[TenTec] TT 238B Question(s)

[k8jdc@sbcglobal.net]

Hi all.  I just bought a used 238B from a ham in CA.  (I'm in OH).  I received the tuner yesterday and have been testing it out.  I've never used a 238 before, nor have I used a tuner with a roller inductor before, so those are new items to me.  I thought I would post a few points and get some feedback from other 238 owners.  (My testing has been primarily done with a 135ft dipole fed with 450-ohm balanced line.  I have the transmission line connected to the balanced inputs plus the extra wire going from one balanced terminal to the single-wire terminal.  Thus far, I have only run 100W thru the unit).

1.  I opened the tuner and have not noted any burn marks or evidence of arcing or abuse.  The only thing I noted visually was that the roller inductor wheel seems to be a little rough to me.  The coil turns are perfectly smooth, but the traveling wheel doesn't seem to be as smooth as I would expect.  The unit overall is in perfect condition cosmetically, so I don't see any signs that the previous owner abused it.

2.  This tuner doesn't seem to be 100% healthy to me.  The 1.5:1 bandwidth (>5% of the band) reported by ARRL in their QST review doesn't seem to be available in my unit.  On 40m, 5% equates to about 350 KHz, or coverage of the entire band with 1.5:1 or better.  My 238B is showing about 115 KHz, which is LESS THAN HALF of the expected value.  Is this because I may be using an improper switch setting on the High/Low-Z switch?  (For the record, my 40m settings were High #1, Cap @ 4.8, and Inductor @ 9.9 using the antenna I described above.)

3.  I found tuning to be VERY difficult.  I followed Tentec's instructions, but it was a lengthy process.  Once I found matches on the various bands, they have been repeatable, so this difficulty should hopefully be a one-time problem, but it was not as intuitive as I expected.  When I tried different switch settings on the High/Low-Z switch, it didn't seem to make much difference in most cases.  Most of the matches that I found used either Low #1 or High #1 settings.  Does this sound right?  Finding a match in most cases involved several minutes of hunting.

4.  The meter on my unit was totally out of whack in terms of accuracy.  The SWR readings are way too low and the forward power readings were way low.  I was able to adjust the pots to fix the forward power discrepancy, but I have not been able to fix the SWR reading.  It is still too low.  I have the set knob adjusted correctly and have tweaked C16 as described in the manual.  While my radio and external Palstar meters are showing a 2:1 VSWR, the 238B meter is showing about 1.3:1 or so.  I can't seem to get it to get any closer.

5.  The roller inductor is not nearly as smooth as I expected.  I've already mentioned that I've never used a roller inductor tuner before, so I'm not certain what I should expect.  When I spin the knob on the roller inductor using the little knob protrusion, it takes enough force that I usually move the tuner around physically.  It doesn't spin effortlessly.  I usually have to hold the tuner with one hand to keep it still while I adjust the inductor.  If I just adjust the knob slowly using the entire knob instead of the little protrusion, this obviously isn't a problem.  I have opened up the unit to inspect the roller inductor while I adjust it and can't really see anything out of alignment.  What should I expect on this?

I would appreciate your feedback on this.  I hate to think that I may have bought somebody else's problem child.  So far, the tuner is certainly usable, but I would have to say that it's not what I expected in terms of quality and performance.  

Thanks and 73,

Dave / K8JDC