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Author Topic: Heathkit SB-200  (Read 6915 times)
K6BRN
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Posts: 489




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« Reply #45 on: December 02, 2017, 09:05:19 PM »

John (K7BIT):

Quote
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?

The band switch wafer that usually fails on the SB-200/201 is the tank circuit wafer ("wafer B" in the Heathkit schematic).  It is the middle band switch wafer located inside the amplifier tube compartment next to the 572B tubes, NOT on the rear panel.  Harbach sells a replacement for "wafer B" for $38 (the "SW-100") and has them in stock right now:

https://harbachelectronics.com/shop/misc/sw-100-band-switch-wafer/

The Harbach SW-100 replacement wafer has more switch positions than the original "Wafer B", but the extra positions can be ignored.

The rearmost SB-200/201 switch wafer is "wafer C" and it is the input tuning network selection wafer.  While this one rarely fails and is the easiest to replace (last one on the switch shaft and outside the amp compartment), a replacement is harder to find and the Harbach "SW-100" replacement wafer is NOT compatible with "wafer C" (too few switch positions).

Make sure you know which wafer is bad before you order a replacement, as they are all unique within the amplifier and tend to be pricey.

Brian - K6BRN

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KM1H
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Posts: 2612




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« Reply #46 on: December 03, 2017, 06:05:47 AM »

Quote
The rearmost SB-200/201 switch wafer is "wafer C" and it is the input tuning network selection wafer.  While this one rarely fails and is the easiest to replace (last one on the switch shaft and outside the amp compartment), a replacement is harder to find and the Harbach "SW-100" replacement wafer is NOT compatible with "wafer C" (too few switch positions).

Based upon many decades of experience I find misalignment causes a cracked wafer and very, very few were burnt from RF.

Carl
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K8AXW
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Posts: 6361




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« Reply #47 on: December 03, 2017, 09:58:19 AM »

The earlier SB-200s had a problem which Heath Co. corrected.  If your amp came with the typical yellow assembly manual, you have one of the earlier models and it has the potential of one wafer on the bandswitch arcing to the switch mounting screw.

If your manual is the two-tone tan assembly manual, this problem has been corrected.

Since the problem and solution involves me getting out of my recliner and going through my files in the basement I'll provide specific information only if requested.

(The arcing completely destroys the involved wafer contact and it is necessary to replace the whole wafer....if one can be found.  I was fortune to have found one!)
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