[Collins] KWM-2A help additional

[Dr. Gerald N. Johnson]

The crystals must be replacements because by '74 it should be a meatball 
emblem or Rockwell. Meatball for sure because that change happened about 
'65. Which mechanical filter does it have? Y case or FA case?

73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association

On 9/19/2010 4:31 PM, Al Parker wrote:
> Hi agn, Jerry et al,
> Well, still no joy. My xtals are dated 8/74, and the skem I'm using is
> from a Nov. 60 manual. Both the xtal osc., V13A & cath follower, V2A,
> are 6U8A's, on the skem & on the chassis. I forgot to mention ystdy that
> I'd also re-tightened all ground screws, some were pretty loose. I tried
> a different 6U8A for the osc., and a 6EA8, no dif.
> C65, the 14mc trimmer in the xtal osc. plate peaks at abt 2/3
> capacitance only. As Jerry analyzed, that ckt won't resonate at the LO
> ~3mc signal. I do need to look into L5 & the possibility of a missing
> C26 or problem in that "balancing" ckt because it seems like there's an
> awfully big 3mc component in the output of the mixer. But that may not
> be a causing the problem, because---
> I had earlier been looking at the signal at the grid of the 6CL6 driver
> tube, V8, being 9v p-p @ 7.1mc, & only 2v @ 14.1. I looked back to the
> plate of the previous tube, V7 RF amp, before the C44 coupling cap, and
> find 14v & 10v respectively. There's much more loss at 14 than at 7.
> That made me suspect the driver tube, possibly bad with more grid to
> cathode capacitance, just plain leaky, etc. Swapped in a new 6CL6, no
> noticeable difference. Now maybe I need to look at the tuned ckt there,
> but like C65 at the osc., C115 peaks OK, and the signal at this point is
> pure.
> I may get back into it tonite, but have another job to do in the AM, so
> it might be later tmw b4 I get at it. One thing I do plan to do is cut
> the plate & screen voltages to the finals, and measure actual signal at
> the final grids. It's not enuf now on 14mc to make any grid current.
> I feel close to the problem. I have another driver 6Cl6, maybe try that.
> The fact that all bands above 7mc are very low points away from
> individual band tuned ckts.
> Still need help, thanks for all the thoughts & suggestions.
> 73,
>
> Al, W8UT
> www.boatanchors.org
> www.hammarlund.info
>
> "There is nothing -- absolutely nothing -- half so much
> worth doing as simply messing about in boats"
> Ratty, to Mole
>