Vebo

BigE · 23rd February 2011, 07:45 PM

I have a concern about a transistor replacement I've made. The transistor is MPSA06, replacing the TIS97. It is configured in a differential pair on the input of the phase linear 400.

The TIS97 has a VEBO of 6 volts, the MPSA06 only 4.

Is there any concern in this application?

Thanks.

nigelwright7557 · 23rd February 2011, 09:51 PM

Differential pairs are often matched transistors.

BigE · 24th February 2011, 01:50 AM

My apologies,

the differential pair are *both* either TIS97 or MPSA06. I just don't know if the different Vebo of the mpsa06 poses a problem.

nigelwright7557 · 24th February 2011, 01:53 AM

Quote:

Originally Posted by BigE

My apologies,

the differential pair are *both* either TIS97 or MPSA06. I just don't know if the different Vebo of the mpsa06 poses a problem.

I would say no, as the transistors are not driven as switches but as amplifiers.

BigE · 24th February 2011, 02:03 AM

Thank you for corroboration!

I find that there is no detectable sonic difference between the two in the phase linear 400.

I'll be putting in another matched pair next week, to replace the existing mismatched differential pair of TIS97 and ECG123. Their HFE is off by 400. Which makes a DC offset of 65 mv. It's more important to reduce that.

Thanks again.

BigE · 24th February 2011, 01:10 PM

According to fairchild, the TIS97 characteristics are the same as PN100.

The Vbe(on) voltage of the MPSA06 is identical. Seems like high hfe versions of the MPSA06 are a valid substitute. Given that it's in a differential pair, the surrounding resistance is supposed to dominate anyway.

So why bother with high hfe?

wg_ski · 24th February 2011, 02:36 PM

Quote:

Originally Posted by BigE

So why bother with high hfe?

Differential balance. Higher input bias currents through the bias and feedback resistors will produce more offset. Anything you do to "correct" this will upset the vbe balance and and produce an increase in distortion. Other distortion mechanisms likely predominate in the PL amps, so it may not be a big issue.

wg_ski · 24th February 2011, 02:41 PM

As to the issue of Vebo specifically, a lower Vbeo will not be able to "stand off" as much input overload before breaking the input transistors down. This will not blow them (avalanching the EB junction will turn a transistor very hard OFF), but long term exposure to this will permanently degrade the Hfe, and possibly increase any mismatch between the pair.

BigE · 24th February 2011, 03:22 PM

Thanks!

23rd February 2011, 07:45 PM	#1
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	Vebo I have a concern about a transistor replacement I've made. The transistor is MPSA06, replacing the TIS97. It is configured in a differential pair on the input of the phase linear 400. The TIS97 has a VEBO of 6 volts, the MPSA06 only 4. Is there any concern in this application? Thanks.

23rd February 2011, 09:51 PM	#2
nigelwright7557 diyAudio Member Join Date: Apr 2008 Location: Carlisle, England	Differential pairs are often matched transistors. __________________ http://www.murtonpikesystems.co.uk PCBCAD40 pcb design software.

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24th February 2011, 01:50 AM	#3
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	My apologies, the differential pair are both either TIS97 or MPSA06. I just don't know if the different Vebo of the mpsa06 poses a problem.

24th February 2011, 02:03 AM	#5
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	Thank you for corroboration! I find that there is no detectable sonic difference between the two in the phase linear 400. I'll be putting in another matched pair next week, to replace the existing mismatched differential pair of TIS97 and ECG123. Their HFE is off by 400. Which makes a DC offset of 65 mv. It's more important to reduce that. Thanks again.

24th February 2011, 01:10 PM	#6
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	According to fairchild, the TIS97 characteristics are the same as PN100. The Vbe(on) voltage of the MPSA06 is identical. Seems like high hfe versions of the MPSA06 are a valid substitute. Given that it's in a differential pair, the surrounding resistance is supposed to dominate anyway. So why bother with high hfe?

24th February 2011, 02:41 PM	#8
wg_ski diyAudio Member Join Date: Oct 2007	As to the issue of Vebo specifically, a lower Vbeo will not be able to "stand off" as much input overload before breaking the input transistors down. This will not blow them (avalanching the EB junction will turn a transistor very hard OFF), but long term exposure to this will permanently degrade the Hfe, and possibly increase any mismatch between the pair.

24th February 2011, 03:22 PM	#9
BigE diyAudio Member Join Date: Aug 2008 Location: Toronto	Thanks!

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