g-2000 head

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frank the crank ny
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Joined: 2007-12-30
g-2000 head

I bought my g2000 head used in 1979. It still cranks ,I have never checked or replaced tubes. I've noticed the tremolo seems to attenuate the volume when used. I can still work around it . Channel 1 seems to have lost a little gain, but I never use it. I'm wondering what tube replacement will do for me. I have never pulled these tubes. I'm afraid I may do damage if I have to force these tubes out. Of the 4 power tubes, 1 has a little blue in it ,I am told this means a bad tube ( t or f )? 2 have a nice orange glow to them, and the last is a little dim.
As for the preamp tubes they have a metel cover over them making it hard to see. I have opened this amp up in '79 to relocate a master volume from back panel to front. I am told a master volume on this amp is a custom job. ( t or f )? . Last question. There is a standby sw. on the back panel. I never use it. Is this bad? Remember I've been useing this almost 30 years? I'm looking for an opinion of ,should I yank and replace the tubes or let sleeping dogs lie ? Also the bright switches dont seem to do much. Im new in here. A thank you to anyone with feedback. Frank

Craig
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Joined: 2007-12-05
Answer to some questions perhaps

Frank,

Blue hue inside the tube could mean that the bias voltage is different than the others (too high I think), but I'm no expert that's for sure. However, it could be the tube's design: For a fixed voltage, or a single point of control of that grid voltage, the variable would be the differences in the tube's creation; the quality of its manufactured final state. Mesa has no bias voltage adjustment to their amps. They argue that if all tubes are created exactly alike, i.e. the current across them for a fixed voltage bias is identical, then there is no reason to have a bias adjustment. I can see their point. Fender says that a blue hue inside your tube means that your bias voltage is set too high. Bias voltage adjustment is made when the tube is replaced usually. However, if that adjustment never changes, then the degradation has to occur inside the tube. If you are going to install new tubes, have a pro adjust the bias voltage. The voltages read around the tubes are high (460V), and you don't want to go arcing and sparking around in your precious EARTH SHAKER! If you are familiar with a VOM, then remember to stand on something insulating and keep one hand in your pocket when digging around in there!

I have an Earth Super Guitar G-2000 with no master volume control. What you have is a custom job.

If you listen closely to your sound, the bright switches do make a brilliance adjustment. If you don't hear any change, you may have a capacitor that needs replaced. The capacitors probably all need changed in your amp anyway. In my last rehearsal, I noticed a low frequency hum when I was not playing. I turned my volume to zero on both channels and still heard the hum! I "flicked" a couple of the preamp tubes and saw flickering in the V10 position power tube. I thought my tubes were bad. When I turned up the volume again, I got nothing!

My amp was a Christmas gift to me from my son. He purchased it from a vintage guitar and amp store in Franklin Ohio, called Fretware Guitars. The proprietor said that he replaced a couple of the 6L6 tubes, so I was concerned about which ones he replaced. He put in two "The New Tube" type tubes and the other two were made in China. So I didn't have a problem buying a new set of tubes from the get-go. Barring any unforeseen anomalies, you will get around 3000 hours of service from a tube; anything more than that is icing on the cake.

I thought that I would take my amp apart and look for other causes for my symptoms and I found one severed resistor and another ready to sever completely on the power amp tube circuit. Apparently I was aggravating an already terrible condition that predated my ownership of the amp. So I'm going to do some fixing up and also going to change the tubes.

Hope this helped some. Good Luck,
Craig
Happy Earth Super Guitar G-2000 Owner

ultimateguitarman
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Joined: 2008-03-29
always turn on your amp first

alway turn your amp power switch on after the tubes warm up 2 minutes then turn the standby swith on other wise you with surge your output tubes and it's not good for the power transformer either.

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