TheRadioBoard

Hi guys.
I've built Dave's 1D8 SW and it works pretty good, but as I bring up the regeneration control close to oscillation I get a wicked fringe howl for a very small section of the regeneration pots dial movement. Then as it drops out, I begin to receive normally while keeping the regeneration pot just above the oscillation point.(just below oscillation audio is very muddy, just above oscillation audio is very clear)
Reading C.F.Rockey's book tells me that fringe howl is usually only present when using an audio transformer. I'm not using a transformer, so can anyone tell me whats going on?
PS thanks for the schematics on your site and for the parts Dave. I also built your twin 1T4 set. Works great.
Steve L

Hi Steve;

The howl may be caused by the headphones as well as a transformer. In that case, it usually occurs at the headphone resonant frequency.

If you tune a transistor pocket radio to the same frequency as the regen set then you can usually hear the howl in the transistor since it modulates the radiated signal.

Replace the headphones with a 20 k resistor. You can still hear the regen in the transistor but, chances are that the howl will have disappeared.


Sometimes you can reduce the howl by increasing the feedback - a larger or closer tickler or by increasing the main tank Q, lighter A_G coupling or a better coil etc. Or try changing the grid leak values.

Regards Don Peters

Regards Don Peters

Thanks Don,
I have a small air cap in the ant input, so I will try varying the grid leak values. I played with the coil quite a bit to get the tickler right so I hope thats not it but I'll check.
I lived in Edmonton for a year a long time ago. Hows the weather out there?
Thanks again, Steve L

Rockey's book says: lower grid cap, up grid resistor, put resistor across transformer secondary, or decrease tickler coupling.
regards,
phil