Re: [regenrx] Need help: use of 262 kcs transformers in 1952 ARRL 4 tube rx & 30 meter notes
> ..... my concern is with the 2nd transformer. My friend asserts that IYou may be able to use the full winding by shunting it with a resistor.
> may have to unwind some of the windings in order to produce a
> secondary winding suitable to turn that winding into a tickler coil
> for the regeneration of the detector. .....
Regeneration is sometimes controlled by shunting the feedback winding
with a pot, but tends to be noisy.
- If you take some of the windings off, the resonant frequency will go
You will then have to parallel capacitance to bring it back in line again.
--- In firstname.lastname@example.org, Richard Brunner <brunneraa1p@...> wrote:
> > ..... my concern is with the 2nd transformer. My friend asserts that I
> > may have to unwind some of the windings in order to produce a
> > secondary winding suitable to turn that winding into a tickler coil
> > for the regeneration of the detector. .....
> You may be able to use the full winding by shunting it with a resistor.
> Regeneration is sometimes controlled by shunting the feedback winding
> with a pot, but tends to be noisy.
> Richard, AA1P
--- In email@example.com, "yborcigarman" <catman351@...> wrote:
> My concern is with the 2nd transformer. My friend asserts
> that I may have to unwind some of the windings in order to produce
> a secondary winding suitable to turn that winding into
> a tickler coil for the regeneration of the detector.
> I don't like the idea of removing turns if I can do an adjustment
> here and there using the built in variable core. The way I see it,
> part of the coupling circuit is governed by that core. Has anyone
> had experience with these receivers and the performing the
> appropriate modifications?
You can add Hartley feedback to a parallel-tuned circuit by inserting inductance between its common end and common. You use this technique to add feedback to your IF transformer without any modifications to the transformer at all.
For a practical example of this technique, go to the Files section of RegenRx and download a copy of a file I posted, "6n7_regen_detector_1938_radio_handbook.png". Open the file in a viewer or editor, scroll far to the right and look at the stage labeled "DET - BFO & AF". The detector (left-hand) portion of that stage is a Hartley design that uses an outboard homemade coil, shunted with a rheostat-connected potentiometer for regeneration control, to equip the tuned secondary winding of a conventional 456-kHz IF transformer with a Hartley feedback tap. (Note: In that schematic style, "M" after resistor values is equivalent to k (kilohms); megohm values are indicated by "MEG." So what looks superficially like a 1-megohm rheostat across the feedback coil is actually a 1-kilohm control.)
In that 456-kHz Jones Handbook implementation, the added winding consisted of 75 turns of #28 double-silk-covered (DSC) wire close-wound on a 1/2-inch wood dowel. From an old radio handbook you can find out how many turns per inch close-winding DSC #28 would produce, and from that you can determine the length of a 75-turn closewound coil made of #28 DSC wire. Once you know the winding length, you can use an inductance formula, or an online calculator that implements the right formula in easy-to-use-form, to determine the approximate inductance of that coil-on-a-dowel inductor. Once you know the inductance of that added coil, you can scale its value to 262 kHz (Divide 456 by 262; multiply the inductance by the answer you get, which is 1.74.)
So you should be able to make a workable 262-kHz regenerative detector or oscillator by building that new-value inductance and installing it between chassis and the would-otherwise-be-grounded-to-chassis wire from the secondary of your 262-kHz transformer. Connecting a rheostat-connected pot (a 5-kilohm Radio Shack job would do) across the added winding will give you regeneration control, just as in the Jones Handbook circuit.
It won't have the pulling resistance of a high-C detector--the grid tuned circuits of IF transformers of old, if not the plate tuned circuits as well, were intentionally made low-C to maximize the voltage applied to the grid--but it should work tolerably well.
If you try this, please let us know your results.