[ARC5] [Milsurplus] 6AC7 tubes?

[CARL HUETHER]

Excellent reply Ken.

Included in that list is the 6AB7 which is a remote cutoff version of the same design but still seriously loads down the input circuits of receivers it is swapped into. Hallicrafters used it in later SX-28's and the SX-28A to replace the 6SK7 first RF amp and its positive and negative effects are very noticeable.

A pair of 6SG7's are a better choice these days along with a 6SB7Y mixer for above 12-14 MHz or so.

Carl





> On October 22, 2019 at 12:17 PM "Kenneth G. Gordon" <kgordon2006 at frontier.com> wrote:
> 
> 
> On 22 Oct 2019 at 5:12, hwhall at compuserve.com wrote:
> 
> > Is there any interest in 6AC7 tubes? I keep passing up a bunch that are probably old stock in 
> > boxes because they don't seem to get any interest at Ebay or elsewhere.  Should I buy some of 
> > these for anyone in the Mailman radio groups?
> > 
> > Thanks,
> > Wayne
> > WB4OGM
> 
> 6AC7 is an excellent tube. Very robust, and exhibits high transconductance. The military 
> ordered millions of them, notably for use in later WWII VHF gear.
> 
> They make excellent crystal oscillators (usually ECOs), IF amplifiers where AGC is not 
> used, and pentode mixers. 
> 
> As mixers, they are noted for being very quiet and having good gain.
> 
> As RF amps, they tend to load the input tuned circuits too much, broadening those, unless 
> the circuitry is adjusted to prevent that.
> 
> For instance, don't sub a 6AC7 for a 6SK7 type. Doesn't really improve matters.
> 
> In addition, they are a sharp-cutoff pentode and thus ruin any AGC action connected with 
> the RF amp.
> 
> I, personally, have at least a dozen NIB here and don't really need any more, but I use them 
> regularly in circuits I build.
> 
> Ken W7EKB
> 
> 
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