Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on June 18, 2010, 11:34:34 am
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Hello all! It's a new day so here we go again:
This is a Stereo amplifier: Class A Configuration with 3 watts RMS per channel so the manual says:
I talked to the manufacturer and they told me 10 watt transformers. Single ended OT?
The customer said he put new EL84 tubes and afterwards the amp smoked and he shut it down
I have lifted the board and checked all PS caps and changed a few resistors that had stray values. Not bad but i changed them anyway
I removed the new EL84 tubes and checked the plate,screen and bias voltages / All is good with plates at 300VDC and grids at -10VDC
I put one of my EL84 tubes in one channel and all voltages are solid and steady / The amp sounds great!
I put in the second channels EL84 and tested all the voltages / The plate voltage drops from 300VDC to 83VDC and a PS resistor starts to smoke
Little sound and very distorted at best. I though it might be the new EL84 Yugoslavian tubes but thats not the case
At this time i have to believe it is the Output transformer for this channel / Any agreements?
http://www.triodeamplification.com/files/Lexicon_Signature_284_Schematic.pdf
(http://i356.photobucket.com/albums/oo5/plexijtm45/LexioconS284.jpg)
(http://i356.photobucket.com/albums/oo5/plexijtm45/Logo.jpg)
(http://i356.photobucket.com/albums/oo5/plexijtm45/PSResistors.jpg)
(http://i356.photobucket.com/albums/oo5/plexijtm45/EL84Socket.jpg)
(http://i356.photobucket.com/albums/oo5/plexijtm45/OTVDCDrop.jpg)