el84 help

[richwalters]

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]

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

[inquisitive]

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.

[richwalters]

Originally posted by inquisitive
My mullard and phillips tubes still sound ok. [/B]

Hi there....... .keep these NOS tubes for an amp that you know works...and ain't going to blow them up.

richj

[inquisitive]

hi,
Turns out you were right giaime half the transformer is dead open circuit. Many thanks to the people who replied.

[Giaime]

I'm glad you found out what's wrong.

If it's broken fix it, if it working mod it.

Keep posting!