The AM Forum

I just acquired a T-195 transmitter to go with my R-392. I would like to talk to an owner of a T-195 about what I should expect from the autotune circuit. What should it do and in what order. This one goes to the presets properly. Using the Test Key it will appear to autotune (the motors run and the light comes on), but there is very little cathode current and no output on the scope. Grid current at lower end of "mark". Lookin' for some good clues as to where to start before I lug the thing out of the case. Your experience could be the information I need.

PM or e-mail with your phone number and I will call you (my dime).

Thanks,
          Bill
          KA8WTK

If the Autotune is workng properly, you should see a gradual increase in cathode current and RF output while holding the test key to tune.  As you approach maximum output there may ne a drop and then another increase in output as the tuning cycles through different amounts of fixed loading capacity.  Eventually, the cathode current should settle out at about mid-scale, and RF output should be about 100 watts (as measured with an external  in-line wattmeter).

It's my experience that the Autotune performance is very sensitive to the DC input voltage supplied to the set.  If it's on the low side of the normal mark on the built in test meter, the Autotune will operate very sluggushly, or not at all, giving the symptoms you described. Try raising the input voltage a bit, if you can and see if that helps.  This behavior is most apparent at low frequecies, such as on 75-80 meters.  My set will often tune up just fine on 40 and 20 meters, but will get "stuck" if I try to shift back to 75.  After I bring the input oltage up a bit, off she goes!  In my case, I am powering the set with a pair of 12V marine deep cycle batteries in series, in parallel with an adjustable high current DC supply.  If the batteries are a bit flat, Autpotune is sluggish, after a full charge, it works fine.

I do not have direct experience with other issues that might be involved.  I believe that there are diodes in a discriminator circuit of the Autotune that sometimes will crap out and also hang things up.

Unfortunately, there are is no access from the front panel to the final amp tuning and loading controls that would allow you to manually tune the set in the case of an Autotune failure.

After reading about low voltage and it's effect on the autotune circuit (here and elsewhere), I tried several different "lash-ups" for a supply. The current setup sags to 27.8 volts from 28.5 volts during the high current pahse of the auotune proceedure. Grid current fine, BATT meter in middle, very low cathode current and no output.
Darn, looks like I got to get inside......