Swan Radio Issues
I’ve repaired a lot of Swans. SOP for any tube Swan that crosses my bench is replace electrolytic capacitors inside the radio except the can capacitor and sometimes that needs to be replaced also. After a half century of deterioration, most are ticking time bombs if you don’t change them. Don’t forget the power supply capacitors. Radial lead capacitors with long leads can be used to replace the OEM axial lead capacitors at a much cheaper cost than new axial lead capacitors. If the new capacitor leads are not long enough to reach the original ground point, it can be tied to any convenient ground point available. Note polarity as there is a -130 volt bias circuit where + does go to ground in both the power supply and the radio. I’ve used small breadboard type circuit boards to replace the can capacitors with individual capacitors as well as adding terminal strips. In some models the can cap only has 2 sections (caps inside the can) so its easier to just hang 2 caps under the chassis than try to replace it. Get a squeal/feedback when volume is turned up? Almost always bad can capacitor section for any of the Swans.
There may be some 160 volt rated capacitors in your radio (usually 80 and 10 uf if OEM). The 80 can be replaced with a 100 uf and new capacitors should be replaced with a more than 250 volt (400-450 is also ok to use) rated parts. It’s best to use 400 or 450 volt rated capacitors for the original 350 volt parts. Also its OK to substitute an electrolytic capacitor with the next higher value if you can’t find one that is similar in value/voltage rating. OEM 100 uf caps in the power supply were 350 volt, I use 450 and usually replace with either 120, 150, or 180 uf capacitors from my supplier. It makes the radio have a little more PEP output, especially if you have the 8950 or 6LB6 tubes in the PA.
Check all 1 and 2 watt resistors and replace if out of tolerance if more than about 10% to 15%. You can almost be assured the 2 watt 150K bleeder resistors are out of tolerance in the power supply. You can use 3 watt metal oxide resistors to replace them and they are same or less size than 2 watt carbon. John Bruchey always changed out the R104 12 K 2 watt resistor in the VFO amp for a 5 or 10 watt 12 K power resistor as they ran hot and changed value over time. Another trick of his was to change R203 from a 4.7K 1 watt to a 4 or 5 watt power resistor on the RF driver. Another common resistor issue is R202 18K 2 watt that feeds the Transmit mixer opening or going off value, causing little or no power output. If you see a round sticker on the can capacitor labled JB, it has crossed his bench.
1/2 watt resistors that are problematic are 100K, 150k, 270K, 470K, and 1 meg ohm. The 100K ohm resistors in the balanced modulator circuit are usually cooked pretty bad. Replace with 1 watt metal oxide as they will last longer, even if the ones that are there check good.
DO NOT DESOLDER A RESISTOR TO CHECK IT! If it doesn’t read within tolerance in-circuit, clip one lead where it can be tacked back together and read it. Heating the resistor lead seems to make most of those that read high move back into tolerance. How long it will stay is not worth having to work on the radio later to correct the issue so replace it if the reading is out of tolerance.
The only bad tubes I have consistently found are the finals (6HF5, 6LQ6, 8950) and to a lesser extent, the 6GK6 tube that is used in both the audio and driver stages. Examine any 6GK6 tube that is used as a replacement to make sure Pin 6 does not have a internal connection going somewhere inside the tube. If it does, either do not use that tube or you must make sure that pin 6 of the socket under the chassis does not have anything tied to it. If I find one of those tubes with the internal connection, I cut pin 6 off flush with the bottom of the tube so it does not make connection to the socket and if plugged into another Swan it won’t cause an issue. If you or someone else has plugged one of those into your Swan and something is connected to Pin 6, it will take out a couple of parts and require more repair.
If someone has used light oil, WD40, or some other solvent/lubricant to spray the Jackson Drives, I feel sorry for you. Nyogel medium damping grease is the only thing available I have found that will fix it and give it the proper “feel”. It will require a lot of work to remove the Jackson Drive from the VFO compartment to clean and replace the grease in it. Don’t waste your time trying to substitute something else, it just doesn’t have the same feel.
If your meter needle is sticking somewhere in it’s movement, its usually because the plastic scale has warped. This requires front panel removal, taking the front meter cover off, removing the 2 screws holding the scale, removing it, and then reforming it so it lays flat. I put the scale between 2 pieces of paper, place that between 2 thin aluminum plates, place in a toaster oven, then turn the heat on while observing progress. As soon as the plates fall flat, off goes the heat and then allow to cool for awhile (10 minutes or more until the plates are cool to touch) before removing the scale. This also works great on the dial if its warped. Don’t over cook it!
That black/brown spot on the plastic behind the dial is caused by using the wrong lamp. This can be replaced with translucent acrylic sheet that is cut/filed/drilled using the old plastic as a templet. The acrylic sheet can be purchased on Ebay. To reduce the heat and prevent future damage, replace the #47 lamps with #44/47 LED lamp replacements. www.cointaker.com sells them in different colors. I prefer the cool white over the original yellow lamps. They are very bright! Both lamps must be replaced with LED lamps as they are in series and only replacing one lamp with a LED lamp will result in burning out the LED lamp.
