On Sat, 29 Mar 97 18:45:52 -0800 Rich Measures <measures@vc.net> writes:
>>Subject: Re: [AMPS] 77DX
>>Sent: 3/29/1997 2:46 PM
>>Received: 3/29/1997 4:57 PM
>>From: Lee Roger Wical, leewical@lava.net
>>To: Rich Measures, measures@vc.net
>>CC: LEEWICAL@LAVA.NET
>>
>>Richard, AG6K:
>> Don't know if I asked you this question or not. Cannot find
>any
>>reference to same.
>> Do you vendor a replacement plate choke for the 77DX
>not any more. I never had much call for the smaller chokes.
>>......so I can use
>>the rig on the 24MHz ...........
>The stock choke will work provided you remove some turns. Check it
>with
>a dipper before you give it the smoke test. Resonances should be
>parked
>at least 5% off the main road.
Removing turns will alleviate the 12M reasonance but it will make the
77DX even less efficient on 160M than it is already. A better solution
is to replace the plate choke with a B&W 802; the original is the B&W
800.
The 802 will operate fine on all 9 HF bands. It is out of production but
an identical replacement is the RK-802 available from Radiokit at $27.
>>PS Same question in using the SB-220 on 12Mtrs/24MHz?
>There are no hv-rfc resonances below 35Mhz, so no mod is needed.
The SB-220 should be limited to 750W or so on 12/17M. I prefer to run in
the CW position when on those bands; the amp is still operating as a
linear. The tank circuit Q's become very high and blown bandswitches can
result. This will happen even with an otherwise perfectly stabilized 220.
A complete upgrade kit for the 220 to permit full 160 to 10M operation is
under development. .....stay tuned.
73....Carl KM1H
>Free unsolicited advice for the 77: The tank is designed to match
>2000
>ohms. When a second tube is installed, the tube output Z drops to
>1000
>ohms. The 77's tri-state bias scheme is nutsville. If you want the
>77
>to sound smooth on the air, a bi-state bias circuit is needed.
>
>R. L. Measures,ag6k,805-386-3734
>
>
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