[ARC5] [Bulk] BC456 vs MD7 modulation

[Tim]

No expert here:  but as to "tuning", I think Walt Hutchins in an ER article
pointed out the HF tuning challenge in a folding-wing Naval aircraft may be
different than in a conventional aircraft.  Pre flight tune up on a hanger
deck or crowded flight deck versus in-flight "ground plane" configuration?

Tim
N6CC

On Tue, Oct 14, 2014 at 9:35 AM, Jack Antonio <scr287 at att.net> wrote:

> On 10/14/2014 11:37 AM, J Mcvey via ARC5 wrote:
>
>> I noticed that one of the differences between the two is that the BC456
>> is a single tube  class A and the MD7 is AB.
>> Is there a noticeable difference in the AM modulation?  One wonders why
>> the change was made.
>>
>
>  Was it cost, or power conservation /efficiency?
>
>
> As far as the what, the AN/ARC-5 transmitters are plate modulated,
> the ATA and SCR-274N transmitters are screen modulated. Thus the
> requirement for the push pull modulator in the MD-7/ARC-5
>
> The AN/ARC-5 was the Navy driven "new and improved" version of the ATA and
> ARA sets, and started showing up in the middle of the war.
>
> Why they made the change? I'd like to see some hard evidence as to the
> reason the changes were made, but the following is a guess on my part:
>
> The ATA and SCR-274N manuals take great pains to stress that
> transmitter tune up is to be made in CW mode, and to *not* retune
> the transmitter for maximum power in voice as this results in
> poor modulation.
>
> I speculate that in practice in the field, this item was overlooked
> and the Navy wanted to eliminate that possible error.  Like I said,
> this is a guess on my part, and I would like to see some hard
> evidence on the matter.
>
> The transmitter components of the AN/ARC-5 are not plug compatible
> with their corresponding ATA and SCR274N counterparts. I have seen
> it said that the larger plug on the AN/ARC-5 transmitters is to
> accommodate the higher peak voltages involved, but I surmise that
> another important reason was to prevent the inadvertent mixing of
> ATA and AN/ARC-5 components in the field. After all, they do *look*
> almost identical, and I would guess that both ATA and AN/ARC-5 systems
> were both in use during the latter half of the war.
>
> Jack Antonio WA7DIA/4
>
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