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Posted: Thu Sep 09, 2010 2:20 pm
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Just ordered one of these as recommended on TGP:

http://www.amp-head.com/product_info.ph ... ucts_id=70

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Posted: Thu Sep 09, 2010 2:58 pm
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That's the one I use, Bill.

You'll have every conceivable base covered -- Fender, Marshall, Vox, Ampeg, Sunn, Traynor......anybody's who's ever made and sold amps going back to when Tommy Edison taught Leo about electricity.

:mrgreen:

Smart move!

Arjay

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Posted: Thu Sep 09, 2010 3:14 pm
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Retroverbial wrote:
That's the one I use, Bill.

You'll have every conceivable base covered -- Fender, Marshall, Vox, Ampeg, Sunn, Traynor......anybody's who's ever made and sold amps going back to when Tommy Edison taught Leo about electricity.

:mrgreen:

Smart move!

Arjay


Thanks.

My main worry with using one of these has been breaking a tube. Guess that's minor compared to the alternative. :shock:

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Posted: Thu Sep 09, 2010 3:18 pm
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I have every confidence in your abilities.

And as for getting "bit" the other night, there isn't anyone among the amp junkie crowd here who hasn't felt a few volts now and then.

You'll be fine, trust me.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Posted: Thu Sep 09, 2010 3:49 pm
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Retroverbial wrote:
...there isn't anyone among the amp junkie crowd here who hasn't felt a few volts now and then.

You'll be fine, trust me.

Arjay


:lol: Absolutely! I used to work for a guy many years ago who would tell us, after we were shocked or flashed, "A good technician ought to be able to choke down 440." :lol: At least you didn't burn/blow anything serious......like my meter lead, ahem, errr... I mean your meter lead. :wink:

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Posted: Thu Sep 09, 2010 5:00 pm
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Thanks, guys.

I worry too much sometimes.

The first (and only other) time I got bit was in college, many years ago. I was working on one of our dorm's wanna be rockstar's BF Twin Reverb. I accidently touched the B+ supply. It knocked me off my stool and into the wall behind me. ICs were just coming into vogue at that time, and I swore I would never touch anything greater than 12 volts! :lol:

Years later, I was on board a Navy destroyer (as a contractor) and watched an old Chief test the klystron high voltage supply of the ship's radar by tapping the output with his finger! Sparks flew everywhere as he laughed and told me he did this all the time. :shock:

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Posted: Thu Sep 09, 2010 9:32 pm
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Bill, I bought the Weber bias probe two yrs ago, because I'm 61 and my hands and eyes are not what they used to be. I always used the trans shunt method to measure the current. But after a few sparks and a few blown meter fuses, I decided it was time to trust their 1ohm resistors and circuit. To be honest, I've gone back a few times to check the probe readings against a meter. And they were very close, close enough for guitar amps. Art

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Posted: Thu Sep 09, 2010 10:02 pm
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aclempoppi wrote:
Bill, I bought the Weber bias probe two yrs ago, because I'm 61 and my hands and eyes are not what they used to be. I always used the trans shunt method to measure the current. But after a few sparks and a few blown meter fuses, I decided it was time to trust their 1ohm resistors and circuit. To be honest, I've gone back a few times to check the probe readings against a meter. And they were very close, close enough for guitar amps. Art


I'm 56 and my eyesight is perfect and my hands steady as a rock.




















For a 90 year old caught in an avalanche. :lol:

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Posted: Thu Sep 09, 2010 10:16 pm
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Well I opened up the amp again tonight for a final checkup.

1. Discharged the caps.
2. Checked all surrounding traces and components associated with the plate and heater power supplies. Everything looked fine.
3. Using a plastic scraper, I poked around pins 2 and 3 of V5. Nothing was loose and no more carbon came up.
4. Dipped my electric toothbrush in a little alcohol and polished up the area around the two pins. This pretty well cleaned up any remaining carbon traces.
5. I checked the resistance between pins 2 and 3. It was greater than 1 meg-Ohm as I hoped.
6. Turned on power and measured all power supply voltages and bias. All were normal. In the process of checking my schematic for the amp, I discovered two test points about an inch away from the tubes which would have allowed me to measure plate voltage with no problem and would have prevented this incident from occuring. Oh, well. Live and learn.
7. I plugged in my guitar and played for a couple of hours. The amp sounded great. Wish I could say the same for my playing. :lol:

All in all, it looks like I did dodge a bullet and the amp suffered no damage beyond a tiny square of toasted PCB. I don't plan on opening it up again until the bias probe I ordered shows up next week. Until then I will play the hell out of the amp and keep a close eye out for any hidden problems. Thanks for everyone's suggestions and words of encouragement.

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Posted: Thu Sep 09, 2010 10:52 pm
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Sounds solid, Bill.

Rawk on!

Arjay

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Posted: Fri Sep 10, 2010 7:51 am
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Retroverbial wrote:
Sounds solid, Bill.

Rawk on!

Arjay


You can count on it. :lol:

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Posted: Fri Sep 17, 2010 10:11 am
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My new bias probe ( http://www.amp-head.com/product_info.ph ... ucts_id=70 ) arrived yesterday and I got to work setting up my amp with it last night. It works great and was well worth the money. As it looks at both tubes individually (even though the bias adjustment is common to both tubes), I found that my two output tubes are balanced within 1.5 mA of each other and the plate voltages are within 2 volts of each other. I used it to set the bias to an average of 35 mA per tube at about 408 volts plate voltage (I don't remember the exact value. It may have been 410). Interestingly enough, the measurement at the Fender bias test point showed about 80 mV. The amp sounds great. :D

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Posted: Fri Sep 17, 2010 12:24 pm
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You do a great job 1.5 ma between tube are very good . You can go to 8 ma.between tubes
35 ma is great if you like the soud, this bias is cold; Long tube life.
You can go up to 43 ma, average bias , safe too.
Try it any ma between 35 and 44 keep the best sound. 35 ma could be thin and 45 warmer.

About the 80 mv or any mv this is no usefull for you. The most important is the ma.


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Posted: Fri Sep 17, 2010 12:52 pm
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stratele52 wrote:
You do a great job 1.5 ma between tube are very good . You can go to 8 ma.between tubes
35 ma is great if you like the soud, this bias is cold; Long tube life.
You can go up to 43 ma, average bias , safe too.
Try it any ma between 35 and 44 keep the best sound. 35 ma could be thin and 45 warmer.

About the 80 mv or any mv this is no usefull for you. The most important is the ma.


I listed the reading at the Fender test point for comparison purposes with my original post.

I actually like the sound at 35 mA. The JJ tubes go a long way toward warmiing things up even with a cold setting. I might try going a little higher after I listen to things awhile, but I prefer to keep the amp sounding clean and using my modded Blues Driver for dirt.

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Posted: Fri Sep 17, 2010 1:26 pm
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Yes, I agreed with you if you like the sound.

have good time with your amp


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