eHam Forums => Amplifiers => Topic started by: 2E0ILY on January 21, 2013, 04:48:00 AM

Title: Anti parasitic strip questions
Post by: 2E0ILY on January 21, 2013, 04:48:00 AM
Please see

My Henry 2000D RF generator that I am converting to a single band linear has an anti parasitic device in a different position to all the schematics of tube linears I have come across. Instead of being between the plate choke and the anode of the tube, it has the plate choke feeding the anode directly, and then the anti parasitic device consisting of two closely mounted and connected brass strips across a big carbon 50 Ohm resistor, feeds to the tuning coil via 2 paralleled caps forming 200pF. Does it matter whether an anti parasitic device is before or after the anode connection, functionally? Just curious as these seems an unusual set to me. Thanks.

Title: RE: Anti parasitic strip questions
Post by: G3RZP on January 21, 2013, 06:14:35 AM
Some designs do it that way: it depends which components are involved in the parasitic resonance. Some transmitters succesfully use no suppressor at all.

Title: RE: Anti parasitic strip questions
Post by: KH2G on February 09, 2013, 03:08:14 PM
Looks to me that the parasitic suppression is in the normal place R801 L802. Top of RFC to the Anode. C804/805 in parallel are the coupling to the tuned output circuitry. You might want to make sure your using the right schematic.
Regards, 73
Dick KH2G

Title: RE: Anti parasitic strip questions
Post by: W1QJ on February 10, 2013, 04:27:05 AM
It appears to me  that this unit uses the internal C of the tube as the tuning C and the plate coil is variable  to control the tuning, the load C is a padded flapper design.  The coil to the right of the flapper appears to be the L of the PI-L design.  The parasitic suppressor is in the normal place.  Nothing unusual about it other than it is the alternate method that accomplishes the same thing.  I would think that the load presented to this amp was constant and did not vary in frequency since the tuning range sems minimal.

Title: RE: Anti parasitic strip questions
Post by: KASSY on February 15, 2013, 05:40:43 PM
Hey,I think I got it.

My guess (not being a designer): it really doesn't matter which end of the BigR/copper strap the plate choke connects to.

But, if you think about it, if an amp had two or more tubes, you could not connect plate choke straight to tube plate(s).  So, in multi-tube ham amps (the most common kind, right), it defaults to the way we usually see it.

The layout in the pic looks clean.  Would have been harder to wire it the other way.

- k