T150-A, knightkit, problems on 80 meters

[KK4RF]

Gentlemen,
     I picked up a nice-looking old T150-A fairly cheap at a local hamfest. It loads up great into a lightbulb with lots of power coming out of it. When I try to load it on 80 meters running it into antennas with SWR 1:1 (measured with my antenna analyzer and using antenna tuners) I get a very HIGH SWR, even with antennas that can be tuned to 1:1 swr with other rigs. It works fairly well on 40 meters and I can get the SWR low with this rig on 40.  I know this radio had problems with lots of spurious emissions , apparently on 80 meters. I read an article on line by W8JI who had some mods for it, which I have tried. Still having the same problem.
     I know this has been a troubled rig for other users. I wondered if anybody else had similar problems and if there are any other fixes that could be tried.
     Thanks for the advice in advance. Hoping for some ideas other than selling it to someone else at the next hamfest HI.   ---Marty, KK4RF---

[N2DTS]

I guess its putting out a lot of power someplace other then 80 meters.

Maybe a band switch problem and its putting out power on 40 meters, or 160?

A spectrum analizer or sdr would tell, but a receiver with an S meter will also.

Its a simple rig, no?

I used to work someone on 40 that had one that sounded fantastic.

[KK4RF]

I ordered some De-Oxit spray and I'm waiting for it to come in the mail. I need to spray all the switch contacts and into all the tube sockets. I'm going to heat all the solder connections with my soldering iron. I thought I might even change some tubes as well.


It is a fairly simple rig, 12BY7A vfo tube, 6CL6 buffer/crystal oscillator tube, another buffer type tube (the numbers escape me at present) and a pair of 6146 amp tube. Does use a 12AX7/6DR7 tube in the audio circuit.

We'll be working on this for a while. I like 80 meters as its not as crowded as 40. I'd really like to get it working at least half-way decent.  Ideas welcome. Thanks again---Marty, KK4RF---

[N2DTS]

40 meters does a lot better with lower power...

Read this:


http://www.w8ji.com/allied_knight_t150.htm

[w7fox]

Marty,

I had a T-150A in 1964.  The pi net caps were not big enough for 80 meters, so I added some switch wafers and some padding caps that would switch in on 80.  On the "A" model, the 80 meter vfo is on 160 but when you tune up on 80 it is very easy to put out a signal on the third harmonic of the VFO, so I used to get OO reports that I was transmitting on 5.58 mc.  That would push your SWR up on your 80 meter antenna!  Good luck.
73 Chris

[KK4RF]

Gentlemen,
     Thanks for the ideas. The added capacity to the pi-network is a great idea. I'll bet you're right about  output on the 3rd harmonic. Wish I had access to a spectrum analyzer. Will hook up my oscilloscope and frequency counter to see what I'm putting out. This has been an interesting exercise even if I can't ever get it to settle down on 80 meters. Working this weekend, so it may be a while before I get back to it. Will keep you all posted.---Marty, KK4RF---

[KK4RF]

Chris,
     You really nailed it. I just got done connecting an oscilloscope and frequency counter to the output of the T150-A. A 50 ohm dummy load and an old Heathkit SWR/Wattmeter also attached. I loaded up on what I thought was about 3.515 mHz. My freq counter gave an output freq of about 5.275 mHz.  In order to get output into  the 80 meter band I had to crank the final tune  to maximum capacitance, and to make the output look like a fair sinewave, the loading control needed to be maxed out as well. It would appear that I need to add some fixed capacitance at both those positions in order to be able to use the rig on 80 meters.
     Maybe if I get home from work early enough tomorrow I can solder in some extra capacitors, maybe under the chassis near the bandswitch contacts. I'm still waiting for my manual to come in the mail.
     Chris, thanks for the tips. 73s to all for now and hope to get this rig behaving.---Marty, KK4RF---

[w7fox]

Marty,

I was 13 when I got that T150A, and I had a lot of fun with it.  It seems to me that the most fun I've had in ham radio involved overcoming some obstacle and learning from the experience.  I wish I still had that transmitter, as I remember I built it in three days, but the real fun was adding the wafers to the band switch and working the bugs out.  I didn't get much sleep those three days!  Have fun.
Chris

[KK4RF]

Chris,
     I did solder in some extra capacitance  for the final tune and the final load capacitors and now I get a nice sine wave output on 80 meters with about 75 watts output. I may need some new tubes in the rig, seems like I should have more output, but I'll keep working on it. Not sure where I could find the wafers. I'm hoping there might be a way to add the fixed caps off the bandswitch as is  underneath the chassis. I'll have to turn the rig over and see if I can find a way. With the fixed caps that I temporarily soldered in , the rig doesn't want to load on 40 very well. At least I know the radio can be made to work with output that looks fairly clean.
     For me, I always learn a LOT whenever I tackle a project and it doesn't work properly when I'm done. It forces me to read, search the internet, old ARRL Handbooks, and ask questions of other hams. It's for me the best way to learn more, and a lot of fun and satisfaction along the way. Thanks again, Chris. ---73s, Marty, KK4RF---