Greetings

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

e-mail address

r@somis.org (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. 

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.

Launch

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

• SB-220 Tune-C melted by VHF parasitic arcing. photo by WA4ZOP.
• 3-400Z s/n Q02888 with VHF parasitic oscillation damage to filament ª(filament-grid BDV 3kV. ). Before autopsy . After.
• Figure 17, bent filament helices in 3-500Z shorting to grid.. p.15 September,1990, QST Magazine..
• eHam Amplifier discussion group was founded by Bill Fisher, W4AN, (SK), who also founded AMPS after the Grate Parasitics Debate ended in late 1996. eHam is a censored group. The censor is George Fremin III - K5TR. A caveat: If you question the gaffes of our recognized amplifier expert**, W8JI, you would do well to expect trouble from the censor.. . . ** see p.71 of QST, Sept, 1994.
• Low VHF-Q parasitic suppressors installed in TL-922 by Chris Hembree, W7CTH: TOP, BOTTOM. Q=1.5@100MHz suppressors
• Replacement TL-922 bandswitches: http://www5a.biglobe.ne.jp/~jh2clv/bandsw4s.htm
• AMPLIFIER DISCUSSION GROUPS: I presently participate in ham_amps on Yahoo Groups. (now at groups.io with all the old threads archived)
• High Speed Switching: We ran out of Mataushita RSD-12v (input) reed relays - which are no longer being manufactured. We no longer carry vacuum relays. Input reed relays can be obtained from Newark: http://www.newark.com/nte-electronics/r74-11d1-12/low-signal-relay/dp/02H7522?Ntt=02h7522 , http://www.nteinc.com/relay_web/pdf/R74.pdf . . Max-gain has surplus/tested vacuum relays.
• - service note - The SB-220 and TL-922 use V-cutoff bias instead of R-cutoff bias during standby. If a stock SB-220 or TL 922 is operated on standby with a filament-grid shorted tube, the +110v PS is shorted to ground -- which causes the unfused filament xfmr to shortly short and burn out. . Converting a SB-220 or TL-922 from V-cutoff bias to R-cutoff bias: will prevent this from happening. The conversion: •• 1. Remove +110v from NC bias contact on relay without disconnecting the +110v lead to the coil. 2. Unsolder the lead of the 100k R that connects to the NC bias contact, move it to the NO bias contact and solder it . When finished, the 100k-ohm R should connect between the arm and the NO contact.  During Rx, the drop across the 100k R is c. 25v.  During Tx, the 100k is shorted out by the relay.     
• Low VHF-Q paraitic suppressors installed in a SB-220 by Brian, KB9VRT.
• TL-922 mods photos: http://ve3fwa.ham-radio-op.net/tl922/index.htm
• photos of Ugly Amplifiers. .plus drawings of PEM nuts. (original "Plywood Box" amplifier photographs courtesy of W6RD, Chuck and Terry, W6RU)
  Articles

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: : ki6sz@sbcglobal.net

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.

"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)

"Amplifiers"

• Part 1 -- Introduction, Classes of Operation, Amplifier Design Considerations, Tubes vs. FETs, Grounded-Grid Versus Grid-Driven, Cathodes, Filament / Heater Considerations.
• Part 2 -- Grid Protection in G-G Service, Glitch Protection, Design Considerations for Indirectly-Heated Cathode Tubes, Safety Devices, Power Supplies, Transformer Ratings.
• Part 3 -- (power supplies) Changing Voltage, Transformer Insulation/Potting, Biasing, Class AB1 grid bias, High Speed RF Switching, Solid State Component Ratings, Breakdown V. Testers / High-Pots, VHF Stability, Designing VHF Parasitic Suppressors.
• Part 4 -- ALC, Capacitors and RF Current, Tuned Circuit Q, Tuned Input Circuits for Class AB2 Cathode-Driven [grounded-grid], Tank Circuits, Skin Effect and Current Capability, Anode HV RF Chokes, Determining Bypass-C, DC Blocking Capacitors, Vacuum Components, Grounded-Grid Amplifier Tune-up, Class AB1 Design Considerations, Grid-Driven Class AB1 Amplifier Neutralization and Tuneup, Distortion, Notes on Measuring Power, Tube Ratings.
• Part 5 Calculating Tank Values, Excel 4 tank calculator work sheet. note: The formulae used are the approximate ones used by Eimac in *Care and Feeding of Power Grid Tubes" (which ignore the Q-contribution of C2) . As a result, the values will be slightly off.
• The Funderberg gold sputter test.
• Official Observer Observer Card
• Bandswitch manufacturer: www.multi-tech-industries.com Example: BTI bandswitch replacement, photo by KM6UC, Dan. .
• Figure 1 (step-start)
• Figure 2 (glitch protection)
• Figure 3 (spst-switchable, dual output V, rectification circuit)
• Figure 4 (Class AB1 electronic-switched grid bias supply)
• Figure 5 (Class AB1 grid input circuit)
• Figure 6 (breakdown-V tester / "high-potential tester / "high-pot". / Source of high-pot DC/DCpower supplies: http://www.emcohighvoltage.com/ourprods.htm
• Figure 7B (high speed T/R switching). Correction - the current through the input to the optoisolator should not exceed 29mA. . .

