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Old 17th Jun 2020, 7:12 pm   #1
ian-gm0uhc
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Default CR100/2 help please

I'm currently working on a CR100/2 on behalf of a friend. There is a label on the front saying that it was modified by Hatfield Instruments ... and I think that relates to the EB91 limiter between the Triode and Tetrode audio stages.

However there are one or two areas which do not conform to the circuit diagram.

The Side-Tone Facility has been replaced by what looks like a Mute relay, which will be why R57 is missing. R41 (HF Gain) is wired almost like R57 was, with one end to chassis and the other end going nowhere (with a resistor across it too). Thus it is NOT connected to R40 which itself does NOT appear to be connected to R39 ... and R7 is connected directly to R39 rather than the +80V line via S13 (looks like it was always wired that way).

A lot of the insulation has gone the way of much rubber insulation of the 1940s, so a lot of wires needing replacing. Also, I found a bundle of severed wires behind the phone jacks in the wiring loom. I think about 5 wires in total. These ran round to the rear where they had been severed near the rear terminals. I'm wondering if these might have been the original wires between the phones sockets and audio transformer?

Cheers,
Ian, GM0UHC

Last edited by AC/HL; 17th Jun 2020 at 7:15 pm. Reason: email address removed
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Old 19th Jun 2020, 10:57 am   #2
ian-gm0uhc
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Default Re: CR100/2 help please

Further to my initial post, I have now ascertained that this particular CR100/2 is a very early model, characterised by R7 and R40 being in opposite locations ... which had me scratching my head for a while as I tried to figure out what was original, what was an official mod, what was an unofficial mod and what might be a mistake.

As previously said, this one bears a label saying it was modified by Hatfield Instruments. So far I have not been able to find any documented references to this mod. Clearly the double-diode limiter inserted in the audio-path forms part of Hatfield's mod. And I reckon that the modification to the wiring around the HF-Gain control is their work too (the wiring style is very similar). However there is also a Mute-Relay and a potential divider wired into the Cathode line that I am not sure about. The solenoid is wired to the Side-Tone Facility sockets, which is logical, and the action of the relay is to alter the bias on two of the IF stages ... quite clever too. But the method of mounting the relay, using a case screw, strikes me as a tad unprofessional, since the relay simply falls away as soon as the case is removed.

When it comes to restoring equipment, I'm a stickler for authenticity. So the big, so far un-answered question is this: Does anyone know precisely the extent of the Hatfield Instruments modification to the CR100/2 ? i.e. Is the Mute Relay part of it?

Ian, GM0UHC
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