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This has me puzzled (resistor change)

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Guest

Sun Jan 20, 2019 11:45 pm   



There is a video on youtube, where a guy re-caps and repairs and tests
out a late 1940's Precision Apparatus E-200 signal generator.

Video name:
"Repair of a late-'40's Precision E-200-C RF signal generator"

This sig gen has a built in audio tone modulator (oscillator). He
replaced a resistor in that circuit, which was out of tolerance. He
replaced it with a modern film type resistor. The audio modulation did
not work afterwards. After testing everything, he went and replaced that
resistor (again) with an old style carbon resisstor, and after that, the
modulation worked.

What the heck?????

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Cursitor Doom
Guest

Mon Jan 21, 2019 12:45 am   



On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

Quote:
I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????


Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.





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Sjouke Burry
Guest

Mon Jan 21, 2019 12:45 am   



On 20-1-2019 23:50, Cursitor Doom wrote:
Quote:
On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.





A bulk carbon resistor has less self-inductance.


Phil Hobbs
Guest

Mon Jan 21, 2019 12:45 am   



On 1/20/19 5:50 PM, Cursitor Doom wrote:
Quote:
On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.


They also have a large negative voltage coefficient.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Tim Schwartz
Guest

Mon Jan 21, 2019 2:45 am   



On 1/20/2019 6:24 PM, Phil Hobbs wrote:
Quote:
On 1/20/19 5:50 PM, Cursitor Doom wrote:
On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.

They also have a large negative voltage coefficient.

Cheers

Phil Hobbs

Also, Carbon composition resistors will take spikes and surges that will
render a film resistor open circuit, and are more tolerant of short term
overloads.

Regards,
Tim

John Robertson
Guest

Mon Jan 21, 2019 3:45 am   



On 2019/01/20 5:23 p.m., Tim Schwartz wrote:
Quote:
On 1/20/2019 6:24 PM, Phil Hobbs wrote:
On 1/20/19 5:50 PM, Cursitor Doom wrote:
On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.

They also have a large negative voltage coefficient.

Cheers

Phil Hobbs

Also, Carbon composition resistors will take spikes and surges that will
render a film resistor open circuit, and are more tolerant of short term
overloads.

Regards,
Tim


If I am not mistaken that is why film resistors are used where you want
flame-proof behaviour.

Carbon comp let out lots of magic smoke...

John :-#)#

John-Del
Guest

Mon Jan 21, 2019 4:45 am   



On Sunday, January 20, 2019 at 9:35:52 PM UTC-5, John Robertson wrote:
Quote:
On 2019/01/20 5:23 p.m., Tim Schwartz wrote:
On 1/20/2019 6:24 PM, Phil Hobbs wrote:
On 1/20/19 5:50 PM, Cursitor Doom wrote:
On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.

They also have a large negative voltage coefficient.

Cheers

Phil Hobbs

Also, Carbon composition resistors will take spikes and surges that will
render a film resistor open circuit, and are more tolerant of short term
overloads.

Regards,
Tim


If I am not mistaken that is why film resistors are used where you want
flame-proof behaviour.

Carbon comp let out lots of magic smoke...

John :-#)#


And when they don't, they change value in a big way when overheated.


Guest

Mon Jan 21, 2019 8:45 am   



On Sunday, 20 January 2019 22:33:45 UTC, tub...@myshop.com wrote:

Quote:
There is a video on youtube, where a guy re-caps and repairs and tests
out a late 1940's Precision Apparatus E-200 signal generator.

Video name:
"Repair of a late-'40's Precision E-200-C RF signal generator"

This sig gen has a built in audio tone modulator (oscillator). He
replaced a resistor in that circuit, which was out of tolerance. He
replaced it with a modern film type resistor. The audio modulation did
not work afterwards. After testing everything, he went and replaced that
resistor (again) with an old style carbon resisstor, and after that, the
modulation worked.

What the heck?????

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????


So IIUC he changes the R value and it no longer oscillates. Presumably he's thereby changed the loop gain. Where is the surprise?


NT


Guest

Mon Jan 21, 2019 9:45 am   



On Mon, 21 Jan 2019 00:10:42 +0100, Sjouke Burry
<burrynulnulfour_at_ppllaanneett.nnll> wrote:

Quote:
On 20-1-2019 23:50, Cursitor Doom wrote:
On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.





A bulk carbon resistor has less self-inductance.


I kind of thought that might be the case....

I prefer using the old carbon resistors in vintage tube gear, but they
are getting hard to find and expensive. They are all NOS now. i dont
think there is any place making them anymore.


Guest

Mon Jan 21, 2019 9:45 am   



On Monday, 21 January 2019 08:22:47 UTC, tub...@myshop.com wrote:
Quote:
On Mon, 21 Jan 2019 00:10:42 +0100, Sjouke Burry
burrynulnulfour_at_ppllaanneett.nnll> wrote:
On 20-1-2019 23:50, Cursitor Doom wrote:
On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.





