Redifon GK203N

[HMV 1120]

Hello,

Would anyone have a round 3-pin AC plug suitable for socket PL6 on the Redifon GK203N exciter (or know what to call it so I can search for one)? I doubt I'll find the matching square plug for socket 2 and plan to insert pins for the handful of connections I need.

Many thanks,

Robert

[G6Tanuki]

It looks to me like it's a white version of the small Bulgin plug/socket.

Google for PX0631

[Herald1360]

It looks like one of these:

https://uk.farnell.com/bulgin/px0631...free/dp/313968

The 50V "rating" relates to the fact that it can be opened without needing a tool, electrically it's mains rated. There is a (more expensive) screwed together right angle alternative.

Should you need a mate for the blue connector, these will fit:

https://www.fclane.com/product-group/gh-lgh-mgh-series

(Various versions of this were (are?) used inside and outside the Siemens MRI magnets I used to work round.)

The rectangular one looks familiar but I can't recall the make. McMurdo maybe?

[Herald1360]

Actually the rectangular one looks like a Belling Lee "Unitor pattern 102" type.

There's a socket (not much help!) offered on Ebay just now.

[HMV 1120]

Thank you all for the help, I have a power plug ordered. I'll report back once first power has been applied.

[Radio Wrangler]

Most of those connections aren't very interesting. The thing was designed to terminate phone lines for audio input.

I drilled a hole in the front panel of mine to sneak in microphone/PTT connector to make it a lot more house-trained.

As it stands, it probably does USB only with a filter offset from the carrier. I found some of the opposite sideband filters, correctly offset, so I added a relay and added a tiny switch to the panel.

Output is 100mW, so the Chris Honey 10W PA will work with it.

David

[HMV 1120]

So, the plug arrived and a cable made up. Output terminated into 50 ohms and power applied.


Nothing. Not even the panel lamp which doubles as a pilot light. All fuses show continuity. I connect a power meter inline to the ac and see that no current is being drawn in either the STANDBY or ON positions of the power switch.

Probing the transformer reveals no AC at it's input terminals. After scratching my head and looking at the diagram, it appears incoming live and neutral makes it's way to FUSE 1 and FUSE 2 via SOCKET 40. I can't find any reference in the manual to SK40 other than it's location on the panel (see attached)and the component details 10 way PYE M10SN LW LR. A matching PLUG 40 (PYE M10P LS H19C) is given in the component listing but no details on it's purpose or wiring.

My guess is that SK40 is part of a wiring harness that allows multiple redundant drive units to be selected from the control panel of a transmitter, and PL40 should be inserted for stand alone operation.

Probing SK40 shows AC mains between points A-C.

My guess then is that PL40 connects:

Mains input:
A-B LIVE
C-D NEUTRAL

L-K 20 V output
E-J 5 v output

I don't suppose anyone has a usable GK203N who could check the connections on PL40?

[HMV 1120]

Having been away with work for a month I came back to this today. The correct arrangement for SK40 is shown below if anyone else finds themselves in the same situation, I simply used cut off component leads.These pins carry live A/C mains regardless of the power switch setting and must be insulated.

With this done we have power, lock and about 150 mW of output showing. I have an IRF150 based amplifier that should pair nicely and produce somewhere around 8-10 watts output, so it's time to make up an 80 meters low pass filter. Then I need to find some suitable pins to connect up the microphone and PTT.

[HMV 1120]

Further progress has been made on the Redifon set. Conventional AM DSB is operating but with rather strangled audio. In MCW (A2A) mode the carrier is modulated via a 1020 hz tone that passes through a filter with a sharp cut-off above 1.5 khz. This filter should be bypassed during AM operation and the audio given a 3 khz cut-off. Unfortunately it remains permanently switched in regardless of the mode setting. This may yet prove to be a poor wafer contact on the mode switch, but access is difficult.

Audio bandwidth in USB modes is in spec as this makes its way to the 3 khz filter via a different route. Initially the various upper side band modes all gave very low output - C. 30 mW PEP rather than the minimum 100 mW. This was easily rectified as the USB output potentiometer was found to have been set to it's minimum value. We appear to have suffered at the hands of the phantom twiddler! Likewise the carrier re-insertion control had been set to minimum, adjusting this restored AM-Compatible operation (A3H - upper side band and carrier), my primary aim.

Operation in conjunction with the QRPLabs IRF150 linear amplifier has proved satisfactory, with the drive adjusted to give 4.5 watts of carrier, leaving plenty of headroom for the modulation. The audio response rolls off above 2.8 khz and best described as 'communications' quality - this is no AM broadcast system! The built-in VOGAD compressor-limiter is quite punchy, aggressive even, probably not a bad thing given the limited power level.

[Radio Wrangler]

The VOGAD system uses a balanced pair of long strings of diodes as current-controlled resistors to vary audio gain. These things were used for ship/shore telephone links and plain ship/shore radio, so audio quality was not a priority.

Mine didn't need a mains link to work. Had someone already bridged it, or was it an option?

If using with a power amp, then adding a set of lowpass filters after the PA is a good precaution. Redifon did a range of power amps for their exciters up to the kW region.

David

(The hitch-hikers guide to radio has this to say about VOGAD constructors...)

[Herald1360]

Vogon, surely

[paulsherwin]

On topic please.