Got drift? It’s a Swan. FIRST – Check the band switch phenolic wafers and see if they are soaked in oil from tuner/contact cleaner/wd40. If so, you have to remove it using denatured alcohol or other non-contaminating solvent. Once all the oil is washed away and its dry, hope it’s fixed. If drift is still there after a 20-30 minute warmup, then its a shot in the dark.
One thing I have done that reduces the drift (provided its not related to oil in the band switch) is replacing all the resistors on the VFO board with 1% metal oxide. This has made great improvements in the radios I have worked on, especially on bands such as 15 and 10 meters. Also I found that most if not all the carbon resistors on the VFO board were usually out of spec quite a bit unless it was in an external VFO. Be sure to clip one end and measure, do not desolder one end to check as the heat can actually change the resistance value.
There could be issues with zener diode regulator circuit. You can try replacing the 10 watt zener diode with a higher value (15 to 25 volts) and inserting a LM7910 voltage regulator with a bypass capacitor on the regulated output between the new zener and let it supply regulated -10v to help stabilize the VFO supply voltage. If a 7910 is not available, you can use a 7909 and insert 2 reverse biased diodes in series with the ground lead to raise the -9 volts to -10.2 volts.
These can be much worse than the HF radios. Most of the drift is associated with the Megacycle tuning dial. If you don’t believe me, blow a puff of air into that area while listening to a signal. In the 250C, Swan overcame some of this by putting the tuning capacitor in a shielded compartment. The most effective way to help stabilize it I have found is to take aluminum heating ductwork tape and seal up the compartment where the tuning capacitor is located. Beware that the tuning range may change and require some tweaking for the dial to read properly. Of course you can always try changing the VFO resistors and changing the regulated -10 volts to the zener diode and LM7910/7909 method if sealing up the megacycle tuning capacitor compartment doesn’t help.
RF AMP/MIXER in the Reciever and PA Neutralization
If the RF AMP/MIXER is out of neutralization, the radio will “HOWL” on receive. Refer to the manual for proper adjustment. If the PA is out of neutralization, it will not tune properly and you will see surges in the power output and not a smooth slope either side of the dip on the PA tuning. Many times I see the neutralizing capacitor set all the way open. Usually I find that is not the correct setting and almost always it is meshed in at least a slight amount. If it doesn’t neutralize properly, you have either bad tube(s) or the cathode or screen grid resistors are not close in value.
It was an “option” on the 250, I am not sure about a 250C. If the calibrator was installed, there will be a 500 khz (250KHZ on a 250C) crystal next to the gray 10.7 IF filter, a mica tuning capacitor, and a 12BA6 tube beside it. Empty holes mean its not installed. Replacements for the crystal itself can be pricey.
However, if you are lucky, there are surplus FT241 crystals made for WW2 radios that turn up on Ebay that are exactly 500 KHZ. If the crystal has a 2 digit number, you want the one labeled 27.0 mc. If the crystal has a 3 digit number, you want one labeled 36.0 mc. If you should happen to purchase a 27.0 mc 3 digit channel number, all is not lost. It will move the calibration point to 50.250 for the first 500 khz segment instead of 50.00 as the 500 khz crystal does. If the crystal hits exactly on frequency as the age of most of them are somewhere between 70 and 75 years old.
After replacing an intermittent 500 khz crystal with one of the FT241 military crystals, I had some issues with it being on frequency and taking several minutes before starting to oscillate. I purchased a 5.000 mhz crystal from Tayda Electronics and put it in the old 500 khz crystal housing. It came up with no issues, strong signal, and could be tuned right on frequency. This was one of the miniature through hole mount crystals. Although I lose the ability to calibrate every 500 kc, most of the operation of this radio will be done between 50 and 50.4 mhz. A 1.000 mhz crystal could be subbed and then each MHZ would have a calibration signal.
S Meter Mod – 250 Only as a 250C has an S Meter
There are 3 ways to do it. One is a “factory” mod from Swan. I’ve seen others that attempted to duplicate the 350 s meter circuit. When I see one of the S meter mods in a 250, I look at how it was done. Then I redo it to my way. If it uses the “factory” mod, I add a DPDT 12 volt relay, remove the connection to the aux relay contacts and and rewire so the S meter works in both Cathode/Output switch position. Any other way someone has attempted to do it gets pulled out and redone to the factory mod with a DPDT relay.
You can find 6146, 6146A, 6146B, and 6146W tubes in most of them. You should read about 6146W tubes before you decide to spend extra money for them. Want to save some money on replacement tubes? 6883B/8032A/8552 tubes are an exact replacement for the 6146B tube but have a 12 volt filament. The catch? You have to rewire the tube filaments from series (6146 is a 6 volt heater, 2 filaments in series) to parallel. Remove the jumper between the filaments that connect the two sockets together and then connect ground and 12 volts so the tube filaments are now connected to the 12 volt filament supply in parallel.