[Milsurplus] 6AC7 tubes?

[Kenneth G. Gordon]

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