#183 voltages

lionaird · Post by **lionaird** » Mon Mar 19, 2012 10:26 am

Ok, fired my #183 up today. Pilot light doesn't work (which should be an easy fix). And the EL34s seem to run too hot...

Measured some voltages without tubes:

B+ 513
B+3 499
B+4 419
B+5 412

V1
1: 404
2: 0
3: 0
4: heater
5: heater
6: 404
7: 0
8: 0
9: heater

V2
1: 410
2: 0
3: 0
4: heater
5: heater
6: 411
7: 0
8: 0
9: heater

V3
1: 494
2: 0
3: 0
4: heater
5: heater
6: 495
7: 0
8: 0
9: heater

V4
1: 0
2: heater
3: 512
4: 0
5: 34
6: 512
7: heater
8: 0

V5
1: 0
2: heater
3: 512
4: 0
5: 34
6: 512
7: heater
8: 0

V6
1: 0
2: heater
3: 513
4: 0
5: 34
6: 512
7: heater
8: 0

V6
1: 0
2: heater
3: 512
4: 0
5: 34
6: 511
7: heater
8: 0

Do those values make sense? Also, how do I measure bias current with my multimeter? For some reason, my bias meter doesn't seem to work...

jelle · Post by **jelle** » Mon Mar 19, 2012 10:30 am

Check your grounds, Also where are you located? Maybe a forum member can look at it for you,

But check your grounds before you fire it up again.

Got the correct fuses in there??

Good luck,

Jelle

lionaird · Post by **lionaird** » Mon Mar 19, 2012 10:38 am

jelle wrote:Check your grounds, Also where are you located? Maybe a forum member can look at it for you,

But check your grounds before you fire it up again.

Got the correct fuses in there??

Good luck,

Jelle

I was actually playing it for a few minutes before the EL34s were starting to get too hot and then switched if off. It actually sounded really good. I'm in Australia...

jelle · Post by **jelle** » Mon Mar 19, 2012 10:44 am

Whoops, I missed the 'without tubes' part of your post.

Ok, so the bias...do you have the 1 ohms resistors installed at the powertube cathodes to ground? If so, measure the current through those resistors as outlined here:

http://www.duncanamps.com/technical/lvbias.html

Many people like these guidelines for the target bias currents:

http://www.webervst.com/tubes1/calcbias.htm

And we have a few members in Oz too. They'll prob check in if asked for.

Have fun!

Jelle

lionaird · Post by **lionaird** » Mon Mar 19, 2012 10:49 am

jelle wrote:Whoops, I missed the 'without tubes' part of your post.

Ok, so the bias...do you have the 1 ohms resistors installed at the powertube cathodes to ground? If so, measure the current through those resistors as outlined here:

http://www.duncanamps.com/technical/lvbias.html

Many people like these guidelines for the target bias currents:

http://www.webervst.com/tubes1/calcbias.htm

Have fun!

Jelle

Thanks for the links. I will measure the voltages again after I've biased the EL34s...

butwhatif · Post by **butwhatif** » Mon Mar 19, 2012 1:39 pm

not much info here, bias and b+, nothin else

Structo · Post by **Structo** » Mon Mar 19, 2012 1:59 pm

You really have 400 volts on V1?

passfan · Post by **passfan** » Mon Mar 19, 2012 2:47 pm

Structo wrote:You really have 400 volts on V1?

Hasn't installed tubes yet.

lionaird · Post by **lionaird** » Tue Mar 20, 2012 8:21 am

It's weird. I can't get any mV reading across the 1 Ohm resistors whatsoever. That's probably why my bias meter only shows me B+ but not the mA. Got rid of the 1 Ohm resistors now. Not sure what the problem is. Might recheck all the wiring of the preamp tubes to make sure I didn't stuff anything up.

Here are the voltages with tubes

V1

1: 203V
2: 0V
3: 1.93V
6: 198.5V
7: 0V
8: 2.022V

V2

1: 153.2V
2: 0V
3: 2.362V
6: 168.8V
7: 0V
8: 2.672V

V3

1: 356V
2: 43V
3: 64.5V
6: 329V
7: 41V
8: 64.5V

V4/5/6/7

1: 0/0/0/0
3: 520/517/518/518
4: 8.48/4.57/14.95/15.4
5: - 46.3/-46.3/-45.5/-45.6
8: 0/0/0/0

B+ 519V
B3 490V
B4 348V
B5 338V

CHIP · Post by **CHIP** » Tue Mar 20, 2012 9:45 am

You should post some pictures.
V2 plates seem low.
V3 plates are usually closer in value to each other, and yours are higher than normal.
What Power transformer are you using?
I think your dropping string needs to be adjusted, but I can't understand V2 plates, Try a different 12ax7 in there, and see what you get there.
Pin 4 voltages on you power tubes seems suspect.

martin manning · Post by **martin manning** » Tue Mar 20, 2012 10:20 am

Looks like there is no screen supply (B+2) connected to the power tubes. That (pin 4) should have been up near the plate voltage (pin 3) without tubes installed. How are you using pin 6? Seems like you forgot to put the screen resistors from pin 6 to pin 4. Pictures!

lionaird · Post by **lionaird** » Tue Mar 20, 2012 10:28 am

Thanks guys. I'll check all the wiring tomorrow. I used Classic Tone trannies for the build: #40-18042 PT and #40-18013 OT...

lionaird · Post by **lionaird** » Thu Mar 22, 2012 12:45 am

Now, I checked all the wiring of the power tubes and it's correct. Looks like I will have to check the whole circuit on the weekend. Some pictures:

[img:764:1024]http://i638.photobucket.com/albums/uu10 ... d609f9.jpg[/img]
[img:764:1024]http://i638.photobucket.com/albums/uu10 ... a26d6f.jpg[/img]
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[img

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[img

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[img

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[img

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[img

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