Cascade Toroids and Power

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From: BFlorip@aol.com
Date: Thu Dec 07 1995 - 02:48:20 EST


Hi Fellow QRPers and QRP-Lers,

Wanted to give you people the results of the last few days
of playing with the Cascade.

A few comments have been made about "remove a couple of
turns from your torroids" and it was bothering me to think
someone may try that without a sort-of-rational reason for
picking which torroid to attack...

At least as far as the Cascade (and Sierra) go a good indication
of proper tuning and associated resonance is the position of
the variable capacitors (trimmer caps). On the Sierra Wayne
went to some lengths to make the initial tuning point on the
trimmers the half way point. Don't get me wrong, if you've
tuned up your radio and the trimmers aren't exactly half way
don't worry. The point to worry is when the best amplitude is
when the trimmer is either all the way meshed, or all the way
open.

On my Cascade, I found the 75 Meter band module had two
trimmers in the fully open position. That means the maximum
signal may not be due to resonance, only to the minimum
position on the trimmer.

In each case (and done one at a time) I removed one turn from
the associated torroid and was able to tune for maximum
signal at other than the fully open position of the trimmer.

In my case L5 was reduced by one turn to get C6 in to about
the 2/3 meshed position, and L4 was reduced by one turn to
get c8 to a nearly meshed position (not fully, about 80%).

The bad news is that with 13.8 Volts on the Supply, and the
75 meter module installed, I started with 70 V peak to peak
on the scope across 52.4 ohms and ended up with the same
value after the changes.

Not all bad for an evening of fun, and no loss of performance.

Still on the Cascade topic... After helping a couple of
others with the
post-build tune-up on their cascades:

When you're installing resistors and capacitors, it makes
tracing signals easier if you stand the resistors up so the
signal end has the long wire instead of the ground end. That
makes it easy to get the scope probe in there...

Secondly take the time to carefully remove the insulation from
each of the leads on your torroids. It's not too obvious visually
that there is enamel on the wire after the plated through hole
is full of solder.

And, last but not least, if you've been "rude" to your final output
transistor on the Cascade. You know, shorted mica washers,
bad probing etc. you may find the output stage has very little
gain. In one case this was due to the two one ohm resistors
in the emitter lead changing from 1 ohm to around 20 ohms
each. This can be checked in circuit (with power off) with the
DVM just be sure there is less than 1 ohm resistance for the
two resistors in parallel.

Sorry for the length for the non-Cascade owners/builders...

Feel free to use this in the QRPp if you want to Doug.

73, Bruce Florip aa7ar/6 Santa Clara, CA.


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