[Boatanchors] Tube Recommendations???

[Rob Atkinson]

I'll venture to say that every ART-13 op has 811As due to the scarcity of 811s.

Comparing the tube data, the inter-electrode capacitances are slightly
different but not so much that it should be a problem.  At 1500 v. in
modulator service, there's a difference in grid bias between the two.
I'll bet that below that both are zero bias.  The 811 p. to p.
impedance at 1500 v. is 18K; the 811A p. to p. Z is 12.4 K.  I don't
have any operating data for the 811 for under 1500 v.  I think those
are the differences besides the obvious higher plate dissipation, and
power capability for the 811A.  I'd put in 811As and see how the rig
sounds because this seems like the 6146_/A/B controversy in the
making.

73

Rob
K5UJ

On Thu, May 21, 2020 at 6:24 PM Michael D. Harmon <mharmon at att.net> wrote:
>
> I have a couple of surplus ART-13A transmitters, and I'd like to get a
> spare set of 811 modulator tubes.  Someone told me some time ago that I
> should use the original 811 tubes rather than 811A's. Is there any truth
> to that?  The 811A's are built heavier than the 811's, and they are
> certainly easier to find.  Is there any reason to try to find a set of
> good 811's or will the 811A's work OK in the transmitter? Are there some
> characteristics that make one better than the other?
>
> Thanks for the advice!
>