[Hammarlund] RE SP600-JX-17

[Richard Knoppow]

----- Original Message ----- 
From: "James A. (Andy) Moorer" <jamminpower at earthlink.net>
To: <hammarlund at mailman.qth.net>
Sent: Saturday, April 05, 2014 8:34 PM
Subject: Re: [Hammarlund] RE SP600-JX-17


> Oh good heavens - that is WAY too, too powerful for 
> alignment. That will light up all the bands - you will 
> hear the signal generator everywhere.
> For alignment, no more than 1 millivolt or so is more than 
> enough. You really want to be careful not to overload any 
> of the stages or you will get images that will drive you 
> nuts. Under no circumstances should you apply more than "a 
> few" millivolts to an antenna input. Don't forget that the 
> maximum overall gain of a sensitive receiver from antenna 
> in to 600-ohm output will be over a million. Easy to 
> overload.
>
> I would suggest making sure that all the bands work 
> properly before trying to align it. They will just fight 
> you and give contradictory or misleading results if some 
> of the bands are not working right.
>
> Enjoy!
> -A
>
> -- 
> James A. (Andy) Moorer
> www.jamminpower.com
>

     I meant to address this: I think the OP was considering 
injecting the IF frequency by means of an induction coil 
wound around the first converter tube. This often works but 
requires a fairly strong signal from the generator. I think 
there are better ways to approach this.
     In general, it is good practice to limit the signal 
used for alignment to a quite low level. You want to run the 
receiver gain as mear maximum as will overcome noise enough 
to get a good adjustment. In receivers with switchable AVC 
its best to do the alignment with the AVC off. The reason 
for this is to eliminate as much as possible any detuning 
effect the AVC bias may have on the tuned circuits. There is 
something called Miller effect, which is an apparent 
capacitance that shows up in tubes that is dependant on the 
tube gain. It is this effect that can result in slight 
detuning. The idea is that you want the sharpest tuning for 
the weakest signals so its best to optimise the tuning by 
using a fairly weak signal for alignment.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com