LT supply in early portables - UK Vintage Radio Repair and Restoration Discussion Forum

joe · 16th Mar 2004, 8:04 pm

A recent posting about a McMichael " Duplex four " led me to wonder what was used to energise the filaments.

A table radio would have used a 2volt lead-acid accumulator, but a suitcase portable, which can be carried at 90[sup]o[/sup]to its normal playing position

Did one really carry a jar of sulphuric acid on a picnic, or was there some other means of getting an LT supply for these early portables? ( if 25-30lb is really portable)

Joe

Darren-UK · 16th Mar 2004, 11:46 pm

Hi Joe,

There were several versions of the Duplex Four; three of which were battery ( only ) sets publicised as being 'transportable'. They were not 'suitcase' portables at all, being more like ordinary tabletop radios of an appearance quite typical of their time. Presumably McMichael called them 'transportable' due to their non requirement of a mains supply and for no other reason.

On the subject of accumulators, all battery sets, regardless of size, were effectively transportables. Don't forget that seventy years ago there was far less paranoia over safety than there is today, so accumulators wouldn't have been seen as a problem. It would have been purely down to the common sense of the radio's owner to ensure the accumulator was kept secure and upright.

joe · 17th Mar 2004, 11:05 am

Thanks Darren

Mine is a type S so it really is like a smallish suitcase, but as it is unlikely to leave the house (loft/garage) I won't worry too much.

Joe

Darren-UK · 17th Mar 2004, 3:04 pm

Type S ? not heard of that one

joe · 17th Mar 2004, 5:39 pm

There is an identical one in Radio!Radio! page 127, fig368.

I got it from a guy in Surrey, free, but a £25 donation to Children in Need. It looks as though its not been touched for many years, and although the battery leads are completely rotten there are still two spade connectors floating loose in the battery compartment which look the right size for an accumulator.

Joe

Robert-UK · 17th Mar 2004, 11:19 pm

Returning to Joe's original question ...

Accumulators made for portables from the mid 1920's onwards were usually of the " unspillable " variety, which meant the sulphuric acid electrolyte was made into a sort of jelly. I've no idea what the technology was (gelatine?)

I believe the cases were often bakelite or celluloid to save (a bit) of weight.

Judging from the mess inside some portables I've seen of the period, the term " unspillable " should be loosely interpreted!

Robert

Chris_C · 19th Mar 2004, 3:02 pm

Hi All

This is a recipe for a 'Jelly Electrolyte' taken from Bernards Radio Manual 'Calling Men At War'

A fast setting mixture which jellifies in 10 minutes is prepared as follows:-
1 part pure sodium silicate of specific gravity 1.200 mixed with 3 parts of cold sulphuric acid of 1.400 specific gravity

I don't know of anyone who's tried it.

GMB · 19th Mar 2004, 3:18 pm

Some " unspillable " accumulators just had some kind of wadding into which the acid was soaked. I have in my loft an example of a (fairly) high tension miniature lead-acid accumulator which I think was intended for something military. You had to fill and top up the cells using a hypodermic syringe!

I'm not sure what would happen today if you went down to the local chemist and asked to buy a hypodermic suitable for acid

16th Mar 2004, 8:04 pm	#1
joe Rest in Peace Join Date: Apr 2003 Location: Edgware, North London. Posts: 307	LT supply in early portables A recent posting about a McMichael " Duplex four " led me to wonder what was used to energise the filaments. A table radio would have used a 2volt lead-acid accumulator, but a suitcase portable, which can be carried at 90[sup]o[/sup]to its normal playing position Did one really carry a jar of sulphuric acid on a picnic, or was there some other means of getting an LT supply for these early portables? ( if 25-30lb is really portable) Joe

16th Mar 2004, 11:46 pm	#2
Darren-UK Retired Dormant Member Join Date: Apr 2003 Location: Blackpool, Lancashire, UK. Posts: 4,061	Re: LT supply in early portables Hi Joe, There were several versions of the Duplex Four; three of which were battery ( only ) sets publicised as being 'transportable'. They were not 'suitcase' portables at all, being more like ordinary tabletop radios of an appearance quite typical of their time. Presumably McMichael called them 'transportable' due to their non requirement of a mains supply and for no other reason. On the subject of accumulators, all battery sets, regardless of size, were effectively transportables. Don't forget that seventy years ago there was far less paranoia over safety than there is today, so accumulators wouldn't have been seen as a problem. It would have been purely down to the common sense of the radio's owner to ensure the accumulator was kept secure and upright.

17th Mar 2004, 11:05 am	#3
joe Rest in Peace Join Date: Apr 2003 Location: Edgware, North London. Posts: 307	Re: LT supply in early portables Thanks Darren Mine is a type S so it really is like a smallish suitcase, but as it is unlikely to leave the house (loft/garage) I won't worry too much. Joe

17th Mar 2004, 3:04 pm	#4
Darren-UK Retired Dormant Member Join Date: Apr 2003 Location: Blackpool, Lancashire, UK. Posts: 4,061	Re: LT supply in early portables Type S ? not heard of that one

17th Mar 2004, 5:39 pm	#5
joe Rest in Peace Join Date: Apr 2003 Location: Edgware, North London. Posts: 307	Re: LT supply in early portables There is an identical one in Radio!Radio! page 127, fig368. I got it from a guy in Surrey, free, but a £25 donation to Children in Need. It looks as though its not been touched for many years, and although the battery leads are completely rotten there are still two spade connectors floating loose in the battery compartment which look the right size for an accumulator. Joe

17th Mar 2004, 11:19 pm	#6
Robert-UK Retired Dormant Member Join Date: Nov 2003 Location: Droitwich, Worcestershire, UK. Posts: 52	Re: LT supply in early portables Returning to Joe's original question ... Accumulators made for portables from the mid 1920's onwards were usually of the " unspillable " variety, which meant the sulphuric acid electrolyte was made into a sort of jelly. I've no idea what the technology was (gelatine?) I believe the cases were often bakelite or celluloid to save (a bit) of weight. Judging from the mess inside some portables I've seen of the period, the term " unspillable " should be loosely interpreted! Robert

19th Mar 2004, 3:02 pm	#7
Chris_C Hexode Join Date: Jan 2003 Location: Darlington (DL3) North East U.K. Posts: 394	Re: LT supply in early portables Hi All This is a recipe for a 'Jelly Electrolyte' taken from Bernards Radio Manual 'Calling Men At War' A fast setting mixture which jellifies in 10 minutes is prepared as follows:- 1 part pure sodium silicate of specific gravity 1.200 mixed with 3 parts of cold sulphuric acid of 1.400 specific gravity I don't know of anyone who's tried it. __________________ Chris C G8TJR

19th Mar 2004, 3:18 pm	#8
GMB Dekatron Join Date: Aug 2003 Location: near Reading (and sometimes Torquay) Posts: 3,095	Re: LT supply in early portables Some " unspillable " accumulators just had some kind of wadding into which the acid was soaked. I have in my loft an example of a (fairly) high tension miniature lead-acid accumulator which I think was intended for something military. You had to fill and top up the cells using a hypodermic syringe! I'm not sure what would happen today if you went down to the local chemist and asked to buy a hypodermic suitable for acid