[ARC5] 12 V Power pentode.

Mon Apr 11 14:04:02 EDT 2016

Ron,

Well, pretty much all-of-the-above. The frame-grid construction buys you a
lot.

They pull higher peak currents for a given plate voltage, which improves
efficiency by allowing a shorter conduction angle for class C service. The
shorter conduction angle also makes them superior as harmonic generators
when used as class C oscillators or as multipliers.  I have achieved up to
60% plate efficiency when doubling to 20M in a single-tube QRP rig and the
keying was excellent.  Absolutely no problem coaxing 5W out of a single
tube in CW service while staying well within plate voltage ratings. They
require less drive power and drive voltage, which leads to less crystal
current or LC loading.  They require less neg bias voltage to implement
grid block keying and when cathode keyed the key-up free cathode voltage is
relatively low across the key.   They have low internal feedback and good
screening and independent suppressor grid pins so the plate doesn't
interfere with the grid's business.  Just a better all-around tube choice.
Think of these video amp tubes as a next generation 12BY7 or 6CL6.  Plus
they are cheap and readily available.  You can fish them out of boxes of TV
tubes at swaps or pull 'em yourself from an old TV or buy 'em on eBay.
Nobody will want them but you....the opposite of fighting off audiophools
for triodes.

Dennis AE6C

On Mon, Apr 11, 2016 at 9:51 AM, Ron Barlow <imalowfer at yahoo.com> wrote:

> Hi Dennis et all,
>  Good info on the video amp pentodes! I am curious--When you state that
> these video amp types will run circles  around the 6F6 in class "C"
> service, are you referring to power gain, DC to RF plate conversion
> efficiency, or some other operating parameter?
>  The ultra high  transconductance rating of 32,000 micromhos, for some of
> these gems, would suggest that their power gain is very high. I have used
> them in xtal oscillator service, but not in a stabilized amp  stage.
>  That 11 watt plate dissipation rating is particularly impressive when one
> realizes that some of the early horizontal deflection tubes (6BQ6, 6AU5,
> 6AV5, etc.) had 10-11 watt plate dissipation ratings.
>                                      73 de Ron
>
>
>
> On Sunday, April 10, 2016 6:08 PM, Dennis Monticelli <
> dennis.monticelli at gmail.com> wrote:
>
>
> Gentlemen,
>
> The video amp power pentodes have significant plate dissipation
> capability, especially those designed for color TVs like 12HG7 and 12GN7.
> They can handle some serious power.  I know because I have built
> transmitters with them.
>
> The 12HG7 is 10W plate dissipation and the 12GN7 is 11.5W.   The 12BY7 at
> 6.5W is a relative lightweight.
>
> Of all the octals mentioned in this thread only the 6F6 can claim to be in
> the same league with its 11W plate rating.  However, it's plate current vs
> grid voltage curves are significantly inferior.  The HG7 and the GN7 will
> run rings around it in class C where peak cathode currents really matter.
> I know this from experience not just IV curves.
>
> If Ken's application is RF then there is the added advantage of plate to
> grid isolation in favor of the TV tubes.
>
> BTW, I have seen 12HG7s in larger diameter envelopes than the standard 9
> pin bottle, giving the appearance of better heat shedding.
>
> Dennis AE6C
>
> On Sun, Apr 10, 2016 at 2:21 PM, Leslie Smith <vk2bcu at operamail.com>
> wrote:
>
>   Hello All,
>   The 1941 RCA handbook (May 1, 1942) lists the 12A6 as a "beam power
> amplifier"
>   I was surprised to see how many "beam" tubes were used, and how few
> "pentodes" (as distinct from 'beam' tubes) were used as power amplifiers.
> Even the 12AQ5 is a beam tube.
>
>   I don't know much about 'tubes' or the history of 'tubes' but it seems
> to me that the 12A6 (or 25A6) was the 'grandfather' of  the beam 'tubes'.
>
>
>    73 de Les Smith
>    vk2bcu at operamail.com
>
>
>
> On Mon, Apr 11, 2016, at 04:26, Dennis DuValll via ARC5 wrote:
>
>
>
> Ken,
>
> How about the 12A6?
>
> Dennis D.  W7QHO
> Glendale, CA
>
> ****************
>
>
>
>
>
>
> On Apr 10, 2016, at 6:03 AM, Phillip Carpenter <carpenterpa at tds.net>
> wrote:
>
> Ken,
>
> All I could come up with was the 12BY7 9 pin miniature and the 25A6 octal
> which has a 25 volt filament.
>
> Respectfully,
>
> Phillip
>
> Sent from my iPhone
>
>
> On Apr 9, 2016, at 11:47 PM, Kenneth G. Gordon <kgordon2006 at frontier.com>
> wrote:
>
> Does anyone here know of a power-pentode, which is 1) not a beam-tube, 2)
> has a 12.6 V filament, and 3) might have an octal base?
>
> #3 isn't all that important: I can build an adapter. But #s 1 and 2 are.
> And #1
> is of prime importance.
>
> I can't think of any.
>
> Anyone?
>
> Kenneth G. Gordon W7EKB
>
> "Courage is being scared to death but saddling up anyway."--- John   Wayne
>
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