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Bias current problems

Robert Hudson
 

Hi

Working on 40m Txcr with Ver 2.2 board.

A little confused about the Bias Current setting.    The procedure says with the bias setting pot turned fully anti-clockwise start turning it clockwise slowly until the current increases 60mA to about 0.54A (that is 540mA).

This seems like a high current.   I have worked on another Tx where the idle current was 60mA only.

 

What current should be drawn with the pot in the anti-clock position?   Is my understanding out  or is it a typing error?


I managed to destroy the final FET and have replaced it, also removed the bias pot to check it, appears ok .

I have made up a test mic plug with a switch as PTT and have a 2 tone board for checking peak envelope power.    The Rx draws 44mA and when the the switch (PTT) is operated the current goes to 1200mA and am unable to adjust it with the bias pot.


 The board was built by a friend and trying to help him out.     

The  Low Pass Filter coils have the correct number of turns (15) but seem loosely wound,  check the circuits with an ohm meter and all appear ok.  Check the toroid transformers and the same applies loose windings but correct turns and continuity with an ohmmeter.   The receiver seems to be working fine.   Just Stuck on the bias current.   Any help would be appreciated.


Bob VK2AOR

JOHN CRONHELM
 

Hi Bob,
Should be soon checking this myself.  As a point of interest where do you check the current amps. From which point to ground?  Sorry can't help you with your problem.
John, vo1jcc.


On Jul 22, 2017, at 8:26 AM, vk2aor@... [CHINA_QRP] <CHINA_QRP@...> wrote:

 

Hi

Working on 40m Txcr with Ver 2.2 board.

A little confused about the Bias Current setting.    The procedure says with the bias setting pot turned fully anti-clockwise start turning it clockwise slowly until the current increases 60mA to about 0.54A (that is 540mA).

This seems like a high current.   I have worked on another Tx where the idle current was 60mA only.

 

What current should be drawn with the pot in the anti-clock position?   Is my understanding out  or is it a typing error?


I managed to destroy the final FET and have replaced it, also removed the bias pot to check it, appears ok .

I have made up a test mic plug with a switch as PTT and have a 2 tone board for checking peak envelope power.    The Rx draws 44mA and when the the switch (PTT) is operated the current goes to 1200mA and am unable to adjust it with the bias pot.


 The board was built by a friend and trying to help him out.     

The  Low Pass Filter coils have the correct number of turns (15) but seem loosely wound,  check the circuits with an ohm meter and all appear ok.  Check the toroid transformers and the same applies loose windings but correct turns and continuity with an ohmmeter.   The receiver seems to be working fine.   Just Stuck on the bias current.   Any help would be appreciated.


Bob VK2AOR

Robert Hudson
 

Hi John

I use an ammeter in the supply line in series to read the current.   The receiver draws 44mA and if the Bias current  was 60mA then the total current draw would be 100mA.   It actually might be a bit less because I think some of the circuit is switched off when the PTT is pressed.  

I recently bought an FT-847 from a deceased estate which was dismantled and in a cardboard box with most of the covers missing.   I have been able to re-connect it and stall worked with VHF, UHF and HF/50mhz.  The only problem was the HF/50Mhz PA board (Power Amplifier board).  The problem was there was no bias current .   After looking around and getting the service manual and staying the circuit I found the bias pot was open circuit.  The interesting thing was that it had a 2 pin header with a link connected for normal use and you could take the link off and connect an ammeter read the bias current only with out the complication of reading the whole radio current draw.      

The way the instruction is written does not make sense to me.  So hoping to get some further explanation.   I have some other information as well to progress with the testing by shorting pins 2 and 3 which makes it operate in the AM mode of one of the NE602 chips but have to read further.   Still need to understand the Bias current setup.

Hope that explains some it for you John.


Bob Hudson







Robert Hudson
 

To John

Just re-read your question posed about where you check the current amps.

" As a point of interest where do you check the current amps. From which point to ground? "

When you check voltage you use  say a voltmeter from earth to a point where voltage might be expected , say a better.  When you check current /amps you need to have you multimeter switch to the amps setting and it is connected in series.   Maybe you had errant finger on the keyboard.

Best wishes


Bob Hudson







JOHN CRONHELM
 

Sorry Bob,
That's not the question I was asking.  Where on the PCB should I touch with the positive probe to read the bias current.
Many thanks,
John vo1jcc.


