[Boatanchors] SB-220 with parasitics
Rodger Singley
wq9nsc at live.com
Fri Dec 24 16:58:17 EST 2021
And this is the response I sent earlier to the original poster, I forgot to hit reply all to his question…:
Keith,
The getter for 3-500Z tubes is the anode and it needs to grow dull red to activate it.
It takes a little work but the SB-220 can be set up to activate the getter at low voltage. What you need to do is feed the amp with 120 VAC but wire ONLY the HV transformer for a 240 volt primary so that HV is cut in half. The filament/bias transformer (and fan) need to run at full voltage.
With it set up to run at ½ voltage, set the band switch to 80 or 40 meters, loading at maximum (10) and throw the plate tune out of resonance. The goal is to maximize the plate dissipation with minimum high voltage. Now apply enough drive in the CW/Tune position so that there is sufficient input that the anode just starts to glow a dark red and adjust drive to hold it at this minimal dark red for three minutes then drop the drive and let it cool for 5 minutes (keep it in transmit so that it is still drawing idle current) then repeat with drive to get it to glow dark red for three minutes. You may have to adjust the drive some during the on periods to keep the anode in the right temperature range. Repeat these on/off cycles for 30 minutes and then let the amp go into standby and run fan only for 5 minutes. Let it cool down completely and make sure that the HV is discharged before rewiring the transformer for normal primary voltage.
Try operating it in CW/Tune in transmit with no drive for 5 minutes with no drive and see if it tries to flash over again. If not, go ahead and try SSB plate voltage and let it idle for a few minutes in transmit (no drive) to get the anodes nice and hot and then let it cool in standby for a few minutes.
Once a tube flashes over, the odds of recovery aren’t great but it is worth a try.
And this is just from gas, not parasitic oscillation. Ignore all of the voodoo “fixes” from Measures, it is a huge pile of BS.
Good luck with the amp, it is nice when working properly. I still have the one I built back in 1976 and I just started building another one I found on Ebay as an unbuilt kit. The original Eimac 3-500Z tubes are still sealed in their boxes and I will run them up and condition them in a parts SB-1000 amp I converted to a tube conditioning stand. It has a variac for HV and variable bias through positive to allow it to cook a tube at low plate voltage in order to activate the getter but if you follow the procedure above, you can accomplish the same with the SB-220 itself.
Good luck and 73,
Rodger WQ9E
Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for Windows
From: w5jo at brightok.net<mailto:w5jo at brightok.net>
Sent: Friday, December 24, 2021 2:54 PM
Cc: Boat Anchors List<mailto:boatanchors at mailman.qth.net>
Subject: Re: [Boatanchors] SB-220 with parasitics
Could someone explain this to me? If a tube leaks, it will also have oxygen
in the envelope with any other gas, wouldn't it?
If it has oxygen in it, wouldn't the filament go flash and burn into?
Over many years I have inserted NOS tubes in transmitters and, following the
proper warm up period just applied power and never had a problem. Just
recently I replaced the 4-250 in my Globe King 500 with a glass bottom tube
made in the 70s without a problem. After 2 or 3 minutes of warm up I turned
on the HV and it worked just fine.
Any tube will have just a minute amount of gas in it, that cannot be
avoided, but that is the purpose of the getter to hold it during the
manufacture of the tube.
In construction this is what takes place and I don' think very many hams can
do it.
>From AI3V: Quote
What is going on is the tantalum is heated hotter than red hot (orange or
even white) while the tube is originally manufactured and connected to the
vacuum pump.
During normal operation the anode is never allowed to get that hot, so it
never outgasses any more.
This superheat or "bombardment " is a fundamental and critical part of
creating a high vacuum.
The other problem with attempting to correct a bad vacuum by sammy hammy
"gettering" is the tube, more or less cold will not work properly.
As you attempt to "getter" the rise in temperature will liberate more gas,
and this gas will condense on any part of the tube that is cooler than the
anode, you have both an electrical runaway condition, and no way possible to
heat the glass red (or orange or white) hot to get the gas back into the
anode.
Unquote
That is the best, short explanation that I have read and why I don't bother
to worry. If the tube has substantial gas it won't go away and you will
have trouble.
Merry Christmas to all,
Jim
W5JO
-----Original Message-----
I half expected them to not
have full vacuum.
______________________________________________________________
Boatanchors mailing list
Home: https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmailman.qth.net%2Fmailman%2Flistinfo%2Fboatanchors&data=04%7C01%7C%7Ccd6b01a8768140228a3508d9c71f83eb%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637759760434367281%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=CnS1NS6HC%2FTs3EY7%2FtFNcKxkolkL%2FVHvACSfk1Iy2eA%3D&reserved=0
Help: https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fmailman.qth.net%2Fmmfaq.htm&data=04%7C01%7C%7Ccd6b01a8768140228a3508d9c71f83eb%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637759760434367281%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=qg%2Fc4dUDxjM7Y8n6DQREH79kWSjZbZI%2FZIrlY95BjgE%3D&reserved=0
Post: mailto:Boatanchors at mailman.qth.net
List Administrator: Gary Harmon, K5JWK
** For Assistance: gharmon at idworld.net **
This list hosted by: https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.qsl.net%2F&data=04%7C01%7C%7Ccd6b01a8768140228a3508d9c71f83eb%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637759760434367281%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=Us%2Fdeieyn9PaS8oXn%2ByReCS0%2B7EhrdXHo3LKChLpmx4%3D&reserved=0
Please help support this email list: https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.qsl.net%2Fdonate.html&data=04%7C01%7C%7Ccd6b01a8768140228a3508d9c71f83eb%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C637759760434367281%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=cUJAofDHwPFDdzQN0Z5r0YFCa61UK860J9pnjsulYYk%3D&reserved=0
Message delivered to wq9nsc at live.com
More information about the Boatanchors
mailing list