Final Voltage Check

[Forte]

Hi,
Have just finished soldering my amp and am up to the final voltage check.

The manual states

"It should not climb higher than about 9 volts and should then drop to zero. If it climbs much higher and/or does not reduce to zero do not plug in headphones until you have worked out the issue and the voltage stays below 9V."

How much higher is much higher?  My amp climbs to 15V and the drops to 0V, is this too high?

All over check are fine, no voltages out by more than 10% and have triple checked all parts and connections and cannot see any errors.

 

[Doc B]

This is probably due to variations in the spec of the 6080. Sometimes they need to cook in a bit to settle to their nominal performance. Try letting the amp run with the volume turned down all the way and without headphones plugged in, for a couple of hours. Then turn it off and let it cool for maybe 15-20 minutes and do the test again.

 

[Paul Birkeland]

You may also have a meter with a very high refresh rate, and you are catching the peak better than we did when we wrote the manual.  The real key with that terminal is that the voltage spike is low and dissipates quickly.  If you measured there and found a constant 50v or something along those lines, it would be a good indicator that one or both of the 2.49k resistors were not hooked up properly.

 

[Forte]

  The real key with that terminal is that the voltage spike is low and dissipates quickly.  

Well I left it on for a few hours and retested and no difference, but after reaching 15V it drops to 0V in seconds so all seems good. Will give it a listen later.

Thanks for your reply's!

 

[tdogzthmn]

My turn for questions!

So I got the amp build and I went through the resistance check which looked good so I proceed to the voltage check where I ran into issues.  Each terminal designated to have a voltage of 90 or 170 caused my meter dial to peak out.  All the terminals which are supposed to be zero seemed fine as the meter did not move.  Any idea of where to start looking?  I did a brief lookover to see how it compared to photos.  Also looked for unsoldered parts and any obvious shorts.  I will do a more thorough inspection in the morning but wanted to ask anyway.

Thanks for the help,

Tom

 

[tdogzthmn]

I have one of the newer kits with the corrections.  The multimeter I am using is an older Leviton and is not digital.

 

[Doc B]

What scale is the meter set on?

 

[tdogzthmn]

I have the meter set to 500 DCV which is the highest setting in the DC range. 

 

[Grainger49]

Then there is something wrong.  I'll bet you guessed that.  It could be the meter, do you have a friend who has a newer meter?

I don't have the information on the Crack so I don't know it produces over 500V DC.  

Are you measuring to the ground or chassis?  

 

[tdogzthmn]

I am going to grab a digital meter from a friends to double check. I was doing my readings with the black lead clamped to terminal 12, the one listed in the manual. I give an update soon once I get the new meter and try it out.

 

[tdogzthmn]

I got the new digital meter and recheck the terminal readings.  These are the results.

Terminal

1  143.5
2  163.5
3  0.023
4  168
5  74
6  .03
7  148
8  0
9  99
10  0.00
11  0.012
12  0.00
13  170
14  0
15  193.5
19  91
20  -0.01

I found a bit of a loose connection on A1 so I am going to resolder but I did chack and the reading was not 90.  Hopefully someone might be able to know whats going on with these readings.  Thanks for the responses so far!

 

[Paul Birkeland]

A loose connection at A1 would explain most of this.  Voltage at terminal 1 is high because no current (well, very little) is being drawn through the plate loading resistor between terminals 1 and 2.  That plate voltage also sets the bias for one half of the 6080, so I'd expect things to fall into line when that connection is remedied.

After fixing your connection, is terminal 1 closer to 75v?  Did the voltage at terminal 7 come down a bit?  99 isn't so bad, but 148 is a problem.

 

[tdogzthmn]

I did a resolder on A1 and rechecked the Terminals but did not get any significant changes.  The terminals which have significant readings were: 1 (143.5), 7 (148), 19 (91), 20 (-0.01).

Here are the readings from the tube pins.  Also noted that only the LED on connection A3 was lit, the LED between A8 and the center was not.

A1  74
A2  0.0
A3  1.583
A4  -0.0
A5  -0.0
A6  148*
A7  0.01
A8  0.002*
A9  -0.001

B1  150*
B2  170
B3  149.2*
B4  74.2*
B5  170.2
B6  99.3
B7  -0.001
B8  -0.001

 

[Doc B]

Check to see if the LED at A8 was installed backwards or has a cold solder joint.

 

[tdogzthmn]

The LED was a bit loose and made sure the connection was correct (silver band facing the center pin as in the photos).  I added more solder and took new readings but I still have zero volts and A8.  Also should both lights be on or off?  Right now only one is lighting up.

 

[Paul Birkeland]

The LED not lighting will also screw up those voltages.  Can you set your meter to measure diodes and measure the LED in both directions?  Also, be sure the connection that ties pins 4 and 5 together is doing its job.  Something is amiss with the 12AU7 socket.

 

[tdogzthmn]

How can I tell if my multimeter can measure the diodes?  I have both an analogue and digital to use.  I checked connections A4 and A5 and made sure they were attached to the pins.  I took another reading of A8 and got 13.2.  While I was poking around A8 I noticed that the other light LED would sometimes go out.

 

[Paul Birkeland]

Resolder A4.  Also add some solder to all of the lower joints on the 9 pin terminal strip. 

 

[tdogzthmn]

I noticed when checking the voltages of terminals 4U and 5U, when I touch the red lead to the terminal the LED between A3 and the center pin with shut off.  The other LED still has not turned on.  I also when through the instructions once again to be sure the components were installed correctly.  I am still stumped as to why my voltage readings are off.

 

[ironbut]

It could just be the picture, but the solder joint on the center common ground looks a little iffy (maybe a cold joint?). I know when I'm soldering diodes with short leads, I get nervous about overheating 'em and sometimes pull the iron off the joint too soon.