Alternative transistors to 2n4427 @ 2cs1947 (used on NRG PLL PRO III - PRO IV boards)

[rigmo]

The 7 Watts in the datasheet for the 2N3553 is maximum dissipation, not power output! In reality, you'll get just slightly less than half of the dissipation as RF - typically around 3 Watts at best. The '3553 was a pretty horrible transistor - it was OK at HF, but ran out of gain at more than about 50MHz (unless you were very lucky).

absolute truth, this drive run 2n3553 only 1.25W and its hot... can run 3W also.. Much much better is with BFS23A less heat more power..

[Krakatoa]

BFS23 is a 28 volt device, and has lesser collector current specs than the BFS22, which is basically the same device but for 12v system. I know because I found easier to blow the '23 than the '22 in typical 12v exciters.

[LeeCavanagh]

Update re NRG PRO IV : I had to replace the Variable tuning capacitor + Variable power resistor + final stage transistor … the 4427 was fine, and didn’t need replacing, but those other three components replaced and now getting a steady 4.5w according to my meter.

[radium98]

The potentiometer howit support such current?

[LeeCavanagh]

The potentiometer howit support such current?

I thought the same thing

[MiXiN]

Update re NRG PRO IV : I had to replace the Variable tuning capacitor + Variable power resistor + final stage transistor … the 4427 was fine, and didn’t need replacing, but those other three components replaced and now getting a steady 4.5w according to my meter.

I've just got hold of a Pro IV and find that after about 2 minutes after switch on, the heatsink gets too hot to touch.

Output power is fine at around 4.5W like yours.

Do you find that the heatsink on your Pro IV gets too hot to touch?

I'm using it "standalone" at present so don't have fan on it.

[Albert H]

You've probably got the wrong heatsink on it - the ones we used were well over 2" tall!

[MiXiN]

You've probably got the wrong heatsink on it - the ones we used were well over 2" tall!

Hello Albert,

The heatsink I have on it is this one. I would say it's around 2" tall.

With a fan on it, the temperature is fine, but I doubt the 1947 would last very long without a fan on the heatsink.

Output power is very stable, it's just the heat that seems excessive.

Screenshot_20230517-235927_eBay.jpg

[sinus trouble]

Update re NRG PRO IV : I had to replace the Variable tuning capacitor + Variable power resistor + final stage transistor … the 4427 was fine, and didn’t need replacing, but those other three components replaced and now getting a steady 4.5w according to my meter.

I've just got hold of a Pro IV and find that after about 2 minutes after switch on, the heatsink gets too hot to touch.

Output power is fine at around 4.5W like yours.

Do you find that the heatsink on your Pro IV gets too hot to touch?

I'm using it "standalone" at present so don't have fan on it.

I have had several NRG PLL PRO boards over the years and the 1947 was notorious for getting hot!

There are some significant points to consider when dealing with this device!

Firstly, its package type! Identical to the 4427 yet outputs over 3 times the gain!

Also the collector to emitter absolute max voltage is only 17V! So already the device is under stress @13.8V to 15V

As Albert mentioned the case is common emitter which means you can get creative with heatsink design?

I use this device in my Band I projects and have not encountered a failure so far? Maybe i am just lucky?

[MiXiN]

Update re NRG PRO IV : I had to replace the Variable tuning capacitor + Variable power resistor + final stage transistor … the 4427 was fine, and didn’t need replacing, but those other three components replaced and now getting a steady 4.5w according to my meter.

I've just got hold of a Pro IV and find that after about 2 minutes after switch on, the heatsink gets too hot to touch.

Output power is fine at around 4.5W like yours.

Do you find that the heatsink on your Pro IV gets too hot to touch?

I'm using it "standalone" at present so don't have fan on it.

I have had several NRG PLL PRO boards over the years and the 1947 was notorious for getting hot!

There are some significant points to consider when dealing with this device!

Firstly, its package type! Identical to the 4427 yet outputs over 3 times the gain!

Also the collector to emitter absolute max voltage is only 17V! So already the device is under stress @13.8V to 15V

As Albert mentioned the case is common emitter which means you can get creative with heatsink design?

I use this device in my Band I projects and have not encountered a failure so far? Maybe i am just lucky?

