[R-390] SP600JX17 - drift

[Llgpt@aol.com]

In a message dated 01/09/02 6:01:54 PM, barry@hausernet.com writes:

<< I suppose this really belongs on the Hammarlund list, but here's my 2 cents

worth anyway:


As heavy as the SP-600's are, the chassis are not all that solid.  If you've

ever picked one up wrong, you may have noticed that they can twist a bit.


In addition to the "brace" on that tube shield (why all the quotations

marks, Rod?), there are possibly some other sources of drift as the receiver

warms up, or from vibration.  For example, the RF strip is right over the

turret with all those spring contacts.  If something is loose or that strip

is missing some screws, I suppose that could be a factor -- and lead dress

under there after a repair or recapping job.


Also, the gauge of the sheet metal is not quite as thick as that with the

'390x's which also benefit from the H-frame/modular design.  Even the front

panels on the SP-600's are thinner -- from the half dozen I've seen.


The chassis has six heavy-gauge corner supports -- don't know what else to

call them -- which should be good and tight.  Many of these rx's are missing

their bottom covers -- a medium gauge rectangle of aluminum with six holes

for the screws that mount up to the ends of those supports.  The chassis is

a lot stiffer with the cover in place.  (Hank Arney may still have repro

covers available).


Just theorizing, but it stands to reason, if that tube shield with the brace

is important, then some of the bigger parts underneath it might be too.


Barry

>>

Barry & Group,

I have owned 18 of these fine receivers. The ones which exhibited little or 
no drift were the three John R. Leary Remanufactured SP-600's. Why???

Just as you stated above, the chassis flexes. John noticed this and in most 
of the 40 odd SP-600's be custom rebuilt, he added cross bars for strengthg 
and stability. One that Chuck Rippel aligned for me a couple of years ago sat 
for hours on 10mc's and after a two hour warm up drifted 10 cycles over the 
next hour...I'd say that's pretty stable.

The present one I own was one of John's earlier efforts and doesn't have some 
of the braces the later ones had. It drifts a little more than the previous 
one.

But, I have replaced the hf oscillator tube with a IERC tube shield and 
noticed no difference whatsoever.



 






Les Locklear

" The two most abundant things in the
  universe are hydrogen and stupidity ".

  Harlan Ellison