[ARC5] 6AC7 and 6AB7

[Tim]

Hi Ken -
The 6AC7 is used as the crystal oscillator tube in the T-784/GRC-109
transmitter.  The circuit produces clean keying and is not fussy about
which particular tube is installed - they are all stable in that circuit.
Tim
N6CC

On Tue, Feb 5, 2013 at 9:07 AM, Kenneth G. Gordon
<kgordon2006 at frontier.com>wrote:

> On 5 Feb 2013 at 8:23, Ian Wilson wrote:
>
> > Where were 6AC7's actually used? They show up regularly in fairly
> > large numbers in piles of metal octals, etc. My guess is that they
> > were used as IF amplifiers in radar sets. I don't recall seeing any in
> > the Surplus Conversion Manual schematics, though, so I wonder when
> > they were introduced?
> >
> > 73, ian K3IMW
>
> You are pretty much right about how they were used.
>
> They were used in large quantities in the IF stages of WWII VHF FM
> receivers like the R-19, and in radar receivers, for instance. I think
> they were
> first introduced about the same time as the 6AG7 for use in TV receivers,
> but
> am not certain.
>
> As Carl pointed out, they tend to load the grid input circuits when used
> as RF
> amps. unless the connection to the grid is tapped down or up to compensate.
> This makes their casual use as substitute RF amps not particularly useful.
>
> Many hams used to plug them in place of the usual remote cutoff tube,
> expecting lower noise and higher performance. In many cases, all that would
> do is turn the RF stage into an oscillator.
>
> They were often used like this in BC-348s. I have no idea if this helped
> with
> that particular receiver or not. The BC-348 has a 915 KHz IF, so using the
> 6AC7 wouldn't hurt its image response too much, I suppose
>
> However, the 6AC7 makes an excellent low-noise mixer and a good IF amp
> when the circuit is designed for them. They also make an excellent
> oscillator.
>
> The military used millions of them and NIB versions are still available in
> bulk.
>
> The 6AB7 is far more difficult to find. It is listed in the RCA HB-3 as a
> "Television Amplifier Pentode" with the same two-condition screen operation
> as the 6AC7. The 6AB7 has a transconductance of 5000 umhos, while that
> of the 6AC7 is 9000.
>
> Ken W7EKB
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