[Amps] 8877 won't load on 80M

[TexasRF at aol.com]

Wonder if you are resonating on the second harmonic of the drive  frequency?
 
Are the tune and load capacitors at or near the settings with the 2300 ohm  
resistor? Should be.
 
73,
Gerald K5GW
 
 
 
In a message dated 3/15/2013 11:49:58 A.M. Central Daylight Time,  
dick at ny1e.com writes:

I've  done it with a 2300 ohm resistor, and it tuned to 1.2;1 SWR  on  the 
analyzer, so I'm assuming the pi-net is good, there is no tuned  input. 
there isn't much left, if the 80M energy was going elsewhere like the  plate 
choke (Dahl 3 amp) or the rf choke across the output, I think  smoke would have 
told me what to replace. I'm almost ready to build a separate  80M monoband 
amp!
When I get the little out on 80 (Less than the  drive power), if I touch 
the plate or load, it drops to zero out and won't  come back until I unkey the 
amp and rekey the rig.

--- On Thu, 3/14/13,  Mike Tubby <mike at tubby.org> wrote:

From: Mike Tubby  <mike at tubby.org>
Subject: Re: [Amps] 8877 won't load on 80M
To:  n8de at thepoint.net
Cc: dick at ny1e.com, amps at contesting.com, "Bob Alexander"  
<realex2 at verizon.net>
Date: Thursday, March 14, 2013, 2:16  PM

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
>>>  _______________________________________________
>>> Amps mailing  list
>>> Amps at contesting.com
>>>  http://lists.contesting.com/mailman/listinfo/amps
>>>
>>  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.
>>
>>  _______________________________________________
>> Amps mailing  list
>> Amps at contesting.com
>>  http://lists.contesting.com/mailman/listinfo/amps
>>
>
>
>
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