[AMRadio] RE: new home brew receiver progress

[Robert Lawson]

Bret,

I think what you are doing is GREAT!  Really enjoy reading all of your email
notes in the theory, design, construction (and hopefully not too much trouble
shooting on the bench HI).  Keep up the good work.  I look forwards in reading
your post, as it is actually a tutorial for us all.   Of note, I am not an
engineer;  I am a retired mental health psychologist.  Don't let the "think
they know it all, but their wives know better" types change your course in this
project as this retarded shrink wishes to be on for the bus ride in the back
seat enjoying the view with you driving. HI

bst 73 de Robert WPE4FGR W4RL Pensacola Florida.

Brett Gazdzinski wrote:

> I am making good progress on the new receiver.
> I have tried lots of circuits for the local oscillator,
> and have come up with a good circuit.
> Its very hard to build a good stable oscillator without
> complex coils with feedback windings.
>
> I found a circuit in the Bill Orr handbook, out of the C-W man's receiver
> that uses one untapped coil, one side goes to ground, a variable cap across
> the coil to ground, an RF choke in the cathode, and a pair of caps
> in series from the grid to ground, the center (between the caps)
> goes to the cathode for feedback.
>
> I tried various coil types, various size ceramic slug tuned forms
> with various gauge wire on them, pre made phenolic slug tuned forms
> that I unwound some wire from till I got to the correct frequency,
> large ceramic coil forms, and B+W coil stock.
>
> The best results are from the B+W coil stock, a much higher
> Q coil, gives less harmonics out.
>
> I changed the design some, instead of using the 6U8, I used a 6C4,
> since the ARRL handbook says a separate oscillator tube results
> in a more stable receiver.
> 2nd harmonics are down more than 45 DB with the B+W coil, much less with
> some of the others, some generate harmonics out to 60 Mhz
> or so!
> The oscillator keeps working down to as little as 10 volts on the plate,
> and I may run it at 75 volts.
> I just tack parts together on the workbench, hooked up to
> the old heathkit variable high voltage power supply,
> so the finished product should actually work better, with
> short wires and a sensible layout.
>
> To switch between 80 and 40 meters, all I need to do is
> short part of the coil to ground.
> One end is always connected to ground, and a tap to
> ground will give 40 meters, I tested it, and it works well,
> no drop in output, no increase in harmonics.
> I plan on putting the coil and switch in a small box to isolate
> it.
>
> I think the mixer tube will be a 6AH6, and I will try to inject
> the osc into the cathode.
> If that does not work well, I can inject it into the grid.
> The ARRL 1967 handbook has lots of good info about
> this sort of mixer stuff on page 99.
>
> I think the IF amps will be 2 or 3 6BZ6 tubes.
> The same handbook gives circuits and values for various tubes.
>
> I have a circuit for the low distortion detector, and the S meter
> amp, but have to change from octal tubes to 7 or 9 pin
> tubes, from a 6SN7 for the S meter circuit, and the detector needs
> a diode, and a triode, like the 6SN7.
>
> I may be able to drive the S meter directly with an IF
> amp plate current, like the Gonset G76 does.
> I found a nice S meter from an old heathkit receiver
> on E bay a while ago. It can be lit up from the back, a nice touch,
> and its only an S meter, not out of a transceiver with plate current
> and so on..
>
> I have the chassis, the side supports and front panel,
> the IF transformers, the digital frequency display, the tuning cap
> and various reduction drives, nice ceramic tube sockets, the antenna
> tuning coil forms, loads of VR tubes, and all the other tubes.
>
> The Kiwi filters have not arrived yet, and I may need to buy a
> power transformer, to give 200 volts out with choke input,
> and filament windings.
>
> Its really getting to be ham radio season, with building and
> operating, and I am having FUN!
>
> Brett
> N2DTS
>
>
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