Another option is to contact Dick Byrd, N4UQ. At one time, he was running
an exchange program where the user sent in a B&W 801 or 802. He then sent
out a pre-wound 802 with a heavier gauge winding. Not sure he still does
this but I exchanged the chokes in my PA-70V and 77Dx this way.
Probably a better method is to swag and lump the taper as Ameritron does
with their plate chokes -- or in the alternative, use a relay to short turns
(e.g., Alpha 89/87A) although getting it right might be tricky for those
without a grid-dip meter. Any value change really requires verfication of
resonances.
Paul, W9AC
----- Original Message -----
From: "Carl" <km1h@jeremy.mv.com>
To: <audioguy@q.com>; <Amps@contesting.com>
Sent: Monday, June 18, 2012 1:03 PM
Subject: Re: [Amps] Alpha PA77 vs 77Dx plate choke?
> The 77's were shipped with a B&W 800 choke and 160 wasnt considered
> important before the US was authorized 1500W. The next step was the 801
> which was better on 160 but fried on 12M when we got the WARC's. Next came
> the 802 which solved the WARC's but was light on 160.
>
> OTOH, having a part of the plate choke become an active part of the 160M
> tank is rather common in several ham amps. How well it works depends upon
> the designers and many opt for the Ameritron choke where it fits.
> Palstar (no longer in production but some stock is available last I heard)
> and QRO chokes fit the 77.
>
> The 802 is still available at an outlandish price.
>
> Carl
> KM1H
>
>
>
> ----- Original Message -----
> From: "Jim Barber" <audioguy@q.com>
> To: <Amps@contesting.com>
> Sent: Monday, June 18, 2012 2:01 AM
> Subject: [Amps] Alpha PA77 vs 77Dx plate choke?
>
>
>> I'm getting around to servicing the blower (again) in my very last
>> complete Alpha PA77, and decided that since I'll have the side off I
>> might as well add the toroid and caps to put it on 160m. Note it's been
>> 20 years or so since I've done this, so memories are a bit foggy... :-)
>>
>> Many things confuse me, but what's relevant to this discussion is that
>> the plate chokes for *both* the PA77 (10-80m) and the 77Dx (10-160m)
>> appear to be 90uh on a ceramic form plus a 15uH molded choke in series.
>> The 77Dx also has a smattering of additional bypass caps, (that part
>> makes sense) but isn't a total of 115uH a bit light for 160m? There's
>> room to put in something like an RFC-3, but I'm wondering what the
>> original strategy was, assuming anyone remembers.
>>
>> I also notice the the 77Dx has no tuned input in the 160m position. I
>> can probably ring out the approximate cathode impedance "offline" by
>> putting 50 ohms (or so?) between the cathode and ground, pulling in the
>> input relay then putting the VNA on the input connector. What I find
>> puzzling is why there would be no tuned input for 160m on the 77Dx,
>> since it was shipped as being capable on 160m.
>>
>> Any remembrances?
>>
>> Thanks,
>> Jim N7CXI
>>
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>>
>>
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>
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