The 922 was fine on 160 for the JA band at the time.
Carl
KM1H
----- Original Message -----
From: "Vic K2VCO" <k2vco.vic@gmail.com>
To: <amps@contesting.com>
Sent: Thursday, January 26, 2012 11:37 AM
Subject: Re: [Amps] 3cx800a7 Grid Current Problem
> The stock 922 apparently isn't optimal at the low end of 160 (or 80). I
> had to add some
> capacity across the loading capacitor to get a reasonable match on mine,
> but output is
> still low compared to other bands. I suspect that there isn't enough
> inductance and the Q
> is too high.
>
> On 1/25/2012 11:14 PM, Mike Tubby wrote:
>> On 26/01/2012 02:40, TexasRF@aol.com wrote:
>>> About a month ago, JE1BMJ reported a similar problem with his SB1000. In
>>> his case, the problem was found to be inadequate bypassing of the plate
>>> rf
>>> choke. Apparently enough rf was reaching the bypass capacitor to heat it
>>> up
>>> and cause it to change value and that was enough to detune the plate
>>> circuit.
>>>
>>> 73,
>>> Gerald K5GW
>>>
>> This appears to be not uncommon across several amp designs - even the
>> venerable TL-922 shows lower output on 160m than it does on 80m/40m and
>> no doubt if the input power is there then the output is going
>> somewhere... okay in the case of the '922 it might not be causing
>> de-tuning and grid current but I bet soemthing's getting warm ;-)
>>
>> Mikie G8TIC
>>
>>>
>>>
>>>
>>> In a message dated 1/25/2012 7:20:22 P.M. Central Standard Time,
>>> at6c@bellsouth.net writes:
>>>
>>> Carl/Paul,
>>> There isn't a fix loading padder (Carl, I think you are referring to a
>>> capacitor pad for 160M correct me if I am wrong) in the HF 1250. There
>>> is a tapped ferrite transformer/coil that is switched in for 40-80-160.
>>> That being the case the problem could be something shorting out part of
>>> that transformer in the 160M position. Also the band switch could be
>>> bad. Have you checked all the components in the RF compartment for
>>> visual damage/overheating/value? The only difference in the
>>> tuning/loading circuit between 80M and 160M is the position of the band
>>> switch and which part of the above coil is in the circuit.
>>>
>>> Another point to consider is that the LP100A has three different
>>> selections for measuring output power(average/peak/?pulse?). I find
>>> that if you are tuning a twitchy amplifier a needle type watt meter is
>>> easier to use than the LP100 (maybe it's just me). I think if you are
>>> not using a pecker tuner, peak is recommended, check the manual. Also
>>> carefully follow the instructions in the HF 1250 manual as to the way
>>> you tune the amp. I found those instructions will prevent surprise
>>> grid
>>> current fluctuations. Good luck.
>>>
>>> 73
>>> George
>>> W2GS
>>> _______________________________________________
>>>
>
> --
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco/
>
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