Electro Harmonix 6v6gt, New build

chunkitup · 03-02-2007, 03:40 PM

How fast could you destroy one of these tubes? I had the wrong resistor in my bias circuit and the tubes ate about 65ma or more with 411v on the screens and 412v on the plates for over 3 minutes and under 7 minutes. I was trying to get sound from the amp at the time and then realized, and no I wasnt drunk or on anything, that I forgot to put the PI tube in. What an idiot I am. Now what I get is a low and loud bull horn sound when I flip the standby on. I cant tell if there is a 120 hum in there because it is really loud(all volume pots at 0) and I shut her down immediately. I dropped the current down to 20ma but I think the damage was done. Any help would be great.

Steve Conner · 03-02-2007, 04:19 PM

If the amp makes a real loud hooting noise, that's probably good, since that implies it can still amplify stuff

If you had killed the power tubes, it would be silent or humming at 120Hz, and probably blow its fuse or smoke its screen resistors.

You might have wired up the negative feedback wrong, or put some wrong component in the PI or feedback loop. I'd suggest checking all those component values, and also, you could maybe try disconnecting the NFB altogether to see if it stops the noise. If it does, you made a mistake somewhere in your feedback loop.

chunkitup · 03-02-2007, 04:29 PM

That is what I wanted to hear. It is a very loud hooting noise. I will disconnect the NFB loop and see what happens. I have checked and rechecked and rechecked the PI and it is right on connection wise. What if the PI tube is bad would that have the same hooting effect?

chunkitup · 03-02-2007, 04:53 PM

The NFB is the culprit!! The amp, she lives. Thanks Steve

chunkitup · 03-02-2007, 08:32 PM

NOW! I need to have the NFB(presence) working and I dont know why it does what it does. The amps highs are a bit untamed (hi-gain amp). The NFB circuit I am using is this one
http://schematicheaven.com/newamps/soldano_atomic16.pdf
The power amp is the same also. If anyone can help me I would appreciate it.

Steve Conner · 03-02-2007, 11:47 PM

Well, the first thing to try is swapping over the connections from the OT to the power tube plates. If those are the wrong way round, the "negative" feedback will actually be positive and the amp will oscillate like crazy.

03-02-2007, 03:40 PM	#1
chunkitup Senior Member Join Date: Dec 2006 Location: York, PA Posts: 145	Electro Harmonix 6v6gt, New build How fast could you destroy one of these tubes? I had the wrong resistor in my bias circuit and the tubes ate about 65ma or more with 411v on the screens and 412v on the plates for over 3 minutes and under 7 minutes. I was trying to get sound from the amp at the time and then realized, and no I wasnt drunk or on anything, that I forgot to put the PI tube in. What an idiot I am. Now what I get is a low and loud bull horn sound when I flip the standby on. I cant tell if there is a 120 hum in there because it is really loud(all volume pots at 0) and I shut her down immediately. I dropped the current down to 20ma but I think the damage was done. Any help would be great.

03-02-2007, 04:19 PM	#2
Steve Conner Supporting Member Join Date: May 2006 Location: Glasgow, Scotland Posts: 2,990	If the amp makes a real loud hooting noise, that's probably good, since that implies it can still amplify stuff If you had killed the power tubes, it would be silent or humming at 120Hz, and probably blow its fuse or smoke its screen resistors. You might have wired up the negative feedback wrong, or put some wrong component in the PI or feedback loop. I'd suggest checking all those component values, and also, you could maybe try disconnecting the NFB altogether to see if it stops the noise. If it does, you made a mistake somewhere in your feedback loop. __________________ "Ohhhh miracle bulb shines feebly"

03-02-2007, 11:47 PM	#6
Steve Conner Supporting Member Join Date: May 2006 Location: Glasgow, Scotland Posts: 2,990	Well, the first thing to try is swapping over the connections from the OT to the power tube plates. If those are the wrong way round, the "negative" feedback will actually be positive and the amp will oscillate like crazy. __________________ "Ohhhh miracle bulb shines feebly"

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03-02-2007, 04:29 PM	#3
chunkitup Senior Member Join Date: Dec 2006 Location: York, PA Posts: 145	That is what I wanted to hear. It is a very loud hooting noise. I will disconnect the NFB loop and see what happens. I have checked and rechecked and rechecked the PI and it is right on connection wise. What if the PI tube is bad would that have the same hooting effect?

03-02-2007, 04:53 PM	#4
chunkitup Senior Member Join Date: Dec 2006 Location: York, PA Posts: 145	The NFB is the culprit!! The amp, she lives. Thanks Steve

03-02-2007, 08:32 PM	#5
chunkitup Senior Member Join Date: Dec 2006 Location: York, PA Posts: 145	NOW! I need to have the NFB(presence) working and I dont know why it does what it does. The amps highs are a bit untamed (hi-gain amp). The NFB circuit I am using is this one http://schematicheaven.com/newamps/soldano_atomic16.pdf The power amp is the same also. If anyone can help me I would appreciate it.

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