Getting big confuse on this transistor!!!

[Willen]

I found 2sc3807 transistor in the list of RF transistors from here:-
www.pcs-electronics.com/schematics/RFPowerTransistor.htm
So I bought this transistor. According to chart of above link, it has 250MHz friquency and 15 watt power and case- TO-126. I cannot find the datasheet of 'C3807' but find 2sc3807, I think both are same. Can I use this transistor as a 5watt FM RF amplifier at 100MHz? Most of the places it is not labeled as a VHF transistor, why? Can I use it as a equivalent transistor of 2sc1971? I cannot find any answers seeing datasheet, please help me! Look at the picture, that is a transistor I bought.

 

[tronitech]

The "2S" is often left off so it's fairly certain it's a 2SC3807.

 

[ronv]

It is not an RF transistor. It has no gain at high frequency.
Look for the 1971.

 

[audioguru]

The Sanyo datasheet for the 2SC3807 is confusing because Sanyo has difficulty with the Engrish language.
Their text says it is a low frequency transistor but says its fT is 260MHz.
But a graph shows an fT of only 3MHz.

The fT of a transistor is the frequency where its current gain is 1 like a piece of wire. An audio TIP31 transistor has a minimum fT of 3MHz.

The 2SC1971 is an RF transistor so use it. It probably needs a buffer transistor to drive its input.

 

[Willen]

-Then what will be the application of this transistor C3807?

- I have 4 same transistors 2N2222 in TO-92 case but from different manufracturers like-
2N2222
PN2222
KN2222 and
TT2222
Are they same and accurate? How different manufracturer can make such accurate?

 

[audioguru]

Why don't you compare spec's on the datasheets of the different transistors?

 

[unclejed613]

-Then what will be the application of this transistor C3807?

- I have 4 same transistors 2N2222 in TO-92 case but from different manufracturers like-
2N2222
PN2222
KN2222 and
TT2222
Are they same and accurate? How different manufracturer can make such accurate?

the C3807 is an audio driver, or used as a bias transistor in audio amplifiers.

the 2N2222 is the most common transistor on the planet. the 2N2222 was developed in the 1960's, so the patent on it's process has expired, therefore everybody that makes transistors makes a 2N2222. the prefixes are whatever prefix a particular manufacturer uses for their transistors, so KEC uses KN2222, fairchild uses PN22222, etc... the transistors are all the same because every manufacturer uses the same etch masks and die making process (i wouldn't trust the KEC ones, as KEC seems to have a problem with the purity of their silicon, which shows up as leakage and noise)

 

[Willen]

Hi, I found another transistor BD135 as a VHF transistor. Friquency is 250MHz and power is 8 watt. Does it fake VHF like C3807? Can I use BD135 in my FM RF amplifier?

 

[audioguru]

BD135, BD137 and BD139 (different voltage ratings) transistors are made by Philips who print accurate datasheets in good English.

They will make a poor FM RF amplifier.
The "typical" transition frequency (current gain of 1 like a piece of wire) is only 190MHz (not 250MHz) so at 100MHz the AC current gain is only about 1.9 which is very low.

Also, they are difficult to cool.

 

[unclejed613]

stop piddling around with "toy" transistors.... here's something more like what you're looking for..... of course, you're not going to get these cheap unless they're fakes

 

[Willen]

I am going to connect 2sc1971 on circuit board but little confuse on its Metal tab to connect with heatshink. Do I need to isolate transistor's metal tab from heatshink using thermal tape or mica between tab and heatshink? Why?

 

[audioguru]

I am going to connect 2sc1971 on circuit board but little confuse on its Metal tab to connect with heatshink. Do I need to isolate transistor's metal tab from heatshink using thermal tape or mica between tab and heatshink? Why?

It is called a heatsink, not a heatshink.
The emitter is the metal tab so you do not need to insulate it. Keep the metal heatsink away from signal wires. Use thermal grease.

 

[Willen]

-Generally, I think the main friquency generator is tank circuit. And friquency depends on L+C+Voltage. But does thr transistor also related to friquency and friquency change? I mean if I have an oscillator of exact 100MHz with 2n3904. And if I replace other VHF transistor (without modificatio) like:- 2n2222 or 2n2219 or BFR97 or BF494, then does the oscillator oscillates exact in 100MHz again?
- Almost, can I use all general purposes VHF transistor as a replacement in RF circuit?

 

[audioguru]

-Generally, I think the main friquency generator is tank circuit. And friquency depends on L+C+Voltage. But does thr transistor also related to friquency and friquency change? I mean if I have an oscillator of exact 100MHz with 2n3904. And if I replace other VHF transistor (without modificatio) like:- 2n2222 or 2n2219 or BFR97 or BF494, then does the oscillator oscillates exact in 100MHz again?
- Almost, can I use all general purposes VHF transistor as a replacement in RF circuit?

There is no oscillator schematic is this thread. You have been talking about many oscillators lately, including crystal oscillators so I don't know which one you talk about now.

A common Colpitts oscillator frequency depends on the total inductance and the total capacitance of the circuit.
The total inductance includes the inductance of the wiring.
The total capacitance includes the stray capacitance of the wiring, the capacitance of its load and the capacitance of the oscillator transistor.

Each transistor has a spec'd range of collector capacitance. The maximum is 8pF at 10V for a 2N2222 but no minimum and no typical is given. The maximum is 4pF at 5V for a 2N3904 and a graph shows the typical is 2pf and is about 1.7pf at 10V. The minimum capacitance is not shown.
So if you change the transistor the frequency will change.

Any VHF transistor can be used as an oscillator since the voltage gain of the circuit needs to be only a little more than 1 for it to oscillate.