[Hallicrafters] HT37 problem----solved?

[Bill Gerhold]

Hey, glad to hear you solved the problem, strange as it is.  Perhaps your
tube tester is not giving you correct information.  That's the only thing I
can think of.

But, why worry.  It just goes to show you that your troubleshooting style is
still intact because you thought of swapping numerous tubes since nothing
else could possibly be giving you the problem.  So in a nut shell, you did
the proper thing and performed magnificent and unimpeachable
troubleshooting. 

K2WH

-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Joseph Trombino
Jr
Sent: Monday, September 12, 2005 6:11 PM
To: Hallicrafters
Subject: [Hallicrafters] HT37 problem----solved?

Howdy Gang:

I have posted to this list my travails in getting my HT37 to arise from the 
dead.

I had been finally able to get full output on DSB and CW but had been unable

to null the carrier in the SSB mode....I was getting full carrier output 
when I went to the MOX position or when I talked into the mike in the VOX 
position.

OK...so I am playing around with it today and just for grins I decided to 
swap out the balanced modulator tubes V4 and V5. (I had installed NOS 
12AT7's from the git-go with no joy)

First I tried a couple of 12AU7 tubes with no joy...then I tried two NOS 
12AX7's with no joy and then from among the NOS 12AX7's I tried another pair

and lo and behold I can null the carrier and can hear good SSB in a monitor 
receiver.

I can't explain why this is happening....I originally checked the 12AT7 
tubes in my B&K 747B tester and they indicated GOOD....and I swapped out the

original tubes with NOS 12AT7's and still couldn't null out the carrier.

Why is this happening????  The tube called for is a 12AT7 not a 12AX7...why 
didn't the several 12AT7 tubes work???

And why do only two out of four NOS 12AX7 tubes work???

I checked all of these tubes on my tube tester previously and they all 
indicated GOOD.

Some might say to not trust a tube tester....if so, then why do we have tube

testers at all???

OK...so now it appears that only one of the balance pots appears to nulling 
the carrier....the other pot does't seem to do anything yet the carrier is 
fully suppressed.......man, do I hate these old boatanchors (grin)

It just isn't fair to play these games on a 60 year old ham who certainly 
isn't the sharpest tool in the shed......my hair is already gray so this 
experience won't hurt me (grin)

I have been on this rig for several weeks off and on and thought it was a 
hopeless case.....just goes to show you about persistence, I guess.

Has anybody had a similiar totally unexplainable, illogical experience???

                                        73, Joe W2KJ 


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