Transformer or choke and RC unit

[AdrianH]

These are starting to intrigue me, in a bits box is an old transformer of unknown make and a Bullphone radio products RC unit.

The transformer has no label on the top as it is missing, but the three terminals from left to right are :-

HT+, C , P&C1. The terminal on the side is labelled Earth.


Typically around 400 Ohms between HT+ and C and C and P&C1 so 800 Ohms in total, In inductance approx 3.7H per section, but 18H total across HT+ and P&C1. No resistance to Earth, guess it could connect to the laminations or it is open circuit.


The next unit is basically a holder for glass style resistors, grid leak and I am guessing Plate load resistor. Terminals are HT, P, G and GB, guessing grid bias battery? The caps in the unit are not very well when being read with my TC1 so I assume very leaky. Perhaps I should warm the unit up to remove the wax and see what is in there.

I have several caps in Bakelite cases and guess they will all be duff by now all in wax so should be reasonably easy to replace. I have a couple of 4 pin valve holders and valves etc so thinking of adding a 1920/1930's early battery style project to my list of to do's.

If anyone knows details of the two objects I would appreciate the information.

Adrian

[radiograham]

Originally Posted by AdrianH

These are starting to intrigue me, in a bits box is an old transformer of unknown make and a Bullphone radio products RC unit.

The transformer has no label on the top as it is missing, but the three terminals from left to right are :-

HT+, C , P&C1. The terminal on the side is labelled Earth.
Attachment 257006

Typically around 400 Ohms between HT+ and C and C and P&C1 so 800 Ohms in total, In inductance approx 3.7H per section, but 18H total across HT+ and P&C1. No resistance to Earth, guess it could connect to the laminations or it is open circuit.

Attachment 257007
The next unit is basically a holder for glass style resistors, grid leak and I am guessing Plate load resistor. Terminals are HT, P, G and GB, guessing grid bias battery? The caps in the unit are not very well when being read with my TC1 so I assume very leaky. Perhaps I should warm the unit up to remove the wax and see what is in there.

I have several caps in Bakelite cases and guess they will all be duff by now all in wax so should be reasonably easy to replace. I have a couple of 4 pin valve holders and valves etc so thinking of adding a 1920/1930's early battery style project to my list of to do's.

If anyone knows details of the two objects I would appreciate the information.

Adrian

Hi Adrian,i am pretty sure the first is a Telsen tapped output choke.If you google Telsen mag they are all on american radio history website.Dont recognise the second unit i'm afraid. Graham.

[radiograham]

Telsen Mag.

[AdrianH]

Thank you Graham, I will have a good look through that mag.

Adrian

[John M0GLN]

Other than posting this scan from a 1930-31 catalogue showing something similar, I can't offer any other info' about them.

John

[AdrianH]

Thanks John

I have just taken the R.C Unit to pieces, well melted out the bitumen, was really hoping it was a hard wax. Found where the cap was connected.



Looking through the magazine from Graham, I guess it makes building a radio a bit like a Meccano build, bolt things down and wire between the connections.

I have downloaded all six of the Telsen Magazines and will print off and have a good read.

Adrian

[PJL]

The RC coupler was a low cost alternative to an audio intervalve transformer. You will find similar markings for P (plate/anode), HT, G (grid), GB (grid bias battery) on the transformers. The disadvantage with the RC coupling is lower load impedance and loss of gain from the transformer turns ratio.

[The Philpott]

It may have been high grade 'stockholm tar', ie derived from wood not crude.
Dave

[AdrianH]

Originally Posted by PJL

The RC coupler was a low cost alternative to an audio intervalve transformer. You will find similar markings for P (plate/anode), HT, G (grid), GB (grid bias battery) on the transformers. The disadvantage with the RC coupling is lower load impedance and loss of gain from the transformer turns ratio.

Now that makes a lot more sense to me, I was initially thinking of being for just one valve, but as the coupling between two valves makes it much more understandable

Originally Posted by The Philpott

It may have been high grade 'stockholm tar', ie derived from wood not crude.
Dave

OK what ever it is I still wish it was a wax, although I can understand the wax melting within a radio set. I may soak in acetone to remove the remnants of the 'tar', not sure what it will do to the Bakelite.

I have approx 9, 4 pin valves, a couple of holders, some other chokes and variable caps, even what looks like a NOS Cossor 2P output valve, should be able to come up with something as a project.

Adrian

[Refugee]

Stockholm tar has a very strong smell of kippers even if it is just a little smudge around the tin lid.
I know because I have seen and smelt it used in a non electronic setting.

[AdrianH]

Then I think it is bitumen, no particular smell to it.

Acetone not working well may try turps.

Adrian

[The Philpott]

Or wd40. It's bakelite-friendly.

[radiograham]

Hi,the imposing looking building on the front of the telsen mags is still there or it was in early 90s.Not as impressive as on the mags,artistic licence much in evidence.Took me a while to find it nestling under a flyover in aston birmingham.

[AdrianH]

Oh I don't know the building looks OK to me, courtesy of google street maps.



I have been checking out so caps or condensers to give them the term of the time.


All basically short circuit, the best i have managed to recover is a 2 mF but at 180 Volts it has 400uA leakage. So at some point I will melt out the bitumen on them and fit modern internals and then try to reseal.

I have some smaller mica caps that may test OK.
A long term idea for a project I think. time to get on with some smaller projects and get them out of the way.

Adrian

[PJL]

The less messy way to remove bitumen is to freeze it then chip it out, just beware that the bitumen chips don't end up on the carpet as when thawed they stick like tar.

[Ed_Dinning]

Hi Adrian, plenty of designs in the Radiomags to use the parts on, but you will need to build your own baseboard and source some material for the front panel

Ed

[AdrianH]

Thanks PJL and Ed.

Yes there are lots out there, I could do with some interstage transformers but have time to try and find some, it is not an urgent project idea.

Adrian

[AdrianH]

Forgot to add looking through the Telsen magazines, the loudspeaker must have been in the hundreds if not K Ohms range?

Adrian

[radiograham]

Originally Posted by AdrianH

Oh I don't know the building looks OK to me, courtesy of google street maps.

Attachment 257074

I have been checking out so caps or condensers to give them the term of the time.

Attachment 257075
All basically short circuit, the best i have managed to recover is a 2 mF but at 180 Volts it has 400uA leakage. So at some point I will melt out the bitumen on them and fit modern internals and then try to reseal.

I have some smaller mica caps that may test OK.
A long term idea for a project I think. time to get on with some smaller projects and get them out of the way.

Adrian

That look's better than i remember,glad to see it is still there. Graham.

[AdrianH]

Graham as an aside, I found another Matsui remote, pm me your address and I will get it to you.

Adrian