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Old 6th November 2012, 02:54 PM   #61
jaycee is offline jaycee  United Kingdom
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Andrew, yeah, but the higher Pdmax is usually assuming it's mounted on a fairly sizeable copper plane. I guess you could make a little PCB with copper on to act as a heatsink, and also as a carrier to take it up to TO-126/TO-220 pin spacing with some header pins
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Old 6th November 2012, 05:00 PM   #62
AndrewT is online now AndrewT  Scotland
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or solder on a little copper flag.
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Old 6th November 2012, 06:34 PM   #63
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Quote:
Originally Posted by jaycee View Post
Ian, problem is CRT's are obsolete so the parts are being discontinued. Im quite surprised its taken this long - most CRT driver boards use an IC such as LM2402.....
Yes, there's no denying that's been the case for some time here too but I was surprised to find these old parts in fair amounts throughout the middle east, for instance.

It would make sense to snap up any old TO126 or similar case BF4XX types which will be absolutely right for the job, at the right price, of course. This might help guys who otherwise can only buy garden variety components or fakes in their region. Buying on-line is not always a simple option in some countries either.
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Old 6th November 2012, 07:26 PM   #64
jaycee is offline jaycee  United Kingdom
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Sanyo (now Onsemi) 2SA1507/2SC3902 seem good.. Cob not as low as it could be but still pretty good. Maybe good drivers in a smaller amp too.

2SA1552/2SC4027 seems to be the same die, in a smaller package. The "TP" package is through hole, but could be a little too small for decent power dissipation.

2SA1418/2SC3648 also look good, lower Cob, but SOT89 - so clever heatsinking needed to get the 1.5W
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Old 13th November 2012, 07:45 PM   #65
Vostro is offline Vostro  South Africa
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Ok so thinking about cascoding.

Firstly, if I cascode the Vas Transistor, I can use BC550 cascoded with MJE340.
But the "darlington" driver must still handle full voltage so 2n5551,
I'm not sure of what other transistor to use here.

Secondly, do I need to cascode the Vas CCS? or is it fine to use MJE350 on its own here?

If I cascode the Vas CCS, what impact does it have on the CCS, R4 need to change?

I've also increased the output to triple EF, since I'm cascoding Vas.

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Old 14th November 2012, 12:07 PM   #66
Vostro is offline Vostro  South Africa
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The Proteus design suite I use for drawings and pcb, has major troubles simulating bigger circuits, so I can't simulate these changes.

But after building Apex SR200, maybe I can change my circuit cascoding like this.

I appreciate all input please
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Old 7th December 2012, 10:53 AM   #67
Vostro is offline Vostro  South Africa
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I'm struggling to stabilise the circuit in post 66.
It goes into low frequency oscillation.

Here is a revised circuit that has some changes, this one is fully working,
No ringing or funny visible oscillations from low input into heavy clipping.
Clipping on bottom half cycle sticks at 20khz driven into hard clipping.
But comes out of clipping perfectly, no unstability.
Output Power is 185W into 8R.

Sounds nice, highs come accross nice and clear, the way I like it.

Can someone please offer some suggestions on how to stabilise post66,
I want both VAS and VAS current source cascoded.

Thanks
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Old 7th December 2012, 11:02 AM   #68
AndrewT is online now AndrewT  Scotland
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what are the differences between sch 66 & 67?
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Old 7th December 2012, 11:16 AM   #69
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Click the image to open in full size.

APT model 1 amplifier driving a triple EF output stage.
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Old 7th December 2012, 12:30 PM   #70
djk is offline djk
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"what are the differences between sch 66 & 67? "

66 is the preferred connection for the cascode voltage reference to the emitter resistor rather than to the rail. 66 also has a cascode around the CCS for the Vas.
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