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PostPosted: Sep Sat 02, 2006 6:44 am 

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11100
Location: Vieques, PR, USA
johnamery wrote:
There is a third capacitor from the second RF amp plate back to the low side of the antenna input tuning coil. Don't know how to adjust it. Still have oscillation at full RF gain, with full fillament voltage on.

May be your REGEN control. May not serve on a strong station but will on weaker ones. Back off that filament and see how it behaves.

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PostPosted: Sep Sat 02, 2006 8:02 pm 

Joined: Jun Fri 02, 2006 9:58 pm
Posts: 97
Location: Elsberry, Missouri, USA
It's not supposed to be a regeneratie receiver.


I have other NEURODYNE radios that do NOT have that 3rd capacitor

This Gilfillan is the first antique I have restored. Perhaps good enough for my first.

John Amery
1251 Deer Run Road
Elsberry, MO 63343-4011

PostPosted: Nov Mon 06, 2017 3:06 pm 
New Member

Joined: Nov Mon 06, 2017 2:35 pm
Posts: 2
Here's how I determine the values for the grid capacitor and leak resistor for the regenerative detector -

1. Make the value of the grid capacitor (condenser) around ten times the total input capacitance of the tube grid (grid to plate plus grid to cathode). This makes the impedance of the capacitor, at the carrier frequency, small in comparison with that of the grid.

2. The time constant of the grid leak and condenser should be no greater than one fifth of the period of the highest modulating frequency to be reproduced, in order for the grid voltage to follow the modulation envelope quickly enough to not reduce the amplitude and distort the waveform of the recovered modulating frequency excessively.

Using these guidelines, the values can be determined:

1. Choose the condenser value:
For example, the grid input capacitance of tube type '01A is published as very close to 11 pF. So, 10 x 11 = 110 pF. The closest common value is 100 pF, it will work perfectly well here.

2. Calculate the maximum value for the grid leak:
If the highest modulating frequency to be reasonably well reproduced is say, 3500 Hz, then 1/3500 = 286 uS. 286/5 = 57 uS. 57 uS divided by 100 pF = 571,429 ohms as the maximum for the grid leak. The closest standard 10% value is 560 k.

So, 100 pF for the condenser and 560 k ohms for the grid leak are suggested, in the example case given.

Of course, experimentation with values up to two or three times higher and lower may be appealing so as to develop a feel for the effect they may have on the audio, regeneration control, sensitivity, etc.

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