[Amps] 8877 won't load on 80M

[Mike Tubby]

As I think I've suggested before, try this:

Remove the tube, remove the supplies, connect a 220R from the tube anode
to ground to simulate RL - assuming you're working at around 3100V on
load and expecting circa 1500W output...  then "look" in to the output
socket using a VNA or antenna analyser and see if you can tune for
anything that approaches a good match.

As Don said you could have too little loading capacity or you could have
too little inductance in your tank coil.

Once you get it "in range" on the VNA/analyser put the tube back and
you'll find it tunes up and loads up somewhere near where you got the match.

Mike G8TIC



On 14/03/2013 01:11, n8de at thepoint.net wrote:
> Perhaps it is NOT the 'blocking' cap, but the 'loading' cap that is
> switched in on 80m.  If it is not of sufficient capacitance, the amp
> won't tune/load.
>
> 73
> Don
> N8DE
>
>
> Quoting Dick NY1E <dick at ny1e.com>:
>
>> I finally got around to digging out another blocking
>> cap, unfortunately, same results. It draws more current with more
>> drive, but plate and load controls have no effect on plate current,
>> grid current remains low....  
>>
>> --- On Sun, 1/27/13, Bob Alexander <realex2 at verizon.net> wrote:
>>
>> From: Bob Alexander <realex2 at verizon.net>
>> Subject: Re: [Amps] 8877 won't load on 80M
>> To: dick at ny1e.com
>> Date: Sunday, January 27, 2013, 8:19 PM
>>
>> On 1/26/2013 5:18 PM, Dick NY1E wrote:
>>> I have a homebrew 8877 that has been working fine for 12 years on
>>> 160 and 40 thru 10, but I never had an 80M antenna. I finally got
>>> one up and the amp wont load on 80. It is stable, draws full
>>> current, but puts out less than the input, I've played around 
>>> adding and removing padders to the plate and load caps. There is no
>>> tuned input.Any ideas???Thanks, Dick NY1E
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>>>
>> Hi Dick,
>> I have experienced this same problem two times over the years.  Once
>> with a homebrew 8877 and once on a SB220.
>> The plate blocking capacitor is open on 80 meters.  Sounds weird but
>> it really does happen.
>>
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>>
>
>
>
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