[Catkins]

Originally Posted by FERNSEH

Superb restoration. These are excellent TV receivers, there are some elements in the circuit design carried forward from the magnificent A42V, Murphy Radio's first TV receiver.

By all accounts the A42V was a technical marvel, no expensive spared.

I don't have any technical information on the A42V, beyond a couple of references made in the A56V service documentation. Regarding V7 (the vision amplifier), the documentation states "This circuit will be found to be very similar to that employed in the A42V except that the latter employed a push-pull rectifier in order to double the frequency of the IF that appears across the diode load", which implies the A42V had very high vision bandwidth.

The A56V has trimmers which affect the thyratron bias, but also has line/frame hold and height/width controls. It is mentioned in passing "Those who are conversant with the A42V will remember the amplitude control in this set controlled the bias on the thyratron valve. It therefore affected frequency as well as amplitude, a similar control is provided in the A56V, but is mainly used to take up tolerances in the circuit".

This does lead to the slightly weird case where you can control both hold and amplitude by use of the trimmers in conjunction with the normal line/frame hold and height/width controls. In practice I set the trimmers which gave me a good range of line/frame hold and height/width on those controls.

I was lucky with my Murphy A58V as the set was in generally good condition. The A58V is the version of the A56V which has the addition of a modified A46 radio receiver.
A CRM92 was used for a time to replace the original CRM91 which had an OC heater. Spacers and special adaptor plates were made to accommodate the slightly longer replacement tube. Later on thanks to HKS John a good CRM91 was found and duly fitted after the adaptor plates were removed. I still have those parts somewhere.

Yes, I had to fabricate new parts to accommodate the CRM92. I'll mention what I did later in the write-up. I'm going to try and write it up in chronological order as that makes most sense, and that's towards the end of the restoration.

Actually, I think the compact A56V is a much nicer looking set than the A58V.
DFWB.

The A58V does have some highly innovative "skids" which I've never seen elsewhere! In contrast the A56V doesn't have casters or any other means of easily moving it around. Which does get to be a pain. I have my A56V sitting on a trolley dolly so it is easy to move it around.