Help with SB-200 input circuit

[Bill Richarz]

>
>
> ----------
>From: owner-heath
>To: HEATH
>Subject: Re: Help with SB-200 input circuit
>Date: Tuesday, September 02, 1997 7:07PM
>
>I think most people will support this comment, and that is that from a
>solid state rig perspective, yes the input circuit does stink. It was
>intended for a tube rig with an adjustable pi-network output stage,
>which was much more tolerant/accepting of swr.
>
>I think AG6K did an article on SB-220 mods that addressed revamping the
>input stage for solid state rigs. I think the premise was designing new
>pi-net inputs with higher Q (something like 3-5, and the original may
>have been lower, if I remember).
>
>Murray
>
>Jim Mullen wrote:
>
>> Hi and thanks for reading this.
>>
>> I have an SB-200 that will not present a good load on 10 and 15
>> meters. The
>> input coils seem to have no effect when tuning them. Checking the
>> setup
>> with a dip meter, reveals good, in-band dips on 80, 40 and 20, but a
>> real
>> strong dip on about 28 and 35 MHz when the band switch is set to 15 or
>> 10
>> meters.
>>
>> I pulled the entire coil & switch assembly out of the amp, just
>> sitting on
>> the bench, I get a very good dip meter dip at 28 MHz.
>>
>> Am I chasing my tail here, because the circuit stinks, or am I missing
>> the
>> obvious? Beats me!  My best guess at this time is the whole assembly
>> is
>> self-resonant at around 28 MHz, and is swamping out the tuning ability
>> of
>> the individual 10 and 15 meter circuits.
>>
>> The switch and all contacts look fine, coils are in good shape,
>> capacitors
>> test OK, and are the right value. Coils and switch are wired
>> correctly.
>>
>> I'm driving the amp with a Kenwood TS-440. Amp tubes aren't the
>> greatest,
>> but shows about 500W key down on 80, 40 and 20.
>>
>> Any help or ideas would be greatly appreciated.
>>
>> Jim Mullen - WA1ZUH
>> 144 Tower HIll Road
>> Brimfield, MA  01010
>> (413-245-3228
>

Are we talking about an SB-200, or SB-220 or both?
I have an SB-200, & someone made some notes on the
caps in the input section, but really cannot make
alot of sense of it. Prehaps someone knows of mods
for using a transistor rig to drive the amps.  My
200 seems to get full output on all bands.

Thanks & 73 de Bill, N4DH
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Bill Richarz <N4DH> ex WA4VAF      | Internet: bill.richarz at transprt.com
10035 Little Creek Rd.             | Packet: N4DH at W4BFB.#CLT.NC.USA.NA
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                     Alternate Email: n4dh at juno.com
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