Marconi 730 marine receiver

[allan]

I appear to have one of the very few examples of the Marconi 730 TRF receiver, not to be confused with the Eddystone having the same model number.
The receiver has a set of plug-in coils marked 0 to 10 which works out to 11 pairs as two are used for each range.
The only information I can find tells me it has ten wavebands. But there are eleven coil sets. My set is missing the pair numbered "4" but I have seen a picture with the number 4 pair present.
On the chassis is a coil for the old 16KHz time signal broadcast but that needs only one coil (mine is missing) and I have seen a picture of this in place plus eleven pairs of coils.
The question must be...Why 11 coil sets for 10 wavebands?
I hope to test the receiver shortly and that might reveal the answer.
Allan G3PIY

[greenstar]

Looks a very interesting set. When does it date from?
Might one coil set give coverage from mid range to mid range to avoid changing coils of a heavily used range?

[dave walsh]

Yes I wondered about the date. Not seen one of these before although there are oblique references to them on the Forum. I passed an Atlanta on to Richard FM from Stockport, who seems to be a bit of a specialist in this area and might have some info perhaps

Dave W

[AC/HL]

A few hits on Google, including a YouTube one, to which someone has added a comment "Built in late 1930s and never used by any Navy": https://www.youtube.com/watch?v=VoIR-Hxht9M

[G3VKM_Roger]

Originally Posted by AC/HL

A few hits on Google, including a YouTube one, to which someone has added a comment "Built in late 1930s and never used by any Navy": https://www.youtube.com/watch?v=VoIR-Hxht9M

If this is the same RX, then it looks like it was used by somebodies navy? Anyone recognise the uniforms in the attached photo? Book credits the photo to Hulton-Getty.

73

Roger/G3VKM

[Dave757]

Hi Allan,

Is range 0 perhaps a pair of blanking plugs installed in the front panel when the set is not in use. Continuity checks of the pins might show if any coils are fitted.

Not sure if you have a circuit, but one is available at www.seefunknetz.de/730.htm

Kind regards
Dave G0ELJ

[M0AFJ, Tim]

Originally Posted by G3VKM_Roger

If this is the same RX, then it looks like it was used by somebodies navy? Anyone recognise the uniforms in the attached photo? Book credits the photo to Hulton-Getty.

73

Roger/G3VKM

Possibly Danish

[allan]

I'd already exhausted the Net's hits thanks.
I powered it up and found it pretty horrible to use. The audio can be quite deafening when tuning and setting the reaction control because the audio volume control is merely a screen voltage adjustment which has little effect.
It does resolve SSB if the reaction control is set to make the thing break into oscillation but with interaction between detector tuning, aerial tuning, reaction and RF gain. I need to check the resistors and condensers next to check none are bad but these early receivers tend to be better in that respect than those from WW2 and later.
When was it made? I should say around 1935 to 1937 but I'll see if there's a clue in any of the printing on the components.
https://www.radiomuseum.co.uk/marconi730.html
Coil 8 brought in Irish Radio 1 on 252KHz (1190m) and Radio 4 on 198KHz (1515m).
Allan G3PIY

[Herald1360]

Originally Posted by M0AFJ, Tim

Possibly Danish

The cuff rank rings suggest the wavy navy or RN(V)R.

[Gridiron]

This set is described in the 1945 edition of Handbook of Technical Instructions for Wireless Telegraphists by Dowsett and Walker ( the info on your site) but not in the 1939 edition, so might be WW2 period although still using old fashioned technology, plug in coils and pre-octal valves.

Mike.

[allan]

It is a bit of a conundrum Mike.
The wiring is typical early 30s (or even late 20s) being 16SWG btc with 50% sleeved.
The general decoupling condensers are metal-cased Type 4703 with those needing less leakage being large Muirhead mica. Resistors are nearly all those from very early 30s. Coil holders are Eddystone. The valves look brand new so may have been replaced.
No military markings that I can see.
Maybe all the decent receivers were being pinched by the Navy and this old model was the only one available to the wavy navy?

I might have discovered a wiring error around the RF gain control but still checking. It looks like the connections to the wiper and live end are transposed. This would mess up not only the grid bias of the RF amplifier but also the output stage. Whether this is due to a previous user who fitted a new pot or a factory error it's hard to say.
I reckon the chassis to HT- voltage should be fixed at say -10 volts and this applied across the RF gain pot. The RF gain would be determined by the setting of the pot from-10 to zero with a fixed bias to the audio amp.
The way it's actually wired would allow the HT- to be progressively shunted to the chassis by the setting of the pot and simultaneously reducing the bias of the audio amp towards zero.
This might explain the grotty performance and ear deafening?
Allan G3PIY

[Station X]

Originally Posted by Herald1360

The cuff rank rings suggest the wavy navy or RN(V)R.

RNR had sleeve stripes in the form of chains. RNVR had sleeve stripes in the form of single wavy lines.

The stripes in he picture in post #5 suggest RNVR, but they're not like any RN stripes I've ever seen.

https://en.wikipedia.org/wiki/Royal_..._Nov._1943.svg