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Author Topic: Heath kit SB-230 tuning capacitor is way off.  (Read 3104 times)
KD0GES
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Posts: 30




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« on: November 13, 2012, 03:15:56 AM »

I have a SB-230 amplifier.
When I tune is for 80 meters the tuning capacitor is in the 20 meter range.
The linkage to the capacitor is correct.
What might cause this?
Thanks for responses.
Dale (KD0GES)
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W1QJ
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Posts: 1496




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« Reply #1 on: November 13, 2012, 03:54:00 AM »

Dale, is this amp new to you or have you used it before and suddenly the tuning is different on 80m?  The setting on both load and tune on any amp is relative to the load impedance so if you have changed antennas perhaps that could be why.  As long as the grid current and plate current jive with the power output that is most important.  The tuning range is only relative.  SOmetimes you might see a difference in load setting on the lower bands if a switched in padding cap opens up. 
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PA3GOS
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« Reply #2 on: November 13, 2012, 04:09:39 AM »

I own an SB-230 as well and have used it for a number of years now. Great amp without fans so no noise!
The padding capacitor that comes in when used on 80 meters did not open up I guess, since that would have caused an even lower capacitance.
Hence, a situation where you would be unable to tune the amp on 80 meters.

If this amp is new to you, someone may have replaced the padding capacitor with one that has more capacitance (i.e. 150 pF). A reason for that could be that the previous owner could not find one with the proper value (100 pF) after the original one went south for some reason.
« Last Edit: November 13, 2012, 04:23:10 AM by PA3GOS » Logged
KA5N
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Posts: 4380




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« Reply #3 on: November 13, 2012, 05:14:23 AM »

You didn't mention what your antenna set-up consists of.   Have you inspected
your antenna lately?   Do you have another amp you can try?
If this amp is new to you, have you gone over it for bad connections/solder joints
incorrect parts, misswires?
If it is just an incorrect value capacitor, that is easy enough to fix.

Allen KA5N
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KD0GES
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Posts: 30




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« Reply #4 on: November 13, 2012, 05:54:23 AM »

This amp is new to me.
I am tuning it into a heath kit canteena dummy load that measures 53 ohms and shows  around 1 to 1 swr on my transmitter.
Thanks
Dale (KD0GES)
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PA3GOS
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Posts: 43




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« Reply #5 on: November 13, 2012, 07:07:32 AM »

Dale, just to make sure everything else is okay, are all other bands fine?
I mean is the tuning capacitor around where you expect it to be?

If so, I wouldn't worry too much about it. Probably like I think.
See my earlier post.

Also, don't tune too long (a few seconds at the most) when driving with more then 40 or 50 Watts.
It's a great amp for SSB. Not so much for carriers.

73 Tjalling.
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K1ZJH
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Posts: 1155




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« Reply #6 on: November 13, 2012, 09:06:26 AM »

Just curious, but where does the tuning knob end up when tuning for the low end of the CW band, say at 3.5000 MHz?

Pete
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K8AXW
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« Reply #7 on: November 13, 2012, 08:59:48 PM »

Dale:  You said the linkage  is OK...... I'm not sure what that means since I don't have the manual for this particular Heath amp.

I'm hoping you do have the manual.  If so, go to the part where it shows how to set the caps and knob positions and and see if they're set properly. 

If they are set properly, then you have something going on in the amp that is throwing the settings off.  GOS asks a very pertinent question.  That answer might shed some light on the problem.
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KD0GES
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Posts: 30




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« Reply #8 on: November 14, 2012, 02:54:02 AM »

Last night I tried it on the lower portion of 80 meters and the tuning capacitor ends up on the high side of the 80 meter band and the load is on 1 and I got 500 Watts out.
On 40 meters it acts the same as 80 meters with 500 watts out.
on 20 meters the amplifier starts to arc at 200ma of drive current.
Tonight I am going to tune it into my antenna in-case my dummy load is getting a high swr under high power.
Thanks for the help.
Dale (KD0GES)
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KC4MOP
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« Reply #9 on: November 14, 2012, 03:31:25 AM »

