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Author Topic: Latest tube radio to play around with  (Read 7380 times)
AD4DQ
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Posts: 11




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« on: June 19, 2014, 06:31:16 AM »

The latest to my collection. A Swan 350 version 1 with the white dial. I have had a few 350's with the 3 different scales on it
and I wanted a white dial as it is easier on my eyesight. All tubes checked and replaced, aligned, neutralized and working fine.
Alot of fun the old tube radios.


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G3RZP
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« Reply #1 on: June 19, 2014, 11:40:15 AM »

Weren't they known as the 'drifty three fifties'?

KW Electronics in the UK did a copy, called the KW Atlanta. So it wasn't so obviously a copy, they effectively turned the chassis through 90 degrees so it became long and narrow. Had all the 350 problems with a few extras.......
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KJ6ZOL
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« Reply #2 on: June 19, 2014, 09:33:23 PM »

Weren't they known as the 'drifty three fifties'?

KW Electronics in the UK did a copy, called the KW Atlanta. So it wasn't so obviously a copy, they effectively turned the chassis through 90 degrees so it became long and narrow. Had all the 350 problems with a few extras.......

I've found that boatanchor aficionados either love or hate Swans. There isn't much middle ground. AFAIK Swan was a budget radio, made for those who couldn't afford one of the big boys (such as Collins or Hammarlund) yet didn't want to buy a Heathkit.
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WB6BYU
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« Reply #3 on: June 19, 2014, 09:54:24 PM »

Quote from: G3RZP

Weren't they known as the 'drifty three fifties'?



While the stability did leave room for improvement,  I think the Swan 250 6m rig was
the one most commonly known as the Swan "too drifty".
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G3RZP
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« Reply #4 on: June 20, 2014, 01:53:43 AM »

I reviewed a Swan 100MX for a magazine. The claim of 100dB plus rejection on the crystal filter may have been met, but couldn't be used because of reciprocal mixing, which showed rather a lack of understanding somewhere in the design process.  I also found that on 15m, it needed a wide band 50 ohm load to be stable - using the Swan matching ATU couldn't make it stable. That wasn't unknown with some of the early SS PA designs - way back in the 1970's, there was an article about stability of wide band HF SS PAs and wide band load requirements in Electronics Design magazine.
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KG8LB
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« Reply #5 on: June 20, 2014, 03:29:54 AM »

... And then there was the Eico "Seven Drifty Three" , AKA Eico 753 .
Someone also coined the phrase "Swans and Drakes belong in lakes" . Seemed unfair to sully Drake to take a jab at Swan .

Nice looking radio , congrats on the find .
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AD4U
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« Reply #6 on: June 20, 2014, 05:56:58 AM »

Not really a Swan fan here, but as a boat anchor guy, I ended up with two Swans. 

The first is the Swan 350A which is basically a re-packaged Swan Cygnet 260, 270, 300.  My Swan 350A is not the same as the 350 in your post. 

After a hamfest the owner was literally getting ready to throw it into a dumpster because it did not sell.  I asked why he was throwing it away and he said he did not have the proper power supply and when he connected a borrowed Swan PS to the Cinch Jones connector on the rear the rig would not come on.  He also said that nobody showed any interest at several hamfests.  I offered him $5 and he took it. 

When I got it home and opened it up it looked almost new.  The chassis was clean with no corrosion.  I noticed the Swan 350A had a built in power supply and the Cinch Jones connector on the rear was only to supply 120V to the built in power supply.  Ironically the "female" Cinch Jones connector on the rear of the Swan 350A WILL mate up to the male Cinch Jones connector on the external Swan PS.  No wonder nothing happened when the previous owner connected an external  Swan PS to the rig.

After downloading a manual and wiring a 120V cord to the Cinch Jones connector the rig came to life.  After an alignment and replacing the single 6MJ6 final tube the rig works perfectly, puts out 120 watts, and after warm up it does not drift much at all.

My other Swan is the 700CX with matching PS.  I bought it cheap when a friend needed some $$$.  It is clean and after an alignment it puts out 400+ watts on 80-20M as measured on my Bird 43 with PEP circuit.  It has two 8950 final tubes, one of which had a loose metal plate cap.  I reattached it with JB Weld and so far it is holding.  After warm up it does not drift much either.

Still not a big Swan fan, but interesting rigs.

Dick  AD4U
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G3RZP
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« Reply #7 on: June 20, 2014, 06:48:14 AM »

What's the sweep tube from which the 8950 was derived?
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AD4DQ
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Posts: 11




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« Reply #8 on: June 20, 2014, 07:26:42 AM »

Quote from: G3RZP

Weren't they known as the 'drifty three fifties'?



While the stability did leave room for improvement,  I think the Swan 250 6m rig was
the one most commonly known as the Swan "too drifty".

The 350 is not bad at all after warmup. Now the 250 keeps drifting no matter what. The Swan 250 was designed around a 10.898 carrier oscillator and used a VFO trippler coil. The mixer adds the 10.9 MHz to the 39.1 from the VFO the to obtain the 50MC range.... IMO the main suspect that caused the drifting. Siltronix radios drift pretty good also. Other swans are very stable, like my 500CX and Cygnet modles are rock solid. The 250 drifts like a sailboat on Lake Eire...... Cheesy
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W9MT
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« Reply #9 on: June 23, 2014, 09:38:38 PM »

The 8950 is the 12VDC filament version of the 6LB6. On the Swan 700 a popular mod is to wire the two 6LB6 filaments in series instead of parallel. Electrically, everything else is the same, pinout and all.

6LB6's can usually be had in matched pairs for about $60. Single tubes go for $20 to $25. Sometimes you're better off buying several 6LB6's and matching them yourself with a tube tester. Just don't mix different brands. There are minor interelectrode capacitance differences between brands like GE/RCA/Sylvania that can make neutralization and operational stability a terror.

8950's are astronomical in price with matched pairs commanding $150 or more. That kind of pricing makes the dual 6LB6 mod look very, very good.

The Swan 300 uses a single 8950. To mod that one takes a power resistor to make up the 6VDC voltage drop so a single 6LB6 runs near its desired filament voltage. That wastes a lot of power and creates a lot of heat. I'd recommend getting a Cygnet 270 or 270B in such case and use the cheaper 6LQ6's. I never liked the 300.
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G3RZP
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« Reply #10 on: June 24, 2014, 05:58:39 AM »

'9MT,

Thanks. The data sheet I found for it made it clear that it was obviously a sweep tube derivative.....
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