On Friday, January 29, 2016 at 6:35:27 PM UTC-5, Tim Williams wrote:
> "Winfield Hill"  wrote in message news:n8gca802s1u@drn.newsguy.com...
> >> Looks great!  Only quirk I see is, why the
> >> staggered TO-220 pins?
> >
> > What, you never got into staggered pins?
> > (BTW, easy to model.)
> >
> 
> An extra second per part, bending the leads so they'll fit?!  You must be 
> crazy!  I hope you never wrote a book or anything! ;-)

More than a second, but I've bent leads like that.
(low volume.)  
Also with the to-220 on the top side of the pcb, 
with a 1/4" brass standoff through a hole 
to the heat sink below. (less heat)

George H. 
> 
> (I never had a need for it, but occasionally you'll see one with the 
> middle lead kicked up like one of the Rockettes, and board routed out 
> around it.  There's a couple of these inside my monitor, for driving a 
> pulsed 1.5kV focus electrode or something.  No better way to get the 
> creepage needed; only downside is, most TO-220's aren't grooved between 
> the leads, so you're very quickly package limited on that.)
> 
> I also like the TO-92s with 0.1" pitch.  (But if I accidentally buy the 
> unformed lead variety, that's *two seconds* wasted!)
> 
> Tim
> 
> -- 
> Seven Transistor Labs, LLC
> Electrical Engineering Consultation and Contract Design
> Website: http://seventransistorlabs.com

On 30/01/16 06:11, rickman wrote:
> On 1/28/2016 9:00 AM, Winfield Hill wrote:
>> Chris Jones wrote...
>>> I wonder whether it is already too late for the
>>> nice fast 300V transistors that used to be used
>>> in the video amplifiers on CRT neck boards.
>>   You have to get a lifetime supply. Some Alibaba
>>   sellers, etc., still have some types.
> I don't feel like I can trust Alibaba sellers.  I see too many reports
> of outright fraud there.  I don't know how well Alibaba protects the
> buyers, but it looks like it isn't good enough.

Alibaba is for wholesalers. Aliexpress protects customers just fine; 
they escrow your payment until you approve the shipment and release it.
I've had ~40 Aliexpress orders. Got the wrong thing shipped twice, and 
neither time did I pay. A bigger problem is ensuring you can tell that 
you got what you paid for and some some manufacturing reject; again, as 
long as you can check that the product works for you before you release 
the funds, you have essentially no risk.

There are good reasons why Aliexpress became worth 7x Amazon.

Den l�rdag den 30. januar 2016 kl. 01.43.33 UTC+1 skrev Winfield Hill:
> Tim Williams wrote...
> > Winfield Hill wrote ...
> >>>
> >>> Looks great!  Only quirk I see is, why the
> >>> staggered TO-220 pins?
> >>
> >> What, you never got into staggered pins?
> >> (BTW, easy to model.)
> >
> > An extra second per part, bending the leads
> > so they'll fit?!  You must be crazy!  I hope
> > you never wrote a book or anything! ;-)
> 
>  One purpose: standing parts will not be
>  prone to being bent over, and eventually
>  suffer a fatigue failure.  Not all parts are
>  vulnerable, but parts around the edges are;
>  this rule always applied solves the problem.
>  And as you say, it's only an extra second.
> 
>  It also sometimes helps with routing, etc.
> 

in my experience stagger pins just means that if they get bent over
it will be where the pins the package and break the pins, instead of 
being some where along the pins where it isn't so critical

-Lasse

Tim Williams wrote...
> Winfield Hill wrote ...
>>>
>>> Looks great!  Only quirk I see is, why the
>>> staggered TO-220 pins?
>>
>> What, you never got into staggered pins?
>> (BTW, easy to model.)
>
> An extra second per part, bending the leads
> so they'll fit?!  You must be crazy!  I hope
> you never wrote a book or anything! ;-)

 One purpose: standing parts will not be
 prone to being bent over, and eventually
 suffer a fatigue failure.  Not all parts are
 vulnerable, but parts around the edges are;
 this rule always applied solves the problem.
 And as you say, it's only an extra second.

