hFE of original PL output transistors

[62vauxhall]

It's an out of curiosity question.

There are a dozen (X)PL909 transistors in a bag that I saved after removal from my 700B. I have no intention of using them but I checked them with one of those cheap Chinese component testers. All of the transistors were identified as BJT - NPN so I assume the transistors are good but the hFE values are all quite low. The highest is 19 and the lowest is 2.

I have not found a data sheet using the number PL909. I assume they went by a different number when not privatly branded for PL. Are those low hFE numbers typical for those devices?

 

[Gepetto]

I think it is your Chinese test equipment

 

[62vauxhall]

I think it is your Chinese test equipment

Could be, it's only a $20 item that happens to read hFE.

I went through a bunch of various TO3 transistors to see which ones passed or failed and recorded hFE numbers for all of them. Other transistors all displayed higher numbers than the old PL parts. Made me wonder if that was normal or if they're just old and tired.

 

[WOPL Sniffer]

Cheesing out on test equipment will get you sooner or later. Don't do it.

 

[Gepetto]

Could be, it's only a $20 item that happens to read hFE.

I went through a bunch of various TO3 transistors to see which ones passed or failed and recorded hFE numbers for all of them. Other transistors all displayed higher numbers than the old PL parts. Made me wonder if that was normal or if they're just old and tired.

More likely old and damaged. Hfe is normally 20+ when measured in accordance with specs

 

[62vauxhall]

Cheesing out on test equipment will get you sooner or later. Don't do it.

I agree and would be happy if I could afford better gear. Better anything really. But not in the cards and even more so the past two years since I've been in negative cash flow. You should see the place I had to move into. Savings dwindle from basic living expenses.

 

[62vauxhall]

More likely old and damaged. Hfe is normally 20+ when measured in accordance with specs

Thanks, they shall go in the garbage.

 

[Gepetto]

I agree and would be happy if I could afford better gear. Better anything really. But not in the cards and even more so the past two years since I've been in negative cash flow. You should see the place I had to move into. Savings dwindle from basic living expenses.

And then comes inflation Gary...

 

[WOPL Sniffer]

Well don't spend what you don't have on crap gear. It's a waste of you money.

 

[Gepetto]

Here is the Delco data sheet Gary, I doubt very much you Chinese tester can provide the 1A collector current at 5Vce to properly test these

 

[62vauxhall]

Here is the Delco data sheet Gary, I doubt very much you Chinese tester can provide the 1A collector current at 5Vce to properly test these
View attachment 68223

Nope, the thing operates on 3.7v from an integrated rechargeable battery. But the hFE numbers on the sheet are lower than I thought they'd be.

 

[Gepetto]

What did you expect them to be Gary? These are power transistors

For comparison, MJ21196G transistors are far superior with a minimum hFE of 25 at 8A collector current.

 

[62vauxhall]

There were some 2N3055's that I checked prior to the 909's. Their hFE was between 175 snd 445. Or so my "device" said. That is why I was expecting to see higher numbers for those 909's.

But I just now looked at the data sheet for ON Semi's 2N3055 and the hFE numbers are nowhere near that high. This thing identifies what it is testing and displays other parameters, For transistors, hFE is one of them. I just happened to notice that.

 

[Gepetto]

There were some 2N3055's that I checked prior to the 909's. Their hFE was between 175 snd 445. Or so my "device" said. That is why I was expecting to see higher numbers for those 909's.

But I just now looked at the data sheet for ON Semi's 2N3055 and the hFE numbers are nowhere near that high. This thing identifies what it is testing and displays other parameters, For transistors, hFE is one of them. I just happened to notice that.

2N3055 transistors are junk transistors and have no where near that hFE. You cannot trust that Chinese tester for much of anything.

 

[Heat-Sinks-R-Cool]

It's an out of curiosity question.

There are a dozen (X)PL909 transistors in a bag that I saved after removal from my 700B. I have no intention of using them but I checked them with one of those cheap Chinese component testers. All of the transistors were identified as BJT - NPN so I assume the transistors are good but the hFE values are all quite low. The highest is 19 and the lowest is 2.

I have not found a data sheet using the number PL909. I assume they went by a different number when not privatly branded for PL. Are those low hFE numbers typical for those devices?

I believe that what you are seeing is indiciative of the "older" power transistors as seen in the data sheet hfe min=10, and no max specified. As a parallel observation, I have original SAE output transistors from a MK IVCM (100watt/ch amp) that measure low hfe as well. My SAE 101's (NPN) hfe measured range is 9-13 vs. MJ15024G's hfe measured range 47-56. The MJ's were replace by previous owner, so I am guessing they are suitable. Their data sheet shows hfe range of 15-60 at 4A IC, so it's validates what I am seeing with my inexpensive aurdino based tester.

 

[mlucitt]

So, the question is... What is the difference in sound quality (tone/accuracy/artifacts), frequency bandwidth (Hz), or loudness (watts) between a PL700B with original XPL909 transistors with hFE of 2-19 AND the same PL700B with new MJ21196G transistors with hFE of 48-63?
Serious question.

 

[George S.]

Indeed.

 

[Heat-Sinks-R-Cool]

From what I understand the output stage is primarily a current amplifier, and hfe(beta) is the current gain(multiplier) with respect to base drive. As my knowledge of the design of the drivers is non existent, I could not comment of what the ideal range of hfe needs to be for this output stage. It's clear that since the datasheets show min 10 hfe, any transistor below 10 should be tossed. A curve tracer graph or the manufacturer's recommended test circuit with results might be the way to ultimately test the transistors.

According to Bob Cordell (Designing Audio Power Amplifiers) "Because transistor beta can vary quite a bit, circuits are usually designed so that their operation does not depend heavily on the particular value of beta for its transistors. Rather, the circuit is designed so that it operates well for a minimum value of beta and better for a very high beta. Because beta can sometimes be very high, it it usually bad practices to design a circuit that would misbehave if beta became very high."

 

[Gepetto]

From what I understand the output stage is primarily a current amplifier, and hfe(beta) is the current gain(multiplier) with respect to base drive. As my knowledge of the design of the drivers is non existent, I could not comment of what the ideal range of hfe needs to be for this output stage. It's clear that since the datasheets show min 10 hfe, any transistor below 10 should be tossed. A curve tracer graph or the manufacturer's recommended test circuit with results might be the way to ultimately test the transistors.

According to Bob Cordell (Designing Audio Power Amplifiers) "Because transistor beta can vary quite a bit, circuits are usually designed so that their operation does not depend heavily on the particular value of beta for its transistors. Rather, the circuit is designed so that it operates well for a minimum value of beta and better for a very high beta. Because beta can sometimes be very high, it it usually bad practices to design a circuit that would misbehave if beta became very high."

In full comp configuration, the outputs are current amplifiers, emitter followers, gain = 1.

In quasi comp, the upper half output set is a current amplifier, emitter followers, gain = 1.

In the lower half, the PNP emulator, there is both current and voltage amplification to make the PNP emulator work properly. Too much or too little transistor gain in either the driver or the outputs can lead to instability (which was not uncommon in PL amps on the quasi side)

In full comp mode, the hFE does not matter all that much and does not need to be matched between paralleled devices in the PL configuration. The 0.33 ohm resistors provide local negative feedback to balance out the current contribution of each output device so that the high gain device does not become a current hog.