[Milsurplus] Internet info lacking

[AKLDGUY .]

Haven't done it, but there's no reason it couldn't be done. One issue: if
you're going to use the original connector on the back of the SCR-274, be
aware that your plan introduces a risk of breakdown from the center pin
(modulated plate supply) to other pins. Under modulation, the plate voltage
of say 550 VDC gets doubled, which didn't happen in the screen-modulated
SCR-274. The ARC-5 transmitter had wider spaced pins to avoid this issue.

Neil ZL1ANM

On Sat, Sep 28, 2019 at 4:49 AM CL in NC via Milsurplus <
milsurplus at mailman.qth.net> wrote:

> I have been involved with this B17F project and getting the radio gear up
> and running.  We now have a complete and working SCR274 setup as it existed
> in the aircraft, and BC348 that runs on its original dynamotor.  Also have
> the BC375 with all the TU's and BC306 tuner which is mine and intend to
> donate, but holding off as long as possible as I use mine at my QTH.  I
> have a BC191 I was going to use instead at the shack, but tubes are the
> issue.  In addition I have a lot of personal ARC and SCR gear, some working
> some not, but am now putting together a proper SCR 274 set up of my own
> with all controls and cabling, but have hit an issue.  I have an MD7
> modulator, not a BC456 I want to use with the SCR transmitters in their FT
> 226 rack. I don't have an ARC 5 TX rack.  Has anybody used the 274
> transmitter which was intended to be screen modulated with an MD7 plate
> modulator?  I have drawn out the differences, know what the pin out for the
> voltages and controls signals between the
>  two transmitters, and have connectors to adapt them, but, an online
> search did not bring up anybody that has actually done this.  Looks pretty
> straightforward, the ARC 5 had both screen and plate getting modulation,
> the 274 only screen, and there is nothing drastically different in either
> TX.  Anybody hooked these up?  Could consider a swap, MD7 for a BC456.
>
> If anybody has an AN5754 gyro compass amplifier, or a AN 5756 caging
> switch gathering dust on a shelf or sitting under a tarp somewhere, let me
> know.
>
> Charlie, W4MEC  in NC
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