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Author Topic: I could use a little more help  (Read 27267 times)
erwin_ve
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« Reply #15 on: August 30, 2009, 09:59:02 AM »
It's frustating when something doesn't work: please be as accurate as you can; all the measurement suggestions I gave you were for my concerns on the 441v on the v3 cathode.

Maybe it's handy for you to use a schematic like the #124; the topology is basiclly the same.
And please learn the basic amp talk language and understandings: if you're building something like this you HAVE to know what the 110k resistor is at the phase inverter(PI).

#124 is here:



Quote from: djroge1 on August 30, 2009, 01:43:13 AM
Ok after that spark I had to leave and go work out... frustration.

The HT fuse .5a fast blow is out and I don't have another one right now so I'll hit the store tomorrow.

I'll measure and look at all the suggestions in a bit.

Thank you guys for the encouragment and help... I know I can get thru this.
* dumble_124_schematic_172.pdf (83.06 KB - downloaded 364 times.)
« Last Edit: August 30, 2009, 10:03:04 AM by erwin_ve » Logged
bluesfendermanblues
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« Reply #16 on: August 30, 2009, 01:10:07 PM »
ditto
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Respect for the big guy's work....we're at this part of the forum because of HAD's amps.
djroge1
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« Reply #17 on: August 30, 2009, 07:31:09 PM »
Well you're right I should learn more. This is the 2nd amp I've built, the first was a single ended class A amp with one 12AX7, one 6L6, and one rectifier tube built and it wasn't a kit. But I'm learning now as I build.
« Last Edit: August 30, 2009, 07:33:02 PM by djroge1 » Logged
erwin_ve
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« Reply #18 on: August 30, 2009, 08:26:45 PM »
Quote from: djroge1 on August 30, 2009, 07:31:09 PM
Well you're right I should learn more. This is the 2nd amp I've built, the first was a single ended class A amp with one 12AX7, one 6L6, and one rectifier tube built and it wasn't a kit. But I'm learning now as I build.

Well sorry if I was a bit grumpy Embarrassed
But it's easier to help you out if we both talk the same language...

Maybe a good link is: http://www.valvewizard.co.uk
It sure helped me a lot to understand how tubes work.
http://en.wikipedia.org/wiki/12AX7 on the pin layout of a 12ax7.

I also did understand more of the schematics when somebody told me that a 12ax7 tube does have 2 triodes which appear apart from each other in a schematic(dUHH).

Maybe you already know this stuff, maybe others will benefit from it:
Plate is where the high voltage is. Pin1 and 6 on a 12ax7.
Grid is where the signal is coming in. Pin 2 and 7 on a 12ax7
Cathode is where current flows to plate when a incoming signal is applied at the grid. pin 3 and 8 on a 12ax7.
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djroge1
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« Reply #19 on: August 30, 2009, 08:49:41 PM »
Quote from: erwin_ve on August 30, 2009, 08:26:45 PM
Quote from: djroge1 on August 30, 2009, 07:31:09 PM
Well you're right I should learn more. This is the 2nd amp I've built, the first was a single ended class A amp with one 12AX7, one 6L6, and one rectifier tube built and it wasn't a kit. But I'm learning now as I build.

Well sorry if I was a bit grumpy Embarrassed
But it's easier to help you out if we both talk the same language...

Maybe a good link is: http://www.valvewizard.co.uk
It sure helped me a lot to understand how tubes work.
http://en.wikipedia.org/wiki/12AX7 on the pin layout of a 12ax7.

I also did understand more of the schematics when somebody told me that a 12ax7 tube does have 2 triodes which appear apart from each other in a schematic(dUHH).

Maybe you already know this stuff, maybe others will benefit from it:
Plate is where the high voltage is. Pin1 and 6 on a 12ax7.
Grid is where the signal is coming in. Pin 2 and 7 on a 12ax7
Cathode is where current flows to plate when a incoming signal is applied at the grid. pin 3 and 8 on a 12ax7.


