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Author Topic: Heathkit SB-200  (Read 6965 times)
KB9RGD
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Posts: 24




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« Reply #30 on: November 27, 2016, 10:22:26 AM »

Believe me, I am as frustrated and bewildered as any of you.  Now I know why my friend KC9BH calls them Griefkits.  LoL
« Last Edit: November 27, 2016, 10:27:47 AM by KB9RGD » Logged
W1QJ
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Posts: 2638




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« Reply #31 on: November 27, 2016, 11:06:16 AM »

Does the amp have any mods or is it bone stock?  Does the relay close properly when the amp is keyed?  The hair brain bias circuit includes  the relay coil and another 10w 4K resistor in the circuit.  Anything in that circuit can be suspect.  Something as simple as a cold solder joint or an open in the B- line anywhere.  75% of the time a visual inspection turns up a problem.  I used to teach a basic electronic/electrical troubleshooting class for a local college which had a division of "outsource" education.  I stressed the "senses" as the first line of defense in tracking down problems.  Sight, smell, touch, and sound.  Perhaps check for problems over by the function switch, thst is a rat's nest area where poor workmanship can cause problems. 
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KB9RGD
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« Reply #32 on: November 27, 2016, 11:43:07 AM »

Does the amp have any mods or is it bone stock?  Does the relay close properly when the amp is keyed?  The hair brain bias circuit includes  the relay coil and another 10w 4K resistor in the circuit.  Anything in that circuit can be suspect.  Something as simple as a cold solder joint or an open in the B- line anywhere.  75% of the time a visual inspection turns up a problem.  I used to teach a basic electronic/electrical troubleshooting class for a local college which had a division of "outsource" education.  I stressed the "senses" as the first line of defense in tracking down problems.  Sight, smell, touch, and sound.  Perhaps check for problems over by the function switch, this is a rat's nest area where poor workmanship can cause problems.  

The relay tested good and works properly, the resistor tested good.  We also checked and touched up many of the solder connections.  Looked at everything under magnification including the function switch.  That was replaced not long ago by a guy with more experience than this last guy.  We couldn't find any bad solder connections there.  The only mod is the addition of a standby switch.  KS9Q checked the mod and concluded that it is not likely to be adding to the problem.  I'm going to be trying something else today.  Have to call KC9BH and have him talk me through it.  New sockets come tomorrow and I am replacing the Parasitic chokes for the tubes as well just for grins and giggles.  
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KB9RGD
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« Reply #33 on: November 27, 2016, 11:54:08 AM »

Going to check for voltage at the relay connection on the amp.  If it's there, I will key the amp and see if it goes away.  I am told it should. 
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KB9RGD
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« Reply #34 on: November 27, 2016, 12:29:54 PM »

OK, I get -130 vdc at the Amp relay jack center to ground.  When I key the amp it goes to -1.2 vdc.  Then I repeated the test at the junction of the 2 33 ohm grid resistors to on the socket bases to ground with the same results.  Am I nuts, or does that mean there is nothing wrong with the grounded grid?  Test was done with no tubes in line.  Oh, and not meter deflection either way.

« Last Edit: November 27, 2016, 12:51:44 PM by KB9RGD » Logged
W1QJ
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« Reply #35 on: November 27, 2016, 03:09:00 PM »

Voltages seem right.  The operating bias should be -2 volts but that varies.  This means the problem is probably in the metering circuit which leads me back to the grid shunt resistor.
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KB9RGD
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« Reply #36 on: November 27, 2016, 05:58:06 PM »

Voltages seem right.  The operating bias should be -2 volts but that varies.  This means the problem is probably in the metering circuit which leads me back to the grid shunt resistor.

Well as I said, we unsoldered one end last night and it is at 1.57 ohms.  So that's not it.  Whatever it was, seems to have been resolved last night with all the putzing and cleaning up solder connections.  The meter is reading positive again.  I also replaced the parasitic suppressors today.  Doubt that was the problem, though.  But they looked tired, they had a brown line around the middle of the 47-ohm resistors.   The newer tubes are working great and the 40+-year-old SB-200 is putting out 600watts.   

