el84 help

inquisitive · 22nd March 2005, 10:54 AM

i have a pioneer sm-83 amplifier. My problem is with one of the el84m. When music is playing one of the tubes pulses along with the signal and the sound distorts in the affected channel.The other tubes are ok. Does anyone know what the problem could be? Many thanks.

audiousername · 22nd March 2005, 11:52 AM

What do you mean by pulses along with the music?

Have you tried putting the good valves from the other channel into the channel which is affected?

richwalters · 22nd March 2005, 08:07 PM

hi there........I ain't got schematic on hand..... decoupling caps could be on their way out.....bit of a stab in the dark..

richj

audiousername · 22nd March 2005, 09:38 PM

I did a search, and came up with the schematic, which can be found here.

inquisitive · 23rd March 2005, 04:31 AM

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

audiousername · 23rd March 2005, 05:21 AM

Hi,

Sorry, I can't really be of much help - the colours of the transformer leads aren't marked on the schematic.

inquisitive · 24th March 2005, 08:54 AM

hi, all
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.

audiousername · 24th March 2005, 08:57 AM

A short? Probably not.

Giaime · 24th March 2005, 09:03 AM

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?

Giaime · 24th March 2005, 09:05 AM

And what about that "pulsating" EL84? I think you have a burnt screen resistor that has burnt the screen grid in that tube. Or just lost bias, check decoupling caps to the EL84 grids.

22nd March 2005, 10:54 AM	#1
inquisitive diyAudio Member Join Date: Oct 2004	el84 help i have a pioneer sm-83 amplifier. My problem is with one of the el84m. When music is playing one of the tubes pulses along with the signal and the sound distorts in the affected channel.The other tubes are ok. Does anyone know what the problem could be? Many thanks.

22nd March 2005, 11:52 AM	#2
audiousername diyAudio Member Join Date: Jul 2004 Location: Melbourne, Victoria	What do you mean by pulses along with the music? Have you tried putting the good valves from the other channel into the channel which is affected? __________________ Jason

22nd March 2005, 09:38 PM	#4
audiousername diyAudio Member Join Date: Jul 2004 Location: Melbourne, Victoria	I did a search, and came up with the schematic, which can be found here. __________________ Jason

23rd March 2005, 04:31 AM	#5
inquisitive diyAudio Member Join Date: Oct 2004	el84 help 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

23rd March 2005, 05:21 AM	#6
audiousername diyAudio Member Join Date: Jul 2004 Location: Melbourne, Victoria	Hi, Sorry, I can't really be of much help - the colours of the transformer leads aren't marked on the schematic. __________________ Jason


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22nd March 2005, 08:07 PM	#3
richwalters diyAudio Member Join Date: Sep 2003 Location: Alps:Tube amp designs over 150W, SMPS guru.	hi there........I ain't got schematic on hand..... decoupling caps could be on their way out.....bit of a stab in the dark.. richj

24th March 2005, 08:54 AM	#7
inquisitive diyAudio Member Join Date: Oct 2004	hi, all 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.

24th March 2005, 08:57 AM	#8
audiousername diyAudio Member Join Date: Jul 2004 Location: Melbourne, Victoria	A short? Probably not. __________________ Jason

24th March 2005, 09:03 AM	#9
Giaime diyAudio Member Join Date: Oct 2004	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?

24th March 2005, 09:05 AM	#10
Giaime diyAudio Member Join Date: Oct 2004	And what about that "pulsating" EL84? I think you have a burnt screen resistor that has burnt the screen grid in that tube. Or just lost bias, check decoupling caps to the EL84 grids.

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