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Adjusting pa bias (RV3) blows one of the final #ubitx

srivatsa KS
 

Hi,

I'm trying to adjust pa bias on my ubitx v4 since 2days. Initial current consumption with both preset (RV3 and RV2) in clockwise position is 150mA. I turn bot preset fully clockwise.
I start with RV3 turning slowly anti-clockwise. Current with PTT on is 350ma to start with. As i start to turn the preset RV3. Some point of time current shoots up very fast and i stop.  By now the final is very hot.  At this point I don't have to press PTT,   current consumption in Recieve is 350ma. One of the Irf510(Q94) gets very hot in recieve itself. Most likely it's gone for toss. This the second time in frying it in past 2 days. Plese help!  Am i doing it the right way? I know the preset needs to be turned very slowly and I'm doubly sure I'm doing it extremely slow. Not sure what is wrong :( 

This doesn't happen with the other irf510 (Q95).  RV2 has is lesser gradient and can be easily turned easily to get a 100m amp more. 

Shouldn't RV3 have similar current gradient on Q94 as RV2 has on Q95 ?

 

If one of the bias adjust pot is slightly skewed then one of the leads below is cut
that is why you are not able to adjust bias. I recommend Bourn's multiturn preset
that is vertical for best results.

Raj

At 29/11/2019, you wrote:
Hi,

I'm trying to adjust pa bias on my ubitx v4 since 2days. Initial current consumption with both preset (RV3 and RV2) in clockwise position is 150mA. I turn bot preset fully clockwise.
I start with RV3 turning slowly anti-clockwise. Current with PTT on is 350ma to start with. As i start to turn the preset RV3. Some point of time current shoots up very fast and i stop. By now the final is very hot. At this point I don't have to press PTT, current consumption in Recieve is 350ma. One of the Irf510(Q94) gets very hot in recieve itself. Most likely it's gone for toss. This the second time in frying it in past 2 days. Plese help! Am i doing it the right way? I know the preset needs to be turned very slowly and I'm doubly sure I'm doing it extremely slow. Not sure what is wrong :(

This doesn't happen with the other irf510 (Q95). RV2 has is lesser gradient and can be easily turned easily to get a 100m amp more.

Shouldn't RV3 have similar current gradient on Q94 as RV2 has on Q95 ?

srivatsa KS
 

Thanks Raj, yes it's skewed! I'll replace the pot with the Bourne multi turn and check. Thanks.

Jerry Gaffke
 

Raj is probably right about replacing the pot.

However, this is puzzling:
>  At this point I don't have to press PTT, current consumption in Recieve is 350ma.

I'd guess that you just blew Q94, and current will remain at 350 ma even after turning RV3 fully clockwise and/or turning power off and then back on.
If current during receive is 150ma initially, it should always be close to that when PTT is not pressed.

The TX power rail into pin 3 of U2 is 12v only when PTT is pressed for transmit, TX should be 0v when not pressed for receive.
So the gate (middle terminal) at Q94 should also be 0v during receive, and Q94 turned fully off (even though there is still 12v at Q94 drain).
If Q94 is conducting (and getting hot) when Q94 gate is 0v, then Q94 is blown and must be replaced.

There should be no current into the Q94 drain when RV3 is fully clockwise with PTT pressed.
That current increases at some point (around 3 or 4 volts at the gate of Q94) as you turn RV3.
If this is the case, then Q94 is probably ok.
.

Jerry, KE7ER

 

On Thu, Nov 28, 2019 at 11:03 PM, Raj vu2zap wrote:
If one of the bias adjust pot is slightly skewed then one of the leads below is cut
that is why you are not able to adjust bias. I recommend Bourn's multiturn preset
that is vertical for best results.

