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All sorts of interesting stuff about Ham Radio and old gear from Steve G3ZPS, near London in the UK

KW Atlanta


Added to the inventory in 2016... a very nice KW Atlanta transceiver with matching external VFO, PSU and Shure 444 microphone. This has been well looked after and is in first class cosmetic and electrical condition

At some point in its past life its been modified to use 6146 tubes in place of the 6LQ6 'sweep tubes', this appears to have been well done and the power out on 40 and 80m is around 100w. The original design claimed 500W PEP input and despite the marketing hype the rig could probably exceed 250W PEP out in its unmodified state With the 6146 valves the output drops off on the higher bands, but it runs cooler and puts less strain on the PSU. On 20m running into a KW1000 linear 400W is easy to achieve and it always gets great reports.

As it was in regular use before it came to me there was very little restoration work to do, although as with all older kit I will change the PSU caps for more modern ones - and for some reason the HT choke in the PSU is missing.

There are very few Atlantas on the air in the UK and little information on the web about them..initially aimed at the US market, KW quickly started selling them them in the UK from around January 1969. Their last appearance in UK adverts was in mid 1973 - so around 4 1/2 years. As with most KW equipment production numbers and dates are a bit vague !

The KW Atlanta is almost a direct component level rip-off of the USA Swan 500C (I have checked the schematics!). OK so they look a 'bit' different, but the radio architecture, tube lineup, audio derived AGC, dial arrangement are all identical. I have no idea how KW got away with directly copying a US rig, knocking it up in the UK and selling it back in the US...although I dont think they sold that many there.

KW copied the Swan PSU as well but made it cheaper (surprise), the smoothing capacitors are all held together with cable ties and one bolt. The carrier 'bal' control is a nightmare in 'tune' mode - all the way left does not mean OFF, thats in the middle..turn all the way to the left and your back to lots of anode current...caught me out and probably quite a few other hams over the years

Unlike the Atlanta the Swan 500C manual is a delight and I could probably use it to fault find the Atlanta, pity KW didn't copy that as well !. To cut cost the Swan design doesn't have any crystals as a premix to a 1st IF, instead the VFO frequency is switched directly by a bank of coils and caps - of course KW copied this as well.

As with the whole Swan 350/500/700 line  the switched VFO design suffers from frequency drift and very poor dial resolution  (a dreadful 10kHz on 10m) . There are lots of VFO coils and trimmers to align to get the dial to read remotely accurately. Thi pi tank is used on receive as well as TX.  The thermal design is also very poor and even with 6146s it gets very hot. Unlike the SWANs perforated cabinet the KW case only has a few vents  The plug in VOX unit on the back also gets in the way of fitting a fan on the rear of the radio.  Running a fan sitting on top of the radio helps a bit

Having said all that its fine on the low bands and the audio is pretty good if you back off the RF to stop the audio derived AGC pops. On recent KW activity weekends (2017, 2018 and 2019)  the rig has perfomed without a hitch hour after hour on 80m, 40m and 20m. I have included a pic of the Swan 500 - same radio but better built. Checkout the Swan 500 I got hold of in the summer of 2018

In Jan 2017 I noticed an annoying problem with the Atlanta that had probably been getting worse since I obtained it..the S meter would gradually move upscale as the rig warmed up - as if the RF Gain was being backed off.  A blip of the PTT put the S meter back to near zero (if no signal was present) and then it would gradually move upscale over 15 mins. This was clearly an AGC fault as the rest of the radio was fine.

Before pulling the radio apart I searched for AGC faults on the SWAN 350/500 and sure enough Chris GM3WOJ (also an avid KW collector) had come across the same problem in a SWAN. There is some sort of diode clamp in the AGC circuit (not sure what it does - there is no info in the manual)..but if the diode leaks a tiny bit it gradually deafens the receiver. It took me a few mins to find it (no layout diagrams exist), but I changed it for a 1N4001 to see what would happen...problem solved

Another fault occured during the KW activity weekend in Jan 2022. This was identical to a fault a few weeks before on my Yaesu FT401. During the operation from my local club the unattended ATLANTA made a short loud humming noise and went dead - the mains fuse in the PSU had failed catastrophically. Within a few minutes I had the top off the PSU and quickly checked for any clues - as with my FT401 the cause was identified as one or more failed diodes in the 800V supply (there are 8). A quick trip round to a ham local to the club came up with  8 IN4007s...not ideal as the surge rating is a bit low but I took a chance. 10 minutes with a soldering iron and the rig was back on the air working fine for the rest of the 2 day event