SB-220 Problems/Mods
N1MM
frequently if the CW/Tune - SSB switch is set to SSB, I get a loud pop.
When that happens, the .82 ohm resistor in the HV meter circuit blows and
I have to replace it. One time the meter went with it. It seems to be
much worse since I changed the amp over from a 15A, 115v line to a 20A,
220v line. I presume because the "under-load" plate voltage is quite a
bit higher now.
I have heard that this problem is either VHF parasitics, or dirty
capacitors. Has anyone in this group solved this problem? Is there a FAQ
on this?
Also, what is the general concensus on directly grounding the SB-221's
grids?
Any help would be greatly apprciated.
Thanks.
Tom - N1MM
Barrie Britton
On 26 Dec 1995, N1MM wrote:
> I'm having trouble with my SB-221. Once in a while on 10 meters, more
> frequently if the CW/Tune - SSB switch is set to SSB, I get a loud pop.
> When that happens, the .82 ohm resistor in the HV meter circuit blows and
> I have to replace it. One time the meter went with it. It seems to be
What you describe is a VHF parasitic. Send a SASE to Rich Measures, AG6K,
at 6455 La Cumbre Road, Somis, CA 93066 or call him at (805) 386-3734.
Rich wrote several articles for QST describing the parasitic problem,
particularly in SB-200/221 amplifiers. He sells very inexpensive (about
$15) parasitic suppressor kits for most amps. Get his article reprints also,
and buy the other SB-220 mods such as the meter protection diodes, and the
lower heat bleeder resistors.
Good luck with this excellent amplifier.
__{__ |
/ \ | Barrie G. Britton, K0WWG ARRL Life Member
| | | Electronic Engineering Done Cheap
| (o)(o) | Your Place or Mine.
@ .---_) |
| | __| | Snail Mail: 5034 Rockledge Drive
| \__/ | Riverside, California 92506
/_____\ |
/_____/ \ | E-Mail : bbri...@prolit.llu.edu
/ \ |
k0wwg | What one fool can do, another can.--S. P. Thompson
W8JI Tom
>I'm having trouble with my SB-221. Once in a while on 10 meters, more
>frequently if the CW/Tune - SSB switch is set to SSB, I get a loud pop.
You could be loosing the tubes, or another component. Sometimes the RF
chokes arc through to the mounting screw, but usually its the tubes.
>When that happens, the .82 ohm resistor in the HV meter circuit blows and
>I have to replace it. One time the meter went with it.
Put a diode protection circuit from the negative end of the electrolytics
to the chassis. The cathode of the diode (band end) goes towards the
electrolytics. Use two diodes in series and bypass them with a .1 uf 50
volt disc cap. It also doesn't hurt to add a 20 ohms 25 watt HIGH VOLTAGE
type resistor in series with the positive supply lead. The SB220-221 RF
choke has very low surge limiting resistance.
>much worse since I changed the amp over from a 15A, 115v line to a 20A,
>220v line. I presume because the "under-load" plate voltage is quite a
>bit higher now.
The problem is likely peak voltage related.
>I have heard that this problem is either VHF parasitics, or dirty
>capacitors. Has anyone in this group solved this problem? Is there a
FAQ
>on this?
The parasitics thing is sort of a "fairy tale", the capacitor thing is
sometimes true, but the tubes are the most likely cause.
>Also, what is the general concensus on directly grounding the SB-221's
>grids?
That should be done if you can do it. That circuit was a design mistake.
It adds unwanted feedback and decreases the performance of the amp. By all
means, ground each grid pin directly to the chassis by drilling a hole
near EVERY grid pin and adding a lug. Remove the tubes first!
But the tubes may just be "gassing up". If so, they will arc once in a
while when plate voltage peaks are reached. Ten meters has the highest Q
and most touchy tuning, so it's more likely the PA peak anode voltages
reaches a few times the dc supply voltage there. When that happens, if the
tubes or some other component is "on the edge" and the peak voltage goes
past the safe point.....pop!
By the way, if the tubes are metal anode types, do you get the tubes red
once in a while to de-gas them?
73 Tom
Wes Stewart
>From: Barrie Britton <bbri...@prolit.llu.edu>
>Subject: Re: SB-220 Problems/Mods
>Date: Tue, 26 Dec 1995 21:43:21 -0800
>On 26 Dec 1995, N1MM wrote:
>> I'm having trouble with my SB-221. Once in a while on 10 meters, more
>> frequently if the CW/Tune - SSB switch is set to SSB, I get a loud pop.
