Hi Carl,
Thanks for the reply. Yes, you are correct, I misspoke when I said shunt
resistors. I meant the resistors on the meter board.
Thanks for the places to look. I will continue my search.
73 Jeff W8CQ
-----Original Message-----
From: km1h@juno.com <km1h@juno.com>
To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: Tuesday, March 02, 1999 10:16 PM
Subject: Re: [AMPS] Kenwood TL-922A Grid Current
>
>
>
>On Tue, 2 Mar 1999 19:56:47 -0500 "Jeff Weinberg W8CQ" <w8cq@indy.net>
>writes:
>>Hello Amp Guru's,
>>
>>I have a question for the multitude. I have a perfectly functioning
>>TL-922A. Recently, I have noticed a strange anomaly. Under keying
>>condition, that is keyed up with no modulation, I am seeing about 270
>>mA of plate current (normal),
>
>High. 200ma in SSB is per the manual.
>
>
>
>
> but am showing approximately 10 mA of
>>grid current. I cannot figure out why I am showing the small amount
>>of grid current.
>
>
>Check the bias zener and C-26 across it. The cap has a history of
>failure.
>
>
>>
>>I have changed tubes between three different amps and three different
>>sets of 3-500Z's and it happens with all tubes. I am sure the problem
>>is in the amp. In addition, I have checked the shunt resistors in the
>>grid circuit, and they all check good.
>
>What shunt resistors?? In an un -voodooed TL-922 there are no resistors,
>just a pair of grid chokes plus 220pf caps per pin. Those original
>chokes are too big, current and low resistance wise. I suggest replacing
>with something in the 750uh to 1.5mH 160ma and 25 Ohms DC resistance
>range...as used in the SB-220. If there are some strange parts in the
>amp, it might be best to throw them away and follow the original design.
>
>
>While you have the half million screws removed( Do Jap designers get paid
>by the screw? The THP and Sigma amps are other examples of a screw
>fetish), replace the VHF choke, L-2, with a 15-20 Ohm 20W real wirewound
>( not cement) resistor. It will do wonders for reliability.
>
> Another common TL-922 problem ( Line voltage dependent) is excessive
>filament voltage. Adding resistance in the filament xfmr primary to
>obtain around 4.8VAC RMS across each tube will result in long tube life.
>It will minimally affect the cut-off bias and relay voltage.
>
>Rich's relay mod is excellent when using a modern fast switching exciter.
>
>
>>Also, the meter is perfectly functioning in the HV or RF position.
>>The grid current aside, all is functioning properly.
>>
>>Anyone have any ideas what may be bad or where to continue looking
>>(Rich or Carl)?
>
>Hope I hit most of the pertinent points Jeff. After a week away I have
>over 200 msgs to answer.
>
>73 Carl KM1H
>
>
>
>>
>>Thanks,
>>
>>Jeff Weinberg W8CQ
>>w8cq@indy.net
>>
>
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