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Old 28th March 2011, 12:54 PM   #1571
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Originally Posted by Salas View Post
Thanks Bob. I asked that because I use them at low current without dominant Miller cap some times and are nicely stable. The beta is also very near between NPN-PNP at low current as you found, that is nice. Do they keep up near at 10mA also? Will use your models as soon as you will make them available, because there is mist around the real characteristics of those classic handy BJTs.
Hi Salas,

These devices, like many, have higher ft and higher beta at 10mA as compared to 1mA.

I'm not sure what you mean by using them without dominant Miller cap. Is this in the VAS location? Are you relying on Miller effect from Ccb (which is quite nonlinear)?

Cheers,
Bob
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Old 28th March 2011, 02:22 PM   #1572
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Originally Posted by Bob Cordell View Post
Hi Salas,

These devices, like many, have higher ft and higher beta at 10mA as compared to 1mA.

I'm not sure what you mean by using them without dominant Miller cap. Is this in the VAS location? Are you relying on Miller effect from Ccb (which is quite nonlinear)?

Cheers,
Bob
I have actually seen some designs (and actual amps) that use the 340/350 do just that .. I don't "trust" just Ccb.

OS
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Old 29th March 2011, 07:52 AM   #1573
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Hello Bob,

I am getting your book! I love good books. I'll post after I finished reading it.

Warm Regards,
James
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Old 29th March 2011, 11:13 AM   #1574
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Originally Posted by rolandong View Post
Hi Bob,

Thanks for writing your book.
I simply can't find book with good grasp on mosfets.

Could you pls. kindly upload LTSpice simulation file for high performance mosfet amplifier from chapter 11 fig.11.17?

thanks in advance,
roland
Hi rolandong,

I'll see if I can dig that simulation out and post it here. Its been quite some time since I did that one. It may take a few days, as I'm still in the middle of trying to finish up some transistor models to post on my website. I'm also heading to Montreal this week for the FSI audio show.

I'm glad you like my book, and understand what you mean about there being fairly little material on MOSFET power amplifiers out there in books.

Cheers,
Bob
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Old 29th March 2011, 03:29 PM   #1575
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Thanks Bob!
I'd appreciate it very much.

Really like the way your book was worded,
very easy to comprehend and understand.
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Old 29th March 2011, 04:14 PM   #1576
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Quote:
Originally Posted by Bob Cordell View Post
Hi Salas,

These devices, like many, have higher ft and higher beta at 10mA as compared to 1mA.

I'm not sure what you mean by using them without dominant Miller cap. Is this in the VAS location? Are you relying on Miller effect from Ccb (which is quite nonlinear)?

Cheers,
Bob
Not for VAS, in regulators.
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Old 29th March 2011, 10:23 PM   #1577
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Originally Posted by PB2 View Post
Hi Bob,

I know you stated way back that the devices in the RCA and Citation amp were probably very slow but I have to disagree with you. The 40409/10 are in the data book that I have
here and ft for both is 100 MHz - not bad at all. The 2N3055 and all related parts do not have ft specified in this RCA data book and I've seen people quote some very low numbers but I'm wondering if those are very much worst case even for the single diffused devices.
Hi Pete,

That's interesting about the speed of the 40409/10 devices. I really did not realize they were that fast. I think there were several vintages of the TO3 version of the 2N3055, with different ft numbers ranging from possibly below 1 MHz to around 2.5 MHz.

I built two clones of the Citation 12 back in 1970.

Cheers,
Bob
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Old 30th March 2011, 10:57 AM   #1578
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Originally Posted by megasat16 View Post
Hello Bob,

I am getting your book! I love good books. I'll post after I finished reading it.

Warm Regards,
James
Hi James,

I appreciate your interest in my book and really hope you enjoy it. I'll definitely be interested in reading your opinions after you read it.

Cheers,
Bob
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Old 30th March 2011, 09:46 PM   #1579
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Originally Posted by ostripper View Post
I have actually seen some designs (and actual amps) that use the 340/350 do just that .. I don't "trust" just Ccb.

OS
Good point.

Using Ccb alone for Miller compensation would be bad for both stability margin and distortion, due to its nonlinearity. Designs which precede the VAS transistor with an emitter follower largely kill the influence of nonlinear Ccb.

Cheers,
Bob
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Old 31st March 2011, 11:33 AM   #1580
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I think this is simpler, just do it at 5 - 10 MHz for audio parts:
MIL-M-38510/108A page 12?
http://www.dscc.dla.mil/Downloads/Mi...38510ss108.pdf
Hi Pete,

This is a really neat circuit technique. I wonder if there are any gotcha's? Looks like its set up for 2.5 mA. At lower frequencies, like 10 MHz, the 0.01 uF cap might want to go to 0.1. Using this circuit, we should be mindful that we oparate at a frequency where ac current gain is substantially smaller than LF current gain and preferably moderately greater than unity.

Cheers,
Bob
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