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Author Topic: SB-200 Replacement Caps.  (Read 1471 times)
WD8PHW
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Posts: 73




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« on: March 23, 2005, 06:20:24 AM »

Hello,

I'm looking for some 125uF @ 450V electrolytics for a Heath SB-200.  Does anyone know where I can find replacements?

Thanks,

Greg
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W7DJM
Member

Posts: 1




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« Reply #1 on: March 23, 2005, 08:08:17 AM »

Just about any of the recognized supply houses, Mouser, digikey, etc.  You WILL NOT find exact size replacements, modern caps are much smaller than originals.
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WB2WIK
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Posts: 20669




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« Reply #2 on: March 23, 2005, 08:38:50 AM »

http://www.harbachelectronics.com

Jeff was "closed" due to flooding, but I understand he just re-opened this week.  Give him a call.
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WD8PHW
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Posts: 73




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« Reply #3 on: March 23, 2005, 09:24:01 AM »

Hi,

Thanks for your responses.  

I found some replacements at http://www.rtoham.com/
No prices though.  It just says "call".  I'll see.

Also, I visited the Harbach Electronics web site, and it states the store is still closed.  I'll give them a call.

73,

Greg
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KA9CCH
Member

Posts: 87




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« Reply #4 on: March 23, 2005, 11:52:54 AM »

Check E-bay.  There are a several stores selling caps at a reasonable rate.

Levert
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KA5N
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Posts: 4380




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« Reply #5 on: March 23, 2005, 12:54:17 PM »


www.allelectronics.com
Has 150 UFd 450 volt 105 degrees C caps for $2.50 each (or $2.20 each for 10).  I just ordered some and they were the cheapest with the best specs I could find.  Similar units go for $4 to $7 from Mouser and Digi-Key.  The problem with all modern snap-in electrolytics is that their terminals don't fit the PCB hole pattern so some drilling will be necessary.
Allen
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N0TONE
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Posts: 173




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« Reply #6 on: March 24, 2005, 07:18:05 PM »

Before putting in those new caps, make sure you need them.  The OEM capacitors in these amps had tolerances sometimes of +/- 50%.  If the capacitor is simply lower in value than when it was new, the amp may work fine.  I have had SB-220s and SB-200s where the capacitors were as much as 60% low in value, and the amps worked great.  The problem that low-value caps causes is ripple.   But in a Class AB linear amplifier the ripple does NOT modulate the output, unless you are driving the amplifier all the way to saturation.  If you're doing that, then you're causing splatter or key clicks anyway.

I've repaired dozens of these amplifiers, and have not encountered a single one that actually needed new capacitors.

AM
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VE7ALQ
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Posts: 349




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« Reply #7 on: March 25, 2005, 04:52:13 AM »

Notone said, "In a class AB linear amplifier, the ripple does NOT modulate the output."

Please elaborate.  I have been given to understand the Heathkit SB200 (like the Yaesu FL2100z) runs class AB2.  I don't know the details on how ripple affects SSB, however I can assure you that ripple on CW causes ripple in the RF output.
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K7KBN
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Posts: 2840




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« Reply #8 on: March 25, 2005, 03:46:55 PM »

If the CW signal with which you're driving the amplifier has ripple on it, then that ripple will be present in the output, appropriately amplified.  However, if you're feeding a clean drive signal to the amplifier, the output will be free of hum unless, as he said, you overdrive the amplifier.
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73
Pat K7KBN
CWO4 USNR Ret.
W9GB
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Posts: 2659




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« Reply #9 on: March 26, 2005, 02:49:49 PM »

Greg -

CDE, Mallory, United Chemi-Com and Sprague replacements are available at Mouser.
Aluminum can type (screw terminal and "Snap-in" models) can be found on pages 482 to 486.