On Jul 22, 2017, at 11:10 AM, Robert Hudson vk2aor@... [CHINA_QRP] <CHINA_QRP@...> wrote:

 

To John


Just re-read your question posed about where you check the current amps.

" As a point of interest where do you check the current amps. From which point to ground? "

When you check voltage you use  say a voltmeter from earth to a point where voltage might be expected , say a better.  When you check current /amps you need to have you multimeter switch to the amps setting and it is connected in series.   Maybe you had errant finger on the keyboard.

Best wishes


Bob Hudson







AA7US
 

Hey gang,

I just finished assembling a CS-40 yesterday and went through the TX alignment.  After reading about all the destroyed IRF510's, I was a bit nervous when setting the bias current.

Here's how it's done:

1. Connect ammeter in the transceiver's power supply lead.  Keep in mind that the current can approach 1.5 amps during the entire alignment process (including TX power peaking), so pick an appropriate range on your ammeter.

2. Make double (triple) sure the SET BIAS trimmer (pot) on the main PCB is fully counter clockwise.

3. IF you've already fiddled with the TX IFT coils, I'd suggest returning them to their factory setting by screwing them back fully clockwise, gently.

4. Apply power to the transceiver.  Take note of the idle receive current draw.  My CS-40 shows about 0.07 amps at 12.7v input power.

5. Key up the transceiver via the PTT switch but DO NOT TALK into the mic.  Write down the current shown on the ammeter for reference.  My CS-40 showed 0.54 amps.

6. With the PTT switch still pressed, turn the SET BIAS trimmer clockwise VERY VERY VERY slowly while carefully watching the ammeter for an increase in current.

7. Somewhere beyond the middle travel of the SET BIAS trimmer's rotation the power supply current will begin to increase.  Occasionally pause between SLOWLY turning the SET BIAS trimmer to let the supply current stabilize.

8. Once the supply current has increased (and stabilized) to approx. 60mA (0.06 amps) beyond the current you started with, STOP.  In the case of my CS-40, I stopped at 0.59 amps total.  That works out as 0.54 amps beginning + 0.05 amps increase of bias current.

9. Unkey the PTT switch.

10. Now you can peak the TX band pass filters (IFT coils) for maximum TX power following the instructions in the assembly manual.

My CS-40 wound up with approx. 8 watts of TX out at full modulation with 12.7v input power.

Hope this helps clear things up for someone.

73,

John
AA7US

Adam Rong
 

Thanks, John.

In TX mode, even there is no voice to drive the RF output, the current consumption is still much bigger than RX mode because of the TX chain bias current and relay coil current consumption. It is the nature of SSB mode that you get RF output only when you speak to microphone. You speak louder, you get higher power before it is saturated.

The RX mode current is increased from around 40-mA to around 70-mA for CS series because the added Sandwich digital VFO will consume more.

Thanks,
Adam

在 2017年7月22日,下午11:45,landrjoh@... [CHINA_QRP] <CHINA_QRP@...> 写道:

Hey gang,


I just finished assembling a CS-40 yesterday and went through the TX alignment.  After reading about all the destroyed IRF510's, I was a bit nervous when setting the bias current.

Here's how it's done:

1. Connect ammeter in the transceiver's power supply lead.  Keep in mind that the current can approach 1.5 amps during the entire alignment process (including TX power peaking), so pick an appropriate range on your ammeter.

2. Make double (triple) sure the SET BIAS trimmer (pot) on the main PCB is fully counter clockwise.

3. IF you've already fiddled with the TX IFT coils, I'd suggest returning them to their factory setting by screwing them back fully clockwise, gently.

4. Apply power to the transceiver.  Take note of the idle receive current draw.  My CS-40 shows about 0.07 amps at 12.7v input power.

5. Key up the transceiver via the PTT switch but DO NOT TALK into the mic.  Write down the current shown on the ammeter for reference.  My CS-40 showed 0.54 amps.

6. With the PTT switch still pressed, turn the SET BIAS trimmer clockwise VERY VERY VERY slowly while carefully watching the ammeter for an increase in current.

