Off subject

[Garey Barrell]

I guess we're into a matter of semantics now...

I don't see the difference between -

"Adjust PLATE for plate current dip and adjust LOAD for maximum power
out.  Do this alternately until there is no further increase in power output."

- AND -

"tune for maximum output" assuming RF TUNE, PLATE and TUNE are the
operative controls, and the final is properly neutralized.

Actually, Drake later issued a change saying to keep final plate current to
a maximum of 340 mA, presumably to comply with FCC regulations regarding
purity of emissions.

Certainly a small fan to exhaust the hot air away from the final
compartment will go a long way to increase the life of final tubes, regardless.

None of which has anything to do with my original statement that running a
final at reduced plate loading results in increased screen current which
applies to both 6JB6's and 6146's!

73, Garey - K4OAH
Atlanta

At 06:12 PM 12/7/2002, Gerald C. Lemay wrote:
>I'm looking at the T-4XC manual. On page 3-1 and continuing on page 3-5 the
>proper tuning procedure is described. Adjust PLATE for plate current dip and
>adjust LOAD for maximum power out. Do this alternately until there is no
>further increase in power output. It doesn't simply state to adjust both
>PLATE and LOAD for maximum power out. Doing so will exceed the plate power
>dissipation of the 6JB6A's. Sure it's possible to much more than 120 watts
>out but your finals won't last too long at that rate. The plate dissipation
>rating of those tubes is only 17.5 watts. I don't know about 6146's but I
>suspect they could probably take much more of a beating because they're
>transmitting tubes.
>
>-----Original Message-----
>From: Heathkit Owners and Collectors List
>[mailto:HEATH at LISTSERV.TEMPE.GOV]On Behalf Of Garey Barrell
>Sent: Saturday, December 07, 2002 4:17 PM
>To: HEATH at LISTSERV.TEMPE.GOV
>Subject: Re: Off subject
>
>
>No-one has mentioned the downside of "lightly loaded" pentode or beam power
>stages.
>
>The screen current will increase, even to destruction.
>
>Drake also says to "tune for maximum output", and running at reduced
>loading will melt screens in 6JB6's.
>
>The correct way to reduce the power output to increase tube life is to tune
>for maximum (or tube specifications if less) and then reduce drive to lower
>the output.
>
>73, Garey - K4OAH
>Atlanta
>
>At 01:47 PM 12/7/2002, Glen Zook wrote:
> >However, the comment that I replied to was that you
> >tune ALL of the pre-1975 equipment, not just the
> >TS-520, for maximum output which is definitely wrong!
> >I did point out that the manuals for some equipment do
> >tell you to tune for "maximum smoke", although those
> >transmitters are in a very definite minority.
>
>snip >>><<<

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