VHF Power Amplifier Construction Rochester VHF Group 9 November 2007 VHF Power Amplifier Construction Presenters: Frank Pollino, K2OS John Stevens, WB2BYP 11/6/2015 Rochester VHF Group.
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Transcript VHF Power Amplifier Construction Rochester VHF Group 9 November 2007 VHF Power Amplifier Construction Presenters: Frank Pollino, K2OS John Stevens, WB2BYP 11/6/2015 Rochester VHF Group.
VHF Power Amplifier
Construction
Rochester VHF Group
9 November 2007
VHF Power Amplifier Construction
Presenters:
Frank Pollino, K2OS
John Stevens, WB2BYP
11/6/2015
Rochester VHF Group
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VHF Power Amplifier Construction
Why more power?
“I don’t know why he wasn’t hearing me…”
“Nobody seems to know we are out here in this
grid…”
“Always keep a few dB in your side pocket…”
“You need more goo…”
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VHF Power Amplifier Construction
Trade offs of higher power?
Pros
Higher contact statistics – more stations to work, open new
modes of operation
Troposcatter circle radius extends
Better link margins – fade bridge, perceived reliability of
communications in QRM and QRN
Cons
Higher potential for interference
Spectral considerations – you will raise profile in the
neighborhood. Harmonic and Inter-Modulation Distortion
(IMD) products need to be managed in the design
Space and Weight
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Triode or Tetrode ?
Cathode Driven Triode (Grounded Grid)
Require higher driving power 50-100W
Simple cathode bias with Zener diode
No neutralization required
No screen supply and screen protection circuitry
Easy tune-up
8877 / 8938 tend to be pricey for new tubes
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Triode or Tetrode ?
Grid Driven Tetrode:
Lower drive requirement
High power gain may require more attention to construction
May require neutralization (plan for it)
Requires a screen supply (typ 200-500VDC 100mA)
Proper tune-up required (monitor g1, g2 currents carefully)
Some Tetrodes can be configured as cathode driven
grounded grid – may have to bypass G2 for RF and apply
appropriate DC voltage
Some Tetrodes can be G2 RF & DC grounded (4-1000A)
Transit time limits this possibility at UHF
Interelectrode dynamic problems – bypassing and low PS
impedance on G1 and G2
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Tube Selection
Triodes:
3-500Z or 3-1000Z
(50 MHz only)
3CX400A7 (8874)
3CX800A7
3CX1200A7
3CX1500A7 (8877)
8938
GS35b
TH-308/318/328/338
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Tube Selection
Tetrodes:
4X150A / 4CX250B family
GS-15b
4CX400A
4CX800A
4CX1000A / 4CX1500B
4CX1600B
4-1000A
7650 / 7213
TH-327 / TH-347
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Tube Socket & Chimney
Socket:
Few dollars to a few hundred dollars for a new unit
Hamfest and e-Bay availability
Coaxial type can be homebrewed
Chimney:
New units are expensive
Hamfest and E-Bay availability
Often can be homebrewed
Choose materials carefully
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Metal Work
Metal Bending Brake
Shear Press
Hand Tools
Snips, Nibbler
Jig Saw
Hole Punches – Greenlee, Hole Saw
Shielding Considerations – overlapped joints,
reduce the possibility of slot antennas, RF
hazards
Plenty of screws – covers top and bottom
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Parts Acquisition
Shop e-Bay and Hamfests – put the word out on the nets / email
Local surplus outlets – Where would we be without Glenwood
Sales, Conkey Ave and Avenue D, etc?
Surplus Sales of Nebraska, Fair Radio, All Electronics, Jameco,
DigiKey
Use appropriate RF connectors on the interconnect, relays and
antennas
Transformers – size for continuous duty
Filter Caps – allow for voltage rise and continuous duty
Diodes – expect transient behavior that will need 2-3X voltage
and current rating
HV Connectors – rated for service
RF Connectors – minimum Type N but consider larger if there is
the possibility of anything other than a flat load. UHF connectors
can and will arc / evaporate.
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Assembly Tips
Consider the fact that RF connections in the output network
have 10’s of Amperes of RF current – connections have to
be heavy, clean, and have good dielectric insulation to
ground or other HV gradient points
Meter everything – inexpensive and crucial for
troubleshooting
Fuse or Circuit Breaker everything you can
Plenty of Air for the Anode and to the Cathode/Filament
seals
If possible make it such that you can get at the output
coupling for loading adjustment – ideally front access
Build in a method for power output measurement
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Power Supplies – Step Start
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Pre-Tune Up
Find a friend to help you with the initial turn-on-smoke-test
Fresh set of eyes to review the implementation
Watch (meter) filament voltage – variac if possible
Electrically purify vacuum on old tubes!
Do an emission – bias check on the tube
Especially for old/used tubes – operate for a test phase with
full voltage and normal idle bias to check for contaminated
vacuum – gassy tube
Glass tubes – look for inter-electrode glow – often a bad
sign – varies with tube type
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Final Tune Up
Bring up power slowly the first time – gain some confidence
Use all your senses – listen for arcs, sniff, look for smoke
Make sense from all the meters - Use a wattmeter that is rated
for the frequency
Take the time to compute both the DC operating conditions
efficiency, and the RF gain / power efficiency
If you can, inspect the spectral content with an analyzer
Two tone test will tell you an important clue – all distortion
products should be at least 30 dB down and 35-40 dB is real
good.
Get some honest believable on-the-air reports from a reasonable
distance – with reduced signal levels
Investigate reports
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Safety Tips
• RF Hazards - Know what
your ERP is and consider the
environment around your
antenna
http://www.ve1alq.com/downl
oads/software/vk3um.htm
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Interface To Station
Ensure that you have a good ground connection that will take
fault current to ground
Keyline to ground vs voltage to key – your choice, but buffer
the keyline that goes to the rig
HV on TX: Bias off the Amplifier vs Key Control of HV –
advantages to both
Sequence the Power Supply and the Antenna Relay
Provide for a protection relay for Preamp
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T/R Relay
Transco 11000 Series “Y”
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Data Sheets for High-Power Triodes
http://www.df6na.de/df6n
a/tubes.htm
http://www.g8wrb.org/trio
des.php
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Data Sheets for High-Power Tetrodes
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50 MHz Power Amplifiers
http://www.qsl.net/gm3woj/8877amp.htm
http://www.nd2x.net/OZ1DPR.html
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13214
http://www.qsl.net/yu1aw/index.htm
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W6PO 144 MHz 8877 PA 1.5 KW
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W6PO 1.5 KW Amplifier
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144 MHz Power Amplifiers
http://web.wt.net/~w5un/8877-1.htm
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13217
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=15726
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222 MHz Power Amplifiers
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432 MHz Power Amplifiers
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13197
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13216
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903 MHz Solid State Amp
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903 MHz Solid State Amps
http://www.vhfsouth.org/tutorials/902.htm
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1296 MHz Amp – DB6NT SSPA
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1296 MHz Amp
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1296 MHz Amp
Multiple 7289 Triode Amps
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1296 MHz Amp
TH-328/338 Triode Amps
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1296 MHz Amp
GS15b Tetrode Amps
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Water Cooling Tubes
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13215
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2304 Solid State Amp
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2304 Solid State Amp
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Commercial Power Amplifiers
http://home.cshore.com/lunarli
nk/info.html
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Commercial Power Amplifiers
http://www.ssbusa.com/be
komos.html
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Commercial Power Supplies
Power Supply
for HV – Lunar
Link
Switcher for HV – www.wattsunlimited.com
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Show and Tell
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