7. Somewhere beyond the middle travel of the SET BIAS trimmer's rotation the power supply current will begin to increase.  Occasionally pause between SLOWLY turning the SET BIAS trimmer to let the supply current stabilize.

8. Once the supply current has increased (and stabilized) to approx. 60mA (0.06 amps) beyond the current you started with, STOP.  In the case of my CS-40, I stopped at 0.59 amps total.  That works out as 0.54 amps beginning + 0.05 amps increase of bias current.

9. Unkey the PTT switch.

10. Now you can peak the TX band pass filters (IFT coils) for maximum TX power following the instructions in the assembly manual.

My CS-40 wound up with approx. 8 watts of TX out at full modulation with 12.7v input power.

Hope this helps clear things up for someone.

73,

John
AA7US



JOHN CRONHELM
 

Thanks John,
Your explanation is excellent and very clear.  Will help me a lot when I get to that point.
Regards,
John  Vo1jcc

On Jul 22, 2017 1:15 PM, "landrjoh@... [CHINA_QRP]" <CHINA_QRP@...> wrote:
 

Hey gang,


I just finished assembling a CS-40 yesterday and went through the TX alignment.  After reading about all the destroyed IRF510's, I was a bit nervous when setting the bias current.

Here's how it's done:

1. Connect ammeter in the transceiver's power supply lead.  Keep in mind that the current can approach 1.5 amps during the entire alignment process (including TX power peaking), so pick an appropriate range on your ammeter.

2. Make double (triple) sure the SET BIAS trimmer (pot) on the main PCB is fully counter clockwise.

3. IF you've already fiddled with the TX IFT coils, I'd suggest returning them to their factory setting by screwing them back fully clockwise, gently.

4. Apply power to the transceiver.  Take note of the idle receive current draw.  My CS-40 shows about 0.07 amps at 12.7v input power.

5. Key up the transceiver via the PTT switch but DO NOT TALK into the mic.  Write down the current shown on the ammeter for reference.  My CS-40 showed 0.54 amps.

6. With the PTT switch still pressed, turn the SET BIAS trimmer clockwise VERY VERY VERY slowly while carefully watching the ammeter for an increase in current.

7. Somewhere beyond the middle travel of the SET BIAS trimmer's rotation the power supply current will begin to increase.  Occasionally pause between SLOWLY turning the SET BIAS trimmer to let the supply current stabilize.

8. Once the supply current has increased (and stabilized) to approx. 60mA (0.06 amps) beyond the current you started with, STOP.  In the case of my CS-40, I stopped at 0.59 amps total.  That works out as 0.54 amps beginning + 0.05 amps increase of bias current.

9. Unkey the PTT switch.

10. Now you can peak the TX band pass filters (IFT coils) for maximum TX power following the instructions in the assembly manual.

My CS-40 wound up with approx. 8 watts of TX out at full modulation with 12.7v input power.

Hope this helps clear things up for someone.

73,

John
AA7US


n7rgw
 

Don't forget to make sure the Final FET is insulated from the case.


On Saturday, July 22, 2017 4:56 AM, "vk2aor@... [CHINA_QRP]" wrote:


 
Hi
Working on 40m Txcr with Ver 2.2 board.
A little confused about the Bias Current setting.    The procedure says with the bias setting pot turned fully anti-clockwise start turning it clockwise slowly until the current increases 60mA to about 0.54A (that is 540mA).
This seems like a high current.   I have worked on another Tx where the idle current was 60mA only.
 
What current should be drawn with the pot in the anti-clock position?   Is my understanding out  or is it a typing error?

I managed to destroy the final FET and have replaced it, also removed the bias pot to check it, appears ok .
I have made up a test mic plug with a switch as PTT and have a 2 tone board for checking peak envelope power.    The Rx draws 44mA and when the the switch (PTT) is operated the current goes to 1200mA and am unable to adjust it with the bias pot.

 The board was built by a friend and trying to help him out.     
The  Low Pass Filter coils have the correct number of turns (15) but seem loosely wound,  check the circuits with an ohm meter and all appear ok.  Check the toroid transformers and the same applies loose windings but correct turns and continuity with an ohmmeter.   The receiver seems to be working fine.   Just Stuck on the bias current.   Any help would be appreciated.

