[Hallicrafters] SR-2000 performance issues

[k0ewu at juno.com]

HI ALL, my experience is that any aluminum chassis and some plated as
many H-C rigs
are may be susceptible to the dreaded hgh resistance grounds.
Sets using riveted socket mounting rings and solderable chassis get the
100
watt soldering iron treatment, solder the ring to the chassis. in the
case
of an aluminum chassis and rivets things get more complicated, either
drill out the rivets (messy job) or do as I do and that is to drill a
very small hole through 
the tube socket flange and the chassis, the size to allow a number 3 self

tapping screw to anchor the socket to the chassis.
This will provide a permanent ground for the socket ring.
I found this out the hard way, in 1956 when the tv station I was with
developed 
"hum bars" rolling thru the TV screen.
It was very hard to isolate this but by substitution of tubes ( a hot
swap)
it was found that a low level rf stage was picking up a few milivolts
from the heater groud and since a grid resistor was grounded to the same
ring it was modulating
 the signal, I grounded the whole bunch of tubes in the modulator.
It was a GE 5 kw tx.  I sent the data to GE, they made aa field mod to
several
 of the rigs.
sorry for such a long winded thing but this is a common problem with our
old boat anchors.
        old jack


On Fri, 19 Aug 2005 10:10:01 -0500 "Jim Liles" <james.liles at comcast.net>
writes:
> Just want to pass along a heads up regarding radios that include an 
> aluminum or other than steel chassis.  We just finished restoring 
> and de-bugging an SR-2000 finding two things that seem to be a 
> problem on the SR-2000 and all of the radios that are built with a 
> non-steel chassis.  The use of the mounting ring for the tube socket 
> for a ground is risky, even though they used a star washer between 
> the ring and chassis.  We found three rings with resistance readings 
> to ground of from 3 to 10 ohms.  This caused low level ripple on all 
> circuits that used the ring for ground reference.  In our case, the 
> noise blanker performed poorly at best and was intermittently 
> non-functional.  We sprayed oxy on the washers and tapped them just 
> enough to turn slightly and 0 ohms was the result with no ripple.  
> The second problem was that the 20 meter band seemed to under 
> perform the 15 and 10 meter bands.  The SR-2000 and SR-400 use a 15 
> ohm resistor in series with the 56PF capacitor in the heterodyne 
> oscillator output tank.  We have found this resistor to be 
> significantly high in all cases usually 25-30 ohms.  The specs on 
> that resistor should be ~<15ohms.  We found 9 other manufacturing 
> bugs that were simply sloppy workmanship.  Is there an SR-2000 
> interested parties list anywhere?  Regards Jim K9AXN       
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