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Old 26th August 2006, 10:39 PM   #1
Klimon is offline Klimon  Belgium
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Default Identifying weird signal transformer

I'm trying to identify a pair of signal transformer rescued from a Philips studio preamps (e80cc & e80f tubes, for phono / tape /mic.?) Checked the Lundahl website to compare taps, prim. and sec. impedances, no close match, a phono step-up x-former came closest .-- It would be great if someone could back up that clue or tell me more about their possible application. they're about EI60 block size:

-- 3 primary(?) windings: 16 / 13 /160ohms (the first two windings were connected in series in the original amps; the resulting two windings were both used = four wires coming out)

-- 3 secondary (?) windings: 160 / 425 / 2100 + ct. (Only the third winding was used + it's centertap = three wires coming out)



Cheers,

Simon
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Old 27th August 2006, 10:44 PM   #2
EC8010 is offline EC8010  United Kingdom
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If it came out of a studio it's not going to be for phono or tape, but it might well be a microphone transformer. When you say "impedances" do you genuinely mean that, or do you actually mean measured DC resistances?
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Old 28th August 2006, 11:00 AM   #3
Klimon is offline Klimon  Belgium
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Hi EC8010,

It's actually the measured DC resistances . You're probably imagining a recording studio but the amps came from a radio studio that used a big tapedeck (old-style) and most probably a couple of turntables. The opts aren't shielded in a mu-metal can, just a screentap on the 'secondary side', maybe this rules out phono? The amps also had input transformers (small shielded boxes) meaning that these are probably something else - opts.

Simon
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Old 28th August 2006, 11:44 AM   #4
EC8010 is offline EC8010  United Kingdom
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As it happens, I used to be a broadcast engineer, so I was thinking in terms of a radio or television studio. The principle is still the same. Broadcasters don't distribute funny little signals from tape heads or cartridges. They always put the special electronics needed in the same crate and distribute a line level signal. From the further information you've given, I would guess that the unshielded transformers are output transformers from a line send amplifier - probably using a push-pull transistor output stage. There were an awful lot of those around. The smaller screened transformers are the input transformers.

It's unusual for microphone amplifiers to exist outside a desk, but not unheard of. Radio stations tend to take a lot of feeds from outside, so the amplifiers might be line receive amplifiers. At the BBC, that meant a fixed gain of 45dB with 600R input impedance and low output impedance. Within a studio centre, there were ring main amplifiers for distributing signals to offices, and these had a gain of 0dB with high input impedance (18k) and low output impedance (3R). Line send amplifiers had 10dB of gain and were high input impedance (18k) and 600R output impedance.

I tried to find domestic uses for broadcast transformers but they really were very specific to their intended purpose. I'm afraid the DC resistance tells you very little - what you really need is to apply 1kHz at about 100mV and measure what comes out to determine the turns ratios.
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Old 28th August 2006, 12:50 PM   #5
Klimon is offline Klimon  Belgium
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Thanks, that brings me a little closer. There weren't any transistors in the amps, IIRC an e80f driver tube and two e80cc. I'll try to test them myself following your guidelines.

Simon
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