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Re: Low Power - Final Amplifier on through - hole kit

 

Hi Mark

There are two ways to measure with a scope as outlined in EMRFD.

First way is with a x10 probe hung on a 50 ohm load. Load is on the o/p.

Second way is with a x1 probe.The probe is plugged into a tee. The other tee connection has a 50 ohm load on it. Then the entire tee is plugged into the scope. The probe is on the o/p.

I have tried both ways and both work.

73

Ken VA3ABN

On Wed, Jan 25, 2017 at 12:25 PM, Mark Baldridge <marktbaldridge@...> wrote:
Alright guys. The big trick here is MEASURE EVERYTHING WITH A x10 PROBE.

That was my mistake. Per Leonard's documentation here:


I re-measured everything. With 2v pk-pk in, I was getting 30v at the collector of Q1, and with 22v in my 6 cell LiPo on the IRF510, I was getting 54v pk-pk into a 50 ohm load. This is 7-8 watts.

The PA is performing as expected. The next step for me is to figure out why the exciter isn't driving the PA as it should. (I should re-measure that with a x10 probe even!)

Lesson learned. Thanks for all your insights and patience everyone. :)

~Mark

On Tue, Jan 24, 2017 at 3:43 PM, Mark Baldridge <marktbaldridge@...> wrote:
One quick question before I do some more tests tonight:

Looking at this version of the Bitx PA:



The resistors at the emitter of Q1 are 22E and 6.2E. Why were they changed to 10E and 10E on the Bitx 3B? (See PDF attachment on original post.)

Wouldn't changing from 6.2E to 10E reduce the gain of Q1?

Thanks all.

On Mon, Jan 23, 2017 at 4:17 PM, Mark Baldridge <marktbaldridge@...> wrote:
Greetings all.

I started tracing my PA with Leonard's documentation.?



The first discrepancy I noticed right away.?

He had 30v pk-pk on the collector of Q1 (2n2218) and I only had 15.94v pk-pk. And the waveform is quite different. My guess is that the problem is around here. I double-checked all the component values, orientation of the 2n2218, and my solder joints. I'm still stumped.

Attached is a capture from the scope.?

My voltages at Q1 were as follows:?

Base: 1.79v
Collector: 10.97v
Emitter: 1.14v

And yes, I am running the entire board from a 20vDC regulated bench power supply (HP3630A), and I am feeding in 2v pk-pk at 14.00MHz from the function generator (Tektronix AFG3251).

Any insights would be much appreciated!

On Sat, Jan 21, 2017 at 6:09 PM, Jorge Luiz Fenerich <py2pvt@...> wrote:
? ?Thanks Leonard for finding this page I was needing it and I need to know also the voltages in Q1 (2N3866) if you know please pass me ok?
? ? Jorge PY2PVT _._

2017-01-20 17:17 GMT-02:00 kc0wox Leeper <kc0wox@...>:

I agree. Some of the below displays may be somewhat different as there will be harmonics at most points before the low pass filter.


I found the web page I was looking for.

This should give plenty of information to isolate a problem in the pa.

Leonard




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? 73 de Jorge PY2PVT
? Campinas SP
? GG67MD




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