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How to Restore Your TubeRadio A Paul Pinyot, Solder Smoke and Burnt Finger presentation at, W3KWH Steel City Amateur Radio Club August 8th 7:30pm
Schedule • March 7, 2012 Open to all! Kick off. This presentation and preparation discussion. • March 8 through 27. Acquire your radio and service documentation (see presentation). • March 28 pick parts and test tubes. I will bring a tube tester, parts bins (capacitors, resistors, lamps) for you to purchase replacement parts at my cost to you. • April 4 and 25, and May 2. Continue restoration at NHARC. • May 17-20 Dayton Hamvention. • May 23 electronic alignment. (see presentation). • End of project.
What you need to COMPLETE your project • An understanding of electrical safety and hazards. • A radio and new replacement components • Service documentation (schematic, alignment data). • A moderate to high soldering skill level • Hand tools including: • Soldering iron >=25w, rosin core solder, small wire cutters, Needle nose pliers, screw drivers • Extension cord for activities at NHARC meetings. • Optional “lead wire twister” (see presentation). • An assortment of other non specified hand tools are helpful.
What you need cont’. • Contact cleaner and light lube oil. • A copy of the steps in this presentation. • About 8 to 16 hours for a five tube radio. • About 10 to 40 hours for > five tube multi-band consumer radio chassis. • Work at home commitment.There will NOT be enough time at NHARC meetings to complete a restoration.
Beyond this project’s scope • Cabinet Restoration • Communications gear including but not exclusive to: • Receivers like Hammarlund, Collins, Hallicrafters (except the S-38 line and similar). • Transceivers. • Transmitters. • Hybrid gear (transistors, IC).
Steps to restoration • Locate your radio. • Find documentation before purchasing. • Inspect and photograph (before restoration). • Test for operation • Disassemble and save all parts • Cold test all Transformers and coils. • Test all tubes.
Order replacement tubes and other long lead items. • Shine up chassis if so desired. • Inspect wire insulation. Replace power cord. • Acquire capacitors, resistors and lamps. • Lay out copy of schematic including red and green pencils • Replace capacitors • Replace resistors • Open IF cans and replace resistors.
Replace power cord • Clean controls and switches • Dim bulb test your work then direct to line. • Alignment • Burn-in for => 8hours • Check alignment • Clean cabinet • Return to cabinet and enjoy.
Locate your radio. • eBay is popular. • Ham fests. • Flea markets. • Garage/Estate sales. • Family.
Find documentation • http://www.nostalgiaair.org/Resources/ Domestic US consumer radios. • http://www.radiomuseum.org/ For European and some domestic • http://bama.edebris.com/manuals/ • Boat anchors/test gear • http://www.ppinyot.com/HomePage.htm • For more links and resources.
Inspect and document • One picture is much better than your (my) memory. Take lots of pictures. This is how most of my web site pictures are captured. Simply as a record of what went where. • The cheapest digital camera is better than no camera at all. • Macro capability is great. Or hold a surplus macro lens in front of a digital camera with out macro capability. It works. Believe me.
Test for operation • This step saves a lot of time. If you can hear the faintest of transmitters then most if not all of your tubes, oscillator coils, chokes, IF transformers, Audio Output Transformer, speaker, band switch, volume pots and many more things are working. • Use a Variac set-up or a Dim Bulb Tester (DBT) to protect the parts made from Unobtainium.
Dim Bulb Tester • Current limiting device. • A “Must Use” on all restored chassis. • To make and use one see: http://www.ppinyot.com/dimbulb/dim_bulb_tester.htm Alternative: Variac plus an amp meter plus a volt meter.
Disassemble • Take the chassis out. Pulling off the knobs can be a challenge. They are often held on with set screws and rust. • Have Zip Lock bags available and a sturdy cardboard box. • The box will help protect your glass tubes. • Wrap and tape the speaker with cardboard. I have put too many screwdrivers through paper cones. It will make you sick. • Take pictures too.
Cold test all Transformers and coils • If you had a successful DBT test you can skip this step. • Use an ohm meter to DC test the coils, transformers, speaker for continuity. • Mark off (highlight) these items in green on your schematic. • Schematics often have a DC resistance on the coil schematic.
Test all tubes • It helps to have all tubes tested. A weak tube can throw you for a loop. • Most tubes will be fine • Guitar amp tubes take a beating. • AA5 audio (50C5) and rectifier tubes (35w4) take a beating too. Look for hot shorts in the rectifier tubes. • Put the tubes back into the chassis or use duds in place. More on this later.
Order long lead items. This is rather self explanatory. • Order needed tubes. • Grill cloth • Rebuild crystal cartridges/idler wheels • Re-cone speakers • Special caps and high watt resistors • Send off cabinet to refinisher. • etc
Shine up chassis if so desired. • PROTECT or remove the variable air condenser (Tuning gang capacitor) !!! • Lots of manual labor and elbow grease. • See: http://www.ppinyot.com/P/shiny_chassis.htm for ideas.
Inspect wire insulation kB3URN
Inspect wire insulation • Many radios manufactured during WWII has rubber insulation that does not last. It is hard as sugar candy or soft and gooey as chewed bubble gum. • It needs to be replaced or covered with “spaghetti” or heat shrink insulation. • Replacement is the desirable solution. • Heat shrink over transformer leads is second best.
