[ARC5] 6AC7 and 6AB7

[Kenneth G. Gordon]

On 5 Feb 2013 at 14:15, Geoff wrote:

> The correct family description is:
> 
> 1851  July 1938 grid cap TV pentode, became 1852 1852   late 1938
> single ended 1851 1853   late 1938
> 
> 6AB7 3/18/39
> 6AC7 3/18/39
> Later versions were marked 1852/6AC7; 1853/6AB7 and the earlier pair
> discontinued as a seperate number.
> 
> 6AG7 5/24/39 Video Pentode, scaled up 6AC7
> 
> All the above were developed as TV tubes; the 6AG7 became known as the
> best tube for a crystal oscillator in ham rigs, commercial and HB.

Mainly due to their very high P-G transconductance, which means very low 
crystal current when used as an oscillator since it takes so little current to get 
them to oscillate. 

Which I have always found to be a bit (but only a "bit") strange, since they 
are used primarily as ECOs. In an ECO the value of transconductance that 
REALLY counts is that between the SCREEN and grid. I have never found a 
value for that parameter listed anywhere, although I know such a listing does 
exist...somewhere.

Even so, the 6AG7 is possibly the best of the octal oscillator tubes....if you 
can handle the filament current. The 6CL6 is supposed to be a 9-pin version, 
of which the military used millions. The 12BY7 is a very similar tube, but not 
used much any more.

Some time ago, I bought 50 NIB military 6CL6s for under $1 each.

> The
> last 3 were available as W versions as well as micanol bases for lower
> RF loss.
> 
> I have all NIB including the very scarce 1851.

I have two NIB 1851s...

I got them very cheaply off eBay. No one else bid on them. They probably 
didn't know what they were...

Ken W7EKB