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Post subject: New HRDIII: mysterious issue
Posted: Wed Jul 01, 2015 2:21 pm
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Strange. I got it as a 'scratch and dent' from American Musical Supply, and as I've often found the case, there's no cosmetic issues whatsoever. So I got a new amp delivered for 579, which is good, but it wasn't producing any noise other than this kind of strangled squeak, and you had to crank it to get that. Poking around, I found the internal speaker was plugged into the jack CLOSEST to the 6L6's. I thought that was right, actually. But I moved it to the jack that's farther from the 6L6's, and now everything's fine. Can someone just confirm for me that its the farther jack that's the correct one?


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Post subject: Re: New HRDIII: mysterious issue
Posted: Wed Jul 01, 2015 3:13 pm
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Why not simply consult the owner/operator's manual to confirm your hypothesis......?

http://www.fmicassets.com/Damroot/Origi ... manual.pdf

Arjay

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Post subject: Re: New HRDIII: mysterious issue
Posted: Wed Jul 01, 2015 3:31 pm
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Retroverbial wrote:
Why not simply consult the owner/operator's manual to confirm your hypothesis......?

http://www.fmicassets.com/Damroot/Origi ... manual.pdf

Arjay


+1

Main speaker jack is the farther from 6L6s, the left one .


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Post subject: Re: New HRDIII: mysterious issue
Posted: Wed Jul 01, 2015 4:27 pm
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Hi markvc1,

Interesting related note: You cranked the amp with a direct short across the OT without damaging the amp. This is more real world evidence that an impedance mismatch, particularly a speaker impedance that is lower than the amps rating, will not harm the amp. This is exactly why modern amps (and many vintage amps) have a shorting output jack, to protect the amp. :wink:

Welcome to the forum, and enjoy that amp! 8)

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Post subject: Re: New HRDIII: mysterious issue
Posted: Wed Jul 01, 2015 7:15 pm
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I think that plugging into the Ext jack switches to the 4 ohm tap of the OT.
This interrupts the 8 ohm tap and the shorting switch to ground
It sounds like the speaker jacks are buggered or the 4 ohmjack is miswired
I guess it's scratched on the inside


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Post subject: Re: New HRDIII: mysterious issue
Posted: Wed Jul 01, 2015 7:56 pm
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TimsAudio wrote:
I think that plugging into the Ext jack switches to the 4 ohm tap of the OT.
This interrupts the 8 ohm tap and the shorting switch to ground


This is true but only if a dummy (open) plug is inserted into the normal 8-ohm jack.

Arjay

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Post subject: Re: New HRDIII: mysterious issue
Posted: Wed Jul 01, 2015 8:26 pm
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TimsAudio wrote:
I think that plugging into the Ext jack switches to the 4 ohm tap of the OT.
This interrupts the 8 ohm tap and the shorting switch to ground
It sounds like the speaker jacks are buggered or the 4 ohmjack is miswired
I guess it's scratched on the inside


Partly correct. It does switch to the 4-ohm tap, however, the shorting part of the main jack is still a direct short across the OT unless something is plugged into the main jack. Nothing mis-wired, this is working as designed.

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Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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Post subject: Re: New HRDIII: mysterious issue
Posted: Fri Jul 03, 2015 8:46 am
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You're right, I'll try less thinking, more schematic reading.


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