[Milsurplus] AN/SRT-4A Marine Transmitter

[AKLDGUY]

Interesting observations on beam tubes as oscillators. What about when the
screen is strapped to the plate, effectively turning it into a triode? Or
did you mean that too?

Neil ZL1ANM


On Friday, August 17, 2018, Kenneth G. Gordon <kgordon2006 at frontier.com>
wrote:

> On 16 Aug 2018 at 9:53, Richard wrote:
>
> > After a bit of thought I've resolved to restore it to original
> > condition.  The 807 oscillator only passes 18 to 20 ma, so if regulation
> > is needed it can be easily done with VR tubes or a handful of Zeners.
> > Looking back, many "surplus conversions," and changes, were ill-advised
> > to downright destructive.
>
> You will get zero argument from me on that issue!!!
>
> IMHO, MOST ham-mods were never well thought-out and actually make the
> involved
> equipment work WORSE afterwards.
>
> Any "upgrade" to older gear (should one feel so inclined) must be
> cogitated on for months
> and every possible event and effect, foreseen and unforeseen, taken
> carefully into account.
> Terman's is a valuable resource for this.
>
> The OT weren't stupid.
>
> I will venture this, though: beam-tubes do NOT make good oscillators.
> There is much too
> much inherent coupling between the cathode and/or grid, and the plate,
> essentially
> bypassing the screen grid, if there is one. I could never understand why
> those were so often
> used. If one "needed" a tube the size of the 807 for an oscillator, the
> much better (as an
> oscillator) 837 should have been used....like the Navy used in so many
> transmitters.
>
> Although the plate dissipation rating of the 837 is about 1/2 that of the
> 807, in oscillator use,
> that doesn't matter.
>
> The 802 (almost impossible to find any more) is also an excellent
> oscillator tube. And the
> 6AG7 is most certainly a far better oscillator tube than a 6V6 or even the
> 6L6.
>
> The Navy even used an 860 as the VFO in at least one transmitter. The 803
> would make an
> excellent oscillator/VFO tube, in fact, although it is kinda big. :-)
>
> No beam-tube should ever have been attempted to be used as an ECO. Period.
>
> Ken W7EKB
>
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