[Hammarlund] SP-600 problem, more data

[James A. (Andy) Moorer]

on 6/28/02 9:06 AM, Wally Gibbons at rockwall@sourceoneinternet.com wrote:

> First, thanks for the comments I've received about my reception problem.
> 
> I've done a little more work on the receiver. I tested the tubes. The
> first 6BE6 mixer was flat. Barely moved the meter on the tube tester.
> BUT prior to replacing I checked the AVC voltage while tuned to the
> local station. 9 volts negative, max.
> 
> I replaced the 6BE6. WOW - big change in AVC. -30 volts now on the same
> station. S-meter almost pins on the station. I don't hear the station
> spread all across the broadcast band now, just near it's frequency. BUT,
> it is now very distorted when tuned to it's frequency....
> 
> So, the next question, is a 150 foot long wire too much for an SP-600?
> I'm thinking this may be the case. 150 feet plus two RF amps, even with
> -30 volts of AVC on the grids the RF amps are probably
> overloaded....more distant stations sound great. This thing was not as
> sensitive as it could have been with the bad 6BE6. It's sure hot now....
> 
> BUT, my R-390 handles a longwire and the local station without overload.
> 
> Any feedback from other SP-600 owners? Do these things overload
> "easily".
> 
> Thanks.
> 
> 
> Wally Gibbons


No, they don't overload "easily" when set to AVC. They do overload easily
when set to MAN, but you should be able to turn it down. It sounds to me
like the AVC isn't working correctly. Probably the 6BE6 had a grid short and
torched one of the parts in the AVC circuit.

When on MAN, can you turn the RF gain down enough to make it sound OK?

If yes, then the AVC voltage is definitely not being generated properly.
Check the 6AL5 AVC V14 - but it could be any of the resistors/capacitors in
the AVC circuit.

If no, then you have other problems. Make sure the AVC voltage gets to all
the appropriate parts - V9, V10, and to a lesser degree V1 and V2.

Since your SP-600 has some AVC voltage on the mixer, I conclude it is the
kind that was set up for optional direction finding, so the AVC voltage is
reduced by a resistor divider before going to V1 and V2. It should show up
at full strength on the grids of V9 and V10.

Hope this helps.


-- 
James A. (Andy) Moorer
Adobe Systems