Heat-Sinks

I first learnt about the heatsink in my early days with VU2LEX around 1994. He showed me the calculations for his cwtx. etc But somehow I never need the heatsinks seriously till I made the IRF640 LINEAR in 2014.

My success with linear is mostly attributed to the first big heatsink I found from flea wendor. It costed me about Rs40/- about half dollar a two years ago. It was a Pentium computer heatsink. Then I found few in Mumbai lamington roads flea vendors and then from my local markets. As such these are not normally sold in shops. But, there is a shop in Mumbai which specially sells the very big  heat sinks, but it will be costly for a single purchase. (will appraise its name later on)

Here are the pictures of various types of the heatsinks available with me ( I am not selling anything he he ... these are for all my upcoming linear projects/devices)
(will update the pictures on 14aug2015)
Empirical calculations for calculating the heatsink temperature.

Basic formula for temperature rise VS area VS power dissipation.

Say your area is 1 square inch and dissipation is 1 watt, ther temperature rise in C is 130 degrees C

increase area to 10 square inches and the temperature rise drops to 13 degrees

130 * (Watts / Square Inches)

How to calculate the required area of heatsink.

the formula you want to use is 130 degrees C / Watt / Square inch

So say you have 80 square inches and the amp will be about 50% efficient so 40 watts dissipation That will be 65 degrees C temperature rise making the heat sink 100 degrees C at 100% duty cycle. SSB is around 30% AM linear would be higher.

2 to 3 square inches of surface area for every watt of dissipation.

Fins vertical is the most efficient heat radiator

Fins up second best

Fins down useless without a fan.

  

15Watt Linear

Here is the schematics and PCB pattern for my 15watt linear.

15watt linear component placement

15watt linear pad placement

Descriptions, History :-

I had made this linear by accident. My 5watt cw tx/ DSB tx was not giving me signal reports. I was worried ! What is the  problem ? Then it occurred  to make a single device linear . One ckt was interesting . Put queries in the Indian Homebrewers forum at Facebook. And lots of reply came. VU2RON, VU2ESE, VU2DEV and lots more friend jumped in.

Finally tried it with IRF510 but it went burst with 25volt dc power supply. Then changed the IRF840/IRF640. Both worked fine. vu2ese had suggested me to put some 200pf at the drain. VU2DEV suggested making a Pi-LC matching. He even pointed out the calculations in the ARRL handbook , which he had gifted me. But, I settled for transformer & toroids. Ron hinted on impedance transformation of this broad band transformer.

Then made it. I used Small pig nose baluns bought from tpsonline Bhopal. Put 6 togather. 3x2, Glued with water pipe glue and it worked. It did not heat-up. The biggest problem with the ferrite is that it heats up and freq response depending on the size and material. So, we have to take care of this problem.

I used in the input a resistive 3db pad. This db-pad solved my problem for loading the exciter, proper match etc. It was happy happy solutions. With pad some fraction of input power is wasted in heat. Its okey.

I put LED to indicate power supply presence. I put a protective diode 1N4007. Not shown here. The VCC line is a big one.  Instead of deriving 12volt from the pcb I used the LM7805 voltage regulator. The simple preset is used on the pcb to bias the gate of IRF. At gate a small value resistor 5 ohm is used to stop parasitics. If you have ferrite bead please use that also. Now, a days we don't find ferrite bead esily.

Filter is classic bilateral 50 ohm three pole. Simplicity. Actually 7 pole filter should be used for more spectral purity.

The relays for changing over the antenna etc are not used here as it was meant to be a beacon / CW tx.

Components & Schematics:-




vu3inj linear
 

Setting up the linear:-

this requires some care & instruments.
Put Digital Multimeter into 10A range. Set the current to about 100mili amp. Now key the exciter. Make sure there is RF. This will increase the linear current to about 1.2 Amp. Use the dummy load or dipole antenna. VU2PTR digital VSWR meter will indicate the 15watt. So, this is the set-up. Nothing more. Mind you the preset tuning is little trickey. Slight increase in the bias and power jumps from 5 watt to 15watt. At one point of time you will feel that heatsink is too much hot but there is no power increase. buck down a little... don't set it for constant 1 amp. at max 300ma is also good. Do little experiments but just care for heat....

This linear has been never tested on SSB. If I ever do, will let you know.My approach was use whatever is on hand. Till date I have made two linears and both work wonderfully. One is with me and one is with VU2TOO.

Heat sink:-

It is one of the most important factor in this linear. You ought to use a biggest heatsink you can find. Old CPU heasink is okey. I also use the fan.

On Air test:-
On one two occasion I asked for listening service from VU3INK now (VU2JYX ), VU2DEV and two more hams. I am thankful to you Kishore for being with me. My signal was good. consistently 55 to 57. In this I had not tuned my antenna at all. SWR was around 2.5, So, the signal reports are not bad.

Will update few more fotos of linears and corrections within two days.

That's it folks the wheel has been re-invented.

Use it and don't forget to customize the bells and whistles ( relays, heatsink , box etc)



 

Linear RF Amp,RM96

The RM96 transmitter is a very successful and re-produceable design. I have used it's different block in various projects. But, never made the tx chain. got the toroids from vu2ptr and started brewing only tx linear part. it is not advisable to make rf ckt on general purpose veroboard. It is good to use the glass epoxy based etched pcb. Manhattan style on copper plane is also a good options. but i dont have those things at my disposals.

fig1.

