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Old 9th Oct 2019, 5:45 pm   #1
David Simpson
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Default Marconi R.B.7.

Privilege & Trepidation - a chum has just recently dropped off his RB7 for me to "Get it Going". I recently put out a Forum request for a Circuit Diagram(25th Sept.) & eventually received the two from Radiomuseum via email. Amazingly, my chum tells me that this RB7 is the one shown on the Radiomuseum page !
Definitely very privileged to be trusted with it, but yet full of trepidation delving inside this 1922 beautifully built scientific quality receiver. Due to its value being far more than all I've ever owned vintage radio/electronics-wise.
5 of its 6 valves(V2 - V6) all tested OK on my DEV.DEQ test rig/VCM MK3. Looks like the Secondary Tuning Panel has been factory modified & differs from the RM diagrams. One half of the Dewar Switch has been removed, and the "FRAME" connections just go straight to a pick-up coil around the wiring between the l/h & r/h terminals.
Are there any early Marconi Guru's out there, who can advise me, please? And - how many pairs of underpants should I wear whilst working on it ?

Regards, David
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Old 9th Oct 2019, 9:30 pm   #2
Herald1360
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Default Re: Marconi R.B.7.

Maybe jumper in some less irreplaceable PM series or even D series battery valves while you play with it. When it's all working nicely with them, risk the bright emitters?


You'll be all right as long as you wear them outside your trousers (as Superman that is, not the Private Eye version).
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Old 10th Oct 2019, 10:11 am   #3
David Simpson
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Default Re: Marconi R.B.7.

Hopefully I wont need to power it up much longer. As last night it came into its own & resolved onto several stations giving good volume into my old 1920's headphones. Amazingly - no whines, squeaks or feedback, etc. associated with old TRF's. Some faint adjacent channel &/or 2nd channel reception.
'Twould be too much fannying about to bodge up an external 6 way B4 valve holder panel to replace the 6 Christian cross profile DEV/DEQ valves. So I'm just keeping the single HT & LV supplies as low as possible.

Regards, David
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Old 10th Oct 2019, 1:47 pm   #4
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Default Re: Marconi R.B.7.

Sounds promising!


Don't think 2nd channel comes into it, though, TRF......



Adjacent or just breakthrough I would think.
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Old 11th Oct 2019, 12:38 am   #5
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Default Re: Marconi R.B.7.

Hi David
Does the RB7 employ tuning capacitors or like the RB12 variable inductances to do the tuning? The RB12 covers 300 to 3000 metres in four switched ranges.
I been searching for more than thirty years for the construction information of the coil assemblies in the RB12.
The DEV was designed to keep the anode to grid capacitance as low as possible. I believe the valves operate on only 40 volts.
In the RB12 a DER triode functions as the RF amplifier and reflex audio amplifier. HT is 40 volts.
Information about the DEV: https://www.radiomuseum.org/tubes/tube_dev.html
The DEQ: https://www.radiomuseum.org/tubes/tube_deq.html
The V24: https://www.radiomuseum.org/tubes/tube_v24.html

DFWB.
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Old 11th Oct 2019, 10:53 am   #6
David Simpson
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Default Re: Marconi R.B.7.

Hello Fernseh, I haven't a clue about the RB12. As I said in post 1 - tis me who needs guidance from a Marconi expert or two.
This RB7 is the 1922 259A version shown on the Radiomuseum site. It would break their rules if I openly posted copies of their circuit diagrams. However, if you go through their security procedures, you can get them to freely email you A4 pdf copies. Does RM have info on the RB12 ? Hopefully they could also send you a copy of the circuit diagram, if there is one.
The circuitry of the RB7 is a wonder to behold. I've found some physical modifications, and as soon as I have time I shall completely redraw the circuit diagram. I've measured the inductance & resistance values of the coils.
If you want to exchange pictures of coils & condensers etc., PM me your email address.
Thanks for the DEV etc. valve links, but I researched them a couple of years back, & built a "Christian Cross" valve profile test rig which connects to my VCM MK3 via a B4 base. (I put out a thread post " Testing DEV Valves"). As I needed it to test about a dozen for the RB7 owner. I'm told that they are "rocking horse manure" , hence my trepidation.

Regards, David
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Old 11th Oct 2019, 1:08 pm   #7
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Default Re: Marconi R.B.7.

Hi David,
I'll send you a PM. Many years ago there was an article about making ersatz DEV and V24 valves in either the BVWS bulletin or the GFGF magazine or it might have been a topic in this forum.
Can't remember the precise details but I seem to remember a miniature wired ended valve of the CK505AX type was fitted into a tubular envelope made to resemble the original cruciform shaped valve.

DFWB.

Last edited by FERNSEH; 11th Oct 2019 at 1:15 pm.
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Old 12th Oct 2019, 8:45 pm   #8
FERNSEH
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Default Re: Marconi R.B.7.

From tube collection,de
More images of DEV and Q valves http://www.tubecollection.de/ura/marconi.htm

DFWB.
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