[Heathkit] SB-200

[jeremy-ca]

----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at verizon.net>
To: <Heathkit at mailman.qth.net>
Sent: Monday, April 30, 2007 2:43 PM
Subject: Re: [Heathkit] SB-200


> On 30 Apr 2007 at 13:56, jeremy-ca wrote:
>
>> > QST, Jan. 1969, page 44 has a mod for converting SB-200 to 6 meters.
>>
>> Try it, it doesnt work; I get several in here to undo the mess and do
>> it correctly. Often times the tubes have been destroyed from
>> oscillation. Ive yet to see a decent "conversion" article in any ham
>> rag.
>
> "Mods" which actually IMPROVE most rigs are definitely in the minority!
>
>> > Power Supply upgrade, soft-key mod, in-rush current upgrade approx
>> > cost is between $100-150 from Harbach Electronics.
>>
>> PS: If it aint broke dont fix it. Besides when the time comes you can
>> get the parts from Mouser a lot cheaper.
>
> Yup. Or off Ebay as I have done. 470 uf 450 VDC 105degree C caps
> cost me about $1.00 each and they were NIB.

Ive never bought caps off Ebay, just dont feel secure with unknowns. I use 
the CDE 381LX Series 105* C 330/450V Made In The USA; everything lines up 
like the originals so it looks neat.  I use the same caps in the SB220.


 I would buy Rich
> Measures resistors though, which you can also buy from Mouser.

Whats a Measures resistor? I replace the 30K with 75K 5W MOX from Mouser. 
Cuts heat way down and with the tolerance quality of the caps the balance is 
excellent.


>
>> In Rush: Totally unecessary and just adds another potential failure
>> point.
> Yup. The FILAMENT transformer in the two Heathkit amps, SB-200 and
> SB-220, already have inrush current limiting for the filament built into
> them, as far as I know.

Absolutely true. Its an unknown to some and others may just be too stubborn 
to admit it. Besides, the resistors in the Harbach kit are low quality junk 
that often blow apart under the surge. Some protection!
In all my years with that amp Ive never heard of a surge related failure.

>
>> Soft Key:  Only if the TX/XCVR driving it cant switch -125VDC
>
> A $5 relay from Radio Shack,  a 9 V battery, and a small piece of perf
> board (if you really think you need it) will do the job.

I build my own right off the bias winding AC, a handful of components and a 
5 lug terminal strip.


>
>> I've converted over 300 SB200's to 6M over the past almost 40 years.
>> With over 10,000 built its not exactly a collector item. Try and find
>> a 700W 6M amp for that kind of money.
>
> Good point. Building one from scratch as I mentioned would probably
> cost a lot more money, and would certainly take a lot more time.
>
> Carl, I am curious though: when you convert an SB-200 for 6 meters, do
> you remove all the lower HF band stuff too? It seems to me that
> converting the 10 meter band switch position to cover 6 meters would
> be a lot less intrusive.
>
> Can you fill us in a little?


Completely stripping HF and building as a 6M monobander is the ONLY way to 
go. Trying to change 10M to 6M is barely possible but it is terribly 
inefficient (cuts tube life way down), parasitic and oscillation prone. 
Several other components are way out of requirements for 6M. Its way too 
much of a compromise....even for cheap hams!

Here is a link which goes into more detail on 6M conversions.
http://www.uksmg.org/1kw.htm

Carl
KM1H



>
> Ken Gordon W7EKB
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