Symphony Radio and Gramophone Company mystery components? - UK Vintage Radio Repair and Restoration Discussion Forum

thevalveset · 15th Feb 2023, 11:21 am

HI,
I am trying to finish off a long running restoration project, namely a 'NATIONAL' 5 valve portable. The set was assembled by The Symphony Radio and Gramophone company in the mid 1920's.
The radio 'chassis' was designed by Plessey and supplied to Symphony as a kit, they sold it as the 'National 5' portable radio.
I have managed to restore most of the set back to almost original condition and the 'chassis' is almost complete.
As you can see, the passive components are quite unusual looking, resembling 'festoon lamps' with 6BA screw fixings at each end.
The mystery is the values of these components as they are just marked NATIONAL 1 or 2 or 3,4,5,6 etc with no indication if they are even capacitors or resistors!
Clearly from the schematic one can determine which is which but not necessarily the value.
As you can see from the 'Layout' (attached) I have determined most of the values but NOT the V2 Grid leak value.
I had 2 of these chassis and fortunately they had a different 'mix' of NATIONAL and DALY components. The Daly ones do have the component value printed on them. Sadly both V2 grid leaks are both NATIONAL 5's.

Any information regarding components marked just as NATIONAL 5 etc seems to be lost from mankind. I feel it would be great for future wireless enthusiasts to get this mystery solved whilst there is still time.

Whilst I realise that grid leak resistors are not too critical, as a purist restorer I want to attribute the correct value to the marking on the outside of the component I am re-stuffing.
I think that the value may be 3M Ohms but for the sake of correctness I would hope that out there somewhere there are other surviving examples of this set that may have the answer?

Finally I know that the Marconi 55 used an almost identical chassis but not necessarily using the same values.
Do you have one of these National sets?
Does it have a Daly (value identified) resistor in this position?
Thanks in anticipation
Dave

Mr 1936 · 15th Feb 2023, 12:45 pm

Hi

The favourite available values of Grid Leak from that era (Also used sometimes as anode loads) were 0.5 Megohm, 1 Megohm and 3 Megohms. Confusingly they are often marked just with a capital 'omega' to indicate megohms.

My best guess would be 1 Megohm for the Detector and 3 Megohms for the Audio amplifier.

No solid information unfortunately, that may be lost in the mists of time.

Cobaltblue · 15th Feb 2023, 1:50 pm

ISTR an article in the BVWS bulletin .

Not sure how detailed it was I will look shortly.

Seems I was mistaken I cannot find any such article

Cheers

Mike T

thevalveset · 15th Feb 2023, 2:11 pm

Hi,
Yes thanks for your swift response.
The grid leak for the audio amplifier was a 2M Ohm on both baseboards. One was a Daly marked 2 Meg. and the other a National unmarked but measured around the same value.
The Symphony Radio and Gramophone companies portable radiogram from the same era used a 3M and a 1M in the positions as you have indicated, but there was definitely a 2M in the audio amplifiers grid.
The front end of the portable radiogram was almost identical to my set though so you are most likely correct about my set.
The V2 grid resistor on one of my baseboards was a Daly one but the pencil marked value was too badly faded to read and it was o/c. The one on the other board was a NATIONAL 5 and measured 2.5M Ohms

I was just hoping that the resistors hadn't bee switched around as there was quite a craze for component sellers (of the day) to try to sell different value grid resistors with wild claims of improved performance. I thought it would be nice to quantify and cross reference all the different NATIONAL marked components for everyone's future reference.
For as you say it seems the 'spell' is lost....

For reference the bodies of the components seem to be made from clear (possibly) nitro-cellulose? DO NOT get them too hot as they 'fizz' in a violent cloud of acrid smoke and disappear!
The labels on the Daly resistors have the value hand written whereas the capacitors are printed.
The trick to getting inside is (as shown in the attached). Gently heat the end cap and pull on the body of the component.
The body begins to soften and releases the end cap.
There are foil strips trapped under the end cap which disappear into the spiral roll of the body. Remove these connecting strips with small pliers, thus disconnecting the original resistive/capacitive elements.
It is then a simple operation to tack an SMT component to the endcap and reassemble the part to look as if it had never been touched.
But will now last forever.
Dave

Gridiron · 15th Feb 2023, 3:46 pm

I've got one of these National portables which I got working some time ago.
On the copy of the circuit diagram I noted that National 5 measured 4.5 Mohms, now I've measured it again it seems to be about 3.9Mohms.
I also have an incomplete chassis, bought for the transformers which were incorrect on the original, National 5 on this is o/c.
Grid leaks of this period don't hold their values very well, so the original value may have been considerably lower.

