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Hello everyone

I ordered and assembled this PA. I followed every step as carefully as I can while assembling.

When the pots closed fully (to counter-clockwise) current consumption is 140mA stable (TX is grounded, no RF) when I apply 12 volts. When I start to turn one of the pots, it is still 140mA stable. Same with the other pot. Nothing is changing. So I cannot adjust them to 125mA (total of 250mA).

I checked transistors (IRF510) and their reading is fine. I cut the power and I touched them first (against static) and checked thier resistance measurement from their legs and their readings are same. They seem OK.

I think I am missing a point. I am newbie about PAs. I send some detailed pictures. Any help would be appreciated.

?

73 TA2CCN

Hi,
Did you ground the tx before measuring current drawn?
Also does the voltage on the drain pins vary as the potentiomer is turned?
Check these first.
Andy
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.

You need to? have a method of proving that the mA setting? (in fact? Gate? bias voltage set ) Potentiometers are in fact? affecting the gates of respective IRF mosfets (by driving up the gate voltage for zero current into the gate )? and preferably eliminate the mosfets ex cct while test is being done ie Gate x 2 are not connected to their pads.? NOw you are at where you are in assly its? going to require you do do some sexy work wiith a solder sucker to get the Gate lines of the IRFs free without? damaging the PCBS.?

Then if you see the? bias V at the free of Mosfet? pad? responding to the respective potentiometer you know that? the bias system is working (you'd expect the bias to be something like 3.8-4.2 V and certainly? movable in this range).? If that's all good you have to suspect the mosfet ccts? ie the Passives that are around the mosfets? (including all your scraping off of? Formvar insulation on magnet wire and soldering that wire? to the pads on the PCBS ,which is often? a show stopper and overlooked , ie both RF? power transformers need close inspection)? and? also the mosfets themselves.? ?If you suspect? the IRFs after all this? then try andfind a? ham with a component tester (microprocessor controlled) or failing that you' will have to build a test bogey? along the lines shown in datasheets to prove each? ?Mosfet is fine under? Dc op condition? and that the transconductance (delta? mA( or amperes)? in? D-G cct versus? delta? V in the gate cct? as a? quotient)? of the IRFs is? within expectations and the two have the same transconductance? (within reason, Hans does not offer them as a formal matched pair).?

The fact that the unit is pulling 140mA base current does not mean that the driver? CCT of BS 170s is all good.... but that numbers sounds about right for linear operation of? BS 170s with a 12 V Vcc,? ie 70mA per BS 170 Drain - Source? circuit.?

?

TEF

Schema for reference and Sh_ts and giggles

Ground tex before? measuring? Tx current Draw : " Wot Dat? Boy ? " **

?

I think you are thinking of the type of PA where the? bias to the high power
Fets is only applied in? Tx mode. The Ten W linear is a straight Pallet amp without even Rx Tx control -that''s? a user hack if the user wants it - there is nothing to ground to force it to Tx mode.? I sent a? Schematic in as? separate post.?

** NZ slang from? out in the boondocks no offense meant.

Well, RTFM and it states ground the tx pad to turn the amp on, days wot that is boy.
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.

You write: When I start to turn one of the pots, it is still 140mA stable.
That suggests to me that you expect the current to increase immediately at the start of the pot. It won't but at a certain voltage on the gate, the IRF510 will start to draw current. Be careful, once it starts it will increase rapidly. At that point you may have to go slowly up and down to get 125mA in each.
73 Brian VK4BAP.

There's an X shown? under the? dropper to GND front end of regulators (as per schematic) .? That's? in fact a form of PTT line.? My poor eyes did not see that first up and of couse I did not RTFM .. what sort of moron do you think I am? ??

? If that had a BS 170 or even 2n7000 squeezed in you 'd have a 5V active PTT (isolated system) .? I'll dig out a very nice? Fr design which sshows? a carrier operated relay system (COR)? basic design for those who well? want to be different.? Remember COR? can be problematic with SSB as when voice levels diminish at some point the? COR relay / mosfets are going to drop out.? With maintained carrier systems like AM and NBFM this is never an issue.

Thank you for replies.

I desoldered both IRF510s and checked them (like in this video):

They both seem OK and have very close numbers when I measured.

After that I gave 13 volts power to PA and measured the voltage on empty GATE holes (As shown in the photo). When pots are fully CCW closed, it is 0 volts. When I open pots CW fully, I read 5 volts each. So, bias system and MOSFETs are working.

I now focused on output transformer and going to remove it and check with all other windings and solderings because I suspect that my soldering work may poor.

I will write again soon. Thanks.

Make sure that the enamel? is completely removed in the areas where you are going to solder. If the holes they are going into are plated through holes? ie PTH then as a temp measure you can use a finer gauge wire such as stripped out? Cat 5e wire which is pure copper once the PE insulation is removed andtack the copper lead outs of the transformers just to the top pad. Then once the whole thing is working you can move the lead out wires? back to fully installed.

?

The? wire going from the BN transformer near words? that look like? C202 on solder mask looks very suspect.? You can heck as soldered connections if you remove a a little more insulation on the magnet wire of the coils so can get one DVM probe in there and one direct to the PCB rondel to check? continuity.? ? If there is ANY doubt at all that the PTH are really? plated through then have enough tinning on the copper? that you can solder both Top? and BOTTOM side? (taking care not to burn components );? ?that will fix the bastardo.?

?

But you would then never know which particular through hole had the issue.? Never mind - it's a one off not a production jobbie.?

First you need to put a load on it for safety.?
Ground the TX enable line or the bias setting will not happen.
The TX line is so the amp can be shut down for RX.


--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.

Timmy,

Who cares.
That amp from Diz is rather nice but does not work at all well on 15 or 10M.

So stay on topic and help the gentleman with his QRPL 10W amp.

--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.

Typical pot setting as the IRF transistors start to conduct (yours may vary, increase very slowly )?

On Fri, Jul 12, 2024 at 06:46 AM, Timothy Fidler wrote:

Remember COR? can be problematic with SSB

COR can be problematic with any modulation, as it will by nature always "hot switch" when drive is sensed, open-circuiting the output of the driving amplifier/radio as the amplifier switches from RX to TX. So you are load-pulling your amplifier every time you key up.
I always use a wired TX signal.
73, Don N2VGU

Ahoy there mon !! as Bob Marley would say .. we are sitting here holding our breath waiting for the story that it was a bad solder joint or a plated through hole (ie PTH that take signals from bottom to top of PCB ) which did not work as advertised...

?

do you have traction yet ?