Bring That Old Rig Back to Life
Brian Harris, WA5UEK
cosmophone@yahoo.com
September 12, 2011
Shack Photo Courtesy K0EOO
Why Use Old Gear?
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Fun to Use
Easier to work on (spacious, no special tools)
Replacement parts readily available
ESD, Surge and Lightning Resistant
Uses mostly standard components
More forgiving of operator error
Costs less (most of the time)
Does not depreciate (and may appreciate)
Restoration
Cleaning
• Remove rig from cabinet (place all knobs, screws, nuts, etc. in a marked
jar)
• Remove loose dirt, dust, dead bugs, etc. with compressed air or a brush
• Remove tubes (only after you are sure you know where to put them back)
• Clean tubes with alcohol so as to not remove markings
• Clean chassis with damp cloth and Q-Tips (water or alcohol)
• Optional – after sealing transformers, IF cans, chokes and meters w/plastic
and masking tape, spray chassis top with Simple Green and clean with
toothbrush
• Rinse well with tap water followed by distilled water
• Important – keep water away from dial scales
• Dry thoroughly in sun or oven on lowest setting
Restoration
Tool List
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Large Soldering Gun
Small Soldering Iron
Solder Sucker and Solder Wick
Magnifying Glass
Hand Tools
Bristol and Allen Wrenches
Non-Metallic Alignment Tools
Brushes
Alcohol, Dexoit, Lithium Grease, Simple Green, Fader Lube,
Mobile One
Restoration
Equipment List
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Analog VOM
Digital VOM
VTVM with RF probe
RF Generator (Alternative - SS transceiver with adjustable power)
Audio Generator
Capacitor Analyzer (Alternative - Variable HV supply with VOM)
Signal Tracer
Oscilloscope
Tube Tester
Sweep Generator
Grid Dip Meter
Noise Generator
Frequency Counter
Restoration
Information, Safety and Initial Work
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Purchase manual or download from BAMA Mirror
(http://bama.edebris.com/manuals/)
Inspect and make note of loose or disconnected wires and modifications
Replace 2 wire power cord with 3 wire (large blade to return, small blade to fuse
and green direct to chassis)
Add fuse if necessary (i.e. Johnson transmitters) on rear panel or under chassis
Tighten tube sockets and ground lugs
Verify correct transformer voltages
DeOxit on wafer switches, relay contacts, tube pins and tube pin sockets
Fader Lube on all potentiometers
Test tubes if you can
Lubricate panel bushings, gears and variable capacitor bearings with Mobile One
synthetic or lithium grease
Restoration
Electrolytic Capacitors
• Power Supply Filter Capacitors - Reform or Replace?
Reform:
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Make/buy/install a solid state rectifier replacement(s)
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Use Variac to apply AC voltage slowly - 10VAC, 25VAC, 50VAC for 10 minutes
each, 75VAC for 30 minutes, 100VAC for 30 minutes, then 120VAC for 30 minutes
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Feel electrolytics. If they are warm, replace them.
Replace: (recommended)
• Rebuild cans or disconnect cans and install new axial leaded capacitors under
chassis using terminal strips
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Test for expected DC voltages (be careful, keep one hand in your pocket)
Restoration
Other Capacitors and Resistors
• If present, replace all Sprague Black Beauty capacitors
• If you can, measure leakage and values of other capacitors (with the
exception of the pink/red/burgundy silver micas and dogbone style, as
they seldom go bad), replacing as necessary
• Inspect and measure all carbon composition resistors, replacing as
necessary (metal film replacements will work in most all applications)
• Install tubes
• Verify voltages at tube pins are correct, take copious notes
• If it works at this point, it’s time for alignment
• If not, it’s time for troubleshooting
Troubleshooting
Receiver Basics
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Work back to front
Is there noise with volume control at max? If so, skip to IF stage checkout
Introduce audio signal in 1st and 2nd audio stages
Introduce modulated IF signal from RF generator or Grid Dip Meter
Introduce RF fromF generator or transceiver or Grid Dip Meter
Troubleshooting
Transmitter Basics
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Work front to back
With a dummy load and in-line SWR/Wattmeter check for power output
If not, listen for desired signal with receiver
No signal? Check signal levels starting at VFO with VTVM or Scope
Inject low level RF signal in early stages
Line Voltage
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Most vintage equipment was designed for 110-115VAC
Line Voltage today is typically 120 to 130VAC
Increased AC input voltage causes increases in internal voltages, power
dissipation and heat
Component life is indirectly proportional to heat
Tube life is indirectly proportional to filament voltage and power
dissipated
Solution: Lower the line voltage, but how?
• Variac
• Bucking transformer
• Constant voltage transformer
Information
Components, Assistance, Reference Material
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http://www.mouser.com
http://www.digikey-com
http://www.boatanchors.org/filtercap.htm#SP-6 (how to rebuild canned electrolytics)
http://www.harbachelectronics.com/001
(Peter Dahl transformers)
http://www.mcmaster.com/# (good source of hardware)
http://bama.edebris.com/manuals/ (free manuals)
http://tubes_tubes_tubes.tripod.com/id4.html (knobs, tubes, transformer rewinding)
http://www.esrcvacuumtubes.com/contact_esrcvacuumtubes.html (tube source)
http://www.nostalgiaair.org/ (reference links)
http://www.tubesandmore.com/ (Antique Electronic Supply)
http://www.smallparts.com
http://www.qth.net (mail lists for boatanchors, heathkit, drake, national, hammarlund, hallicrafters, etc.)
http://k9sth.com (Glen Zook – Richardson)
http://www.angelfire.com/electronic/funwithtubes/Testing_caps.html (how to test capacitor leakage)