When pur­chas­ing a clas­sic receiv­er or trans­mit­ter, unless you absolute­ly know assume the radio will need work. Often you can get a top-of-the-line radio need­ing a bit of repair or clean-up inex­pen­sive­ly. Don’t wor­ry these radios were designed to be repaired by their own­ers and curi­ous­ly, except for cos­met­ic parts such as cab­i­nets and knobs, parts are much eas­i­er to find for 60-year old radios than a 20-year old import­ed trans­ceiv­er! Chances are the radio has gone for years with­out use. Even if it has been recent­ly used, don’t com­plete­ly trust com­po­nents that might be 60 or more years old. Don’t start by plug­ging in your new acqui­si­tion! To do so might dam­age a hard-to-replace pow­er trans­former, or cause a fire. Instead, if the radio didn’t come with its owner’s man­u­al, get one.  Armed with the man­u­al, remove the radio from its cab­i­net. You very like­ly will find evi­dence of unsight­ly repairs, mod­i­fi­ca­tions, or even dan­gling wires. While mod­i­fi­ca­tions aren’t nec­es­sar­i­ly bad, they can cer­tain­ly add some dra­ma to any nec­es­sary sub­se­quent trou­bleshoot­ing. It’s up to you to reverse or remove them.

 Component Replacement

Cor­rect any obvi­ous prob­lems such as dan­gling com­po­nents. Replace the line cord with a 3-wire, ground­ed plug for safe­ty. If the radio is one with a “live” chas­sis, you should oper­ate it from an iso­la­tion trans­former for safe­ty. It’s also a good idea to add a fuse, if the radio doesn’t orig­i­nal­ly have one. Are we ready to give it the “smoke test”? Not so fast! “RECAPPING” Obvi­ous­ly, aged com­po­nents dete­ri­o­rate, and capac­i­tors are par­tic­u­lar­ly prone to devel­op­ing leak­age or short-cir­cuits with age. There are as many opin­ions on capac­i­tor replace­ment as there are radio col­lec­tors, but at the very least you should replace the elec­trolyt­ic fil­ter capac­i­tors. Here’s why: they will short cir­cuit some­time, and when they do, they’ll prob­a­bly take the rec­ti­fi­er tube and the pow­er trans­former with them. Mod­ern high volt­age elec­trolyt­ic capac­i­tors are reli­able and much small­er than their clas­sic coun­ter­parts. You can mount the new capac­i­tors under the chas­sis by mount­ing a new ter­mi­nal strip (do not just wire them to the old capac­i­tor ter­mi­nals), you can re-stuff the old capacitor’s can with new capac­i­tors, or you can buy a new can from places such as ham­fest.  In any event, fol­low the manufacturer’s schemat­ic — don’t assume that the “–” (minus) end of the capac­i­tor goes to ground, as in some radios the ground path is through a resis­tor so as to devel­op bias for the audio out­put stage or RF gain cir­cuit. Observe the polar­i­ty or you’ll soon be clean­ing up a stinky mess! Old paper-wax and black plas­tic tubu­lar capac­i­tors should also be replaced. Again, a short cir­cuit in one of them could take out oth­er com­po­nents, too. Mod­ern film capac­i­tors of the appro­pri­ate volt­age are great replace­ments. Opin­ions vary as to whether all should be replaced, but replace­ments are cheap and you have the radio apart now, so why not?

REMOVING AND REPLACING COMPONENTS

Replac­ing capac­i­tors and/or oth­er com­po­nents isn’t dif­fi­cult, unless they are buried under oth­er com­po­nents. The Hal­l­i­crafters SX-28 and SX-42 receivers are exam­ples of receivers that have extreme­ly dif­fi­cult to reach com­po­nents. Like the “re-cap­ping” ques­tion, there are dif­fer­ent schools of thought on the “prop­er” com­po­nent replace­ment method. You can use sol­der wick and/or a des­ol­der­ing tool to remove the sol­der from a ter­mi­nal, unwrap the wires, and install the new com­po­nent by wrap­ping the lead around the ter­mi­nal and sol­der­ing it secure­ly. The pro­po­nents of this method point out that this is the pre­ferred mil­i­tary and com­mer­cial method. I find it often will need­less­ly dam­age oth­er com­po­nents such as tube sock­ets and cre­ate sol­der droplets inside of the radio. Back in the day, radio repair­men clipped out a com­po­nent leav­ing a short stub of wire, made lit­tle coils in the new lead, then sol­dered the coiled lead to the old stub. This is a much faster, eas­i­er and neater method.