 It also sometimes helps with routing, etc.


-- 
 Thanks,
    - Win

"Winfield Hill"  wrote in message news:n8gca802s1u@drn.newsguy.com...
>> Looks great!  Only quirk I see is, why the
>> staggered TO-220 pins?
>
> What, you never got into staggered pins?
> (BTW, easy to model.)
>

An extra second per part, bending the leads so they'll fit?!  You must be 
crazy!  I hope you never wrote a book or anything! ;-)

(I never had a need for it, but occasionally you'll see one with the 
middle lead kicked up like one of the Rockettes, and board routed out 
around it.  There's a couple of these inside my monitor, for driving a 
pulsed 1.5kV focus electrode or something.  No better way to get the 
creepage needed; only downside is, most TO-220's aren't grooved between 
the leads, so you're very quickly package limited on that.)

I also like the TO-92s with 0.1" pitch.  (But if I accidentally buy the 
unformed lead variety, that's *two seconds* wasted!)

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com 

rickman wrote...
>
> Winfield Hill wrote:
>>
>>  Most signal generators are limited to 10 or
>>  20V to drive their 50-ohm output resistors.
>>  This voltage is cut in half at the load, if
>>  there's the expected nominal 50-ohm load.
>
> There's little reason to drive a 50 ohm resistor
> with double the output voltage to get a 50 ohm
> source.  I did a design with limited Vdd and 
> used positive feedback to make a 12.1 ohm resistor
> look like a 50 ohm output impedance.  I was
> able to get an 8 volt swing into 50 ohms from 
> an LM8272 op amp on a unipolar 12 volt supply.

 The LM8272 is a well-controlled op-amp, doing
 that with a RF power amplifier with margin
 phase characteristics is a risky proposition.


-- 
 Thanks,
    - Win

On 1/27/2016 8:19 PM, Winfield Hill wrote:
> George Herold wrote...
>> Winfield Hill wrote:
>>> George Herold wrote...
>>>>
>>>> I spy a bunch of carbon comp resistors.
>>>> (Can you say why?)
>>>
>>> Low inductance and transient power-handling.
>>>
>>>> I assume the amp is class A?
>>>
>>> Yes.  Here's a schematic of a slowish version.
>>> https://www.dropbox.com/s/xwy4l5audcozylw/AMP-70A-2_sch_.pdf
>>
>> I sorta lost the signal path in the middle,
>> OK I found the feedback.  But the output!
>> I was thinking the 3.3 ohm balancing R's
>> were big, and then I saw 50 ohms on the
>> output.  Doesn't that suck up all your
>> voltage?  What's the load?  Driving a coil?
>> (is there a big capacitance path I'm missing?)
>
>   Traditionally signal generators have 50-ohm
>   outputs to match the coax they'll be driving.
>   They have a 50-ohm source resistor to insure
>   proper coax-transmission-cable driving.
>
>   {Please see AoE III, 12.10.1, pages 858-874,
>   and Appendix H, pages 1116 to 1130.
>
>   Most signal generators are limited to 10 or
>   20V to drive their 50-ohm output resistors.
>   This voltage is cut in half at the load, if
>   there's the expected nominal 50-ohm load.

There's little reason to drive a 50 ohm resistor with double the output 
voltage to get a 50 ohm source.  I did a design with limited Vdd and 
used positive feedback to make a 12.1 ohm resistor look like a 50 ohm 
output impedance.  I was able to get an 8 volt swing into 50 ohms from 
an LM8272 op amp on a unipolar 12 volt supply.

