Title: Solved! Trouble with Bias
Post by: WD8BXS on 29. November 2018, 15:38:00
I have a new Ver 7 on the bench. The Bias will not change with the bias setting.
The voltage going to the Mosfets is changing, but the bias current does not.
I changed the finals, but no change is the result.
Scratching my head!!
Any ideas as to what I am missing??
de Chuck WD8BXS |
Title: Re:Another NEW Issue
Post by: DF8OE on 29. November 2018, 15:57:48
If the BIAS is ZERO the gate voltage of the finals is out of range for mcHF circuit. Take a look at the datasheet: it can vary widely - and move upon the maximum voltage the circuit can provide.
Another possibility is a wrong wound power supply transformer. Put a bulb 12V/5W between Drain and ground. Does it light? If not: no power at drains...
If it is non zero and does not change by different gate voltages your finals may be fakes - but "fakes of a new generation"...
vy 73
Andreas |
Title: Re:Another NEW Issue - Trouble with Bias
Post by: WD8BXS on 29. November 2018, 21:38:02
Power supply Transformer?
These are the same finals I have always used from RF Parts.
|
Title: Re:Another NEW Issue - Trouble with Bias
Post by: WD8BXS on 29. November 2018, 23:02:55
12 volts at the Drain.
4.5 volts at the Gate with Ptt pressed.
no change in bias current.
Do you suggest I put the 3k resistor in the bias circuit to get more bias voltage??
Thanks,
Chuck |
Title: Re:Another NEW Issue - Trouble with Bias
Post by: DF8OE on 30. November 2018, 04:48:01
If you do not get BIAS: try increasing BIAS voltage. If you do not get BIAS at 4.7...5V your finals are fakes or out of specs...
vy 73
Andreas |
Title: Re:Another NEW Issue - Trouble with Bias
Post by: WD8BXS on 30. November 2018, 22:32:59
Installed another set of Finals, no joy!!
Started re-soldering components and it started working!
A great mystery hihi
Thanks, Chuck |
Title: Re:Solved! Trouble with Bias
Post by: DF8OE on 01. December 2018, 08:17:28
Bad solderings are no mystery ::)...
But you rarely would think that a copper track with solderings can loose voltage - often that is the cause of issues...
vy 73
Andreas |
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