On Sat, 18 Oct 1997 22:22:45 -0500 w5hvv@aeneas.net (Rod Fitz-Randolph)
writes:
>WA4VWR just bought a pair of Eimac 3-500Zs (found them in Washington
>state) to replace the pair that he had been running since 1974. Much
>to his amazement, when he plugged them in and fired them up, they
>drew only 140 ma of resting plate current instead of the usual 190 ma
>of plate current that he was use to seeing.
>
>Further, he says that there is a little bit of crossover distortion
>on this new pair that did not exist on the previous set.
What on earth is "crossover distortion" ? That sounds like an audio term
related to speaker networks.
Why did he replace the originals?
It sounds as if one or both of the replacements may be soft.
Check idling current one tube at a time. Also try running one tube at a
time on 40M with 50W of drive. Record the outputs; they should be almost
identical.
If the originals were replaced due to a failure be sure to check the
chokes and caps at the grid pins.
>When I questioned him as to what the manual said they should draw, he
>confessed that he has misplaced his user's manual and doesn't
>remember.
All the manual says is approximately 120 ma in the CW position.
In the SSB position 180-200ma is fine.
GL Carl KM1H
>All he remembers is that the previous pair drew 190 ma vrs 140 ma on
>the new set; the new set has more crossover distortion; and the new
>set
>does not give him as much power out (by 100 watts) as the old set did.
>
>He wonders if he got a bad set of tubes. I volunteered to put the
>info
>on the AMP reflector and would relay any e-mail messages to him.
>
>Any experiences, ideas, opinions on this is most welcome.
>
>Thank you and 73,
>
>Rod, N5HV
>w5hvv@aeneas.net
>
>
>
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>
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