[Hammarlund] JAN tube caveats

[Jim Wilhite]

Craig you story is very interesting.

However my experience is quite different with JAN tubes.  I, like 
many of us, have several receivers with 6BE6s in them.  Over the 
years I have had my share of the commercial versions.

I own an HRO 60 which began to loose sensitivity a few years 
back.  I found a 6BE6 that had gone soft so I replaced it with a 
NOS version I had in my stock.  Before I installed it I checked 
it on a Western Electric KS15650 tester.  The tube just made 
specs.  I also had a Hickok 600 and tested the tube on it only to 
find the same results.

I installed it and the radio perked up quite nicely for about a 
year.  It developed the same symptoms so I checked the 6BE6 again 
and it was weak.  I thought I had circuit troubles so I did 
resistance and voltage checks of the circuit.  Everything checked 
  just fine so I went to the stock to pull another 6BE6.  So 
happened I had the JAN equivalent so I put it in the WE tester. 
To my surprise it checked well above the specs for the tube.

I put the 5750 in the receiver and it came back on just fine.  It 
has been playing now for over two years without a hint of trouble.

It is my understanding that when checking tubes on the line, 
those that checked better than the norm were marked for the 
military and those that just made quality control went to the 
commercial market.

This is not to say you won't have failures with either in 
service, but my testers say the JAN versions has far more 
transconductance than the commercial versions.  If that is the 
case, they should last longer in service.

I have since ordered JAN versions for everything I need and, when 
checking on the tester, they have better emissions.  I wonder if 
you found a used batch or a bad batch from the factory.  It is 
highly unusual to find different tubes with the same problem. 
Can't explain that.

73  Jim
W5JO


Craig Roberts wrote:
> It's happened again -- twice!
> 
> Arriving home after a pilgrimage to Howard Mills' place last Friday, I 
> was anxious to listen to my "new" Collins R-388 after "the man"  had 
> played with it. It was sure that it would sound much better after Howard 
> had aligned the radio (he does this in about 15 minutes as opposed to 
> the hour and a half it takes me), and housed it in one of his beautiful 
> powder coated cabinets (he's still got some -- and they're well worth 
> the $$$$).
> I was wrong.  In fact, the radio sounded worse. It barely played at 
> all.  Sure, the S-meter wiggled convincingly and signals could be heard, 
> but they were very faint -- barely audible with either speaker or 
> headphones. After staring under the new flip-top hood for a couple of 
> minutes, I started wiggling things.  When I got to the back of the radio 
> and tweaked the audio tubes, I heard an odd crunching sound from one of 
> the 12AX7s.  I removed the tube shield and half the glass envelope came 
> with it.  A CLUE!!  Replacement of the tube solved the problem.
> Okay, it wasn't a "real" 12AX7. It was a JAN 5751.  I had opted for it 
> when retubing because the military tube costs a few bucks and is readily 
> available from the guys who have inherited the vast stocks of the 
> gummint surplus tubes that will outlast us all.  A "real" 12AX7 -- one 
> of the Holy Grails among the audiophile/guitar amp junkie set, is now 
> priced at $20 and up -- way up.
> 
> The 5751 and 12AX7 are not the same tube.  The gain of the 5751 is about 
> 30 percent less and the current draw a little more.  On the other other 
> hand, it's allegedly "smoother" (according to famed guitarist and 
> apparent vacuum tube aficionado Stevie Ray Vaughn).  I doubt that any of 
> this matters much to us low-fi boatanchorites, but there it is.  Fact 
> is, my 5751 broke in half for some reaon.
> 
> Then yesterday my R-388 suddenly lost sensitivity and some AVC action.  
> The sensitivity issue went undetected for awhile since the bands 
> yesterday (to use technical jargon) sucked, but the audio distortion was 
> unmistakeable.
> Now, the old manuals always adviseus to suspect bad tubes first when 
> troubleshooting.  Despite the fact that the age of our boatanchors' 
> components can spell failure almost anywhere in our sets, it's still not 
> a bad idea to check tubes first.  I did, and found a three-day old NOS 
> 6BE6 to be faulty.  Okay -- once again -- it wasn't a "real" 6BE6, but a 
> JAN 5750 "equivalent".  This tube was physically intact, but betrayed an 
> internal short.  Plugging in an old, "real" 6BE6 solved the problem.
> 
> A couple of similar JAN tube failures, including another spontaneous 
> glass envelope cracking in an OA2WA, have struck other gear in my shack 
> over the past year or so.  On the other hand, none of my "civilian" 
> tubes has failed in catastrophic fashion -- ever.
> Sometimes, JAN and civilian equivalents aren't equivalent at all. (I had 
> a 32S-1 that simply refused to work with JAN tubes in a couple of 
> circuits). Tube data sheets will reveal the differences. And sometimes, 
> I suspect, the quality control of JAN tubes suffered. In my experience 
> the bad JAN tubes seem to be the ones produced in the later years (after 
> the Vietnam era).  So, I would advise anyone retubing a boatanchor to be 
> a bit cautious about the JAN tubes -- especially the later ones -- and 
> check them first if and when something goes wrong suddenly.  Of course, 
> the best course of action might be to follow the advice of many 
> knowledgeable folks and not retube just for the heck of it. Y'know, "if 
> it ain't broke...etc."
> 
> Anyone else had interesting adventures from the use of JAN tubes?
> 
> 73,
> 
> Craig
> W3CRR
>