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Heathkit SB220

Crusher

Well-Known Member
May 12, 2007
841
388
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Louisville, KY
Have a heathkit here, everything looks right, have to hook up my external V meter and see if plate V meter is correct. Looks kind of low. May just be meter. Anyways I was just using a barefoot 148 to test amp. With maybe 15w pep in, I am getting close to 200pep out. But what I don't like is the tubes are starting to cherry. I can see if I was doing 1kw pep. But not 200W. Anyways, wanted to know what you all use for bias V. I figure might need a little more bias or something. Looks like original caps, so that will be changed as well. Just hate buying the set from Harbach for $140. But still not a bad deal. Fan makes some noise, so I will try oiling. If that doesn't do it, time for a fan. Might as well change HV/ metering as well. Looks like diodes went south at one point and blew a hole thru CB. Gotta clean relay and see what that looks like. Also plan on changinhg output connector. Its pretty loose. I have to see what zener is in there. May change it to higher rating or run a diode stack. Not sure yet. Just wondered if anyone has changed this to higher rating. This thing has original eimac tubes. Not the graphite type.
 

A lot of info on the SB 220 on the net including upgrades and mods.

Zener is behind the rectifier board.

I like harbachs up grades for the rectifier board, the cap board is a little expensive but is a direct fit.

Those old 3-500 should turn red, dunno about with 15 watts of drive though.

This is also a good amp to do the fuse protection in the zener bias of the cathode. you will have to be creative if you want to use the original bias circuit, or just use the resistor and the relay to bias it to cutoff in receive.

The bias voltage is also the keying voltage for the relay.

Most likely resistors out of tolerance on the metering circuit.

I had one on the bench two weeks ago, burned up HV PS rectifiers. Rebuilt it and told the guy he had a weak tube. (tested in my HB-1000, fuse protected every which way it can be.) Guess he finally blew that tube or shorted it. Got a call saying it started smoking and popping.

Those old 220 wont take a lot of drive in the AM mode. HV TR does not have the amps.
 
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Agreed. No more than about 300w carrier. And not a lot of drive.

Yeah I was looking at some links tonight. I gotta call guy and ask how much he wants to spend, but I'm recommending new cap bank and Hv/meter board. Probably replace zener as well.
 
Heathkit SB-220 & SB-221 | Product Categories | Harbach Electronics, LLC

The rectifier board is worth every penny of the price, it uses a string of diodes for bias and all in a nice neat small board.

The caps can be found less expensive if you shop around.

If it is a BIG AM'er then a fuse in the B+ line and maybe a fuse between the voltage doubler board and rectifier board may save you some headaches the next time the op decides to over drive the shit out of the amp. I have even installed a fuse in one side of the TR secondary. Can never have enough protection.

Funny how the same one's keep burning there equipment up.

I sit them down and explain to them manufactures ratings, how much the power supply is capable of producing etc etc , how much drive is actually needed to make full output.

I then explain about gain from antennas and how a 100 watt radio into a four element yagi will sound just like a 1000 signal into a IMAX2K.

Long story short, they keep talking to the meter and looking at that swing in their thing, I keep repairing them.

Life on eleven meters
 
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Thanks for the suggestions about fusing HV. I thought about glitch. But the extras would be nice. Metering board for sure. Fan needs replaced. Oiled but its still is clunking. The caps are original. Been looking on ebay. But haven't even found caps.
 
QTH classifieds has some decent 450 vdc 220 mf look under classifieds hf amplifiers.

I have used a few dozen of these and they work fine.
 
more than likely the zener is gone . what it the idol current should be about 175 mills plate i have seen people just replace the zener with 1 1n5004 makes the idol current too high thell conduct close to 250 mills plate like that . if there is no bias thell glow like crazy if the diode is open

the harbach metering board changes the zener to a chain of 1n1004 7 in sires the new metering board is way nicer than the original and has meter protection built in and metering shunts that you can actually find and for the price it fixes 90% of all the problems youll find with the 220
 
more than likely the zener is gone . what it the idol current should be about 175 mills plate i have seen people just replace the zener with 1 1n5004 makes the idol current too high thell conduct close to 250 mills plate like that . if there is no bias thell glow like crazy if the diode is open

the harbach metering board changes the zener to a chain of 1n1004 7 in sires the new metering board is way nicer than the original and has meter protection built in and metering shunts that you can actually find and for the price it fixes 90% of all the problems youll find with the 220

"Idol current"? That comes from running it Baals to the wall...:whistle:
 
New cap bank and meter board arrived last night. Assembled both last night. Hopefully install later today. Yup, the new bias is 6.8V instead of the factory 5.1V. Should help out nicely.
 
If you haven't heard about it or already done it, you might think about dropping the filament voltage slightly. That will extend the life of the tube greatly. I don't remember the 'numbers' but it's a slight drop, something like half a volt.
- 'Doc
 
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If you haven't heard about it or already done it, you might think about dropping the filament voltage slightly. That will extend the life of the tube greatly. I don't remember the 'numbers' but it's a slight drop, something like half a volt.
- 'Doc

I think the Heathkit runs around 4.9 v on the filament, that is why with proper use the tubes will last a very long time, of course the line voltage of the qth will come into play with this also.

http://www.somis.org/SB220ci.html

Good link and Rich has a paragraph on the filament voltages.
 
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New cap bank and meter board arrived last night. Assembled both last night. Hopefully install later today. Yup, the new bias is 6.8V instead of the factory 5.1V. Should help out nicely.

yeah is stuff is nice every 220 or l4b im am asked to work on the first thing I do is tell the owner to buy all upgrades from him . and on the l4b the original design grounds the center tap of the filament transformer causes a 270ma idol current I stole his idea and solder in series diodes to get it down to 175ma


I love to rebuild those old 220's what a work hoarse I only wish they had 160
 

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