I have a couple of 1930s TRF and superhet sets that are too selective. They clip off too much of the outsides of the AM sidebands, resulting in poor fidelity, particularly for highs. I guess the Q is too high for the RF/IF xfmr stages. I'm wondering what approach would be best to widen the bandwidth.

I think Scott had some kind of adjustable ckt that would widen or de-tune the IF stages. I don't need to have it adjustable, I just want to broaden the bandwidth, permanently.

Try making one of the tuned sections untuned. This will broaden the bandwidth. Look at other radio circuits that do this such as RCA R-32.

MRO

:I have a couple of 1930s TRF and superhet sets that are too selective. They clip off too much of the outsides of the AM sidebands, resulting in poor fidelity, particularly for highs. I guess the Q is too high for the RF/IF xfmr stages. I'm wondering what approach would be best to widen the bandwidth.
:
:I think Scott had some kind of adjustable ckt that would widen or de-tune the IF stages. I don't need to have it adjustable, I just want to broaden the bandwidth, permanently.

Also I believe adding a resistor across the coil will lower Q and increase bandwidth. Stagger tuning may also help.

MRO

:Try making one of the tuned sections untuned. This will broaden the bandwidth. Look at other radio circuits that do this such as RCA R-32.
:
:MRO
:
::I have a couple of 1930s TRF and superhet sets that are too selective. They clip off too much of the outsides of the AM sidebands, resulting in poor fidelity, particularly for highs. I guess the Q is too high for the RF/IF xfmr stages. I'm wondering what approach would be best to widen the bandwidth.
::
::I think Scott had some kind of adjustable ckt that would widen or de-tune the IF stages. I don't need to have it adjustable, I just want to broaden the bandwidth, permanently.

Doug,
If you're sure its the RF and not an overdriven audio section. I would think a high value resistor of 100K or so across the primary of the LC networks would lower the Q. Access to the tuning cap in parallel with the inductor, and a trial and error process would be easy. My last TRF didn't provide an easy method of tweaking the LC networks other than trimmers on the tuning cap, so stagger tuning might be a bit of a chore.

marv

:I have a couple of 1930s TRF and superhet sets that are too selective. They clip off too much of the outsides of the AM sidebands, resulting in poor fidelity, particularly for highs. I guess the Q is too high for the RF/IF xfmr stages. I'm wondering what approach would be best to widen the bandwidth.
:
:I think Scott had some kind of adjustable ckt that would widen or de-tune the IF stages. I don't need to have it adjustable, I just want to broaden the bandwidth, permanently.

Hi Doug

In the case of TRF's it might be audio interstage transformers limiting frequency response? You could use R/C coupling which can greatly improve audio quality but transformer gain is lost.

For a superhet how about stagger tuning IF Transformers? Adjust each screw to opposite sides of the peak.

Norm

:Doug,
:If you're sure its the RF and not an overdriven audio section. I would think a high value resistor of 100K or so across the primary of the LC networks would lower the Q. Access to the tuning cap in parallel with the inductor, and a trial and error process would be easy. My last TRF didn't provide an easy method of tweaking the LC networks other than trimmers on the tuning cap, so stagger tuning might be a bit of a chore.
:
:marv
:
::I have a couple of 1930s TRF and superhet sets that are too selective. They clip off too much of the outsides of the AM sidebands, resulting in poor fidelity, particularly for highs. I guess the Q is too high for the RF/IF xfmr stages. I'm wondering what approach would be best to widen the bandwidth.
::
::I think Scott had some kind of adjustable ckt that would widen or de-tune the IF stages. I don't need to have it adjustable, I just want to broaden the bandwidth, permanently.

That, and the very small condenser on the plate or volume control of the 1st Af tube can chop off a lot of highs. You want it to chop off that nasty high frequency sound, but not the music. Also, experiment with the condenser on the plate of the output tube. Staggering will improve fidelity, though none of my radios seem to have a lack of good fidelity. They are all extremely superior to most modern auto AM radios, which chop off every hint of treble.

Thomas