A bulk carbon resistor has less self-inductance.

I kind of thought that might be the case....

I prefer using the old carbon resistors in vintage tube gear, but they
are getting hard to find and expensive. They are all NOS now. i dont
think there is any place making them anymore.


Rapidonline does carbon comps. I'm sure it's far from the only supplier. There's no upside to them other than pulse power ability & for some cases looks.


NT

Look165
Guest

Mon Jan 21, 2019 10:45 am   



Carbon resistors are noisy.

We used that for making white noise and then by filtering, make sine
wave or else.

With metal resistors there is not enough noise.

tubeguy_at_myshop.com a écrit le 20/01/2019 à 23:33 :
Quote:
There is a video on youtube, where a guy re-caps and repairs and tests
out a late 1940's Precision Apparatus E-200 signal generator.

Video name:
"Repair of a late-'40's Precision E-200-C RF signal generator"

This sig gen has a built in audio tone modulator (oscillator). He
replaced a resistor in that circuit, which was out of tolerance. He
replaced it with a modern film type resistor. The audio modulation did
not work afterwards. After testing everything, he went and replaced that
resistor (again) with an old style carbon resisstor, and after that, the
modulation worked.

What the heck?????

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????


Ralph Mowery
Guest

Mon Jan 21, 2019 4:45 pm   



In article <2450f296-8d19-4c68-bad1-16493d1ebb2e_at_googlegroups.com>,
tabbypurr_at_gmail.com says...
Quote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

So IIUC he changes the R value and it no longer oscillates. Presumably he's thereby changed the loop gain. Where is the surprise?




Could it have been possiable that the new resistor was bad, or maybe the
color code was read wrong so the wrong value was put in ?

John Robertson
Guest

Mon Jan 21, 2019 5:45 pm   



On 2019/01/20 7:16 p.m., John-Del wrote:
Quote:
On Sunday, January 20, 2019 at 9:35:52 PM UTC-5, John Robertson wrote:
On 2019/01/20 5:23 p.m., Tim Schwartz wrote:
On 1/20/2019 6:24 PM, Phil Hobbs wrote:
On 1/20/19 5:50 PM, Cursitor Doom wrote:
On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.

They also have a large negative voltage coefficient.

Cheers

Phil Hobbs

Also, Carbon composition resistors will take spikes and surges that will
render a film resistor open circuit, and are more tolerant of short term
overloads.

Regards,
Tim


If I am not mistaken that is why film resistors are used where you want
flame-proof behaviour.

Carbon comp let out lots of magic smoke...

John :-#)#


And when they don't, they change value in a big way when overheated.


On our jukebox tube amplifiers we test every resistor as many of them
have happily drifted off-spec more than their tolerance. Usually plate
of cathode resistors of course because they pass the most current.

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
www.flippers.com
"Old pinballers never die, they just flip out."

John-Del
Guest

Mon Jan 21, 2019 6:45 pm   



On Monday, January 21, 2019 at 10:20:31 AM UTC-5, Ralph Mowery wrote:
Quote:
In article <2450f296-8d19-4c68-bad1-16493d1ebb2e_at_googlegroups.com>,
tabbypurr_at_gmail.com says...

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

So IIUC he changes the R value and it no longer oscillates. Presumably he's thereby changed the loop gain. Where is the surprise?




Could it have been possiable that the new resistor was bad, or maybe the
color code was read wrong so the wrong value was put in ?


Prob not "bad", but maybe just way off value (or read incorrectly as you surmised). I've been given tons of old parts including resistor assortments. You can't believe how often the wrong resistor (usually multiplier) was in the wrong drawer.

When sorting new old stock carbon carbon comp resistors, I don't sort them by printed value, but actual measured resistance since so many of them are closer to the next value up or down than they are to their own printed value. I only keep them to put in old tube radios for authenticity's sake.


Guest

Mon Jan 21, 2019 8:45 pm   



On Sunday, January 20, 2019 at 6:25:07 PM UTC-5, Phil Hobbs wrote:
Quote:
On 1/20/19 5:50 PM, Cursitor Doom wrote:
On Sun, 20 Jan 2019 16:33:41 -0600, tubeguy wrote:

I was always under the impression that film resistors are identical
(electrically), and their only difference is appearance. Now I learn
that is not true.....

WHY?????

Really need to see a schematic. AFAIK the only functional difference
between film and carbon is that latter are noisier.

They also have a large negative voltage coefficient.

I was going to say they also have a negative temperature coef.
But I'd be wrong. A 1.5 kOhm CC in hot air gun and resistance rises.
(I know we use to use these as low T (LN2/ liquid He) temp sensors
with a resistance that rises with lower temp.
(Kinda like it was a thermally activated semi-conductor.))

So I stuck the same 1.5 k resistor into LN2... R increased to 2.1 k!

George H.


Quote:

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com


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