Mallory CGS series is used in the HV supply Alpha amplifiers (e.g. Alpha 76A).  
Just installed replacements in an Alpha 76A, which uses screw mount: CGS211T450R4C found on Page 484.

w9gb
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W9GB
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Posts: 2659




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« Reply #10 on: March 27, 2005, 11:13:59 AM »

Greg -

First, get the prt numebr and mfg from your old capacitors.

Sorry - forgot the links (great links)!

Here is the Mouser catalog page for Mallory caps (there are other pages in the catalog)
http://www.mouser.com/catalog/621/484.pdf

Youc an ALSO go to the CDE web page (South Carolina) .. and order specific models and values.
They have the CDE brand name as well as Mallory !

Some of the nice 105 degree values (not normally stocked by Mouser) as well as 500 volt units.
http://www.cde.com/

w9gb
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N0TONE
Member

Posts: 173




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« Reply #11 on: March 28, 2005, 06:14:42 PM »

VE7ALQ...ripple in a class AB amplifier only causes modulation if you are driving the amplifier so hard that you're clipping it.  That's how plate modulated rigs work.  They drive the PA extremely hard, well past the point of saturation, then they vary the power supply voltage, via a modulation transformer, to get AM.  If you use less driving power, so that the amplifier isn't saturating, then the modulation doesn't work.

At the plate of the tube, a given RF input power "demands" a min and max instantaneous plate voltage.  This varies, of course, at the rate of the RF.  For the 572B type tube, the minimum you can get to is roughly 200 volts.  If you try to drive harder, so that the plate voltage (instantaneous - you have to look on a scope with an RF-capable high voltage probe to see it - your plate voltage meter won't read this) goes even lower, then the thing saturates, clips, causes IMD or keyclicks.

So, to keep the amp clean, you back off the drive a little.  Let's say, then that at your drive level, you're only expecting the 572B anodes to drop down to 500V at the RF minimum.  You'ge got 300 volts of "margin" available.  The HV power supply could drop by 300V, and you won't get any reduction in output power.

Wanna see this for yourself?

1) Load up your amp
2) Hang a bit of wire on the input to your oscilloscope
3) Key the amp, with the rig sending a steady carrier
4) Use the rig's drive control to increase/decrease the power delivered to the amplifier and watch the 'scope.

You'll notice that you can see ripple when the drive is cranked up hard, but not otherwise.

AM
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VE7ALQ
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Posts: 349




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« Reply #12 on: March 28, 2005, 06:59:51 PM »

O.K. I'll take your word for it.  I am driving the Yaesu fl2100z at less than 500 milliamperes plate current, and the ALC is connected but not developing a voltage, so I assume that I am not overdriving the linear. Unfortunately I do not have an oscilloscope to look at the actual RF output, but nobody has complained about clicks on my CW.
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KE4MOB
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« Reply #13 on: April 09, 2005, 10:05:50 PM »

An amp may work fine *and* show no symptoms of trouble, but still need the caps replaced.

I recently acquired an SB-200 which worked great.  Just for kicks, I unsoldered one of the filter caps and looked underneath.

Sure enough, the cap had leaked and left a black sticky mess on the board.  I removed the rest to find half the caps on the PS board had leaked.

But the amp worked fine.
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N0TONE
Member

Posts: 173




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« Reply #14 on: April 14, 2005, 12:38:07 PM »

KE4MOB wrote:

"An amp may work fine *and* show no symptoms of trouble, but still need the caps replaced.

"I recently acquired an SB-200 which worked great. Just for kicks, I unsoldered one of the filter caps and looked underneath.

"Sure enough, the cap had leaked and left a black sticky mess on the board. I removed the rest to find half the caps on the PS board had leaked.

"But the amp worked fine.

I would humbly submit to you that leaky capacitors do not qualify in your first sentence "show no symptoms".  Leaking is most definitely a symptom!

How certain are you that the black sticky mess came from the capacitor, rather than being charred resin from the low-grade solder that Heathkit supplied their kits with?  If it was really capacitor guts that had come out, they would have eaten their way through the PC board.  If the PC board was intact, then the mess did not come from the capacitors.

AM
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