[Kenwood] TS-50 problem

[Clif Holland]

First, the bias circuit has nothing to do with power out. It determines 
the linearity of the final unit for SSB usage.

The power out is controlled by the ALC circuit. There are several 
factors which can cause higher than normal power out. Most of which are 
traced back to leaking/open electrolytic caps. Leakage damages 
traces/thruholes. Open causes reference voltages to be incorrect, mainly 
the -6v supply.

I'm not familiar with the 2SC5894's as the TS-50 and most Kenwoods of 
that era use the 2SC2879.

Clif Holland KA5IPF
www.avvid.com
214-850-0973

On 8/5/2018 2:27 AM, Steef PA2A wrote:
> Chuck,
>
> the 10 and 50 watt levels can be adjusted by variable resistors but 
> there must be some problem in the bias circuit of the finals where the 
> power level is set by fixed resistors. A cold solder joint or a 
> changed resistor value can be the cause of the changed bias.
>
> The 2SC5894 's can dissipate 250 watts of heat each so 200 Watts is no 
> problem for them except ferrite transformers will run a bit hot. In 
> SSB increased intermodulation products can appear but in CW there is 
> no big problem. The TS850 has the same amplifier and running 180 Watts 
> in CW was no problem.
>
> 73s Steve PA2A
>
> chuck via Kenwood schreef op 2018-08-05 00:59:
>> I have a TS-50 that I recently brought back on line and found that
>> everything worked...….except the output power into a 50ohm dummy load
>> was a whopping 200 watts.  I immediately stopped, went to SSB mode and
>> whistled up 200watts.  A quick try in CW and AM produced the same
>> results.
>>
>> I had this rig repaired a few years back by Clif @ AVVID.  He put it
>> in tip-top shape and I used it periodically afterward.  Fast forward
>> to now (3+ years later) when I got it from the closet and found the
>> above described problem.  It's been in a controlled environment and
>> not subjected to humidity or high temperatures.
>>
>> I'm guessing an electrolytic has given up and the bias on the finals
>> is in trouble.  But that's only a guess.  Anyone wish to comment?  I'm
>> not equipped to service it unless there is something obvious that
>> doesn't require precision work.  I'm one of the dinosaurs who is
>> linked to BA gear where I still do my own repairs, etc.
>>
>> Thanks for the read.
>>
>> 73 de W4MIL
>> Chuck
>>
>>
>>
>>
>> チャーリー ミルトン
>>
>>
>>
>>
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