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Old 22nd Aug 2018, 9:03 pm   #1
Ed_Dinning
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Default R1155 output transformer

Hi Gents, I'm doing some work on a PSU and amp for this set and I see the output is intended to drive headphone, possibly 600 ohm units.

The output transformer in The DDT anode circuit is a 10K/12139, does anyone have any data on this transformer?

Thanks, Ed
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Old 23rd Aug 2018, 1:54 am   #2
Terry295
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Default Re: R1155 output transformer

Hi Ed

I have a friend who did an absolutely wonderful restoration of one of these sets and in the process it was necessary to repair the O/P transformer (I also have one that needs this done but haven't got round to it yet), so I quote from his note to me concerning this part:-

"However, it tells me that there are 2600 turns of 0.07mm wire on the secondary of the L30 audio output transformer. On an original transformer that I had not touched the primary has a DC resistance of 1kOhm and secondary a resistance of 800Ohm. Fortunately you will find the secondary was wound on last so only the top layer of windings needs to be removed.. On the transformers that I rewound there was a layer of tape between the secondary and primary which made it easier to remove the secondary windings without disturbing the primary. The only point of care are the two wire ends out to the contacts. During one of the rewinds I managed to brake the wire once and soldered then taped the join before continuing the wrapping, which seemed to work well. I had to hand tension and sweep the wire across the width of the bobbin as it was being rewound. To do this I wore a leather gardening"

I hope this information is of some use to you.

Regards Terry C
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Old 23rd Aug 2018, 8:54 am   #3
M0FYA Andy
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Default Re: R1155 output transformer

Ed,
AP1086 tells us that 10K/12139 is a Transformer Type 133, with primary inductance 12.5H and DC resistance 1528 ohms, secondary inductance 14H and DC resistance 1063 ohms. No information on wire gauge or number of turns, unfortunately.

Andy
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Old 23rd Aug 2018, 8:05 pm   #4
Ed_Dinning
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Default Re: R1155 output transformer

Hi Gents, many thanks for the info. I had supposed that the transformer was possibly a 6:1 step down to drive 600R phones from a triode valve.
From the figures given it looks to be about a 1.06:1 ratio; I estimate that both winding use the same gauge of wire.

I have found that feeding the headphone output straight into a 6V6 or similar gives a low output. The standard mode was to RC couple the 6V6 from the anode of the set's DDT where there should be a greater voltage swing.
I was hoping to avoid mods to the set so wanted to use the phones output by "reversing" the ratio of this transformer to drive the 6V6 with a higher signal level.

Thanks, Ed
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Old 23rd Aug 2018, 8:16 pm   #5
ms660
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Default Re: R1155 output transformer

Output impedance quoted as 5k and output quoted as Max. 200mW into 5k in the details I'm looking at.

Mine drove a loudspeaker via a bog standard S/E output transformer connected to the 'phones output, was loud enough for me.

Lawrence.

Last edited by ms660; 23rd Aug 2018 at 8:38 pm. Reason: clarification
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