Yes the cabel length with its inductance and the capacitive coupling
between them (cbe)
influenced the controll loop in this circuitry and made it too slow.
The upper switchmode frequency is reduced to much and the switching
behavior was very
bad ( therefore it produces more losses and needs now the beside-board
heatsink-condition).
Therefore it could not keep constant the output voltage under load
and or input voltage drops.
But in any case the max +5volts value limitation has worked,
because the circuitry could reduce the frequency under low load
conditions. (receive,standby,power voltage high).
The unit has worked, yes ,but not efficient.
I know from my former businees, such circumstances could happen in any
electronic production.
I am not worrying about it.
Many thanks for the interrest.
73, Heinz ,DJ8LX
Am 13.01.2011 18:14, schrieb Dr. Gerald N. Johnson:
> If the BD246 wasn't faulty, just slowed by the length of the leads, how
> did the radio ever work? Might the aging of an electrolytic have
> contributed to the poor regulation?
>
> 73, Jerry, K0CQ
>
> On 1/13/2011 7:59 AM, Heinz Dietmar Karl wrote:
>> Thanks for the feedback.
>> May I explain my impression that not the transistor BD246C itself is the
>> problem.
>> It was not defekt.
>> Also not whether it was manufactured (see datasheed Bourns) . Yes the
>> Datas between
>> BD and Original NTE 378 are slightly different comparing the
>> dynamics,switching times,
>> dc current gain, and I would in any case also prefer the Ten Tec design
>> with the matched
>> complementary transistors in the A9.
>> The real problem was the different housing and because of this,
>> the extern 8 cm -fare away -beside the board mounted one
>> of these usualy pair of transistors (377and 378 in this switching mode
>> supply).
>> I had some luck to remembering myself to have worked 30years ago as an
>> development member
>> designing switchmode power supplies for ac drive inverters for a short time.
>> best regards
>> Heinz,DJ8LX
>>
>>
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