AJS/Symphony/National parts identification please?

[thevalveset]

Hi Experts,
I am in the middle of restoring a 'corroded out' Symphony/National 5 valve portable. The set uses a tufnol baseboard with brass 'printed circuit' looking 'tracks' made I believe by Plessey in the 1920's.
I acquired two of these chassis many years ago in a box of wireless spares and at the time didn't know what wireless they were from. Subsequently I discovered they were from a Symphony Gramophone and Radio Co or a subsequent National portable set.
The resistors and capacitors are unusual as they have the appearance of a festoon lamp and are fixed to the baseboard with a 6BA screw at each end.
Sadly they are labelled just with the word NATIONAL and a single number 1 to 6. Plus a patent number :-
https://worldwide.espacenet.com/publ...C&locale=en_EP
I have completely stripped the whole baseboard and re-manufactured the rivet-able valve sockets. I have sourced replacement tubular rivets from China to restore the board to pristine condition. I have repaired or rewound the chokes and repaired the intervalve transformers but now I am stuck....

My question is:-
Does anyone have the definitive data as to what each of the NATIONAL components is and it's correct value?
For instance a NATIONAL 4 is a capacitor but what is its original value?

There are various circuit diagrams on the web that have one or two values given but don't agree with each other. The Marconiphone 55 is one such example.
My chassis has three components that are are actually marked with DALY as the maker and a value but again they don't agree with the schematics. They are all open circuit BTW so I can't measure even one!
I know I can guestimate what they might be but there must be someone out there that still has the spell!
As I am trying to restore the set back to exactly the day it was made I am hoping someone knows for certain what the NATIONAL part numbers/values were from new?

Please help if you know the answer to this riddle.
Thanks in anticipation
Dave

[PJL]

How about some pictures?

[Mike. Watterson]

Daly made capacitors. They should measure open circuit on Ohms, though I doubt that they do with 100V DC across them!
DVMs and ordinary capacitor meters are no use to test capacitors used above 25V

[crackle]

Daly electrolytic capacitors are also well known for turning leaky.
Mike

[thevalveset]

Hi everyone,
Sorry should have added in the picture... now attached. (i hope)
Having found the 1925 patent documentation and fully read how the Daly/National resistors and condensers are made, I managed to get one to bits.
As you can see from the attached jpg the components are similar looking to a car festoon lamp. The central part is a rolled up length of celluloid with resistance material or condenser plated interwound. Small metal tabs are included that stick out the ends of the tube as it's rolled and are connected to the resistance/ condenser plate. The metal tabs are then folded over and into the tube whereby when the metal end caps are pushed into the tube they connect with the tabs.
On the one I took to bits these tabs had corroded away hence the capacitor was O/C. All the resistors and Caps are O/C so I can't measure anything.
The components are not marked with values just NATIONAL 1 or 2 or 3 etc.
Hence my question:-
If anyone has original descriptions of what the NATIONAL numbering system means and their correlated values?
Thanks Dave

[PJL]

The resistors should be around 1M ohms but will almost certainly be open-circuit. The capacitors just might still work but have you got a meter to measure them? None of the values will be critical.

Interesting set BUT those rivets look like a very poor connection method and you will need to check continuity.

[thevalveset]

HI yes, there are several versions of this baseboard and the resistors range from 0.25M through 1M, 2M and even 3M so whether the manufacturers developed the circuit values as they went along I don't know.
But whilst I can guesstimate the values I hoped someone out there actually knew what they really were and what the NATIONAL numbers mean?
The capacitors are more of a mystery as they are all open circuit due to their lead-out foils having corroded away.
Yes the rivets were badly corroded which is why I drilled out every one, removed all the brass strips, pickled them in HP sauce and then re-rivetted them with brand new tubular rivets. I also re-manufactured every valve socket and re riveted those back in place so all connectivity is restored.
The interstage tfms needed repair and I rewound the HF chokes.
Just need to know what to secrete inside the passive components to complete the set.
I have just finished building a Gecophone BC2001 from scratch making every last bit. Knobs, valve holders, variometer (including the paxolin tube), reactance unit, tuning condenser, fixed capacitors, panels, sockets ..... (everything except the valves and BTC) so this restoration is a doddle ...LOL
Pictures attached.
Enjoy...Dave

[thevalveset]

Other than these pesky component values of course.
Thanks in anticipation,
Dave

[PJL]

I guess you found this? http://www.historywebsite.co.uk/Muse...y/Symphony.htm

The 'National' identity numbers would most likely have been to keep the values a trade secret so I suspect there is not much hope of getting an answer!

[thevalveset]

HI, Yes thanks for the link to the Symphony site I have been in touch with the owner several times regarding this wireless restoration.
I agree that National probably used incognito components to either foil industrial espionage or just make it easy for factory workers to place the right parts in the right locations without needing to understand electronic nomenclature?

I have however made some progress.
By making a 'disassembly' jig I have managed to non-destructively take the components apart.
I have discovered that the 'lead out' tabs (as mentioned in the patent) had corroded and become insulated from the nickel plated end caps. (I just hoped that the opposite ends of the lead out tabs were still in electrical contact with the inner 'works' of the component).
As it turned out they were, and with careful cleaning of the corroded tab remnants it was possible to reconnect to the part.
My measurements are as follows.

Condensers:-
NATIONAL 1 = 300pF
NATIONAL 2 = 1000pF (1nF)
NATIONAL 4 = 10,000pF (10nF)

The resistors are not so conclusive as their construction relied on a pencil line of conductive ink on a paper strip and may have degraded with age?

Resistors:-
NATIONAL 5 = 2.5M Ohms (or 1.5M Ohms see below)
NATIONAL 6 = 2.0M Ohms
The National 5 on my second chassis only measures 1.5M Ohms

These capacitor values seem in keeping with the expected values 'guesstimated' by correspondents replying here, so thanks everyone for your thoughts. I am not quite sure what to make of the resistor values as schematics from different wireless sets using the same chassis also don't agree between vendors.
I hope my investigations prove useful to others out there who have puzzled over the NATIONAL numbers game? And I look forward to hearing my National portable wireless set bursting back into life after lying dormant for 80 years or more.
Thanks once again.......
Dave