AG6K passed on January 4, 2018 - SilentkeyHQ
This page is an archive

e-mail address (don't expect any replies)

Phones: cell 805-509-****, Home 805-386-****.


Last revised:, 14 July, 2016, conducted by: Richard L. Measures, AG6K .

Newer items are in RED

**** La Cumbre Road, Somis, CA, 93066 U.S.A.

Kodachrome transparency of yours truly standing with my parents in a field of wildflowers at the South end of the San Joaquin Valley (1944). Around 12 years thereafter, I built my first RF amplifier. 

AG6K with quadrupedal friend Luey the Cat. ; Luey as an orphan, ; Luey was initially saved by feeding fed him Egg yolks mixed with goat milk and whipping cream. Luey had a brother who starved to death before I found Luey.. - note - Most cats get diarhea from cow's milk but they thrive on goat milk


The How and Why of VHF Parasitic Oscillation

In order to have a VHF parasitic oscillation in a HF amplifier three things are necessary: An amplifying device that has VHF gain, a feedback path from the output to the input, and a VHF parasitic resonaant circuit, in the output. All electron tubes and all transistors have a feedback path. Example: 4, 572Bs have a feedback-C of 2.4 pF and they have a fair amount of gain at 100MHz.

- note - @ 100MHz 2.4pF has c. 700-ohms of Xc feedback from the output to the input..

The third requirement, the VHF resonant circuit, is a given in all HF amplifiers. This resonance is formed by the anode to grid C and the L of the lead between the anode and C-Tune.. For a 50kW amplifier a parasitic resonance c. 40MHz is typical. For a 10kW amplifier 60MHz is typical. For a 1kW amplifier 100 to 150 MHz is typical. . To find the VHF parasitic resonant frequency yourself, unplug the amplifier from the mains, and couple a dip-meter to either side of the DC blocking C.


A VHF parasitic oscillation begins in the anode's VHF resonant parasitic circuit. Whenever the anode current abruptly ends this circuit rings at its resonant frequency, whereupon some of the VHF signal is fed back through the feedback-C to the input. If the tube can amplify at the parasitic resonance's frequency, an even larger signal appears at the anode where some of the now larger signal is fed back through C-feedback to the input where it is re-amplified by the tube. In short order the amplitude of the VHF signal becomes large. This would not be a problem if the VHF energy had a resistive load -- however, the typical output circuit is a HF low-pass Pi-network which blocks VHF - so the VHF energy runs amuck and causes arcing.

Avoiding Launch

There are two ways to avoid launching VHF parasitic-oscillations: 1. Reduce C-feedback and 2. Reduce VHF amplification. . Since there is no way to decrease C-feedback in a transistor or or in an electron tube, the only game in town is to reduce VHF gain. This can be done by decreasing the VHF RL seen by the anode - which is what a parallel L/R parasitic suppressor does. Tbus, a VHF suppressor does not suppress VHF parasitics, it suppresses VHF amplification at the parasitic resonance in the anode circuit so there is not enough VHF amplication to sustain oscillation.

Parasitic suppressor Q:

Q is important for two reasons:

1. the ringing V across the VHF resonant anode circuit is proportional to Q, A lower R/L suppressor Q produces less ringing V to be fed back to the input and be amplified.

2. The lower the supppressor's Q the lower the VHF RL on the anode and the lower the VHF amplification.

The tradeoff with a lower Q suppressor is that it costs c. 0.1db of output at 28MHz.

--- congrats to QST's Technical Editor, F.E. Handy, W1DBM for realizing this in 1926.

- end

Rich, AG6K

High Potential Tester (a.k.a. 'high-pot.')

Circuit Improvements and Maintenance Procedures for the TS-830S

Circuit Improvements for the TS-430S

Circuit Improvements for the TS-440S

Circuit Improvements for the TL-922 [condensed version], , , Replacement TL-922 bandswitches: :

QSK for the TL-922 and SB-220 With Circuit Improvements for the TL-922

Copy of March 1989 QST article "Calculating Power Dissipation in Parasitic-Suppressor Resistors": 1st page, 2nd page, 3rd page, 4th page.

Fyler, G. W. ''Parasites in Transmitters'', Institute of Radio Engineers journal. Sept. 1935. Conclusions.

Original Manuscripts, updated where appropriate

"Improved Anode Parasitic suppression for Modern Amplifier Tubes", {October 1988 QST,}

"Adding 160 Meters to HF Amplifiers" {1/89 QST}

"A Balanced Balanced Antenna Tuner" {2/90 QST}

"Circuit Improvements for the Heath SB-220 Amplifier" (updated manuscript for Nov.-Dec., 1990 QST article).

