Help with data sheet 2SB877 VS TIP36C

[Low_Boy]

We have talked about this before but I was trying to compare data sheets for the TIP36C and the 2SB817. While everyone says the TIP36C is stronger / better and I am probably looking at this wrong in some respects the 2SB817 looks stronger. What is the main thing to look for?
Collector base voltage is better on the 2SB817.
Collector emitter voltage better on the 2SB817.
Max emitter base voltage better on the 2SB817.
Max collector current is the only thing that really seems better on the TIP36C. I May be looking at the wrong things so hopefully someone can explain what to look for.
Thanks.

 

[nomadradio]

Higher breakdown-voltage ratings are not so important in a 12-Volt radio.

Current and power ratings mean more when the part is used as a radio's AM modulator.

The TIP36 comes in four versions. No suffix letter, and the "A", "B" and "C" versions. The suffix letter only indicates the breakdown-voltage rating. The "no suffix" type is rated to take 40 Volts. The "A" is 60, the "B" 80 and the "C" 100 Volts.

Other than that, they are the same part.

The TIP 36 is the (tiniest bit) tougher part at 12 Amps and 125 Watts. The 2SD817 data sheet shows 12 Amps and 100 Watts. Not enough difference to count for much.

The spec I worry about is the "hfe", or "DC beta". Shows the transistor's current gain. The ratio of collector current to base current.

If it has a beta of ten, the driver transistor will have to pump 6/10 of an Amp into the base terminal to pump 6 Amps into the final and driver. This would get the driver transistor kinda hot, since it doesn't have a heat sink.

A beta of 100 would make the driver transistor's load only 6/100 of an Amp. The driver transistor would not break a sweat this way. The higher the transistor's collector current the lower this 'beta' number becomes in the working circuit.

Both these types are similar in this department, too.

73

 

[Low_Boy]

Thank You Nomad. Basically the Tip36C is really not much better than the 2SB817 but a bit of a better value for a replacement part I am thinking.?

 

[Handy Andy]

Look at your Collector Current ratings - one is only 12A - 15 A Max
While your TIP36C is rated for a lot more...

Let the numbers speak for themselves...

2SB817...


While the TIP36C has this -



You actually want the TIP36C for several reasons...

Emitter - Base Voltage - may be lower but that is not much different than what you use now...there is also A SECONDARY relative relationship with that number to the ability to amplify small signal and handle the drive the radio will supply to the section you're putting it in...it "saturates" quicker.

The linearity between both as far as on times and current draw for that - the 2SB817 will win - but only due to the power curve it has over the TIP36C part.

IF you were only using a SINGLE final Bi-polar - the 2SB817 wins, hands-down, due to the linearity and power "on" curve. A Heatsink will be required.

IF you are using MULTI-PART (Hint DUAL) Final MOSFET - YOU NEED THE WATTAGE DISSIPATION CAPABILITY of the TIP36C - the current draw and switching - is handled more effectively at higher current (amp) draw those finals need when they reach peak envelope or required power demand for their Rise times and inrush current. WITHOUT QUESTION - YOU WILL NEED AN ADDITIONAL HEATSINK.

Remember the Top-Gun Modulator - this may be more effective in using this part with your new paring - the 3rd stage drive levels would be maximized using this "extra stage" to develop power curve - versus using only 2 parts as a simple Darlington.​

Just posting this so those that want to play along at home...

Use at your own peril...
:+> Andy <+:

 

[nomadradio]

Look at your Collector Current ratings - one is only 12A - 15 A Max
While your TIP36C is rated for a lot more...

Sure enough. Dropped the ball on that one.

73

 

[Handy Andy]

I've got your back...

It can get rough out here...

 

[Handy Andy]

If I could have a moment...

One of the many issues I've lost my shirt on, and there have been several more than I'd care to admit - deals with this type of upgrade.

Firstly - remember that the radio is designed by an engineer with one thing in mind - make money.

Secondly - how to make more money by margins...

Margins? Meaning - we know that PCB copper clad boards cost money, the more you etch off the board, means less you can recoup later. Means more etchant - more cost added to replace that etchant.

Also the cladding of the boards, their actual thickness. There will be spots on these boards that have to carry current thru a considerable length of run. Too much current thru it- it will overheat the copper and pop it like a fuse.

Same for the components. And you need spacing and all the details for the SMD or discrete mountings to work.

What I'm trying to express here is, be sure you are ready for the problems you may encounter during and after the upgrade - for the loss of the PCB traces due to power pull shorts and breaks can take the whole mess into the dumpster if you're not careful.

So be ready to add solder to the traces - thicken them so they can handle the current surges that may occur as well as it will reinforce them as they pass along and dissipate heat amongst the board and from other traces - but be careful not to cause blobbing or bridging of solder that will short out your work and damage it.

People use to kid around about the Red Wire On Bottom - or the RWOB mod - so they can jumper a final and let the pass transistors operate cooler. This is not that far from it. Because the wire is paralleled across power supply feed to the final transistor and meets up with it there - bypassing the Drivers' and Finals original feed branch - only RWOB sets that branch as just for the Driver. The mod can still be done, only it is like the 148's or Grants - where they wired directly to the feeds for the Final and Driver, using heavier gauge (# AWG) wire soldered in only from the same spot - output from the pass transistor.

There is a considerable size difference between a 12 amp fuse and a 25 amp one - the same applies to the PCB and it's copper cladding - if it's too small of a AWG gauge - how could you tell? Truth is you really can't - only trust the supplier - but at what # AWG (Gauge) did the supplier whom made the board for that radio you're gonna' put this all in, use? IF you don't know, then remember to Measure TWICE, Cut ONCE...hope it will carry that power thru the trace to make the circuit work. Again provide solder across the length of the run if you can - or use "magnet wire" as a means to apply a thicker layer of solder and the copper bracing the wire can provide flowed in on top and along with it in the trace.

It will require scraping off the enamel to expose the copper cladding - but any pinch points that can have a layer or two of solder added - is extra margin for your work to perform work..

:+> Andy <+:

 

[Low_Boy]

Thanks Andy. That explanation helps.