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So I Bought A Swan 350

Discussion in '"Boat Anchor" & Classic Equipment' started by AF6LJ, Jul 11, 2014.

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  1. AF6LJ

    AF6LJ Ham Member QRZ Page

    Some of the latter day sweep tubes would actually last just as long in aproperly designed circuits as the good old 6146 family of tubes would. The Swan-350 came out at a time when power was being sold as the main feature you want in a radio. Swan, Yeasu, Helicrafters, National, nearly all were caught up in the race to build the radio with the biggest punch.
  2. N2EY

    N2EY Ham Member QRZ Page

    Yep. Swan's efforts are shown here. Yaesu did similar, Hallicrafters made the SR-400 and SR-2000, National the NCX-500 and NCX-1000. Drake was in the game, sort-of; both their separates and transceivers used sweep tubes in the final and ran more than the typical pair-of-6146s 100 watts.

    Only Heathkit and Collins stayed out of that game and stuck entirely with the 6146 family, and the 100 watt class. One reason is that Heath made the SB-200, SB-220 and HA-14 amplifiers, and didn't want to compete with themselves. Collins, meanwhile, wasn't going to change the basic design of the KWM-2 or 32S-3 just to get more power.

    It should be remembered that, back in those days, "speech processors" were relatively uncommon. Note that there's no provision for a processor in the 350. Swans were SSB rigs primarily, with CW tacked on and RTTY not really considered - RTTY ops of those times used separates almost exclusively.

    As you mentioned before, cost was a factor - sweep tubes generally cost less than 6146s, because they were "receiving tubes", and IIRC made by more manufacturers. I remember some hams in those days telling me that sweep-tube finals were actually an advantage, because replacements could be had from any TV repair shop, electronics house, or even a hardware or drug store in a pinch (back when "U-Test-Em" testers and a stock of popular tubes was a common sight in those stores).

    I also recall the term "dollars per watt", which sums up the issue.

    Yes, sweep tubes could last quite a while - if not pushed too hard, and if the op learned to tune up quickly and accurately.

    Good to see those old classics being brought back to life and radiating some RF!!!

    Which raises a question I will take up in a different thread.
  3. AF6LJ

    AF6LJ Ham Member QRZ Page

    I saw your post in the other thread and replied.....

    We do have a new issue with the Swan-350....
    As I said I picked up all the electrolydics for the radio, the power supply was rebuilt but the caps in the radio itself were not replaced. Now that the radio has had twenty or thirty hours of operation and some time on transmit, it worked great yesterday in morning rag chew. Yesterday afternoon after putting the radio where it will sit (Morphy's law takes over...) The radio now has intermittent loss of PA bias. I suspect it is the electrolytic that is across the bias supply shorting out, but will investigate before actually firing up the soldering iron.....

    Stay Tuned..............
  4. AF6LJ

    AF6LJ Ham Member QRZ Page

    Oh and on a side note.....
    The 350 drives the SB-220 rather wall, keeping the grid current below 300ma the SB-220 has no difficulty generating 1100-1200 PEP.....
  5. KC4UMO

    KC4UMO Ham Member QRZ Page

    I got a chance to put this Swan on the air tonight. Talked with k3vox on 40. Very nice guy and has some Swans also. Gave me a great signal report but did say I had a bit of a 60 cycle hum. He recorded it and played back and it is there. I done nothing to the rig but clean controls so I may as well replace all the tired caps in the power supply and rig.

    BTW, Lee is looking a S-meter for a 350
  6. N2EY

    N2EY Ham Member QRZ Page

    Yep - ain't that the way?

    Could indeed be the electrolytic. Or a resistor with a hairline crack deciding to open up when it gets to just the right temperature.....or a cap shorting - or something else.....

    Hope it's easy to find.

    It will drive the SB-220 easily, and the finals will last practically forever in that service because they don't have to run all-out to do so.

    You know the following already, but for others:

    Sometimes an electrolytic can test fine by the charge-it-up-and-see-how-long-it-takes-to-discharge test, and the leakage test, yet still be "bad". What happens is the cap's ESR (Equivalent Series Resistance) goes up, so its ability to filter ripple goes way down. It's as if there were a resistor in series with the cap, isolating it from the B+ line (or whatever needs filtering).
  7. AF6LJ

    AF6LJ Ham Member QRZ Page

    I have been watching the bias with an external meter, and have not been able to see the loss of bias.
    The symptom has not reappeared. I don't like to just replace parts for the sake of "shotgunning the problem".

    Monitoring the grid bias allows me to see a spectrum of causes.
    Screen to control grid short...

    Loss of bias ether by a short in previously mentioned cap or by intermittent contact of the bias control wiper.

    Leaky Drive plate coupling cap...

    The orginal symptoms were loss of RF out and high resting cathode current.

    What has changed since the Intermittent stopped being so...
    Addition of the wire to the cold end of the PA grid choke, and readjustment of the bias pot.

    Circumstantial evidence points to an internittent wiper on the bias pot.
    More testing today, I'll set the bias to just above 60ma and we shall see what happens.
  8. N2EY

    N2EY Ham Member QRZ Page

    Yep. Often one replaces everything BUT the bad part!

    Agree on the bias pot - particularly since it probably hadn't been touched in years.

    Also possibility of cold solder joint and such.


    One thing I like about homebrewing is that I get to decide what gets metered, and how it gets metered. For example, most MOPA rigs have just one meter, and a switch to read grid or plate current, because meters were expensive. But since 1976 I've provided separate meters for grid and plate currents, because I had the meters.
  9. AF6LJ

    AF6LJ Ham Member QRZ Page

    That is one thing I don't like about many of the new radios.
    No collector current metering. That is a useful thing to have.

    The early Swans only provided for cathode current, granted that is all you really need for metering to tune up the radio. The Heath SB-Series gear was more generous in meter functions.

    If it turns out to be the bias pot, that is something that could be "lived with" for a time until a good drop in replacement is obtained. It is a 10K wirewound pot, I would have to pull it to see what the wattage rating is but my money is on it being 2 Watts. If I replace that, there are two other resistors in that netowrk that are worth replacing, especially the 10K 2W resistor on the low side of the bias pot, it happens to be mounted under three wirewound sand bar style resistors and is most likely "well done". :)

    Next time I go to the junque store I am going to see if they have some decent ten or twelve conductor cable.
    I want to replace the power supply cable and the connector on the end...

    Well back to chores.........
    Stay Tuned.........................
  10. N2EY

    N2EY Ham Member QRZ Page

    All good stuff.

    As to meters:

    Way back in 1977 or so I built a small 40 watt MOPA (6AG7-807). with two panel meters. (Southgate Type 5 family or equipment). The smaller meter was 0-1 mA, and was used mostly for reading grid current. Because I had a nice rotary switch, it could also read screen current, plate voltage, screen voltage (all 807 voltages except heater).

    There was also a position which connected the meter coil to a pair of banana jacks on the front panel. The idea was that the meter in the rig could double as a test meter if needed, using an external resistor box.

    That rig and its matching receiver were both built on the kitchen table while I was living in a small apartment with no HF antenna.
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