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August 07, 2020, 06:09:15 AM

Author Topic: Resistor Issue  (Read 3116 times)

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Offline Grinnell

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Resistor Issue
« on: October 19, 2009, 03:32:35 PM »
So i hooked up a new diy tonearm cable and it sounded fine then it seemed that i was getting a stronger signal out of the right channel so i played around with things (change cables and tubes, turning it off before changing things) then the sound got muddy and flat, even my wife noticed.  Looked at the guts and noticed a resistor (Dale rs-2b 1.2 ohms 1%) that looked a bit fried, dull and maybe a bit misshapen.  attached is a photo not great but shows where it is.

if it isn't this resistor what could it be?  I didn't build this but will get the chance to fix it :)

Thanks


Offline Grainger49

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Re: Resistor Issue
« Reply #1 on: October 20, 2009, 03:49:29 AM »
The power supply is common to both channels.  But I'm not sure, did the muddy sound come from both channels?

To trouble shoot the heater DC supply (that is what is pictured) measure the resistance of the resistor in question.  But first... measure the resistance of the meter leads.  Otherwise you can think the resistance is off.  With a resistance this low the meter leads will add to the measurement.

Post back.
« Last Edit: October 20, 2009, 06:57:53 AM by Grainger49 »

Online Paul Birkeland

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Re: Resistor Issue
« Reply #2 on: October 20, 2009, 06:43:18 AM »
Looked at the guts and noticed a resistor (Dale rs-2b 1.2 ohms 1%) that looked a bit fried, dull and maybe a bit misshapen. 

Oh, that is quite the ugly, misshapen resistor, isn't it?   Unfortunately for you, it looks just fine.  Is the muddy sound coming from both channels, or just one?  You might try swapping the tubes between channels to check.

Do the LED's attached to the tube sockets light?  If you  have C4S boards, are they lighting?

If the LED's light, and that black resistor measures OK, I would next take measurements of the plate voltages.  This can be done by measuring the DC voltages at the metal portion on the back of the black MJE350 transistors, or if you don't have C4S boards, there are the large tan colored plate loads, and the plate voltage can be measured where those resistors connect to the 220 ohm carbon comp plate stoppers.  My guess is that you will find something like 75v on 3 of the 4 plates, and maybe 115 on the fourth, which would indicate a tube or connection problem. 

-Paul
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Grinnell

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Re: Resistor Issue
« Reply #3 on: October 22, 2009, 07:48:35 AM »
Thanks for the advice.  My wife leaves for 5 months in Berlin on Sunday so after that its troubleshoot time.  I have the original build manual and notes from the PO so that should help.

Thanks and I will report back.

Karl
Missing the sweet sound of Seduction