EMI audio transformers - UK Vintage Radio Repair and Restoration Discussion Forum

Retrotechie · 17th Nov 2020, 11:13 pm

Hi, just wondering if anyone has any info on these transformers.

I have attached two photos of each type, and have two of the first type and five of the second type. These may have been used in EMI TR tape recorders or even a mixing desk.

Thanks,
Retrotechie

knobtwiddler · 21st Nov 2020, 5:21 pm

EMI made a plethora of items, to the extent that it can be very difficult indeed to find data on some items, unless you literally have a contact who has datasheets or connections with ex-employees.

Have you tried working out the turns ratios and general configurations? Simply knowing ratios could be quite revealing as to where a TF was used. Of course, you can get deeper and work out primary inductance and what kind of Z they're designed to work with, but you may get some indications by simply knowing the ratio and general primary / secondary topology.

You should be careful about letting these get into the wrong hands! Assuming they have fairly conventional audio specs, there are charlatans out there who may try and cobble them together with other obscure 'EMI' parts, and sell the creation as a 'rare EMI preamp / EQ' or similar. I have definitely seen more than a few 'EMI' items over the years with questionable provenance. If a part has been used in one of the mixing desks, it could be highly sought after.

Ed_Dinning · 21st Nov 2020, 8:20 pm

Possibly audio coupling transformers, normally low power and used with balanced feeds to break hum loops; almost certainly using a high Ni content lam, so quite expensive to make.
Would probably work well with a lo Z mike.

Ed

yestertech · 24th Nov 2020, 1:49 pm

The first one is definitely from one of EMIs REDD units or mixing desks
A similar one can be glimpsed in this youtube video about 5'10 in :

www.youtube.com/watch?v=zrHtmCyZYA0

The 'RSA' designation would suggest 'Response Selection Amplifier' so used somewhere in the EQ/equaliser section of the desk.
Extremely high quality of course and likely to be of low or 1:1 ratio designed for balancing input or output at other than mic.level.

Andy

PS the guys at Chandler will probably know more : https://chandlerlimited.com/

knobtwiddler · 24th Nov 2020, 3:11 pm

If it has the same code as one used on the Redd console it will potentially be extremely sought after. If Chandler make you an offer for it, you'll know why!

I stand by my comment about someone cobbling together a preamp or EQ out of EMI-branded components and trying to sell it on Ebay for a 4-figure sum. This really happens. There are plenty of rarities out there and few have the knowledge to prove provenance, which gives plenty of scope for hustlers.

knobtwiddler · 24th Nov 2020, 3:28 pm

NB - It'd be lots of fun to connect the TFs to an audio analyser and watch the harmonic distortion change with level / load, as well as the frequency response. You could also see how well the shielding keeps 50Hz hum at bay. Modern TFs use expensive alloys for this purpose. I wonder what EMI were using?

Retrotechie · 1st Dec 2020, 9:16 pm

Many thanks for the responses. I do have a contact at Abbey road but don’t like to bug him too much.
Chandler sounds like a good bet.
I haven’t done any checks on the transformers. They belonged to my late father & have been stored for about 40years.

17th Nov 2020, 11:13 pm	#1
Retrotechie Pentode Join Date: Apr 2011 Location: Bromley, Kent, UK. Posts: 234	EMI audio transformers Hi, just wondering if anyone has any info on these transformers. I have attached two photos of each type, and have two of the first type and five of the second type. These may have been used in EMI TR tape recorders or even a mixing desk. Thanks, Retrotechie Attached Thumbnails

21st Nov 2020, 5:21 pm	#2
knobtwiddler Octode Join Date: Mar 2016 Location: London, UK. Posts: 1,046	Re: EMI audio transformers EMI made a plethora of items, to the extent that it can be very difficult indeed to find data on some items, unless you literally have a contact who has datasheets or connections with ex-employees. Have you tried working out the turns ratios and general configurations? Simply knowing ratios could be quite revealing as to where a TF was used. Of course, you can get deeper and work out primary inductance and what kind of Z they're designed to work with, but you may get some indications by simply knowing the ratio and general primary / secondary topology. You should be careful about letting these get into the wrong hands! Assuming they have fairly conventional audio specs, there are charlatans out there who may try and cobble them together with other obscure 'EMI' parts, and sell the creation as a 'rare EMI preamp / EQ' or similar. I have definitely seen more than a few 'EMI' items over the years with questionable provenance. If a part has been used in one of the mixing desks, it could be highly sought after.

21st Nov 2020, 8:20 pm	#3
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: EMI audio transformers Possibly audio coupling transformers, normally low power and used with balanced feeds to break hum loops; almost certainly using a high Ni content lam, so quite expensive to make. Would probably work well with a lo Z mike. Ed

24th Nov 2020, 1:49 pm	#4
yestertech Nonode Join Date: Dec 2002 Location: Coulsdon, Surrey, UK. Posts: 2,130	Re: EMI audio transformers The first one is definitely from one of EMIs REDD units or mixing desks A similar one can be glimpsed in this youtube video about 5'10 in : www.youtube.com/watch?v=zrHtmCyZYA0 The 'RSA' designation would suggest 'Response Selection Amplifier' so used somewhere in the EQ/equaliser section of the desk. Extremely high quality of course and likely to be of low or 1:1 ratio designed for balancing input or output at other than mic.level. Andy PS the guys at Chandler will probably know more : https://chandlerlimited.com/

24th Nov 2020, 3:11 pm	#5
knobtwiddler Octode Join Date: Mar 2016 Location: London, UK. Posts: 1,046	Re: EMI audio transformers If it has the same code as one used on the Redd console it will potentially be extremely sought after. If Chandler make you an offer for it, you'll know why! I stand by my comment about someone cobbling together a preamp or EQ out of EMI-branded components and trying to sell it on Ebay for a 4-figure sum. This really happens. There are plenty of rarities out there and few have the knowledge to prove provenance, which gives plenty of scope for hustlers.

24th Nov 2020, 3:28 pm	#6
knobtwiddler Octode Join Date: Mar 2016 Location: London, UK. Posts: 1,046	Re: EMI audio transformers NB - It'd be lots of fun to connect the TFs to an audio analyser and watch the harmonic distortion change with level / load, as well as the frequency response. You could also see how well the shielding keeps 50Hz hum at bay. Modern TFs use expensive alloys for this purpose. I wonder what EMI were using?

1st Dec 2020, 9:16 pm	#7
Retrotechie Pentode Join Date: Apr 2011 Location: Bromley, Kent, UK. Posts: 234	Re: EMI audio transformers Many thanks for the responses. I do have a contact at Abbey road but don’t like to bug him too much. Chandler sounds like a good bet. I haven’t done any checks on the transformers. They belonged to my late father & have been stored for about 40years.