"The Nearly Perfect Amplifier" (1/94 QST)

Dovetron's 10m mod for the TL-922, page 1, page 2.
What follows is the updated manuscript I wrote under contract for the amplifier chapter (13) of the 1995 ARRL Handbook


Relays for QSK
Input RF relay, RY1 0 ..... note - this is an NTE substitute for the SPDT Matsushita RSD Figure 7B, To use the (DPDT) NTE relay, wire the 2 sections in parallel and adjust the value of the 200 coil shunt resistor to obtain 12v across the coil.

If you find a glitch in Amplifiers, a fuzzy explanation, a technical error, or a typo, please let me know. If you think I left something important out, please say so.

The title 'Amplifiers' is somewhat misleading. Only linear amplifiers are discussed in detail. If you are interested in building a Class B or Class C amplifier, 'Amplifiers' is not going to be of much help.

---------------We Sell------------------

Low VHF-Q parasitic suppressor retrofit-kits for most types of amplifiers -- both mfg. and home-brew. Price List--Information Sheet

High-speed switching parts-kit for retrofitting an existing non-QSK amplifier. p/n 47 (See January, 1994 QST , "The Nearly Perfect Amplifier", page 33---or see Figure 7B above) The kit includes the NEC optoisolator (Q2), the 10A transistor (Q1), two (1 plus a spare) 1500w 47v bi-directional transient voltage suppressors (D1), needed resistors/capacitors and a 300v 0.5a NPN switch transistor for controlling the amplifier with a radio that supplies +LV on TX to key the amplifier. // The price of a HSS parts kit is $10 plus $1 for shipping to US addresses.


High-reliability, high-stability MOF resistors for electrolytic filter capacitor equalizer R service. Matsushita, 100k-ohm, 3w, 500V max. matched within 1%, part number 86, $0.48 each.
We no longer sell telephone RFI filters. However, you can buy the parts for them from Mouser Electronics [1-800-346-6873]. The part number for the 470 micro-Henry inductor is 43LS474. The current price for 100 is $29. 100 inductors will build 50 single-section filters or 25 double-section filters. The value of the [1000pF to 3000pF] capacitors is non-critical. The capacitors have little effect on the suppression ability of the filters--except perhaps on 10m. Put one inductor in series with each side of the telephone line. The filter should be close to the telephone. If the interference persists after one filter is installed, try a double-section filter. Phone filter filter Instructions.


League Fatigue

- The Background Story behind the following story-

On page 24 in the February, 1996 issue of QST, Editor Mark Wilson, AA2Z, writes:

"The rebuttal that Rich provided was, in our view, repetitious of his articles that were previously published in QST. Readers who are interested in knowing more about his design philosophy have a wealth of material in print with which to work."

Maybe the Rebuttal is repetitious of the QST articles, or perhaps not. I thought that the people who read QST might like to have the opportunity to decide this matter for themselves. After all, Mark Wilson works for them. It's probably a good idea for an employer to check up occasionally on employees.

Mark Wilson said, "We should have sent 'The Nearly Perfect Amplifier' for technical review and dealt with any questions about its accuracy prior to publication, ...." Apparently, Mark expects people to believe that QST does not perform an adequate technical review of articles with its own technical review group. Unsliced bologna. No article gets accepted without the approval of QST's technical review group. Mark seems to have forgotten that "The Nearly Perfect Amplifier" did receive a final technical review just before it went to the printer. The final reviewer was QST's then-Editor, Mark Wilson.

Mark Wilson suggests that there were some technical errors in the article -- but he doesn't mention a specific error to support his allegation. So far, I have become aware of one technical error in the article. Eimac recommends a Q of 5, Not a Q of 2, for the tuned input of a G-G amplifier. The person who found the error was the author of the article. If you find another technical error in the article, please telephone me, collect if you like, or E-mail me.

I apologize for the length of the Rebuttal. It is longer than I would have liked. However, the Rebuttal is designed to address each point of contention in the September. 1994 QST [pages 71-74] critique. There was much material to cover. The critique by the six "contributors"/critics (Fred Telewski, WA7TZY; Tom Rauch,W8JI; Reid Brandon,W6MTF; Bill Clemow, KE7CX; John Fakan, KB8MU; and Steven Katz, WB2WIK) amounted to 5500 words -- an all-time record for QST.

letter from Eimac® (text) is mentioned in the Rebuttal. Letter from Eimac® (photocopy)

October 1988 QST
January 1989 QST
February 1989 QST
March 1989 QST
April 1989 QST
January 1990 QST
February 1990 QST
March 1990 QST
September 1990 QST
October 1990 QST
November 1990 QST
December 1990 QST
February 1991 QST
January 1994 QST
September 1994 QST
February 1996 QST

link to 'The Somis Library' (related to bipedal-parasites instead of the electronic type)