FM through a 1930’s Pye MM Transportable – Can it be done? - UK Vintage Radio Repair and Restoration Discussion Forum

SurreyNick · 14th Aug 2019, 12:07 pm

My next project is the restoration of a Pye MM Transportable, which is a mains operated 2-band TRF receiver from the early 1930's. However, I’d like to find a way to use the existing circuitry to play Radio 2 through it, which of course is broadcast on FM, while preserving the radio’s functionality and originality.

No provision is made for an external speaker and I appreciate the audio frequency signal chain and the existing speaker is probably not capable of reproducing higher frequencies so I may have issues with quality and volume. But the trader sheet does indicate that a low impedance 2Ω speaker can be connected across the secondary of T2, so I was wondering if I can exploit this, especially if the existing speaker turns out to be beyond use (I haven’t stripped the receiver down yet).

The receiver also has provision for a gramophone pick-up which I assume provides a high impedance connection directly into the receiver’s audio amplifier and I am wondering is it possible to use this for the connection of an audio device which does pick up FM and perhaps even an iPod, and if so how would I go about doing so to best effect?

PJL · 14th Aug 2019, 3:17 pm

First thing to check is the state of the tuning condenser. These and the knobs are made of monkey metal and are prone to falling to bits in the Pye sets of that period.

This post points you to a few converters https://www.vintage-radio.net/forum/...d.php?t=137154.

You might get better results wiring a small FM receiver to the phono input though but you should make sure the chassis is earthed. There are plenty on ebay and there was a period when cheap mono FM receivers were given away as promotional items. The other option is a bluetooth adaptor that can be used from your mobile phone.

Herald1360 · 14th Aug 2019, 3:20 pm

Should work fine using the PU input. There's no disconnect for the radio front end so you might want to pull the RF valve when using the set as an amplifier. (Or add a discreet switch).

The speaker field is used as a smoothing choke- if that's shot you'll need (at least) an equivalent resistor in its place. With that, the original speaker is lo Z so any 3-4 ohm PM one will work from the transformer secondary.

The psu is interesting- it's a voltage doubler. If the MRs are shot, the usual suspects plus resistors will do. Use fast recovery ones to avoid unwanted RF hash or add 10n caps across slow ones.

Have fun!

Silicon · 14th Aug 2019, 3:32 pm

This radio from 1932 has a number of 'design challenges'.

The volume control is a 350 Ohm variable potentiometer and a variable capacitor on the same spindle. It was designed to change the bias on V1 and alter the reaction coupling.

It may be possible to use the original volume potentiometer if you use the headphone output of a receiver module but some circuit modification will be necessary.

The loudspeaker is an energised or field coil type.

Fortunately it has a 4V heater winding that could be used to provide DC power for a low current FM receiver module.

SurreyNick · 14th Aug 2019, 5:59 pm

Thank you for the prompt replies, and it seems I have more than one option - good news!

The pre-programmed FM-AM converter is an attractive option and I'll have a thorough digest of that thread. By extraordinary coincidence this afternoon I also came across a YouTube video of a Pye MM Transportable with a DAB radio modification and that looks appealing too.

So now I know it can be done I better get to work stripping the receiver down and seeing what I have to work with

14th Aug 2019, 12:07 pm	#1
SurreyNick Heptode Join Date: Apr 2014 Location: Wigton, Cumbria, UK. Posts: 728	FM through a 1930’s Pye MM Transportable – Can it be done? My next project is the restoration of a Pye MM Transportable, which is a mains operated 2-band TRF receiver from the early 1930's. However, I’d like to find a way to use the existing circuitry to play Radio 2 through it, which of course is broadcast on FM, while preserving the radio’s functionality and originality. No provision is made for an external speaker and I appreciate the audio frequency signal chain and the existing speaker is probably not capable of reproducing higher frequencies so I may have issues with quality and volume. But the trader sheet does indicate that a low impedance 2Ω speaker can be connected across the secondary of T2, so I was wondering if I can exploit this, especially if the existing speaker turns out to be beyond use (I haven’t stripped the receiver down yet). The receiver also has provision for a gramophone pick-up which I assume provides a high impedance connection directly into the receiver’s audio amplifier and I am wondering is it possible to use this for the connection of an audio device which does pick up FM and perhaps even an iPod, and if so how would I go about doing so to best effect?

14th Aug 2019, 3:17 pm	#2
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: FM through a 1930’s Pye MM Transportable – Can it be done? First thing to check is the state of the tuning condenser. These and the knobs are made of monkey metal and are prone to falling to bits in the Pye sets of that period. This post points you to a few converters https://www.vintage-radio.net/forum/...d.php?t=137154. You might get better results wiring a small FM receiver to the phono input though but you should make sure the chassis is earthed. There are plenty on ebay and there was a period when cheap mono FM receivers were given away as promotional items. The other option is a bluetooth adaptor that can be used from your mobile phone.

14th Aug 2019, 3:20 pm	#3
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,536	Re: FM through a 1930’s Pye MM Transportable – Can it be done? Should work fine using the PU input. There's no disconnect for the radio front end so you might want to pull the RF valve when using the set as an amplifier. (Or add a discreet switch). The speaker field is used as a smoothing choke- if that's shot you'll need (at least) an equivalent resistor in its place. With that, the original speaker is lo Z so any 3-4 ohm PM one will work from the transformer secondary. The psu is interesting- it's a voltage doubler. If the MRs are shot, the usual suspects plus resistors will do. Use fast recovery ones to avoid unwanted RF hash or add 10n caps across slow ones. Have fun! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

14th Aug 2019, 3:32 pm	#4
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,169	Re: FM through a 1930’s Pye MM Transportable – Can it be done? This radio from 1932 has a number of 'design challenges'. The volume control is a 350 Ohm variable potentiometer and a variable capacitor on the same spindle. It was designed to change the bias on V1 and alter the reaction coupling. It may be possible to use the original volume potentiometer if you use the headphone output of a receiver module but some circuit modification will be necessary. The loudspeaker is an energised or field coil type. Fortunately it has a 4V heater winding that could be used to provide DC power for a low current FM receiver module.

14th Aug 2019, 5:59 pm	#5
SurreyNick Heptode Join Date: Apr 2014 Location: Wigton, Cumbria, UK. Posts: 728	Re: FM through a 1930’s Pye MM Transportable – Can it be done? Thank you for the prompt replies, and it seems I have more than one option - good news! The pre-programmed FM-AM converter is an attractive option and I'll have a thorough digest of that thread. By extraordinary coincidence this afternoon I also came across a YouTube video of a Pye MM Transportable with a DAB radio modification and that looks appealing too. So now I know it can be done I better get to work stripping the receiver down and seeing what I have to work with