Raj

 

At 29/11/2019, you wrote:
Hi,

I'm trying to adjust pa bias on my ubitx v4 since 2days. Initial current consumption with both preset (RV3 and RV2) in clockwise position is 150mA. I turn bot preset fully clockwise.
I start with RV3 turning slowly anti-clockwise. Current with PTT on is 350ma to start with. As i start to turn the preset RV3. Some point of time current shoots up very fast and i stop. By now the final is very hot. At this point I don't have to press PTT, current consumption in Recieve is 350ma. One of the Irf510(Q94) gets very hot in recieve itself. Most likely it's gone for toss. This the second time in frying it in past 2 days. Plese help! Am i doing it the right way? I know the preset needs to be turned very slowly and I'm doubly sure I'm doing it extremely slow. Not sure what is wrong :(

This doesn't happen with the other irf510 (Q95). RV2 has is lesser gradient and can be easily turned easily to get a 100m amp more.

Shouldn't RV3 have similar current gradient on Q94 as RV2 has on Q95 ?

Lawrence Galea
 

Apart from the suggestions by our friends, best is to use a current limited supply so that if it goes above the setting it will protect the set or use a car lamp in series with the supply which will also provide some protection.
As suggested a multi-turn pot is better to adjust the bias.
Happy weekend
Lawrence

On Fri, Nov 29, 2019 at 5:00 AM srivatsa KS <srivatsak.s@...> wrote:
Hi,

I'm trying to adjust pa bias on my ubitx v4 since 2days. Initial current consumption with both preset (RV3 and RV2) in clockwise position is 150mA. I turn bot preset fully clockwise.
I start with RV3 turning slowly anti-clockwise. Current with PTT on is 350ma to start with. As i start to turn the preset RV3. Some point of time current shoots up very fast and i stop.  By now the final is very hot.  At this point I don't have to press PTT,   current consumption in Recieve is 350ma. One of the Irf510(Q94) gets very hot in recieve itself. Most likely it's gone for toss. This the second time in frying it in past 2 days. Plese help!  Am i doing it the right way? I know the preset needs to be turned very slowly and I'm doubly sure I'm doing it extremely slow. Not sure what is wrong :( 

This doesn't happen with the other irf510 (Q95).  RV2 has is lesser gradient and can be easily turned easily to get a 100m amp more. 

Shouldn't RV3 have similar current gradient on Q94 as RV2 has on Q95 ?

Jerry Gaffke
 

Any particular "car lamp"?
There's headlights, tail lights, brake lights, dash lights, turn signals, ...
There's incandescent, halogen, LED, ...

My guess is that you are thinking of something like an 1157 incandescent light.
    https://www.amazon.com/SYLVANIA-1157-Miniature-Contains-Bulbs/dp/B0031HAN92

This has two different filaments, try the thinner tail light filament first.
If the voltage drops too much at the required current then try the thick brake light filament.
Could get a little bit more ummph by running both filaments in parallel.

Seems an incandescent light is well suited to this sort of thing since the resistance goes up drastically when it's hot.
So it has little effect at low currents, but severely restricts high currents.
An 1157 plus jumper cables to a 12v source is a quick and easy current limited power supply.
Assuming you are happy with a rough current limit of something under 1 Amp.

I have never tried it.

Jerry, KE7ER



On Fri, Nov 29, 2019 at 07:21 AM, Lawrence Galea wrote:
Apart from the suggestions by our friends, best is to use a current limited supply so that if it goes above the setting it will protect the set or use a car lamp in series with the supply which will also provide some protection.
As suggested a multi-turn pot is better to adjust the bias.
Happy weekend
Lawrence

srivatsa KS
 

Thanks for the suggestions guys. Much appreciated. I de-soldered RV3 and discovered 2 pins broken . Probable while adjusting the bias the pins below suddenly came in contact during last mile of the turn and bleu the finals. 



I had a Bourne 10k single turn lying around my shack which i used. I also replaced the blows IRF 510 today .


Rx only consumes 150ma. TX no modulation takes 350mA. Adjusted pa bias 100mA from each IRF510. So max consumption(no modulation) is 550-560ma . 
While speaking to mic there is no significant increase in current. Max 600-650mA. Output power measured on my swr meter is 2-3watt max with me shouting into the PTT on 40m . Is this normal?

Harry Latterman
 

Why do you have the + VDC wire hooked to the negative power post???



On Friday, November 29, 2019, 11:00:08 AM MST, srivatsa KS <srivatsak.s@...> wrote:


Thanks for the suggestions guys. Much appreciated. I de-soldered RV3 and discovered 2 pins broken . Probable while adjusting the bias the pins below suddenly came in contact during last mile of the turn and bleu the finals. 



