[R-390] 12be6

[Al Parker]

Hi Steve,
    Your subject says 12BE6, the body says 6BE6.  I hope you're using 6BE6's 
in your SP-600, 12's sure would have to be "specially selected" to work.
    Get your manual out (if you don't have one, go to The Hammarlund 
Historian website and download one for free), and do some voltage and 
resistance checks at the mixer (you don't say which one, 1st or 2nd).  The 
SP-600's are notorious for 2 things, bad, leaky, BBOD's, and resulting 
resistor value shifts.  If your SP-600-JX-17 has a ser. no. above about 
17,500, then it probably has disc ceramics, and much less problems.  If it's 
the 2nd mixer that's your problem, directly check the resistors around that 
tube, particularly ths screen dropping resistor, R40 20k 1 watt, and the 
subsequent bypass cap, C106.  If it's the 1st mixer, you'll have to use the 
resistance chart in the manual as a guide, as you can't get to that tube 
socket without removing the RF deck, but can get creative.  If you have 
BBOD''s rather than discs, you'll want to remove the RF deck and replace all 
20+ of them, and check all resistors in there.  Not a trivial job, but one 
that can be done.
    There's a great article by Ray Vasec, W2EC, in the Service section 
that'll give you some good pointers on how to do the complete job.
73,
Al, W8UT
New Bern, NC
www.boatanchors.org
www.hammarlund.info

----- Original Message ----- 
From: "Steve Hobensack" <stevehobensack at hotmail.com>
To: <r-390 at mailman.qth.net>
Sent: Wednesday, June 27, 2007 7:47 PM
Subject: [R-390] 12be6


>
>    My SP-600 jx17 is finicky about the 6be6 mixer. Some seemingly good 
> 6be6 will not work. I wonder what passive component in the associated 
> circuit might be getting out of spec ?
>  ...Steve...N8YE
>
> Message: 5
> Date: Tue, 26 Jun 2007 15:19:02 -0400
> From: "Tim  Shoppa" <tshoppa at wmata.com>
> Subject: Re: [R-390] Tube testers
> To: <r-390 at mailman.qth.net>, "Joel Richey" <richey2 at mindspring.com>
> Message-ID: <46812E660200003700008CFE at gwiavs.nservices.wmata.com>
> Content-Type: text/plain; charset=US-ASCII
>
> W2DBO wrote:
>>of em, they all tested good, took the rx outa the
>>cabanit and grabed the voltmeter and check all plate
>>and screen voltage everything looked good, worked
>>on that radio for 3 days, the 4th day my Pop came up
>>to me and handed me a box with a 12BE6 and said put
>>this in and I said I had checked all the tubes and their
>>are all good, I put the tube in and 45 seconds later
>>it was playing
>
> Seeing how the 12BE6 is a heptode and in a AA5 used
> as both an oscillator and a mixer, not too surprising that
> the tester got stumped by it :-).
>
> Most likely it wasn't oscillating and the tester used
> a grid not for oscillation for its test!
>
> I was recently working on SPICE models for heptodes
> and no tube book gives useful information for modeling.
> Had to do some 3-dimensional curve tracing!
>
> Tim.
>
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