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el84 help

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inquisitive

Member
Joined 2004
hi jason,
i have voltage on the green wire of the output transformer for one valve that seems all ok but the the red wire connected to the other valve is showing negative very low volts. does this mean i have a shorted transformer? . theres still volume coming out of the affected channel but its distorted. Any help would be much appreciated .
thanks
 
Giaime

Giaime

Member
Joined 2004
giaimeugliano.tk/
If you have few millivolts on the plate, check all connections (sockets, wires, these things) between the plate and the output transformer. Check also by swapping tubes around. If the plate pin (with every tube) remains very low, you probably have an open transformer. You hear sound because the other half of the push pull (the other EL84 in that channel) is still working, but probably in AB class so the waveform is heavily clipped, and the sound is distorted. But the question is, how did you burnt that transformer?
 
richwalters

richwalters

Member
Joined 2003
the wires i was talking about are connected to the plates of the el84s , one valve has the right voltage at the plate 450v and the other, negative millivolts,would this indicate a short in the transformer. [/B]
Click to expand...

Hi there......(would this indicate a short in the transformer)
Noop..... sounds more like an open circuit B+ on one half..
...Question: Does the centre B+ come out of each prim halves of the o/p tranny separately and are joined up elsewhere ? (suspect duff solder joint)

A strong case for a resistance check........Note this tip may help.. When using a DMV to measure prim resistance make sure there is not a trace of B+ juice and the o/p trany secondary is short circuited...WHy ? The high primary inductance shags up the auto function of DVM's and many won't settle.....moving coil meters don't suffer from this.

450V B+ will stew the EL84's ....OMO....

richj
 
I

inquisitive

Member
Joined 2004
hi, thanks for the reply,
will measure the resistance of the good tranny and compare it to the problem one.The 450v on the plate is per the circuit diagram.It used 7189s stock standard out of the box, however i had this amp given to me about 11 years ago without any tubes and a blown output tranny!I had the trannies rewound replaced all the caps resistors and finally after using 6bq5s for a time settled on sovtek el84m , and this is the first trouble i have had to date.My mullard and phillips tubes still sound ok.
 
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