Relays for QSK

Input RF relay, RY1 http://www.newark.com/nte-electronics/r74-11d1-12/low-signal-relay/dp/02H7522?Ntt=02h7522 0 ..... note - this is an NTE substitute for the SPDT Matsushita RSD relay.in 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.

• Output RF relay;RY2, Max-gain Systems, RJ-1A Jennings or equivalent, http://www.mgs4u.com/RF-Microwave/vacuum-relays-SPDT.htm
• High Speed Relay Mounting Instructions. Photos of relay mounting bracket installed in a TL-922 - courtesy of Ed Kulchenko, VE3FWA. photo 1, photo 2, ECBS.
• Figure 8 (screen V regulator)
• Figure 9 (tuning pulser)
• Figure 10 (shunt-type screen V regulator)
• Figure 11 (anode contactor for tubes with handles)
• --------------------------------------------
• Other illustrations, info, and photographs
• Figure 12 (Rp measurements for different types of VHF suppressors)
• Figure 13 (VHF-resonant circuits in HF amplifiers)
• Figure 14. Arced bandswitch contact on Fl-2100 bandswitch, courtesy of Will, K6NDV.
• Figure 15 (arced bandswitches) [AL-80 bandswitches courtesy of Richard P. May, KC0HH, <rjmay@iguana.ruralnet.net> and George Drysdale, WA6ALQ, gdrysdal@ix.netcom.com. ETO bandswitch courtesy of Bud Henley] Also see page 33 of "Parasitics Revisited" in the October 1990 issue of QST for a photograph of a VHF parasitic-arced TL-922 bandswitch.
• Figure 16 (arced bandswitch wafer removed from a 3CX1000A7 amplifier). Bandswitch courtesy of Charles M. Alessi, W6IEG. Note: this is a large, high-resolution photograph of a large bandswitch.
• Figure 17, bent filament helices in 3-500Z shorting to grid.. p.15 September,1990, QST Magazine..
• Arced AL-82 bandswitch.
• Figure 18. Excerpt from "Calculating Power Dissipation in Parasitic-Suppressor Resistors", March, 1989 QST, page 7, 'Finding Impedance by Solving for Admittance'. .® The American Radio Relay League, Inc.
• Figure 20. Circuit Improvements for NCL-2000..
• Figure 22. SB-220 Diagram. 2x magnification. Print with reduction to fit on legal size paper.
• Figure 23 - Burned TL-922 bandswitch photo, on page 33, "Parasitics Revisited", October, 1990 *QST*.
• General Instuctions for building low VHF Q parasitic suppressors, pages 1-4; p.5 drawing; pages 6a-6b: p.7 drawing. Photo of a suppressor retrofit for 2, 3-500Zs.
• QTH
• Figure 24 -- Photo of gold-sputtered 8877 (s/n HSZ 501) with mix of gold meltballs.(smallest particles) and sawing residue (largest particles). This 8877 was removed from an AL-1500 amplifier that has reportedly gone through four 8877s.
• Figure 24.1 -- Photo of AL-1500 anode circuit showing the lack of a VHF parasitic suppressor.
• Figure 25 -- TL-922 diagram.
• Figure 26 Diagram. Double, low Rp, parasitic suppressors for two 3-500Zs. (diagram from parasitic suppressor retriofit kit)
• Figure 27. Official Observor Observor Card. Use this to reply to anal OO cards.
• Figure 28. Diagram for 2, 572Bs with low Rp, parasitic suppressors.
• Figure 29, Henry Radio Co. 3K amplifier diagram. 29B, 3K Power Supply.
• Figure 30. High-resolution SB-200 wiring diagram.
• Figure 31: 3-500Z with a filament to grid short. p.15, September. 1990 QST Magazine.
• Photo of retrofited parasitic suppressors in a SB-220.
• TL-922 mods photos: http://ve3fwa.ham-radio-op.net/tl922/index.htm
• Replacements for no longer manufactured bandswitches:

  Multitech Industries.

  64 So. Main or PO Box 159

  Marlboro, NJ 07746

  732-462-6100

  Attn: Skip Coleman. / / Photo of Multitech bandswitch replacement for toasted BTI bandswitch (left).

• - service note - if a stock SB-220 or TL 922 is operated on standby with a filament-grid shorted tube, the (unfused) filament xfmr will shortly short and melt down. . Converting a SB-220 or TL-922 from V-cutoff bias to R-cutoff bias: will prevent this from happening. The conversion: •• 1. Remove +110v from NC contact on relay without disconnecting +110v from the coil. 2. Unsolder the end of the 100k‡ R that connects to the NC contact, move it over and solder it to the NO contact of the same section. When finished, the 100k‡ R should connect between the arm and the NO contact.  During Rx, the drop across the 100k R is c. 25v.  During Tx, the R is shorted out by the relay.      

   

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.

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

• We receive orders that have no mailing address. We can not send an order until we receive a mailing address.
• Payment: Personal cheque, cash in either U. S. dollars or Euros wrapped in newspaper comics, or PayPal is ok, but you need to add 4% to pay for PayPal's take.

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 Diagram.......phone filter Instructions.

- 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.

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