[HBR] Fixed a nasty problem (non-HBR)

[Whitebear1122]

Congrats on the discovery!  You had a good inspiration to check out the 3 Mc IF.  Hope that cleans everything up down the chain.   I know some folks build their radios from the audio amplifier and go backwards.  Me, I'm starting at the RF front end.   I'm a few weeks away from wiring my HBR13.  The mechanicals have been slow going.  I have just 5 holes left to drill in theRF front end now that I've lined up the 3 section variable capacitor with the Eddystone.  I have the RF front end shielding aluminum cut and just need to tap and screw together, then the mechanical is done.   My plan is to wire the RF front end first and check that out before moving onto the 1610 Khz IF amplifier stage on the main chassis, and then move on to the three stage (and 4 transformers) 100 Kc IF, checking each stage out before moving on to the next.  This is my first radio construction project so I need to take small steps lest I end up with multiple mistakes in many sections that are difficult to resolve. 

Good luck with your project.  I'm curious to hear just how well it works out!   If you get it going and are pleased to talk about it, I'd like to hear offline about your design and implementation.  73, Scott WA9WFA

On Jul 4, 2014, at 10:06 AM, Ian Wilson <ianmwilson73 at gmail.com> wrote:

> [OT but relevant I hope to receiver homebrewers].
> 
> One or twice a year I dig out my over-ambitious homebrew
> dual conversion receiver, based on the 75S3-C. This uses
> crystal-controlled downconverters followed by a ~3MHz tunable
> IF tuned by a PTO.
> 
> Last time I lost patience with the rig I ripped out the HR-10
> frontend and for the moment have a 6BZ6 (biased for low gain)
> and toroids / dual-gang variable cap for preselector tuning.
> 
> This "sort of" worked but the audio was really horrible. This had
> to be intermodulation or something in an early stage.
> 
> A few days ago I blew the dust off the rig and tried again. This
> time I had an inspiration: listen to the output of the 3MHz bandpass
> filter with a general coverage receiver. So we just have the RF amp
> and first mixer in circuit. Aha! really horrible signals! Nothing to do
> with the second mixer, xtal filter, IF strip....
> 
> This time around, I have a Tek 7704A scope that can show VHF
> signals. It showed a vicious 200MHz squegging oscillation when
> looking at the plate of the RF amplifier (through a tiny capacitor).
> This disappeared when I removed the connection to the mixer
> (at present a 6DJ8 second-generation Pullen). I had forgotten
> to add a stubber resistor on the mixer grid. Added that, and
> things improved enormously.
> 
> I guess I'll keep this project on the workbench for a while longer :)
> 
> 73, ian K3IMW
> ______________________________________________________________