thevalveset · 15th Feb 2023, 5:01 pm

HI
Thanks for your replies.
Yes I guess its hardly surprising that the values are 'all over the place' considering they are nearly 100 years old.
Interestingly I just disassembled the National 5 resistor that appeared o/c and as I removed one of the brass 'shim' connecting tags, the resistive element pulled out too. (see attached)
The 'resistive element' appeared to be a carbon 'loaded' strip of card that (judging by its trapezoidal shape) looked as though it had been trimmed to value with scissors?
I measured the resistive card with my DMM and it measured 3M Ohms. Just as Mr 1936 suggested. (though I could get various other values depending on how hard or where I pressed the probes!)
So adding all the evidence I have collected, I fitted a 3M Ohm 1206 SMD resistor inside the casing and reassembled it, and will fit it in the grid circuit of V2 and press on.......
So my investigations seem to suggest that NATIONAL Component values so far, are as follows:-

NATIONAL 1 = 0.0003uF
NATIONAL 2 = 0.001uF
NATIONAL 3 = not present
NATIONAL 4 = 0.01uF
NATIONAL 5 = 3M Ohm
NATIONAL 6 = 2M Ohm

I hope this helps other restorers in the future.
Please feel free to add to the database.

Gridiron, did the set work well, or after all my restoration effort will I be met with disappointment...lol?
Thanks
Dave

Gridiron · 16th Feb 2023, 12:02 pm

It worked fairly well, on LW I could get RTE1 as well as Radio 4, on MW could get the stronger stations although there's not that many left here now!
Reaction helps a lot, although as I remember, fairly critical for best results, the frame aerial needs to be oriented for best results of course.
I will have to give it another try.

15th Feb 2023, 11:21 am	#1
thevalveset Tetrode Join Date: Oct 2007 Location: Nottingham, Nottinghamshire, UK. Posts: 73	Symphony Radio and Gramophone Company mystery components? HI, I am trying to finish off a long running restoration project, namely a 'NATIONAL' 5 valve portable. The set was assembled by The Symphony Radio and Gramophone company in the mid 1920's. The radio 'chassis' was designed by Plessey and supplied to Symphony as a kit, they sold it as the 'National 5' portable radio. I have managed to restore most of the set back to almost original condition and the 'chassis' is almost complete. As you can see, the passive components are quite unusual looking, resembling 'festoon lamps' with 6BA screw fixings at each end. The mystery is the values of these components as they are just marked NATIONAL 1 or 2 or 3,4,5,6 etc with no indication if they are even capacitors or resistors! Clearly from the schematic one can determine which is which but not necessarily the value. As you can see from the 'Layout' (attached) I have determined most of the values but NOT the V2 Grid leak value. I had 2 of these chassis and fortunately they had a different 'mix' of NATIONAL and DALY components. The Daly ones do have the component value printed on them. Sadly both V2 grid leaks are both NATIONAL 5's. Any information regarding components marked just as NATIONAL 5 etc seems to be lost from mankind. I feel it would be great for future wireless enthusiasts to get this mystery solved whilst there is still time. Whilst I realise that grid leak resistors are not too critical, as a purist restorer I want to attribute the correct value to the marking on the outside of the component I am re-stuffing. I think that the value may be 3M Ohms but for the sake of correctness I would hope that out there somewhere there are other surviving examples of this set that may have the answer? Finally I know that the Marconi 55 used an almost identical chassis but not necessarily using the same values. Do you have one of these National sets? Does it have a Daly (value identified) resistor in this position? Thanks in anticipation Dave Attached Thumbnails

15th Feb 2023, 12:45 pm	#2
Mr 1936 Heptode Join Date: Mar 2017 Location: Romsey, Hampshire, UK. Posts: 521	Re: Symphony Radio and Gramophone Company mystery components? Hi The favourite available values of Grid Leak from that era (Also used sometimes as anode loads) were 0.5 Megohm, 1 Megohm and 3 Megohms. Confusingly they are often marked just with a capital 'omega' to indicate megohms. My best guess would be 1 Megohm for the Detector and 3 Megohms for the Audio amplifier. No solid information unfortunately, that may be lost in the mists of time.