Thanks for all the tips.  Glad to know there are guys out here willing to help. 
« Last Edit: November 27, 2016, 06:02:56 PM by KB9RGD » Logged
K8AXW
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« Reply #37 on: November 27, 2016, 11:17:13 PM »

RGD:  They can be called "Griefkits" or POS or any other derogatory term but the bottom line is they can be worked on....can be fixed.  Many other nicer amps....not so easy.  Glad you got 'er goin!  I've had one for a few years now....gave me grief in the beginning but that was because it was used and abused by some CB'r. 

When I took it home I felt like I had rescued a scroungy dog from a pound.  There was grief, doubts and anxiety in the beginning but it was worth it all in the end.
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W1QJ
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« Reply #38 on: November 28, 2016, 04:50:02 AM »

You must have hit on a bad solder joint.  If you read any Heathkit manual Haethkit will tell you that 99% of the problems they fix is due to bad soldering.
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KB9RGD
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« Reply #39 on: November 28, 2016, 06:28:07 AM »

You must have hit on a bad solder joint.  If you read any Heathkit manual Heathkit will tell you that 99% of the problems they fix is due to bad soldering.

That was my thought exactly.
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KB9RGD
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« Reply #40 on: November 28, 2016, 06:34:20 AM »

RGD:  They can be called "Griefkits" or POS or any other derogatory term but the bottom line is they can be worked on....can be fixed.  Many other nicer amps....not so easy.  Glad you got 'er goin!  I've had one for a few years now....gave me grief in the beginning but that was because it was used and abused by some CB'r.  

When I took it home I felt like I had rescued a scroungy dog from a pound.  There was grief, doubts and anxiety in the beginning but it was worth it all in the end.

Oh, I know.  It is wonderful when it is working as it should.  Not working on electronic's every day or very often is a handicap for me.  So when something happens to it, there is an extra level of anxiety for me and I overload and shut down.  LoL  Well, for now, all is good.
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G3RZP
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« Reply #41 on: November 28, 2016, 06:43:22 AM »

 
Quote
If you read any Heathkit manual Haethkit will tell you that 99% of the problems they fix is due to bad soldering.

Not just limited to Heathkit builders. At one time, almost 60 years ago, Marconi studio TV equipment had similar problems down to poor soldering.
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K8AXW
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« Reply #42 on: November 28, 2016, 08:58:32 AM »

Quote
So when something happens to it, there is an extra level of anxiety for me and I overload and shut down.

RGD:  I know that feeling very well.  The older I get the worse it becomes.  I think in my case it's lack of confidence that I can fix it, even though I've "fixed" things as well as build many pieces of gear.

When I was young I used to look down my nose at an older guy and former radio and TV repairman as well as a knowledgeable ham when he said he could no longer work on ham gear because it made him "nervous."  I finally learned my lesson on this.....the hard way.

It's just something one has to deal with.
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K7BIT
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« Reply #43 on: December 02, 2017, 08:50:42 AM »

I too have a SB-201 with blown 33ohms, 1.5ohm and rear bandswitch burned.  Looking to buy a Harbach replacement but picture does not look same as SB-201 wafer and cant see the back side.  Has anyone used the Harbach part to replace the original bandswitch?

One other thing I found is the original owner miss wired the filament wires between tubes,  instead of wiring to out side of both sockets, they ran them between the pins. forming a perfect Jacobs ladder 3/8" gap.  that insured that even if you could not see the arc, it was constantly discharging even with amp not keyed. 

Tuning of course as you go in and out of resonance, takes supply voltage and multiplies it as much as 4x making the arcing problem worse. 

I picked this amp up at SK sale couple of days ago, did the Harbach PS install, plan W7RY soft start, QSK, reed/vacuum relay install, added glitch resistors in anode and cathode side, the work as shock absorbers during tuning, and blow with hard amp faults, fusing with 200MA fast blow fuse on 90VAC winding, replacing dooknobs with 15KV ceramic units, all electrolytics, and removing the 11M filter which was burned up. 

Done a lot of SB-220/221 this is my first 200.  Any parts sources and tips would be great.

73's and happy holidays all
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W1QJ
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« Reply #44 on: December 02, 2017, 09:06:48 AM »

The wafer Harbach has is the same for the SB-220 or SB-200.  IF HE HAS THEM
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