I know some of the language, but obviously not enough. I'll check out those web sites. I have read The Guitar Amp Handbook by Dave Hunter and Dave Funk's Tube amp Workbook. Both have a lot of info, but perhaps I just didn't retain nearly enough.

Anyway, I have a new fuse in and all of the V readings are about where they were before.
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erwin_ve
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« Reply #20 on: August 30, 2009, 08:53:38 PM »
Ok! Did you measure the 22k resistor(is it really 22k with amp off)?(at the power supply dropping string)
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hywelg
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« Reply #21 on: August 30, 2009, 09:20:50 PM »
Quote from: djroge1 on August 29, 2009, 09:46:18 PM

The spark was where I had my probe. I think I may have made an arc - like when you weld to get the weld started?


OK you just might have been lucky  Wink Before you go again, get some heatshrink tubing and cover all but the last 6-8mm of the probe ends. If they have a little notch near the end cover just up to that. That might prevent this happening again. It happened to me once, the probe slipped but thankfully it didn't contact with anything.
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djroge1
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« Reply #22 on: August 31, 2009, 03:18:27 AM »
Quote from: erwin_ve on August 30, 2009, 08:53:38 PM
Ok! Did you measure the 22k resistor(is it really 22k with amp off)?(at the power supply dropping string)

It reads 20.6
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hywelg
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« Reply #23 on: August 31, 2009, 08:18:16 AM »
Can you go through the attached layout and read the voltages at the marked points? All DC. That should help pinpoint where your problem is

* V1V2Tests.png (229.56 KB, 1800x1309 - viewed 678 times.)
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djroge1
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« Reply #24 on: August 31, 2009, 10:18:58 PM »
I'll check those and post as soon as I get home from work. Thanks.
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djroge1
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« Reply #25 on: September 01, 2009, 12:46:33 AM »
OK here are those voltages

1. 437
2. 439
3. 379
4. 53
5. 53
6. 19
7. 10
8. 14
9. 33
10 37
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parrhasius
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« Reply #26 on: September 01, 2009, 03:07:04 AM »
What about that 22uF 450V electrolytic cap on the wall near the first tube - shouldn't that be the other way around?

Compare it to this photo from the Ceriatone web site:

http://www.ceriatone.com/images/completeAmpsPic/CTOvertone/board/Leftend2B.jpg

Phil
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djroge1
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« Reply #27 on: September 01, 2009, 03:58:14 AM »
Quote from: parrhasius on September 01, 2009, 03:07:04 AM
What about that 22uF 450V electrolytic cap on the wall near the first tube - shouldn't that be the other way around?

Compare it to this photo from the Ceriatone web site:

http://www.ceriatone.com/images/completeAmpsPic/CTOvertone/board/Leftend2B.jpg

Phil

Bingo! I bet that is a major problem and I don't have to look at your link I see it in the wire diagram.  Huh?  Shocked  Angry Embarrassed  Embarrassed  Embarrassed I can't believe I missed that. I'm going to turn that around and I'll post the results. Thanks.
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djroge1
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« Reply #28 on: September 01, 2009, 04:25:49 AM »
Still no sound from the input jack but the voltages are looking better. I hear a hum and I get a crackle when measuring V3.

V1:
Pin 1 - 152
pin 3 - 1.6
pin 6 - 172
pin 8 - 1.5

V2:
Pin 1 - 164
pin 3 - 1.8
pin 6 - 182
pin 8 - 1.5

V3:
Pin 1 - 285
pin 3 - 59
pin 6 - 273
pin 8 - 59

V4:
pin 3 - 450
pin 4 - 449
pin 5 - 37
pin 6 - 450

V5:
pin 3 - 450
pin 4 - 449
pin 5 - 37
pin 6 - 451
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parrhasius
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« Reply #29 on: September 01, 2009, 06:51:20 AM »
preamp plate voltages are still low - they should be around 200V.

What are the new voltages at points 5, 6, 7, 8, 9 & 10 on hywelg's layout?
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