Teardown & Brief discussion of the Swan 400 SSB transciever and 420 VFO - Page 1
Forum section: electronics / rf-microwave

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 05:27:05 pm
content: I tend to gravitate toward older ham gear, the simplicity of design and the level of performance attained back in the last half of the 20th century make the gear interesting and fun to run.The fun just isn't there with the all digital / software defined gear of today.The Swan 400 was built from the early sixties to the mid seventies. The version I have here is an example from the mid sixties.Note the lack of any way to set or change the operating frequency, we will get to that later...For those who want to see manuals for this gear and it accompanying accessories go here...http://bama.edebris.com/manuals/swan/400/Herb Johnson founded Swan Electronics, which was sold to Cubic Corp sometime in the late sixties.https://en.wikipedia.org/wiki/Swan_ElectronicsThe Wikipedia page is lacking in information however is factual.Swan built a commercial version of this radio in the late sixties and into the early seventies. I have actually seen one. This model radio has some notoriety due Senator Berry Goldwater (K7UGA) using one in his corvette Stingray as a mobile radio.On with the tear down....The radio employs a single conversion super-het design for the receiver and single conversion to generate the output signal. The early Swan-400 like the early Swan-350 used a crystal filter made from five crystals wired in a lattice network. While this filter provides good transmit audio quality it is not the best for receive selectivity.The sixth crystal located to the left of the other five in the mid section of the chassis is a 100KC crystal used to calibrate the radio's VFO from harmonics generated by the calibration oscillator.Rear panel view showing the connectors PA Bias, and S-Meter zero controls.A set of dry relay contacts are supplied to control external devices such as linear amplifiers and receiver preamps.Next post........

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 05:41:04 pm
content: These were all hand wired back in the day, the tube sockets are held in with screws, nuts, and washers, not riveted in, that is a good things as gear like this gets older grounding issues can occur as the rivets loosen up from temperature cycling.Adlinment points screened on the bottom of the radio makes servicing much easier. the bottom cover does have to be in place for proper alignment.The Swan 420 frequency control unit (VFO) was the first in a series designed to be used iwth the Swan-400. The amateur bands are covered in 200KCS band segments, there is also a 14.5-15.0 MC band segment which allows reception of WWV in order to set the crystal calibrator on frequency.I have to mention the RF gain control on the VFO. The RF gain control has nothing to do with the VFO operation, it was put there for maybe one of two reasons, maybe both.1. There is no room on the front panel of the Swan-400 for the RF gain control.2. in mobile operation the VFO was put under the automobile's dash board and access to the RF gain control is necessary.Back in the day receiver AGC circuits were not very well refined, it could even be said that in some instances no AGC was better than the provided AGC circuit. (Automatic Gain Control).Receivers especially SSB receivers would be overloaded by strong signals. Better distribution of the total gain and better AGC design has eliminated this problem from the early seventies on.Not much to look at on the rear panel.Next post...

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 05:56:32 pm
content: Inside the 420 we see a whole bank of adjustments (coils and caps) along with the 2 transistor colpits oscillator. The top of the chassis has a rib spot welded in to stiffen up the chassis.Sorry for the crappy image, sometime today I will replace it.Above is the oscillator and emitter follower.For every band there is trimmer cap, and coil to establish the proper L to C ratio to provide the 200KCS bandspread.The main tank coil is wound on a ceramic form which is securely bolted to the chassis by way of standoffs. The bandswitch is rather substantial the far left wafer selects the coils used to set the lower limit of the frequency span. The center wafer selects the tap off the main tank coil to be used. The far right wafer selects the trimming cap used to set the high end of the selected band.The RF gain control can be seen down in the lower right. Under the RF Gain control is the dial set trimmer. Copper strap and heavy gauge wire are used throughout the VFO.Next post....

author: German_EE
author_rank: Super Contributor
timestamp: January 15, 2018, 06:03:14 pm
content: Sorry Sue, no pictures.

author: tautech
author_rank: Super Contributor
timestamp: January 15, 2018, 06:05:30 pm
content: Sue, why won't your pics show in Chrome ?All I get is a gray circle with a white line through it.Another forum member suggested I place;imagebefore the closing  to ensure they display correctly in all browsers. This doesn't work in this case, tried it.Must be your host settings Sue.EditNo pics in Opera either.