-- 

Rick

On Thu, 28 Jan 2016 23:47:06 +1100, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

>On 28/01/2016 12:19, Winfield Hill wrote:
>>   Traditionally signal generators have 50-ohm
>>   outputs to match the coax they'll be driving.
>>   They have a 50-ohm source resistor to insure
>>   proper coax-transmission-cable driving.
>>
>>   {Please see AoE III, 12.10.1, pages 858-874,
>>   and Appendix H, pages 1116 to 1130.
>>
>>   Most signal generators are limited to 10 or
>>   20V to drive their 50-ohm output resistors.
>>   This voltage is cut in half at the load, if
>>   there's the expected nominal 50-ohm load.
>
>I was interested to see some ADSL modem transmit amplifiers that don't 
>do this. Provided the load impedance is about right, they simulate the 
>right output impedance with a lower value series resistance than the 
>cable characteristic impedance. I think the circuit is something like a 
>Howland current pump but slightly re-adjusted to give a high (50 Ohm) 
>but not infinite output impedance. In this article it is figure 3:
>http://www.eetimes.com/document.asp?doc_id=1277049
>
>This advantage (of not needing the supply voltage to be more than double 
>the output voltage) wouldn't be generally applicable for lab equipment 
>where someone might run it into an open-circuit and might actually want 
>and expect twice the voltage that they would have got with a 50 Ohm 
>load, without clipping.
>
>I am also a bit leery of using ADSL driver chips in a lab function 
>generator, as they are liable to be discontinued when the market for 
>ADSL chips changes.

Don't try to use THS3062!


 Still that also happened to the Elantec EL2009 and 
>also the MAX038 that I might have also used in that function generator, 
>so maybe the ADSL drivers would not have been the first to go obsolete. 
>I wonder whether it is already too late for the nice fast 300V 
>transistors that used to be used in the video amplifiers on CRT neck boards.
>


Some of the now-gone horizontal-output transistors had really
interesting c-b junctions, accidentally a great drift step-recovery
diode.



>Chris

-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

On Thu, 28 Jan 2016 21:41:12 -0800, Phil Hobbs wrote:

>>As my eyes get less flexible I find more need to resort to a microscope
>>for reading part numbers (or part "markings" & good luck finding an
>>actual part number to map to it these days on little parts, if they even
>>are marked.) I don't have good one for working under.
> 
> Some of the Chinese ones are actually pretty decent for the price. Check
> out Amscope on the slightly higher end, or Andonstar for a cheapie
> webcam version:
> <http://m.ebay.com/itm/2MP-USB-Digital-Microscope-Video-webcam-
Magnifier-Camera-Stand-Cam-Andonstar-LW->
> 
> I used my Andonstar earlier today to help with aligning infrared beams
> on really small (60 um) photodiodes. Good medicine for $50.

Your link didn't work, but typing Amscope into ebay's search line got a 
bunch of good hits.

I got mine free from a customer who otherwise robbed me blind (with my 
collusion -- you can't be ripped off for labor unless you allow the 
account to climb to rip-offable heights).  Having one, I think it'd 
definitely be worth $500 for another one, getting a cheap Chinese one for 
1/3 the price is even better.

My one complaint with the thing is neck strain -- if I spend all day 
populating boards without remembering to put a heat pad on my neck first 
then I'm very sorry the next day.  I wonder if something with a USB 
camera and a screen that I can look at while sitting in a normal posture 
wouldn't work better.

I suppose that going too far down that road would just have me building a 
semi-automatic pick & place machine.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

On 1/28/2016 9:00 AM, Winfield Hill wrote:
> Chris Jones wrote...
>>
>> I wonder whether it is already too late for the
>> nice fast 300V transistors that used to be used
>> in the video amplifiers on CRT neck boards.
>
>   You have to get a lifetime supply. Some Alibaba
>   sellers, etc., still have some types.

I don't feel like I can trust Alibaba sellers.  I see too many reports 
of outright fraud there.  I don't know how well Alibaba protects the 
buyers, but it looks like it isn't good enough.

-- 

Rick