor 72 or is it a 396?

[boater sam]

I have seen a Cossor 72 radio for sale but cannot find this model listed anywhere. It looks for all the world like a model 396 which I can find pictures and details of.
I am interested because if it is a 396 it has a desirable triode valve, a 4XP.

Does anyone know of model 72?  Or is it a completely different set from a 396?

[Mike Watterson]

http://classicwireless.co.uk/Cossor_72.htm
and
http://www.cossor.co.uk/rogues-gallary-f...t-war-sets

First and second hits on Duck Duck Go search on my Browser.

[boater sam]

Thanks Mike.

Same cabinet but not the same chassis, 396b has an RF amp front end, 4PX rather than 2PX if all the details are correct. 
Strange that there is no circuit diagrams on my disc nor on the Radiomuseum site.

[Cobaltblue]

Cossor did not supply circuit information for all their models.

From 1939 onward Cossor often just adapted existing models, some models have several distinct variants with the same model number.

The model 74 has at least 3 variants that I know of.

Cossor didn't see the need to issue service information for these variants as the competent serviceman would just work with what he had finding the nearest circuit if needed.

Replacing a 4XP with a 2XP or even a 2P was common especially in 40/41 before they discontinued production completely.

So even if you do get a circuit diagram there will be no guarantee a 4XP will be fitted.

Cheers

Mike T

[boater sam]

I examined this Cossor 72 today, all there apart from one small knob. Looks to be untouched.
It is fitted with a Mazda PA20 output valve which would date to 1936. Not  a direct equivalent to the 2P.

[Mike Watterson]

http://www.r-type.org/exhib/aav0001.htm
The PA20 is a PX4 style of triode. Perhaps a wartime old stock replacement.

While some "Audio" people want them there is nothing great about triode PAs. Pentode/Beam-Tetrodes are far better. It may only have been due to royalties that PA triodes were made so long rather than Pentode/Beam-Tetrodes being used universally.

A nice little set to have if it cleans up OK, even just for display.

[boater sam]

I note that it is a hand assembled triode. I can't imagine that there is much demand for a 2v filament PX4 even from the audiofools.
All 4 filaments look to be intact surprisingly. The PA20 has a higher output than the 2P which is supposed to be in there.

Though having a common control and chassis layout with the models 77, 63, 66 etc. the 72 has the addition of an RF amplifier first stage.
Does anyone have the circuit diagram for 72 or know which in which model the chassis is the same?

The dial cord is broken but I enjoy restringing these, am I a masochist?

[Mike Watterson]

I only see a few RGD sets with the PA20 on the Radiomuseum. I'd certainly not heard of it before. Could be rarer than the Cossor!

[boater sam]

Searching other Cossor sets, the model 74 looks to be the same chassis as the 72 but without the tuning eye.  Similar valve line up with the triple gang tuning capacitor and RF amplifier stage.

[Cobaltblue]

Looks as if the PA20 is a replacement for the 2P although the filament current of the PA20 is 2A its only 0.7A for the 2P

The 2XP has a 2V 2A filament but has a higher Va then the PA20

Later versions of the PA20 had a higher Va making it a better match to replace a 2XP

The GM of the 2XP is 7 and VA 300V 

Does the set have its back? most Cossor sets of this period have the valve line up and their location pasted onto the back.

Sadly your wrong about lack of demand for 2V triodes almost all Cossor sets of this period are now plundered for the triode.

Lots of these sets have a random valve in the socket or empty when offered for sale.

Cheers

Mike T