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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 9:59 pm
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Quote:
I think a remedial course in "Soldering 101" is in order.


Actually, a beginners course is in order. Never could solder worth a damn. Weld? Yes. Solder, no.

bluesky636, the wires around that socket are cramped, and my hand just moved a couple of millimeters too close. Had I not done that, the amp would be making music right now. I'm buying new sockets and wire, and it will look nice and tidy when I'm done. I'll post a photo for your approval. ;)

This isn't near as hard as this:

Image


Which I turned into this:

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And this:

Image


All by myself. Electrical, too. :)


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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 10:18 pm
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Some people are good at some things and not so good at other things. Me, I can't nail two boards together, but I can build amps. :D

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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 10:35 pm
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How clean and neat is this .. :!:


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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 10:39 pm
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Monkeyleg wrote:
Quote:

Image

Image


Awesome car. Oh those SU carbs are a BEAR to adjust.

Try a small to medium flat solder tip. I find that this gives a much better flow than the round tip. Cleaning and prepping the site is THE key. Just like welding.

http://www.amazon.com/Weller-ETA-Screwd ... d_sim_hi_9

Good luck!


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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 10:46 pm
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Properly tinned wires might also be a big help......

Arjay

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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 11:05 pm
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Arjay,

Most correct! Favorite solder:

http://ecx.images-amazon.com/images/I/513MmJ4FLCL.jpg

Solder flux paste:

http://ecx.images-amazon.com/images/I/7 ... L1500_.jpg


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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 11:08 pm
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Quote:
Some people are good at some things and not so good at other things. Me, I can't nail two boards together, but I can build amps.


Awesome looking amp. Good solder joints, too. ;)


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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 11:12 pm
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monkeyleg, We live for good tone and amp porn!

:lol: :lol: :lol:


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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 11:17 pm
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It's a treat to see people who have pride in their work, no matter how big or small or important the job may be.

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Post subject: Re: What burns out power tubes?
Posted: Sun Jan 26, 2014 11:28 pm
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Aaron,

Yes. We must strive to try and meet her standards. Goddess of Soldering! Lupe Lopez! :D :mrgreen: :D


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Post subject: Re: What burns out power tubes?
Posted: Tue Feb 04, 2014 10:37 pm
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Okay, back to the problem. I replaced the sockets for V7 and V8, the 6L6GC tubes. I replaced any wires that were scorched. I replaced the R70 and R71 resistors for the V7 and V8 tubes. I did pretty good solder joints, I think.

I put in new power tubes, and biased them to 32 on the V7 and about 35 on the V8. I kept swapping out preamp tubes with different ones. No change in the bad sound, though.

I took readings at the test points. I've put the values shown on the schematic in parentheses after the read values.

TP7 2.02VDC (2.02VDC)
TP10 2.15VDC (2.12VDC)
TP33 98.3VDC (93.6VDC)
TP36 -42VDC (-32VDC or -52VDC, can't read it)
TP37 35mVDC (33mVDC)
TP38 33mVDC (33mVDC)
TP39 469VDC (433VDC)
TP33 98.3VDC (93.6VDC)
TP36 -42VDC (-32VDC or -52VDC, can't read it)
TP13 2.08 (2.06VDC)
TP22 2.2VDC (2.01VDC)
TP26 -7.25VDC (-5.50VDC)
TP27 2.02VDC (2.02VDC)
TP28 12.3VDC (13,2VDC)
TP2 462VDC (433VDC)
TP3 450VDC (420VDC)
TP4 411VDC (385VDC)
TP5 -63VDC (-50.2VDC)
TP1 467VDC (435VDC)
TP18 7.7VDC (7.6VDC)

There's a hum that increases with the volume knobs on both the guitar and the amp. There's no hum if the guitar isn't plugged in, or if the guitar volume knob is set to 0.

Any ideas, anyone?


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Post subject: Re: What burns out power tubes?
Posted: Wed Feb 05, 2014 1:10 am
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Your bias is still a bit cold, I would bump it up to 40 mA on the highest tube. I would double-check the two 100 watt resistors on the heater circuit, make sure the traces and solder job are good. You might have fried a coupling cap somewhere in the preamp, maybe even a Plate resistor or two, although your test voltages look OK. The filter caps would be the next place to look for problems. Have you tried a new rectifier tube?

The description of "bad sound" is subjective and not very helpful in diagnoses.

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Post subject: Re: What burns out power tubes?
Posted: Wed Feb 05, 2014 8:23 am
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Thanks for the reply, shimmilou. The bias is recommended to be 30-37 by a whole bunch of sources (including BMW2002Ti, who's been helping me on this). It was the bias I had set before things went south, and sounded the best. I've replaced the filter caps, the resistors for the filter caps, and the rectifier tube.

The "bad sound" is muddled and gritty distortion when the strings are hit hard. If I go up the fret board on the low E string, the sound gets fuzzy, more so than even fret buzz. If I play a chord with the low strings (E, A and/or D), it's very muddled and harsh. It only sounds this way with the amp volume knob higher than three on either channel. At three or below the sound is clean.


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Post subject: Re: What burns out power tubes?
Posted: Wed Feb 05, 2014 8:34 am
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" There's a hum that increases with the volume knobs on both the guitar and the amp. There's no hum if the guitar isn't plugged in, or if the guitar volume knob is set to 0. "


You have a ground loop. Somewhere between the guitar pickup and the input of the amp. Try another patch cord. Try a different guitar.


Good luck!


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Post subject: Re: What burns out power tubes?
Posted: Wed Feb 05, 2014 8:53 am
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I've tried two different guitar cords, and three guitars. No difference. No difference which input jacks I use, either.


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