Some good points there, Sinus; it's quite a powerhouse of a Transistor thinking about it & working near its limit like you mention.

There's not a lot of space around the 1947 to add anything in terms of width with an alternative heatsink, so I think something taller would be the way forward.

I've not noticed any taller TO-5/TO-39 heatsinks anywhere than what I already have, so I think I'll box this up and just use a fan to air cool it.

[Albert H]

I have seen them placed under the board, in contact with the metal case - a friend of mine used to put big washers around the 1947 case, and sink the transistor to the metal cac that the exciter was housed in, making the whole box the heatsink! We did experiment with pairs of 1947s (since we got them for pennies!) and found that we could get around 10 Watts out of the pair for about 500mW input.

Stephen Moss and I experimented with a 2SC1971 output for the Pro III. We made a metal flange / heatsink that fitted across the board, with the regulators and the '1971 bolted to it. It also provided a grounded shield, separating the output lowpass filter from the rest of the circuit. There were a couple of problems with this approach - we found that the regulator tabs had to be insulated from the heatsink to prevent circulating earth currents (leading to hum), and it was essential to use heatsink paste beneath the 1971 to ensure good heat transfer. We also found that - because the '1971 had less gain than the '1947 - we had to get more drive from the '4427 stage, so it ran warmer, and needed a heatsink of its own! The prototypes developed around 6 Watts, and we planned to reduce that to 5 Watts to make the thing "unburstable". Unfortunately, Stephen's demise put paid to further developments, though it might be interesting to dig out the design.... I might still have the sketches somewhere. The two boards that were made disappeared a long time ago!

[rigmo]

You can't without forced air circulation. that refrigerator in the picture is just beautiful. it is not efficient enough and the heat remains on the transistor itself. if you don't believe me, take a thermal camera and follow it.. there are only 6 small touch points for transferring the temperature.. that would be only about 30% (maybe I said too much) of the surface for temperature transfer.
the longer ones is are much better than the others, which transfer over 90% of the heat and provide a longer service life.

[sinus trouble]

I've just got hold of a Pro IV and find that after about 2 minutes after switch on, the heatsink gets too hot to touch.

Output power is fine at around 4.5W like yours.

Do you find that the heatsink on your Pro IV gets too hot to touch?

I'm using it "standalone" at present so don't have fan on it.

I have had several NRG PLL PRO boards over the years and the 1947 was notorious for getting hot!

There are some significant points to consider when dealing with this device!

Firstly, its package type! Identical to the 4427 yet outputs over 3 times the gain!

Also the collector to emitter absolute max voltage is only 17V! So already the device is under stress @13.8V to 15V

As Albert mentioned the case is common emitter which means you can get creative with heatsink design?

I use this device in my Band I projects and have not encountered a failure so far? Maybe i am just lucky?

Some good points there, Sinus; it's quite a powerhouse of a Transistor thinking about it & working near its limit like you mention.

There's not a lot of space around the 1947 to add anything in terms of width with an alternative heatsink, so I think something taller would be the way forward.

I've not noticed any taller TO-5/TO-39 heatsinks anywhere than what I already have, so I think I'll box this up and just use a fan to air cool it.

A miniature fan works well to get the air flowing! I often used a 40mm 24V fan operating @ 15V to keep it simple and noise to a minimum!

Another theory (Which not tested) is to mount the device below the PCB pressed into the chassis or housing of the rig!

With accurate and careful drilling? A snug fit can be achieved!

[radionortheast]

They use the c1971 in the 7w 8066 transmitters, they use a transistor abit bigger than the general purpose blacks ones, afew surface mount transistors before. I’ve got two, they’ve never broken, I use the amplifier in a different transmitter, it dose afew watts, the heatsink dosen’t get warm. The problem with surface mount devices, think they are mosfets, will often by bonded to the board, are hard to replace even if you know what that are, you can’t do anything when they break, except throw them in the bin, i’ve broke afew little amplifier modules throught not knowing what the input drive, i’ve only lately beable to measure it. The c1971 is a leaded device, its fairly easy to replace, the heatsink is large, easy to unscrew or screw to some metal or make your own heatsink. I’ve not beable to make a circuit from scratch with it as it seems abit complecated to get working, they use a ferrite inductor in the 8066 transmitters