I had a Bourne 10k single turn lying around my shack which i used. I also replaced the blows IRF 510 today .


Rx only consumes 150ma. TX no modulation takes 350mA. Adjusted pa bias 100mA from each IRF510. So max consumption(no modulation) is 550-560ma . 
While speaking to mic there is no significant increase in current. Max 600-650mA. Output power measured on my swr meter is 2-3watt max with me shouting into the PTT on 40m . Is this normal?

Clark Martin
 

It’s the black wire connected to the black terminal. It just has a strip of red from where it separated from the red wire.

Clark Martin
KK6ISP

On Nov 29, 2019, at 11:02 AM, Harry Latterman via Groups.Io <harrylatterman@...> wrote:

Why do you have the + VDC wire hooked to the negative power post???

Harry Latterman
 

OK Clark,

I have used wires like that for years and sometimes it is easy to mix the hot with the ground do to the markings on the wire... That one sure looked like the hot wire was on the ground pole... Good luck with your radio. I will be starting working with my V3 and making it a modified V4 in a couple of months..

73 Harry K7ZOV

On Friday, November 29, 2019, 4:08:40 PM MST, Clark Martin <kk6isp@...> wrote:


It’s the black wire connected to the black terminal. It just has a strip of red from where it separated from the red wire.

Clark Martin
KK6ISP

On Nov 29, 2019, at 11:02 AM, Harry Latterman via Groups.Io <harrylatterman@...> wrote:

Why do you have the + VDC wire hooked to the negative power post???

 

Try adjusting the drive  control VR1 and see..

Raj


At 29/11/2019, you wrote:

I had a Bourne 10k single turn lying around my shack which i used. I also replaced the blows IRF 510 today .

[]
Rx only consumes 150ma. TX no modulation takes 350mA. Adjusted pa bias 100mA from each IRF510. So max consumption(no modulation) is 550-560ma .
While speaking to mic there is no significant increase in current. Max 600-650mA. Output power measured on my swr meter is 2-3watt max with me shouting into the PTT on 40m . Is this normal?

MVS Sarma
 

Before powering fresh, you should first keep both pots fully clockwise so that both gates are at zero potential. 


On Sat, 30 Nov 2019, 11:35 am Raj vu2zap, <rajendrakumargg@...> wrote:
Try adjusting the drive  control VR1 and see..

Raj

At 29/11/2019, you wrote:

I had a Bourne 10k single turn lying around my shack which i used. I also replaced the blows IRF 510 today .


Rx only consumes 150ma. TX no modulation takes 350mA. Adjusted pa bias 100mA from each IRF510. So max consumption(no modulation) is 550-560ma .
While speaking to mic there is no significant increase in current. Max 600-650mA. Output power measured on my swr meter is 2-3watt max with me shouting into the PTT on 40m . Is this normal?

M0OOZ
 

An indicator lamp (incandescent) is sufficient

M0OOZ

On Fri, 29 Nov 2019, 17:18 Jerry Gaffke via Groups.Io, <jgaffke=yahoo.com@groups.io> wrote:
Any particular "car lamp"?
There's headlights, tail lights, brake lights, dash lights, turn signals, ...
There's incandescent, halogen, LED, ...

My guess is that you are thinking of something like an 1157 incandescent light.
    https://www.amazon.com/SYLVANIA-1157-Miniature-Contains-Bulbs/dp/B0031HAN92

This has two different filaments, try the thinner tail light filament first.
If the voltage drops too much at the required current then try the thick brake light filament.
Could get a little bit more ummph by running both filaments in parallel.

Seems an incandescent light is well suited to this sort of thing since the resistance goes up drastically when it's hot.
So it has little effect at low currents, but severely restricts high currents.
An 1157 plus jumper cables to a 12v source is a quick and easy current limited power supply.
Assuming you are happy with a rough current limit of something under 1 Amp.

I have never tried it.

