2n3866 Transistor confusion

[Damo666]

Hi,

On one of the well known auction sites I've found a VHF Transmitter using a 2N3866 as the final Transistor that claims to do 1W output with a 15V supply.

Now, looking at datasheets for this Transistor suggests it will only provide 1W at 28v. I'm not great at reading datasheets, but am I missing something?

In a nutshell, I'm trying to work out what this Transistor will "realistically" produce at a 15V supply? Is the seller exaggerating claims?

Many thanks in advance.

 

[Nigel Goodwin]

The output power of a transmitter isn't specifically related to the supply rail, as it's not a DC function (or indeed a simple AC one).

The 2N3866 has long been used in 1W VHF transmitters - in fact it's probably the only RF power transistor who's number I instantly recognise .

 

[Damo666]

Thanks for the reply, Nigel.

Am I allowed to post a link to a website in which people who have used them state they've not obtained much more than 0.5W out of them at a similar voltage, or are links to other forums disallowed?

The link I refer to is Pirate radio based, and many of the members assemble, use, and sell Transmitters, Amplifiers, etc', so it all gets very confusing.

 

[Nigel Goodwin]

Thanks for the reply, Nigel.

Am I allowed to post a link to a website in which people who have used them state they've not obtained much more than 0.5W out of them at a similar voltage, or are links to other forums disallowed?

The link I refer to is Pirate radio based, and many of the members assemble, use, and sell Transmitters, Amplifiers, etc', so it all gets very confusing.

Probably best not to post links to sites of a dubious and illegal nature

The power output rather depends on how you care to measure it, commonly (back in the day) it was simply by measuring the DC power to the output stage - and this value was what your licence conditions referred to.

As I recall?, my amateur radio licence allowed 150W DC input (for FM or CW) and 400PEP for SSB.

 

[Damo666]

I allreet for the replies muckers, and many thanks.

 

[Colin]

You get about 30% max output

 

[Damo666]

You get about 30% max output

So, circa 300mW at 15v 100Mhz?

All these different replies get extremely confusing!

 

[Nigel Goodwin]

So, circa 300mW at 15v 100Mhz?

All these different replies get extremely confusing!

Not really, as I said before it simply depends how you measure it.

 

[Colin]

I am saying you will require 3 watts to produce 1 watt of RF output.

 

[Damo666]

Aha, my apologies, sorry.

I misinterpreted Colin's reply and presumed he meant the Transistor will only do 30% of 1 Watt at the specified frequency and voltage.

So in a nutshell, am I right in thinking that the Transistor PA stage will draw something like 200mA at 15v alone based on this 30% efficiency?

 

[Nigel Goodwin]

Aha, my apologies, sorry.

I misinterpreted Colin's reply and presumed he meant the Transistor will only do 30% of 1 Watt at the specified frequency and voltage.

So in a nutshell, am I right in thinking that the Transistor PA stage will draw something like 200mA at 15v alone based on this 30% efficiency?

Like I mentioned earlier, power output is normally measured as the DC input to the final PA stage, however efficiency is nothing like as bad as the 30% claimed by Colin - who seems to know little about electronics or radio.

What are you trying to achieve?.

 

[Hypatia's Protege]

Sorry that my comments are a bit 'late in the day', as it were -- It is my hope that someone will find them helpful!

Like I mentioned earlier, power output is normally measured as the DC input to the final PA stage

Nowadays RF power is typically observed via direct measurement (via a metered directional coupler followed by correct termination) --- In point of fact, compliance with (US) regulations stipulates direct measurement...

FWIW: Re: the 2N3866 and similar devices (e.g. 2n3553, 2n6255, M9466, M9657, etc...)
Maximum rated RF output is readily obtained at collector EMFs of even 13.8V --- and efficiently so in 'class C' operation... --- I apologize that I've not had occasion to make a quantitative assessment of efficiency, howbeit, inasmuch as a small 'top hat' heatsink proves quite adequate up to 3W (RF out) it can't be too bad! --- That said - I do not 'endorse' operation of devices beyond their absolute maximum specifications and accept no responsibility for consequences thereof!

Best regards
HP

 

[spec]

Hi,

On one of the well known auction sites I've found a VHF Transmitter using a 2N3866 as the final Transistor that claims to do 1W output with a 15V supply.

Now, looking at datasheets for this Transistor suggests it will only provide 1W at 28v. I'm not great at reading datasheets, but am I missing something?

In a nutshell, I'm trying to work out what this Transistor will "realistically" produce at a 15V supply? Is the seller exaggerating claims?

Many thanks in advance.

Hi Damo,

This link may be of interest to you. One thing to be wary of is that unless your 2N3866 comes from a reliable supplier you are liable to get a rip-off device which will not meet the device specification by a wide margin.

 

[audioguru]

The input power must be more than the output power. The circuit in the video uses 12V at 130mA which is only 1.56W. 16V at 300mA was mentioned which is 4.8W but it does not say which output transistor was used.