1946 HMV 1804.

[Murphyv310]

These modifications could be way ahead David, with all the uncertainty in the world, a sensitive receiver is what we need once a certain leader close to where Samsung's come from starts playing with his new found toys and all those semiconductors get fried.

[Geordie McBoyne]

Hi Trevor,
because of our unique skills with valve equipment we'll be on the reserve list as communication equipment engineers.

Geordie McBoyne.

[Bassoonbloke]

Come on McBoyne,

Hoover it out, put a plug on it and give it some juice !!
What could possibly happen

Looks like a bit of a challenge, but I know that you're up to it.
More pictures please as you go along.

Cheers,
Alan.

[Geordie McBoyne]

Hi Alan,
           Yes, I must restart the 1804 resto project.   I've spent too much time on that Sparton radio. Today, the radio chassis was refitted into the cabinet and the set has been put aside until good medium and long wave aerial coils are found.
So the first task is tidy up the HMV chassis.  That interlace filter device must go.  I can either return the interlace circuit back to the original EMI single diode arrangement or wire in the two diode interlace filter around the valveholder of V8 (D63/6H6).
The first attachment shows the interlace device which was probably made by the same engineer who modified the RF, the mixer-oscillator and IF amplifiers. The second picture shows the two diode interlace filter as used in the Pilot CV34. The third picture shows the original HMV single diode interlace filter.

Geordie McBoyne.

[Bassoonbloke]

Morning Geordie,

I must admit that i think i would be inclined to go for original circuit, see how it works and then modify it for the Pilot version if i felt it would make a real improvement.
I assume that all the original chassis posts and things are in place to re-build the original layout, so it shouldn't be too much aggro (famous last words !!).
Keep up the good work.

Alan.

[Geordie McBoyne]

It's been suggested that the modifications were carried out by a Pye engineer, after all the set came from Cambridgeshire. There's no doubt the interlace filter is similar to the circuit employed in the Pye FV1 and that square screening can is a Pye component. Also, a Pye engineer would be familiar with the EF50 RF pentode. Evidently the Z66 pentode wasn't all that good even though it is similar to the Mazda SP61. Both the Z66 and SP61 are greedy for heater current, 0.63amp is not good, EF50 is better at 0.3amp.

Geordie McBoyne.

[Murphyv310]

I still think that the set should be left with the mods intact. No one knows whose done the mods but it could have been a Pye engineer doing a homer!!!
A high gain set may be of use once Heritage 405 line broadcasts start up in the not so long future.

[Geordie McBoyne]

Hi Trevor,
I'm coming around to that point of view, but with two exceptions. That interlace filter unit has to come out, it's just an untidy mess and the Mazda SP61 valve in the sound IF amplifier must be exchanged for an MO valve.
So plan is to get the set working again and then compare it's performance against the electrically similar Marconi VT50A.

Geordie McBoyne.

[Geordie McBoyne]

More evidence that the modifications were performed by a Pye engineer. The original frame blocking oscillator transformer had been replaced with a Pye component, the same one that is used in the D16. Now that good news for me because I been on the lookout for that particular part for years. After the connections have been traced out the transformer can be fitted into my D16. A normal two winding blocking transformer can be fitted in the HMV.
The interlace filter unit has been removed and the circuit will be returned to the original HMV circuit. A standard Plessey blocking oscillator transformer can be wired in.
Further examination of the modified RF and IF circuits shows that the work had been carried out in a competent manner.

Geordie McBoyne.

[Geordie McBoyne]

The frame blocking oscillator transformer removed from the HMV.   This transformer has the sync injection winding as used in the Pye D16.

Geordie McBoyne.