>> When that happens, the .82 ohm resistor in the HV meter circuit blows and
>> I have to replace it. One time the meter went with it. It seems to be
>What you describe is a VHF parasitic. Send a SASE to Rich Measures, AG6K,
>at 6455 La Cumbre Road, Somis, CA 93066 or call him at (805) 386-3734.
>Rich wrote several articles for QST describing the parasitic problem,
>particularly in SB-200/221 amplifiers. He sells very inexpensive (about
>$15) parasitic suppressor kits for most amps. Get his article reprints also,
>and buy the other SB-220 mods such as the meter protection diodes, and the
>lower heat bleeder resistors.
Before you do this, locate the "Technical Correspondence" letters in QST
regarding these articles. I don't have them at hand, but they were written by
a couple of knowledgeable people, including one from EIMAC. They basically
debunk the articles. Don't try to contact the EIMAC guy, however; I tried,
including a SASE and never got the courtesy of a reply :(
W8JI Tom has better advice.
>Good luck with this excellent amplifier.
73, Wes
N1MM
parisitic mods, and they did not seem to help. I'll give the other advice
a try. Anyone else have experience taming a '220?
Tom
P.S. Thanks again.
Tom - N1MM
C. J. Hawley Jr.
snip:
> By the way, if the tubes are metal anode types, do you get the tubes red
> once in a while to de-gas them?
What happens here to the gasses? Do they change chemically and become attached to
something? Something like the getter? How did that work? Wasn't it Magnesium or
some such which was vaporized inside the tube and chemically or mechanically
bonded or absorbed the gas and stuck somewhere? If the plates are made hot, then
this would work against the getter residue, so they must not use getters in
transmitting tubes? But, the plates would absorb gases if they are made out of
Tantalum (and what other materials?) and became very hot. I read that (Terman)
Zirconium will absorb Hydrogen up to 350C but will give it back above that. Then
if you have Zirconium also at 1400C it will greatly absorb other gasses. They can
put two Zirconium filaments in at these two temps to clean up continuously. What
does Eimac make.....say the 3-500 plates out of and if there are hydrogen and
other gasses inside the tube over time then what is the analysis if you raise the
tube plate to cherry red. All hydrogen? Is that better or worse than never going
above 350C? Is that impossible in a transmitting tube? How hot is just below any
color change? I suppose Eimac has studied this?
Sorry....just triggered my interest, cause it sounded like a well known fact that
I am ignorant of.
Chuck, KE9UW
W8JI Tom
In article <30E1A9...@aries.scs.uiuc.edu>, "C. J. Hawley Jr."
<haw...@aries.scs.uiuc.edu> writes:
>What happens here to the gasses? Do they change chemically and become
>attached to something? Something like the getter? How did that work?
<snip>
That's my understanding. The gas attaches to the getter and move it down
the periodic chart a bit. Different materials work at different
temperatures. I'm not up on small tubes that work at room temp. 3-500Z's
have Moly anodes coated with Zirconium. That's the gray powdery looking
stuff you see. It's built to run at around 1000 deg C, so the red color of
the anode activates the getter! If you don't run "em red, they can
eventually fail from gas!! That also limits shelf life, because how do you
de-gas a gassy tube if the anode has to be operated at color to activate
the getter?? (Well I know how, but it takes a variable HV supply and an
adjustable positive grid bias, hi).
>If the plates are made hot, then this would work against the getter
residue, so they >must not use getters in transmitting tubes?
Yes they use getters, just different getters with higher temp ranges.
> But, the plates would absorb gases if they are made out
>Tantalum (and what other materials?) and became very hot. I read that
>(Terman) Zirconium will absorb Hydrogen up to 350C but will give it back
above that.
>Then if you have Zirconium also at 1400C it will greatly absorb other
gasses. They
>can put two Zirconium filaments in at these two temps to clean up
continuously.
Gotta watch mixing the wrong materials. The 8877 uses a heat dam of
Tantalum discs on the fil/cathode assembly because Zirconium would poison
the oxide cathode.
If they used a Tantalum anode as the exclusive getter in the 3-500 it
would not cover the temp range. Everything gets too hot.
They do stuff differently depending on the application. I'm sure they
often use a material just because they are comfortable with it, and they
know it worked in other similar tubes, hi.
Phew.
Anyway, here's the rule Chuck. If you have a Eimac thoriated tungsten
power triode with a gray powdery looking anode you betta keep that anode
red. If you don't, you'll probably get gas in the tube. (and if you think
a kindney stone hurts, wait til that happens)
>Is that better or worse than never going above 350C? Is that impossible
in a >transmitting tube?
It is in a 3-500! The filament operates around 1500c and the anode should
be run at around 1000c!
73 Tom