A little description of the components shown on board:-(fig.1) 2n2222 a small transistor, then 2n2218 with crown heat sink and lastly bd139 with a bigger aluminium heat sink (found from junk, used parts). will feed it with dsb modulator freq 7058kc, see earlier posts on this blogs for this dsb modulators. Then probably this will drive a single ended linear based on irf830 or any other push pull amp.

.

fig.2

Finished the soldering today morning.(25feb) Done little touch-up, visual inspections and then it is time to hot test.

For this test, i did drive this amplifiier with one spare 20 meter (TA7358ap with xtal) based modulator. Linear ckt was powered with 12v. 1 Amp dc supply. 4 watt dummy load also connected as output rf load.

 When the power transistors are touched by finger, it indicates the hot/cool property of temperature. I touched 2n2218 it was hot faithfully. Then, i become happy and touched the BD139. It was as cool as 2n2222. Hmmm,,,,,That means not working/drawing up the dc current. Something fishy. Visual inspection done.  Needs to look for dry connections. Bd139 base shows 0.67 voltds dc. Ok. but collector shows the dc voltage variations 6 to 7 volts. Dry connections and as a rough rf test when touched 2218 it shows increase in the strength of signal in com rx, but when bd139 is touched it does not show any increase that means it is not producing the rf and not radiating to near by com rx.

On voltage test found that when 12v, 1 amp capable power supply was used line voltage dropped to the 11volts. When current increase beyound normal capacity of transformer line voltages becomes low. OK. There was no smoke. Now, it is time to use the real 12v,5amp power supply and it remained at the 12 volt dc..The RF amplifier takes 220 ma constant dc. if bd139 was conducting it should be drawing up more current. say if we consider 50% efficiency then it would require for 550 ma to 1 amp current and peak will be more to produce the 3 to 5 watt rf.

*****

So, work in progress. I had a made two module using the xtal 14318kc dsb once was used in earlier project and this was a spare one. So, far so good. once it is working. it should produce minimum 1watt rf. with it will drive a linear.

I will air test these setup only after more then 10w to 22w external linear is successfully made. I dont want people to look after when it was even not radiating in the locality.

26feb2014:- somehow BD139 was showing some problems, not heating up or producing any rf so removed it. i noticed one thing during experiments, when the 2N2218 stage heats up signal strength meter in the receiver signal stregth goes high up, from 0 to 3. It means, due to heat-up current is increased and so does the rf. a perfect case of thermal run-away. 12.6 volts, 150ma current. also toroid gets heated up as it is not driving anything. Interesting.

26feb2014:-evening. I removed the 470ohm and 1n4007 diode network for bias and instead installed a 10k pot. it increased the current and at the 330ma,12vdc it gave me optimum result. please dont forget to put the 10ohm in emiter leg. Also changed the  bd139 with c1162 and it made a good change. Rf has increased but not heating up the 4watt resistors. Only heating up the heatsinks, he he.
Its time to reduce the dc current of 2n2218 stage from 130 ma to about 100ma. and also try to  use irf510 instead of c1162 and see whether it  produces some usefull RF at 12 voltage or not !

27feb2014.
in the emiter leg of bd139/c1162 according to the hmy2k8 ckt there is 10 ohms but vu3prx it is 6 ohm and rm96 it is 1 ohm. ohh thats  seems to be my culprit. let me see you.

rm96 linear amplifier stage

rm96 linear amplifier stage

Test set-up for rf and dc

rf amp test for power

  














From a dsb modulator (ta7358 with xtal ) signal is given to the 2n2222 stage and output is taken from the last transformer T2 on 50 ohm load. RF voltage measured and signal heard on com. rx. 14331kc.


01March2014 ,
this feb is only 28 days. I did rewind the transformer of last bd139 stage, did put the 10 ohm resistor on its base. also put the 1k resistor across 470 ohm in the base of 2n2218. it reduces the current to 80 ma around and there was less heat. but over all power coming out from the c1162 halved that means  it is just putting power in the miliwatts. not even a single full watt. wow ! when the ready made pcb is used those designer / elmers have solved the bugs and made it workable. pity is , somehow we dont  got the transfer  of tech due to the limitation of the bandwidth or space on the magazine or suveniours etc. I hope new homebrewers get the benefit of their techniques  from my quest.

so i  will put one more stage but i  am doubting and want to know first what went wrong. if it does not give me 1 watt how i am going to drive it to other stages ? now i will make one more stage irf510 or 2C2068.... i dont know.

with swamping resistors rf power is reduced but quality improved and self oscillations reduced. it becomes broad band. 

modified bias network

modified bias network

I changed the bias of last stage instead of 470 ohm, 1n4007 network a 10k preset was used. 10 ohm resistor on base of bd139 stage is not used.

 This gives me visual indications. just eye-candy.

But, a very useful visual aid for rf strength indications, if the stage is self oscillating presence of rf also can be seen.
Best test for oscillations is done on comm.rx or oscilloscope and spectrum analyzers.


I feel that:-
There should be one more stage of amplifications & filtering ahead of the 2N2222 stage. As, all these amplifiers are "class-A" stages ,more the input signal more will be output at T2 secondary.  Ok, then, i can put the swamping resistors back and enjoy. Efficiency will be very low, say typical 25% for class-A.

Also can try another stage of class-AB amplifier after  the c1162/bd139 to reach the elusive 5 watt level.

You must get the proper toroids, without them project will fail. I will put another page link (here )for showing the voltage charts , references, toroids windings , rf power meter etc.


So, thats it. now will tweak it little to box it. End of write-up. There will be no further editing etc (2march2014)

wheel has been not re-invented fully, but still you can use it as it is.....