[ARC5] 6AC7 and 6AB7

[Geoff]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at frontier.com>
To: "ARC-5 List" <arc5 at mailman.qth.net>
Sent: Tuesday, February 05, 2013 3:20 PM
Subject: Re: [ARC5] 6AC7 and 6AB7


> 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

Tube collectors may be after the 1851 if enough of them are around. I just 
like octal tubes, especially metal ones. Might make a good swap for a noisy 
6K7 followed by a 6L7/6K8 but you need an old tube socket pin as a grid cap. 
Then just use it on 10-15M where the AVC action wont be hurt too much on a 
quiet band and images not a bother.

Yes, the 6CL6 is the 6AG7 equivalent, I also have a bunch but not 50!

The 12BY7 (also developed for TV) was used in all the Kenwood hybrids as a 
driver and also several other rigs, also the HFO in the SX-101A. Now its an 
audiophool tube and getting a bit scarce in some places.

Cant figure where the micanol base has an effect. Ive tried the 6AB7, 6SK7, 
6SG7, and 6SA7 in a SX-28 to 44 MHz and didnt see any difference between NOS 
of either type. Also tried the 6SB7 and 6SB7Y which was developed in 1946 
for the current FM band. Have to try all in a NC-183 next which goes to 54 
MHz.

Carl