Bring That Old Rig Back to Life

Bring That Old Rig Back to Life Brian Harris, WA5UEK cosmophone@yahoo.com September 12, 2011 Shack Photo Courtesy K0EOO

Why Use Old Gear? • 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)

RestorationCleaning • 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

RestorationTool List • 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

RestorationEquipment List • 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

RestorationInformation, Safety and Initial Work • 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

RestorationElectrolytic Capacitors • Power Supply Filter Capacitors - Reform or Replace? Reform: • Make/buy/install a solid state rectifier replacement(s) • 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 • 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 • Test for expected DC voltages (be careful, keep one hand in your pocket)

RestorationOther 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

TroubleshootingReceiver Basics • 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

TroubleshootingTransmitter Basics • 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 • 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

InformationComponents, Assistance, Reference Material • 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)

Bring That Old Rig Back to Life