15th Feb 2023, 1:50 pm	#3
Cobaltblue Moderator Join Date: Dec 2010 Location: Exeter, Devon and Poole, Dorset UK. Posts: 6,865	Re: Symphony Radio and Gramophone Company mystery components? ISTR an article in the BVWS bulletin . Not sure how detailed it was I will look shortly. Seems I was mistaken I cannot find any such article Cheers Mike T __________________ Invisible airwaves crackle with life or at least they used to Mike T BVWS member. www.cossor.co.uk Last edited by Cobaltblue; 15th Feb 2023 at 2:04 pm. Reason: Mistaken

15th Feb 2023, 2:11 pm	#4
thevalveset Tetrode Join Date: Oct 2007 Location: Nottingham, Nottinghamshire, UK. Posts: 73	Re: Symphony Radio and Gramophone Company mystery components? Hi, Yes thanks for your swift response. The grid leak for the audio amplifier was a 2M Ohm on both baseboards. One was a Daly marked 2 Meg. and the other a National unmarked but measured around the same value. The Symphony Radio and Gramophone companies portable radiogram from the same era used a 3M and a 1M in the positions as you have indicated, but there was definitely a 2M in the audio amplifiers grid. The front end of the portable radiogram was almost identical to my set though so you are most likely correct about my set. The V2 grid resistor on one of my baseboards was a Daly one but the pencil marked value was too badly faded to read and it was o/c. The one on the other board was a NATIONAL 5 and measured 2.5M Ohms I was just hoping that the resistors hadn't bee switched around as there was quite a craze for component sellers (of the day) to try to sell different value grid resistors with wild claims of improved performance. I thought it would be nice to quantify and cross reference all the different NATIONAL marked components for everyone's future reference. For as you say it seems the 'spell' is lost.... For reference the bodies of the components seem to be made from clear (possibly) nitro-cellulose? DO NOT get them too hot as they 'fizz' in a violent cloud of acrid smoke and disappear! The labels on the Daly resistors have the value hand written whereas the capacitors are printed. The trick to getting inside is (as shown in the attached). Gently heat the end cap and pull on the body of the component. The body begins to soften and releases the end cap. There are foil strips trapped under the end cap which disappear into the spiral roll of the body. Remove these connecting strips with small pliers, thus disconnecting the original resistive/capacitive elements. It is then a simple operation to tack an SMT component to the endcap and reassemble the part to look as if it had never been touched. But will now last forever. Dave Attached Thumbnails

15th Feb 2023, 3:46 pm	#5
Gridiron Heptode Join Date: Apr 2010 Location: West Midlands, UK. Posts: 662	Re: Symphony Radio and Gramophone Company mystery components? I've got one of these National portables which I got working some time ago. On the copy of the circuit diagram I noted that National 5 measured 4.5 Mohms, now I've measured it again it seems to be about 3.9Mohms. I also have an incomplete chassis, bought for the transformers which were incorrect on the original, National 5 on this is o/c. Grid leaks of this period don't hold their values very well, so the original value may have been considerably lower.

15th Feb 2023, 5:01 pm	#6
thevalveset Tetrode Join Date: Oct 2007 Location: Nottingham, Nottinghamshire, UK. Posts: 73	Re: Symphony Radio and Gramophone Company mystery components? HI Thanks for your replies. Yes I guess its hardly surprising that the values are 'all over the place' considering they are nearly 100 years old. Interestingly I just disassembled the National 5 resistor that appeared o/c and as I removed one of the brass 'shim' connecting tags, the resistive element pulled out too. (see attached) The 'resistive element' appeared to be a carbon 'loaded' strip of card that (judging by its trapezoidal shape) looked as though it had been trimmed to value with scissors? I measured the resistive card with my DMM and it measured 3M Ohms. Just as Mr 1936 suggested. (though I could get various other values depending on how hard or where I pressed the probes!) So adding all the evidence I have collected, I fitted a 3M Ohm 1206 SMD resistor inside the casing and reassembled it, and will fit it in the grid circuit of V2 and press on....... So my investigations seem to suggest that NATIONAL Component values so far, are as follows:- NATIONAL 1 = 0.0003uF NATIONAL 2 = 0.001uF NATIONAL 3 = not present NATIONAL 4 = 0.01uF NATIONAL 5 = 3M Ohm NATIONAL 6 = 2M Ohm I hope this helps other restorers in the future. Please feel free to add to the database. Gridiron, did the set work well, or after all my restoration effort will I be met with disappointment...lol? Thanks Dave Attached Thumbnails

16th Feb 2023, 12:02 pm	#7
Gridiron Heptode Join Date: Apr 2010 Location: West Midlands, UK. Posts: 662	Re: Symphony Radio and Gramophone Company mystery components? It worked fairly well, on LW I could get RTE1 as well as Radio 4, on MW could get the stronger stations although there's not that many left here now! Reaction helps a lot, although as I remember, fairly critical for best results, the frame aerial needs to be oriented for best results of course. I will have to give it another try.