Jerry, KE7ER



On Fri, Nov 29, 2019 at 07:21 AM, Lawrence Galea wrote:
Apart from the suggestions by our friends, best is to use a current limited supply so that if it goes above the setting it will protect the set or use a car lamp in series with the supply which will also provide some protection.
As suggested a multi-turn pot is better to adjust the bias.
Happy weekend
Lawrence

M0OOZ
 

From experience, a mutiturn pot is not only unnecessary, it is less durable than a 'normal' pot. 

May the peace be with you. 

M0OOZ

On Fri, 29 Nov 2019, 09:23 srivatsa KS, <srivatsak.s@...> wrote:
Thanks Raj, yes it's skewed! I'll replace the pot with the Bourne multi turn and check. Thanks.

srivatsa KS
 

Replaced the mic.  Now I'm able to get better power . Around 5 watt max while speaking normally to the PTT. Current consumption peaks to 1.2 , occasionally, but unable to make out (ssb) . I don't have a key (i'm bad at cw).
When i scream (literally) into ppt, i get around 8 to 9 watt on the meter. This is fine? Or should i expect more?

 How to adjust RV1. I tried moving clockwise. Current increases to around 2 amp when i shout . Not sure if this is ok.  So i moved back . I've blown 3 irf510 in 3days and don't want to spend time replacing again. So I'm a little cautious. 
Generally how do we adjust rv1?

Thanks for all the help.

 

Sri,

Some boards have a 40M low output problem, check on 80M and tell us.

Raj

At 30/11/2019, you wrote:
Replaced the mic. Now I'm able to get better power . Around 5 watt max while speaking normally to the PTT. Current consumption peaks to 1.2 , occasionally, but unable to make out (ssb) . I don't have a key (i'm bad at cw).
When i scream (literally) into ppt, i get around 8 to 9 watt on the meter. This is fine? Or should i expect more?

 How to adjust RV1. I tried moving clockwise. Current increases to around 2 amp when i shout . Not sure if this is ok. So i moved back . I've blown 3 irf510 in 3days and don't want to spend time replacing again. So I'm a little cautious.Â
Generally how do we adjust rv1?

Thanks for all the help.

Michael Bauer
 

I found on my ver 5 ubitx build that mic audio level greatly affects RF output power for voice mode.  I added a standalone mic preamp with a level pot to adjust my RF output for voice modes.  In parallel to the mic input to the ubitx board I added a level pot for digital mode audio power.  I adjust the level to a bit shy of max SSB RF output.  Too much level on either will give more energy into the harmonics.  I verified the operation of my build with a spectrum analyzer with an attenuated dummy load.  My takeaway, different mic audio levels, or even different mics will affect RF SSB output.

If you add a key, then the raduino will inject it's own audio freq  into the TX chain, and you can compare voice SSB RF output levels to the key RF output levels. The PA design is not flat power across all bands, but you should be able to get comparable key and SSB power levels within each band.

srivatsa KS
 

Hi raj

Forgive me for the long gap. I checked my ubitx on 80m it gives around 6w output only. 
Is this normal?
Thanks
Srivatsa


On Sat, 30 Nov, 2019, 7:40 PM Raj vu2zap, <rajendrakumargg@...> wrote:
Sri,

Some boards have a 40M low output problem, check on 80M and tell us.

Raj

At 30/11/2019, you wrote:
>Replaced the mic.  Now I'm able to get better power . Around 5 watt max while speaking normally to the PTT. Current consumption peaks to 1.2 , occasionally, but unable to make out (ssb) . I don't have a key (i'm bad at cw).
>When i scream (literally) into ppt, i get around 8 to 9 watt on the meter. This is fine? Or should i expect more?
>
> How to adjust RV1. I tried moving clockwise. Current increases to around 2 amp when i shout . Not sure if this is ok.  So i moved back . I've blown 3 irf510 in 3days and don't want to spend time replacing again. So I'm a little cautious.Â
>Generally how do we adjust rv1?
>
>Thanks for all the help.




Rene
 

De mijne geeft cw op een dummyload van maximaal 2 watt, sommige banden zelfs 0,5 watt. Ze zeggen dat alle boards zijn getest voordat ze worden verzonden. Ik denk dat ze de mijne zijn vergeten?😥😥😥 regards
Rene
Netherlands