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 Post subject: One more take on the use of the RFC in a regen..
PostPosted: Sep Sat 15, 2007 5:29 pm 
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I've had good luck skipping the 2.5 mH RFC in many HB regens in the past; and I've never noticed a big difference in performance.

However, as a recent experiment I included the RFC, and I also used a 600 pF compression mica as the plate bypass on the regeneration winding instead of a fixed value bypass cap. The compression mica ("throttle cap") let me optimize the settings for differences between different plugin coils... thus the regeneration pot has the smoothest possible regen authority.

Just a suggestion.

Pete


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PostPosted: Sep Sat 15, 2007 7:49 pm 
Silent Key

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Pete- I have always found the best way to control regeneration with triodes is the throttle condensor method. When using a screen grid, I use both the throttle condenser and a bypassed pot in the screen grid circuit to vary the screen voltage. With both of these adjustments, you often wonder why you don't have three hands, but it allows you to optomise the circuit at a particular frequency and you can get the regeneration as smoothe as silk.
Curt

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PostPosted: Sep Tue 18, 2007 7:17 pm 
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I have a real dumb question. Why does the tickler needed to be bypassed to ground through a capacitor? I know that when I dissconnect it the radio dies.


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PostPosted: Sep Tue 18, 2007 8:46 pm 
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tubeAMP wrote:
I have a real dumb question. Why does the tickler needed to be bypassed to ground through a capacitor? I know that when I dissconnect it the radio dies.


Without the bypass cap the RF current through the tickler coil would be greatly reduced, reducing the coupling to almost nothing. It provides a complete path for the RF (which is an AC signal.)

Peter


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 Post subject:
PostPosted: Sep Fri 21, 2007 3:21 pm 
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Peter Bertini wrote:
tubeAMP wrote:
I have a real dumb question. Why does the tickler needed to be bypassed to ground through a capacitor? I know that when I dissconnect it the radio dies.


Without the bypass cap the RF current through the tickler coil would be greatly reduced, reducing the coupling to almost nothing. It provides a complete path for the RF (which is an AC signal.)

Peter


Not disputing what happens without the capacitor, however, I think the confusing idea for me is that RF is AC and a capacitor passes AC. Except that in this use the capacitor goes to ground, so, the question for me is; why is the AC path sent to ground. I am used to thinking of and using a bypass cap to ground to kill out unwanted AC not to boost wanted AC.


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PostPosted: Sep Fri 21, 2007 4:47 pm 
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Hi

This cap is after the detector. It's a fairly small value to bypass RF AC to ground. You still have audio AC after this point which you want to amplify.

For regen you need RF signal in the tickler coil. If you don't have the cap the RF signal will be divided between tickler coil and other components in the circuit, audio interstage transformer, resistor, choke etc. This bypass cap limits the RF to being across the tickler coil.

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 Post subject:
PostPosted: Sep Sat 22, 2007 12:48 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
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Location: Sandpoint, IDAHO 83864
Electrons are dumb. All they want to do is to seek out a more positive place to migrate to. So we have bypass capacitors and RF chokes to keep the critters where they should be. In a regenerative set, you have to keep the RF where it belongs, in the oscillatory circuit. If it gets into the audio circuits, it will be lost.

Without the bypass capacitor (throttle condensor) on the tickler, the RF would be fed into the power supply and audio sections and everywhere else that was connected to the far end of the tickler coil. The capacitor provides an easy path for the RF to go to ground, hence it completes the circuit thru the tickler, RF wise.

The RF choke offers a high impedance to the RF so it keeps it out of places where it should not go.
Curt

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(Connoisseur of the cold 807) CW forever!


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