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Output stage emitter resistors
Output stage emitter resistors
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Old 16th August 2019, 11:23 AM   #61
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by kecapmanis021 View Post
Interesting, will try. Thanks.
I was trying to create a LR circuit.
Clearly in this case that isn't quite true as the L has a 100R of resistance too.
But if the inductance makes no difference in this circuit then it wont in an amplifier. The amp output is a transistor (variable resistor) in series with LR emitter resistor.
A better test would be 0r1 WW in series with 0r1 none WW.
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Old 16th August 2019, 01:11 PM   #62
DF96 is offline DF96  England
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Quote:
Originally Posted by nigelwright7557
Very easily. I just made a potential divider with 100r metal film resistor and 100r wire wound resistor.
I put one scope lead on input and another at the connection of the two resistors and compared relative phases on the scope at 2MHz.
No shift in phase at all.
No noticeable shift in phase, which may mean phase shift less than perhaps 10 degrees? To do this test properly you would need to do sine wave drive and X-Y scope. In either case the test shows the difference between the two resistors, not their absolute inductance.

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But if the inductance makes no difference in this circuit then it wont in an amplifier. The amp output is a transistor (variable resistor) in series with LR emitter resistor.
If only life were so simple! In a typical amp the emitter resistors are much lower resistance but possibly similar inductance so any inductance will have greater effect. Also, there is more to a follower than a variable resistance followed by the load. You can make a follower oscillate by adding some capacitance; a variable resistor will not oscillate.

The only way to check if a particular resistor will cause trouble in a particular amplifier is to try it. Simulation is unlikely to help. Fortunately, most resistors will be fine in most amplifiers.

Last edited by DF96; 16th August 2019 at 01:16 PM. Reason: extend
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Old 16th August 2019, 01:13 PM   #63
nigelwright7557 is offline nigelwright7557  United Kingdom
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Originally Posted by DF96 View Post
No noticeable shift in phase, which may mean phase shift less than perhaps 10 degrees? To do this test properly you would need to do sine wave drive and X-Y scope. In either case the test shows the difference between the two resistors, not their absolute inductance.
The inductance is a factor too of the collective impedance/resistance.
I was using 2MHz so any "significant" inductance at that frequency would give a high impedance. In practice it gives next to none.
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Old 16th August 2019, 02:38 PM   #64
danny_66 is offline danny_66  Belgium
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I use the Isabellenhuette PBH resistors.
They're 3 watt and with heatsink 10 watt.
In the current noise resistor test doc they're the best, see page 10 figure 8, line at the bottom (zoom in the graph for better distinction in line styles)

You can buy them at Buerklin
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Old 16th August 2019, 05:02 PM   #65
Bensen is offline Bensen  Belgium
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Originally Posted by danny_66 View Post
I use the Isabellenhuette PBH resistors.
They're 3 watt and with heatsink 10 watt.
In the current noise resistor test doc they're the best, see page 10 figure 8, line at the bottom (zoom in the graph for better distinction in line styles)

You can buy them at Buerklin
Interesting paper Danny,
To bad those Isabellenhuette resistors are that expensive. 6 each. That would mean over 100 for my current amplifier.
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Old 16th August 2019, 08:57 PM   #66
SemperFi is offline SemperFi  Norway
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Quote:
Originally Posted by nigelwright7557 View Post
Very easily. I just made a potential divider with 100r metal film resistor and 100r wire wound resistor.
I put one scope lead on input and another at the connection of the two resistors and compared relative phases on the scope at 2MHz.
No shift in phase at all.
Click the image to open in full size.
100R resistors don't count. How much inductance do you need before it starts to make a difference to 100ohms? A lot.
1ohm and less and suddenly you don't need so much inductance to make a difference.
So your test should be done with proper emitter resistor values, such as 0.33R. I bet you'll get a different picture. But of course, long leads on the reference resistor (the known good one), and suddenly it too is inductive...

Not to drag this thread into the extreme, WW are fine in my opinion, but there are samples that are really poor, as in really inductive, and one example was shown in post 45.
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Old 16th August 2019, 08:59 PM   #67
SemperFi is offline SemperFi  Norway
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Originally Posted by anatech View Post
Hi SemperFi,
What model of HP network analyzer are you using? I have a 4195A with the impedance measuring kit, but no stages and no APC-7 connectors to build one or more.

-Chris
4194A
We bought a modern take on this instrument a few years ago, from Keysight, but the HP4194 is always used, and the Keysight never used... it's just such a great instrument.
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Old 17th August 2019, 12:53 AM   #68
kecapmanis021 is offline kecapmanis021  Indonesia
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Quote:
Originally Posted by SemperFi View Post
100R resistors don't count. How much inductance do you need before it starts to make a difference to 100ohms? A lot.
1ohm and less and suddenly you don't need so much inductance to make a difference.
So your test should be done with proper emitter resistor values, such as 0.33R. I bet you'll get a different picture. But of course, long leads on the reference resistor (the known good one), and suddenly it too is inductive...
I always thought the higher the R the more inductive a WW become since more winding is needed, this off course assuming low R and high R WW are manufactured using the same wire material, and same construction method.

Using different material might be not economical from production cost perspective.

Last edited by kecapmanis021; 17th August 2019 at 12:54 AM. Reason: Addition
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Old 17th August 2019, 02:36 AM   #69
anatech is offline anatech  Canada
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Output stage emitter resistors
Hi kecapmanis021,
The high resistance swamps out the inductance (lowers the Q a lot).

Hi SemperFi,
Nice instrument indeed.
Quote:
... but the HP4194 is always used, and the Keysight never used
I hear your plight though. That nasty Keysight instrument? I'll suffer using it if you want. I can see many late painful nights learning how to get around in the menus, but I would soldier through and get 'er done.

Nothing sadder than a piece of test equipment sitting around unused and unloved.

-Chris
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Old 17th August 2019, 05:43 AM   #70
kecapmanis021 is offline kecapmanis021  Indonesia
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Quote:
Originally Posted by anatech View Post
Hi kecapmanis021,
The high resistance swamps out the inductance (lowers the Q a lot).

-Chris
Hi Chris, thanks for pointing out.
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