Last night I tried it on the lower portion of 80 meters and the tuning capacitor ends up on the high side of the 80 meter band and the load is on 1 and I got 500 Watts out.
On 40 meters it acts the same as 80 meters with 500 watts out.
on 20 meters the amplifier starts to arc at 200ma of drive current.
Tonight I am going to tune it into my antenna in-case my dummy load is getting a high swr under high power.
Thanks for the help.
Dale (KD0GES)

OUCH!!!
watch that grid current....things are not right in that amp...
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PA3GOS
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Posts: 43




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« Reply #10 on: November 14, 2012, 06:18:43 AM »

Dale, your answers leave me a bit in the dark.
"On 40 meters it acts the same as 80 meters with 500 watts out."
Do you mean the capacitorsettings are the same as on 80 meters?

You also say that on 20 meters the amp starts arcing. Can you determine what exactly is arcing?
It might be a capacitor, the tube or even a somewhat loose connection.

And to KC4MOP, I think Dale is referring to platecurrent. Not gridcurrent.
The gridcurrent should be around 20 mA at 500 Watts. Per the manual less then 40 but 20 should be about right.
If not, increase (clockwise) the loadcapacitor somewhat and perhaps retune a little.
The grid of a 8873 is very sensitive so be careful while tuning.

73 Tjalling
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KD0GES
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Posts: 30




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« Reply #11 on: November 14, 2012, 06:59:14 AM »

On 40 meters the tuning capacitor is on 15 meters.
I need to open the case to findout what is arcing tonight.
The plate current is what I was referring to.
The gridcurrent is around 15 mA
Thanks
Dale (KD0GES)
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PA3GOS
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Posts: 43




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« Reply #12 on: November 14, 2012, 08:19:34 AM »

Dale,
Thanks for your answers. First of all, before opening the case unplug the mains and make sure there is no HV left in the filtercaps.
To check this set the meterswitch to HV and take a good look at the meter. It should read nothing.
When the top cover is removed, put something heavy, like a book or so, on the interlockswitch.
From this point on stay away from the inner parts. I know it's probably something you already know but still.
Plug the mains back in and switch the amp on.

Now carefully increase drive on 20 meters and do the check for arcing. Make this quick!

Now switch the amp off, unplug the mains and leave it for a while to let the filtercaps loose their charge.
After having a cup of coffee or so check the HV meter for zero Volts. Keep the amp unplugged from the mains!

Now check the alignment of the knobs of both the load- and tuningcapacitor.
With the tuningindicator to the left (lowest part of 80 meters, left end of the white band) the cap should be fully meshed.
The same should be the case for the loadcap on the 1 position.

If one or both is/are not aligned properly it should be easy to fix.

So far I'm not sure whether or not the arcing is related to the seemingly misaligned caps.
It is possible that one or both the caps is/are damaged i.e. bent plates.
Maybe you can check this too while you are at it. Bent or crooked plate(s) may also be the cause of both.

I will read your findings later and respond.

73 Tjalling.
 
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KA5N
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Posts: 4380




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« Reply #13 on: November 14, 2012, 10:38:36 AM »

I think there is something amiss with the bandswitch.  There is a 100 pf cap that is
switched into the circuit on 80 meters only.  There is a 500 pf capacitor that is added
to the load variable on 80 meters.  There are two wafers on the bandswitch.  Either
something has slipped so that the capacitors aren't switched in on the correct band
or the contacts are damaged or there is a bad connection. 
I have no idea what the arcing might be.
Allen KA5N
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PA3GOS
Member

Posts: 43




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« Reply #14 on: November 14, 2012, 02:57:15 PM »

Indeed Allen. There's yet another possibility.
Not completely though. The padding capacitor(s) not switching in on 80 meters will never cause the tuning knob to be in the 20 meter region.
Simply because, as I explained in an earlier post, in that case there won't be enough capacity to tune on 80 meters at all.
But it won't hurt to check the bandswitch. In fact, that may well be the arcing object if the contacts are dirty or otherwise intermittent.

So Dale, please check the bandswitch too. By the way, you will notice you need to remove the perforated cover from the tubecompartment.
Ofcourse, the variable capacitors are also in that compartment. Before doing so reassure that the amp is still disconnected from the mains!

73 Tjalling

 
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