Bob VK2AOR


Brian Schmitt
 

Bob,

If I remeber correctly from my build of knq7a, the counterclockwise  amperage is approx 480mA (540mA - 60mA). The pot gets turned clockwise to increase the bias approx  60mA up to 540mA. 

I do remeber having to re read that part of the manual a few times.

Brian



On Sat, Jul 22, 2017 at 3:56 AM, vk2aor@... [CHINA_QRP]
wrote:
 

Hi

Working on 40m Txcr with Ver 2.2 board.

A little confused about the Bias Current setting.    The procedure says with the bias setting pot turned fully anti-clockwise start turning it clockwise slowly until the current increases 60mA to about 0.54A (that is 540mA).

This seems like a high current.   I have worked on another Tx where the idle current was 60mA only.

 

What current should be drawn with the pot in the anti-clock position?   Is my understanding out  or is it a typing error?


I managed to destroy the final FET and have replaced it, also removed the bias pot to check it, appears ok .

I have made up a test mic plug with a switch as PTT and have a 2 tone board for checking peak envelope power.    The Rx draws 44mA and when the the switch (PTT) is operated the current goes to 1200mA and am unable to adjust it with the bias pot.


 The board was built by a friend and trying to help him out.     

The  Low Pass Filter coils have the correct number of turns (15) but seem loosely wound,  check the circuits with an ohm meter and all appear ok.  Check the toroid transformers and the same applies loose windings but correct turns and continuity with an ohmmeter.   The receiver seems to be working fine.   Just Stuck on the bias current.   Any help would be appreciated.


Bob VK2AOR

AA7US
 

That's a good point to remember about the CS series transceivers having higher RX current due to the operation of the sandwich VFO.

Keep in mind the sandwich VFO assembly instructions mention you can disable (destroy) the status LED on the Arduio Pro Mini's circuit board to save 1.5mA of current consumption.  I opted not to do this because I was too worried I'd inadvertently harm the circuit board.

73,

John
AA7US

---In CHINA_QRP@..., <rongxh@...> wrote :

The RX mode current is increased from around 40-mA to around 70-mA for CS series because the added Sandwich digital VFO will consume more.

Thanks,
Adam

AA7US
 

Question for Adam:

How does the IRF510's gate bias current affect transmit power?

Thank you,

John
AA7US

Adam Rong
 

The gate bias for IRF510 60-mA is a good point to work in class AB to balance amplification linearity and power consumption. From my observation, if it is too small, the RF output will be a bit negatively affected. In your senario, if you increase from 50-mA to 60-mA, probably you can get a bit more output but don't set it any bigger.

于 2017-7-23 8:04, landrjoh@... [CHINA_QRP] 写道:

 

Question for Adam:


How does the IRF510's gate bias current affect transmit power?

Thank you,

John
AA7US

Robert Hudson
 

Hi John

I used a power cable plugged into my fused supply and removed the fuse and using crocodile clips on my AVO 7 multimeter  so it is in series with my power supply, the red lead goes to the plus supply and the black lead goes to the radio.  The negative has no connection.   Hope that helps.

Bob Hudson







Robert Hudson
 

Hi All thanks for your comments and help .   To John AA7US a very concise description.  Thank you John


Bob Hudson







JOHN CRONHELM
 

Thanks,At last I have got it now.   I have no fused power cable from my gel cell. I could perhaps could cut the axial lead after the large diode connected to the power supply and connect a power lead to both cut ends to check bias current. When I am finished with the tests I can make it into a switch to turn the radio on and off.
What do you think?
73 de John vo1jcc.


On Jul 22, 2017, at 9:54 PM, Robert Hudson vk2aor@... [CHINA_QRP] <CHINA_QRP@...> wrote:

 

Hi John


I used a power cable plugged into my fused supply and removed the fuse and using crocodile clips on my AVO 7 multimeter  so it is in series with my power supply, the red lead goes to the plus supply and the black lead goes to the radio.  The negative has no connection.   Hope that helps.

Bob Hudson







AA7US
 


That's exactly how I plan to wire up a power switch for mine.

73,

John
AA7US 

---In CHINA_QRP@..., <johncronhelm@...> wrote :

I could perhaps could cut the axial lead after the large diode connected to the power supply and connect a power lead to both cut ends to check bias current. When I am finished with the tests I can make it into a switch to turn the radio on and off.