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Mistake on OPT connections : have I damaged something ?
Mistake on OPT connections : have I damaged something ?
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Old 9th March 2009, 05:15 PM   #1
mahleriana is offline mahleriana  France
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Default Mistake on OPT connections : have I damaged something ?

I try to decide my mind between 2a3 and el84 and i use screw connectors in all my amplifier : 15 minutes change between the two types
Changing my connections, i made a mistake on the secondary of one of my OPT (hammond 125 series) :I connected both 2,5kohm and 10kohm taps together on one channel.
I pressed play to warm the amp and went to another room for ten minutes.
When i went back, this channel was in fact totally silent.
The amplifier still works ok, but I think there is a slight change in quality since then but not so sure as i changed parts every day recently...
Do you think this would have damage something (perhaps speaker ?)
thanks in advance
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Old 10th March 2009, 12:58 AM   #2
HollowState is offline HollowState  United States
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Location: Taxland, New Jersey
Hi Eric,
You question was a little confusing until I looked up the Hammond 125 series transformers to see how they were configured. So, apparently you shorted out part of the secondary for a while. You say the amplifier still works which is a very good sign and I would imagine everything is ok as long as the transformer didn't overheat. (It should not have) To be certain, with the amp turned off and the speaker disconnected, check for continuity with an ohmmeter between all the secondary leads. Also check the primary's two leads. Tubes are very forgiving, and I doubt that the speaker suffered any damage either.

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Old 10th March 2009, 02:06 AM   #3
ErikdeBest is offline ErikdeBest  Switzerland
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Join Date: Mar 2003
Location: Zürich
Hi Eric

Victor already treated the theoretical part...so I just want to say something - a sort of personal rule - about the practical part of amplifier building, and mostly, circuit prototyping:

Never leave a prototype alone!!!

I always wear safety glasses, stand a safe distant from the prototype, turn off any background music, all to see, hear and sniff if everything is right, at turn on and in the minutes afterwards. Components that work good at the start may become a problem after a couple of minutes, such as a resistor with dissipation close (or above) its ratings, etc...

This is something personal as I have already seen things going quite bad... therefore there is also a fire extinguisher in the hobby room!

my surname is indeed 'de Best': neither misspelling nor snobbism! Ask SY!
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Old 11th March 2009, 11:45 PM   #4
mahleriana is offline mahleriana  France
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Join Date: Nov 2007
I checked all primaries and secondaries and everything is similar between the two OPTs.
In fact it is one of my EL84 that has lost a lot of its musicality. 10$ to change this...

For safety rules, i often wear safety glasses ...especially when playing with caps and i always wait a minute or two to see if nothing catch fire (it happened once !)
This time was just a change in load...never enough secure !

thanks for your help
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