[Milsurplus] AN/SRT-4A Marine Transmitter

[Richard]

Ja Wohl! (yes, certainly)  See "Intrinsic Negative Resistance as a Cause 
of Parasitic Oscillations in Beam Power Tubes," by David Newkirk.  
(search on the title)  They have one-port negative resistance, and are 
hard to tame.  Having had miseries with the 807 I tend to practice Beam 
Power Tube Avoidance.  Well, this set MUST have worked ok, so I will 
give it a try.  On the other hand, many marine transmitters had rotten 
signals...

Richard, AA1P

On 08/16/2018 02:09 PM, Kenneth G. Gordon 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
>