 Powering Up the Equipment

Get out your volt-ohm meter and mea­sure the resis­tance from the B+ line to ground. Fil­ter capac­i­tors will cause a ini­tial low-resis­tance read­ing that increas­es as the capac­i­tors charge. If the resis­tance stays low or does not increase beyond tens of kΩ, find the short cir­cuit before you pro­ceed. Now it’s time to plug in the radio. It’s best to use a vari­able trans­former such as a Vari­ac and ramp up the volt­age slow­ly, or use a “dim bulb tester” (a 100-W light-bulb wired in series with one leg of the ac pow­er). Turn on the radio, and watch for any spark­ing, flash­ing or a red glow from the plates of the rec­ti­fi­er tube, or smoke. If any of these occur, imme­di­ate­ly remove pow­er and cor­rect the prob­lem. Observe that the tube fil­a­ments should light (although you won’t see the glow from met­al tubes, you should be able to feel them warm up). Again, any tubes that fail to light should be replaced before you con­tin­ue. Now hook up a speak­er and anten­na, and test the radio. With any luck you’ll be greet­ed by a per­fect­ly-per­form­ing radio. Sel­dom, how­ev­er, is that the case. You may encounter any num­ber of prob­lems at this point. Dirty bandswitch­es and oth­er con­trols man­i­fest them­selves by inter­mit­tent­ly cut­ting out; they can be cleaned by DeOx­it con­tact clean­er applied with a cot­ton swab (don’t spray the switch direct­ly!). Scratchy vol­ume or RF gain con­trols can be cleaned with some DeOx­it; in some cas­es you might need to remove the con­trol and uncrimp the cov­er to reveal the car­bon ele­ment inside.If a receiv­er is total­ly dead at this point but the fil­a­ments and dial lights are lit, dou­ble- check to see that the “Receive-Stand­by” switch is in the receive posi­tion, and any bat­tery plug or stand­by switch jumpers (as described in the man­u­al) are in their cor­rect place. Although com­pre­hen­sive trou­bleshoot­ing is cov­ered else­where in this chap­ter, the next step is com­par­ing volt­ages with those stat­ed in the user man­u­al. If the man­u­al doesn’t have a volt­age table denot­ing the expect­ed volt­age at each tube pin, expect between 200- 350 V at the tube plate ter­mi­nals, a few volts at the cath­ode (unless it’s direct­ly ground­ed), 70–200 V at the screen, and slight­ly neg­a­tive volt­age at the grid. If you’re faced with this sit­u­a­tion and a new­com­er to trou­bleshoot­ing vin­tage gear, help can be found at  forums that cater to boat-anchors and/or vin­tage radio repair and restora­tion.

Alignment

Over the years hams have been cau­tioned that align­ment is usu­al­ly the last thing that should be attempt­ed to repair a radio. In gen­er­al this is true — but it’s also a cer­tain­ty that a 50 year old radio will need align­ment in order for it to per­form at its best. In any case, replace the capac­i­tors and any oth­er faulty com­po­nents before you attempt align­ment  it’ll nev­er be right if it still has bad parts! You’ll need a good sig­nal gen­er­a­tor and a volt-ohm-meter or oscil­lo­scope. Fol­low the manufacturer’s instruc­tions, and with care you’ll be reward­ed with a radio that per­forms as good as it did when it was new. Addi­tion­al infor­ma­tion on align­ment can be found in the sec­tion “Test­ing With­in A Stage.”


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