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 06:14:27 pm
content: Back on top with the access cover removed you can see the trimmer caps used to set the high end of each band.Removal of the other access cover on top and the coils used to set the low end each band are seen here.The bottom cover also is ribbed to stiffen it up.This VFO is a solid design in spite of being band switched.The conbination make for a reasonably good radio back in the day, It's still is a good radio for rag chewing, while not a high preformance radio one would use for DX'ing it is pleasent to listen to and for being over 50 years old quite stable. I haven't ran the radio across my bench yet to see how well the receiver preforms, I'll do that after I finish the 8569B project.At 220W out it is very capable for daytime 40 meter use.Using the Swan-400 to drive my SB-220 I have to keep the drive around 125W, much more and there is too much grid current and I would be in danger of damaging the tubes in my SB-220. I don't have the VOX unit for this radio, I had one that came with my Swan-350 but it needed to find a new home with a friend.Herb Johnson was good at designing ham gear to a cost.So I now have three Swan radios in my modest collection, a 350, 500CX, and my Swan-400.I also have two Atlas radios, Johnson went on to form Atlas Radio in the early seventies.I have an Atlas 215, and a 350 with a power supply.Fun stuff....

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 06:19:18 pm
content: I don't know I linked them the same way I have before, I see them here

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 06:23:37 pm
content: Hit refresh and try it again.I changed some of the settings for that album.

author: tautech
author_rank: Super Contributor
timestamp: January 15, 2018, 06:35:22 pm
content: Quote from: AF6LJ on January 15, 2018, 06:23:37 pmStill nothing.....Anyone seeing them ?QuoteMaybe for you but not me.So if you can see them, maybe some setting to make them publicly visible is needed.

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 06:42:42 pm
content: I don't know what to tell you, If I go to my copy of chrome which is loged into another account I cannot see them.I don't know what the hell is going on.One day I can link to google photos the next day I cannot, I give up.Screw it.I am about ready to delete the thread and not post here anymore.

author: tautech
author_rank: Super Contributor
timestamp: January 15, 2018, 06:45:28 pm
content: Quote from: AF6LJ on January 15, 2018, 06:42:42 pmNooooo don't go.How big are the images ? More than the forum 1 Mb limit/pic ?

author: tautech
author_rank: Super Contributor
timestamp: January 15, 2018, 06:59:41 pm
content: Sue, are you grabbing the pic URL from the host URL bar or right clicking on the pic and selecting 'copy URL' ?Or is it a host setting that's stuffing it all up ?I'll be pulling any of my posts out when you get this sorted to keep your thread tidy.Must be a settings issue Sue as no problem with the imagry in the last few pages of your other SA thread.https://www.eevblog.com/forum/repair/hp-8569-spectrum-analyzer-repairs/The URL's and syntax settings are similar so it must be host settings.

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 07:39:05 pm
content: Quote from: tautech on January 15, 2018, 06:59:41 pmI am getting the image URL right from the image not from the address bar

author: tautech
author_rank: Super Contributor
timestamp: January 15, 2018, 08:15:50 pm
content: I'll let you sort out the previous posts Sue and then I'll tidy up mine.

author: Radio Tech
author_rank: Frequent Contributor
timestamp: January 15, 2018, 09:11:13 pm
content: Please do not give up Sue. Your knowledge is much needed.I can see the picture in post #13 but not the others.I do know this forum sometimes has issues with large pictures when uploading, I have never linked many images here so cannot relate on that.

author: AF6LJ
author_rank: Unknown
timestamp: January 15, 2018, 09:31:28 pm
content: Well I cannot make the other pictures work.This is not a good day.

author: medical-nerd
author_rank: Regular Contributor
timestamp: January 19, 2018, 03:09:00 pm
content: HiyaDitto for post 13 having a picture, nil for the previous ones on IE and Chrome.Really looking forward to seeing the pictures!!Cheers

author: AF6LJ
author_rank: Unknown
timestamp: January 19, 2018, 04:39:10 pm
content: I can fix this however I won't have time to do this until later today, or maybe on Sunday...It will get fixed.

author: deepskyridge
author_rank: Regular Contributor
timestamp: January 25, 2018, 03:19:29 pm
content: Would love to see the pictures.When I was a young fellow, either 1967 or 1968, I drove to S.D. and got a tour of the Swan factory.Pretty cool.Gary K5DSR

author: AF6LJ
author_rank: Unknown
timestamp: January 26, 2018, 05:44:51 pm
content: Quote from: deepskyridge on January 25, 2018, 03:19:29 pmI also had a tour of the factory.I am finally seeing the end of the tasks that have diverted me from this thread....I should have the time this weekend to fix the pictures.