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September 15, 2019, 11:03:14 AM

Author Topic: Resistance check is off?  (Read 1510 times)

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Offline jake111

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Resistance check is off?
« on: March 20, 2016, 07:15:36 PM »
#10 is 4.98k, should be 1.4k
#20 is 4.76k, "                   "
C1 is 4.79k,   "                   "

I installed the impedance switch kit and didn't think to check the resistances beforehand. So don't know if it was like this before.
Would the difference be noticeable?
All the other measurements check out fine. What should be done next?
Thanks, Jess

Online Paul Birkeland

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Re: Resistance check is off?
« Reply #1 on: March 21, 2016, 08:00:12 AM »
I'm a little confused here.  You've posted in the Stereomour I forum, which was the original Stereomour that is now discontinued (it has one 9 pin socket, and no balance control).

The resistance for terminal 10 on the Stereomour 1 is 0 Ohms. 
If, by chance, this is a typo, and you have 4.98K on terminal 11, your 4.7K resistor is probably well connected, but not the 1.6K resistor.  This is most likely caused by a flaky solder joint.

The same issue looks to be happening on terminal 20. 

Sometimes the 220uF cap across these resistors can cause some problems, and you can temporarily remove the wires going into the "K" pads on the power supply PC board to recheck these resistance measurements. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline jake111

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Re: Resistance check is off?
« Reply #2 on: March 21, 2016, 08:20:48 AM »
Ooops, yeah I meant #11.

Offline jake111

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Re: Resistance check is off?
« Reply #3 on: March 21, 2016, 08:56:59 AM »
You nailed it Paul. The 1.6k has failed. It's not the same as the one in the manual. Should I replace it or get a pair of the ones pictured in the manual?

Offline jake111

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Re: Resistance check is off?
« Reply #4 on: March 21, 2016, 09:06:46 AM »
Is this a common part I can get locally? I'm in Portland.

Online Paul Birkeland

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Re: Resistance check is off?
« Reply #5 on: March 21, 2016, 09:34:06 AM »
Yeah, that's a 5W resistor where we supply a 10W part.  I would just order a pair of 1.6K 10W resistors from Mouser or Digikey.  If anything else in the amp isn't what it's supposed to be, now is probably the time to check.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doc B.

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Re: Resistance check is off?
« Reply #6 on: March 21, 2016, 10:08:57 AM »
This appears to be a prototype, and thus some parts may be different than the production model.
Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.

Offline jake111

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Re: Resistance check is off?
« Reply #7 on: March 21, 2016, 10:38:04 AM »
Yes it is. I think I'll just replace the two resisters since I liked it the way it was.

Offline jake111

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Re: Resistance check is off?
« Reply #8 on: March 22, 2016, 10:13:37 AM »
Are these acceptable?

Online Paul Birkeland

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Re: Resistance check is off?
« Reply #9 on: March 26, 2016, 06:48:05 AM »
Those are 1.6 Ohm and 4.7 Ohm.  You want 1.6K and 4.7K, which are 1600 Ohms and 4700 Ohms respectively. 

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline jake111

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Re: Resistance check is off?
« Reply #10 on: September 30, 2016, 07:20:42 PM »
The 2A3 on the same side of the blown 1.6k resistor has failed.
Could the time it was playing before I fixed it have caused damage to the tube?
Thanks, Jess

Online Paul Birkeland

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Re: Resistance check is off?
« Reply #11 on: October 01, 2016, 06:56:29 PM »
Yes, if one of the cathode bias resistors fails short, then the 2A3 is allowed to draw excessive current and dissipate excessive heat.  This will damage the tube and/or plate choke in short order.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man