Re: QDX Owners & Users... Limit your ! CURRENT !
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Hans, A little off topic here but what power out can you expect with 3x BS170 on 50MHz??? I know QDX is not a 6M rig ( yet ).? ?Would 1X BS170 be better than 3 (at 50Mhz) to lower gate capacitance?
TNX! Bob WA1EDJ
Sorry I meant 500mA current. Typo. Power dissipation rating 833mW?
"More powerful transistors" go hand in hand with higher device capacitance. Efficiency goes down, driver power goes up, heat dissipation goes up, it gets harder to produce the Watts at higher frequencies. No free lunch.?
Three BS170s are used in QCX and in other QRP Rigs. It's characteristics are pretty ideal for QRP. In view of the higher duty cycle expected in QDX (digital modes), I put four in.?
Furthermore being push pull the voltage on each side is half what it would be in an equivalent powered single ended design, giving more headroom before the transistor voltages limits are reached.? The QDX design is already reasonably conservative, guys! OK not bullet proof. But as long as you don't go wild, nothing goes pop.? -------- Original message -------- From: "Adam via " <qrp-labs= [email protected]> Date: Wed, Aug 10, 2022, 7:09 PM To: [email protected]Subject: Re: [QRPLabs] QDX Owners & Users... Limit your ! CURRENT ! Hans Summers <hans.summers@...> wrote:
> Note that the BS170 is rated 500mW continuous current. There are four of
> them. Granted they probably don't share the load equally but you have to be
> really badly mismatched to get to over-current situation.
It makes me wonder... do you think it would be a good idea to swap them
with more powerful transistors? Not to get more power, but to get more
protection in case of mismatch.
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