Hi Pete, been up on the 170' tower most of the day so sorry I missed ur
post. Anyway here are my own comments.
On Sat, 06 Sep 1997 13:23:18 Pete Smith <n4zr@contesting.com> writes:
>Thanks to all who responded to my tale about the flash/bang/bad smell
>in my
>SB-220.
>
>Turns out that a non-standard 1-ohm resistor in one anode lead had
>failed open.
Yep, told you to take that junk out of the plate circuit awhile ago.
SNIPS.
>
>Anyway, next step was to replace both parasitic suppressors with ones
>supplied by KM1H. With both tubes back in their sockets, I applied
>plate
>voltage - no problems. I then keyed the amp's bias on. Trouble. At
>a
>resting current of about 140 ma in SSB position (about 100 ma in CW
>position), one of the final tubes (I *think* the one that didn't have
>the
>anode resistor failure)
"Think" is not acceptable....which is which?
is showing slight color. In the tune position
>on
>my TS-930, in CW position on the SB-220, with about 25 watts indicated
>drive, indicated output power is about 300 watts, but the same tube is
LOTS OF SNIP
>
>The amplifier appears to operate normally on all bands, except for the
>unbalanced tube color. BTW, on 10 meters operation is very similar to
>that
>before I replaced the parasitic suppressors.
What does that mean? A 220 will typically run 900W out on 10M even when
it will do 1300W on 20 or 40. That stock Pi-Net and associated wiring is
NOT an efficiency enhancer.
Output on the lower
>bands is
>right where it was before.
>
>It's possible that the tube color has unbalanced been this way since
>day 1.
> I'm looking a lot harder, and the outer cabinet is off now, where
>before I
>could only see them from directly above.
There could be an inbalance. Are both tubes original or from the same
production run? Is one with and the other without the phenolic base?
Are they both from the same mfg? Its been weeks since we started
this...excuse any memory lapses Pete.
Assuming no damage, the one running the hottest is the better of the
pair. It is doing a higher percentage of the work and therefore shows
more color.
>
>Finally, my questions: Is this imbalance perhaps a function of
>something
>happening during the glitch? Should a 3-500Z show color while idling
>at 70
>ma (140 ma for 2)?
The 140ma tells me both tubes are quite functional particularly if you
see 70ma per tube.
This makes me wonder about the cooling.
The 220 MUST have the rear aluminum plate in place otherwise cooling
suffers dramatically. The 220 is also known for fan slowdown with time.
Any combination of the above WILL result in problems AND the cooling
circuit does not treat each tube equally. Get a Harbach High Speed fan if
you decide to replace...the extra $1 is well worth it.
I have noticed, many times, unequal color and simply swapping position
often helps. I have no intention of trying to explain why....or even
give a hoot. To paraphrase the great Yogi Berra " What woiks, woiks".
Hey...1300W is not shabby. Enjoy the Sprint....
73....Carl KM1H
I leave the heavy stuff to the "experts"
All other things appearing OK, will I do any
>additional
>harm operating the amp in a short, intense CW contest? Should I be
>looking
>for a new tube or pair?
>
>Thanks all, for your help and patience.
>
>
>
>73, Pete Smith N4ZR
>n4zr@contesting.com
>
>
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>
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