[Heathkit] parasitic suppression - Better Title

[rbethman]

Carl,

Pick up one of the Radio Handbooks - look at the equipment design section. 

*Parasitic Resonance*

There are *TWO* types!  A Low frequency type, I.E., your circuit is 
designed to resonate at 7Mc, and you *also* have a low freq. parasite at 
2Mc.

The other is *indeed* the VHF type.

*MY* error was using the term *to ground*.

Neither YOU or I *know* where Jorge is looking, doing, or going!

Since a parasitic suppressor was explained to him once before *and* he 
has come back again, I CANNOT assume I *know* what he *really* is asking 
*NOR* can YOU!

The first type has *TWO* possible solutions.

1. Neutralization

or

2. Grounding of tube elements, because bypassing will not work in the 
design.

The second type has ultimately *ONE* solution.  That indeed *is* the 
coil/inductor with a resistor in parallel with it.  We *normally* see it 
in the manner that the resistor is INSIDE the coil/inductor

The low frequency parasitic resonance, which *IS* dealt with by the two 
possible solutions is *still* in existence today.  The question comes 
down to whether He, You, or I, are building a transmitter *AND* dealing 
with the final amplifier - Be it an 807, a 1625, a 6146, or even a 
6JSC6, (And there *are* others!). *OR* He, You, or I, are building an 
*external* amplifier, where the *second* type is *MOST* prevalent.

Therefore, your statement * Completely wrong information. * is *NOT* 
necessarily true!

As I said, the phrase "to ground", *ONLY* applies in the FIRST type - 
*NEVER* in the second type!

Bob - N0DGN

 > jeremy-ca wrote:
> Completely wrong information.
>
> A parasitic is always near the upper VHF frequency limit of the tube 
> and self oscillation is at or near the HF frequency the amplifier is 
> tuned to.
>
> Neutralization is required when interelectrode capacitances and the 
> tank circuit are of the correct value to cause self oscillation at or 
> near the operating frequency. A small portion of the signal is fed 
> back to the input 180* out of phase.
>
> Many without sufficient knowledge of amplifier theory often confuse or 
> combine the two very different items.
>
> A good amplifier tube makes a great oscillator. In the 20's and 30's 
> tubes were run that way deliberately and were called TNT or TPTG 
> circuits.This was before crystal control was developed. You can still 
> hear these rigs on the air during special events, 20's or 30's night, 
> etc; they can really sound great. Im still looking for a pair of 211's 
> to build my own. The regenative detector as used in receivers is a 
> form of TPTG.
>
> Grounded grid amplifiers usually have sufficiently low gain that 
> neutralization is not required but certain tubes still require 
> attention to detail and short lead lengths. The 811A and 572B (same 
> design going back to the 211 of 1928 and the original 811 of 1938) are 
> marginally stable in some amps. The SB-200 is borderline at 10M and 
> the FL-2100 series is less stable and very prone to oscillation due to 
> the incorrect neutralizing scheme (feedback is in phase!!) used.
>
> Modern amps such as the MFJ-Ameritron 811 and 572 series are neutralized.
>
> Most ceramic/metal tubes do not require suppressors or neutralizing; 
> the 8877 is an excellent example of an extremely stable tube.
>
> High gain grid driven tubes as used in exciters almost always require 
> neutralization. This includes all sweep tube and 6146 rigs.
>
> Carl
> KM1H