Inspect wire insulation continued. • Spaghetti is third. • Avoid paint on insulation. Thickness is not controllable. • Keep a tube in all the sockets. This is where socket breakage is high! • Use 600 volt UL rated insulation. • Use stranded for any connection off of the chassis (i.e., speaker, dial lamps, antenna, etc).
A Tube Socket story • A broken tube socket degrades the performance of a radio. Dust and dirt accumulate and cause a short. Once an arc has occurred a carbon track is laid down. It is very hard to remove all the carbon and replace with a high insulation material. • Put a tube into any socket before soldering or de-soldering any pin connector! • Practice this preventative measure and all will live happily ever after.
Acquire capacitors, resistors and lamps • Most schematics have a list of parts. Electrolytic and paper containing capacitors are a priority for replacement. Mica and ceramic caps are good to keep. • Use 630 volt polypropylene (<1 uf) capacitors in all positions (unless a higher voltage is needed). • Use 450 volt Electrolytic capacitor in the power supply (160 volts for AA5) • I will bring my parts bins to pick your parts. (Your $ cost will be my $ cost. No mark-ups.)
Tubular Axial Capacitors Orange Dips Metalized Polypropylene Film Good replacement for Wax/paper caps. Metalized Polyester Film Self-healing property • Metal-Foil Polypropylene Film • Orange epoxy coated for superior heat, solvent and moisture resistance. • Excellent stability for High Current / High Frequency / Temp. Compensation Applications. 500 Volt Dipped Silver Mica Capacitors 1 pF to 5000 pF, • Metalized Polyester Film • Highly reliable with "self-healing" performance Electrolytic Capacitors Y2 Safety and Interference Suppression Capacitors Line to Line (X) and Line to Chassis.
Micamold & “Black Beauties” • Mica Mold is a company that made nano and pico farad capacitors that look like mica or ceramic “domino” capacitors. But they used paper. • These capacitors must be replaced! • “Black Beauties” or “Bumble Bee” capacitors also have paper inside and MUST be replaced.
Acquire capacitors, resistors and lamps continued. • Most carbon composition resistors are bad. If not now they will be later after getting hot. They have been sitting absorbing moisture and thermal cycling for decades of non use. • Just replace them now and avoid the failures later. • Use ½ watt 5% Carbon Film resistors. • Use new Carbon Composition for circuits operating over say 18 MHz (HF). • Do NOT use New Old Stock (NOS) carbon composition resistors. They go bad on the shelf.
Metal Film ½ w about 11 cents • 1 % tolerance • Epoxy coated precision resistors POWER Resistors Wire Wound very inductive. 5 watt $0.37 Power Supplies Candohm replacements 10 watt $0.50 AKA Sand, cement, Ceramic, wire wounds Carbon Film 1/2 w 5% about $0.07 Carbon composition ½ w about $0.20 • Use above 18 MHz • 5 % tolerance • Low inductance • Low capacitance • Watch for inductance. • High quality performance at economical prices • 1/2 & 1 Watt • General shotgun replacement. Metal Oxide 1 and 2 watt 12/17 cents • 5 % tolerance • Power Supply section. • Cathode Bypass • Candohm replacements
Lay out copy of schematic with red and green pencils • Mark off or Highlight components in Red when replaced. • Trace the connections in green to verify the circuit is original factory design. • Undocumented, unapproved, mods were made to gear when parts were not available (war time) or the shop was too cheap to properly repair the fault.
Replace capacitors • Replacing the capacitors first will give you more room to replace other parts. • Use hook and crimp method. This makes for a fast and strong replacement. It also more importantly keep the part in the same relative place as the original. • The performance of plenty of radios is affected by parts placement and wire dress.
Replace resistors • Use the hook, crimp and solder method. • A Lead Twister tool is really helpful with resistor replacement.
Lead Twister • A lead twister adds little coils to the lead wires of the new parts. • Cut out the original part near the body. • Slip the new part’s coils over the old lead wires and solder. • This maintains the original component position and makes for a quick secure solder joint. • See: http://www.ppinyot.com/lead_twister.htm to make one.
Open IF cans and replace resistors Sliver Mica disease (AA5) Replace Resistors See: http://www.ppinyot.com/if_transformers.htm
Hot test restored chassis Please use a dim bulb tester…….
Hot test restored chassis • Use a Variac, volt and amp meter OR DBT. Once passed then plug directly into the line (mains). • Tune in a strong station on Broadcast. • More than likely you will hear a station or more. • If you are lucky the dial frequency may be close.
Alignment • Get alignment data. • Warm up RF generator and frequency counter. • Connect voltmeter to AGC or AC meter to speaker terminals. • Perform Alignment
Trouble? • If the DBT passes trouble shoot after your first alignment. The IF transformers could be so far off the radio will not receive. • If still dead use appropriate trouble shooting techniques to repair.
Alignment • I will bring alignment gear. • Follow the alignment procedures. • An RF generator with AM modulation is commonly required. • A Frequency meter (or general coverage receiver) is needed to set the RF gen. • Burn in the radio 4 to 8 hours. • Perform the alignment again.
Put it all back together. • Clean your cabinet. • Make cosmetic improvements. • Check for electrical safety again. • String up an antenna and enjoy your new old radio.