[R-390] 6BJ6/6BH6 sub

[Dan Merz]

Hi all,  I'm back with a 6BJ6 in the 390 i.f. in place of the make-do 6BH6
sub that I used for a week or so.  Much thanks to the generousity of one of
you for sending me what I didn't have on hand.  The radio seemed to operate
about the same with either the 6BJ6 or the 6BH6 (i.e. the signal I was
listening to sounded the same)  but I can't say I explored any extreme
situations that might reveal a difference with regard to agc action and
front end overload.  But I'll accept the conventional wisdom and feel happy
that my 390 is now operating more like it was intended to operate,  thanks
all,  Dan.

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of David Wise
Sent: Monday, March 06, 2006 2:26 PM
To: r-390 at mailman.qth.net
Subject: RE: [R-390] 6BJ6/6BH6 sub

Affirmative, strong-signal performance will be suboptimal, with increased
vulnerability to overload and cross-modulation.
If it takes less AGC than normal to achieve a given gain (the case with a
6BH6 sub), then the front end is running hotter than intended, which means
it takes less signal to drive them positive.
Your carrier meter will also read low.

The "3D" in your copy of my old post is the tilde character, meaning
"approximately".
Most of those tubes can't be compared apples-to-apples from the specs, as
some are tabulated for a given plate current, others for a given
transconductance.  (It would be possible to get closer with many models of
transconductance tube tester.)  I only meant to list all the ones I could
find that would operate, with no implication that they would do well.
It seems odd to me that the 6DC6 is less than abundant; it was made for
TV's.

73,
Dave

> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of n4buq at knology.net
> Sent: Tuesday, February 28, 2006 11:52 AM
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] 6BJ6/6BH6 sub
> 
> 
> Okay.  I had them reversed.  I thought that didn't make sense, but now 
> it does.
> 
> Thanks!
> 
> Barry
> 
> On Tue, 28 Feb 2006 14:23:37 -0500, "Tim  Shoppa" <tshoppa at wmata.com> 
> wrote :
> 
> > > Okay, now it's time to educate me on this issue.  If the 6BH6 is a
> > remote
> > > cutoff tube, then it won't go into cutoff as "early" as the sharp
> > cutoff
> > > 6BJ6, right?
> > 
> > Other way around: 6BJ6 is remote cutoff, 6BH6 is sharp cutoff.
> > 
> > The 6BJ6 was the original IF tube. 6BH6 is the sub.
> > 
> > >  If that's the case, then why will you see distortion on strong 
> > > signals with the remote cutoff tube?
> > 
> > Actually either will distort with very strong signals. And when 
> > you're subbing around it's likely that biases etc will be quite 
> > unoptimal for critical use.
> > 
> > Tim.
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