Help! Bad Speedball Voltages

[castelletti]

Here are a list of the out of spec voltages.  I listed them with my measurements first and then what it should read in parentheses

1 90 (75)  

5 107 (75)  

9 123 (100)

A1 104 (75)

A6 87 (75)

B1 87.7 (75)

B4 102.9 (75)

B6 121.8 (100)

B7 5.8 (0)

Any help would be greatly appreciated.  Everything was in spec as far as i can remember before I installed the Speedball and really sounded great through the HD600.

All LED's are lit up but the ones on the smaller boards are somewhat dimmer than the rest.

 

[castelletti]

for the life of me i cannot figure out why i am getting a 5.8v at B7 when it's supposed to be grounded.  i went back and resoldered everything and im still getting the same funny readings.

 

[Paul Joppa]

At B7 you should have 6.3vAC and zero net DC. Many meters give funny numbers when reading DC voltage on the AC scale, or AC voltage on the DC scale. B8 is grounded, not B7.

Assuming the heater voltage is 6.3vAC, I would guess that your 12AU7 is getting weak. It's quite possible that the amp still works fine.

 

[castelletti]

hmmm.... ok  well i havent  plugged in the heaphones since i did the speedball upgrade because the specs were wacky.  ive only had the kit a couple days up and running.  i appreciate you taking the time to look into it.

 

[Laudanum]

Catelletti, I assume you are using an autoranging meter.  Like Paul mentions, they can read funny when measuring for DC voltage on some thing that carries AC.  I had a meter that did the same thing so it would autorange to the millivolt scale and show a small DC voltage (in millivolts) and I had to be careful to check what scale it was measuring in.  So if you can override the autoranging on your DMM and manually set the range to DC volts you can try measuring B7 again and might find you actually have no DC voltage there.  I dont have the Speedball upgrade myself.

 

[castelletti]

Thanks, I'll have to borrow my neighbors meter.  Any  ideas as to why the other readings are so high? 

 

[Grainger49]

Without looking at the schematic which is upstairs, high voltages usually mean that the tube is not turning on.  Since the tube, the plate resistor and the cathode resistor do not "drop" any voltage the power supply voltage appears above and below the plate resistor.  The cathode and the attached resistor usually have no voltage on them.

Often the cathode connections are the cause of this problem.  Rewetting those solder connections is easy and might do the trick.

 

[Doc B]

Can you measure B3 and B8?

 

[castelletti]

Unfortunately, I'm up in Long Beach today but I'll post them up tonight when I get home.

 

[castelletti]

B3 reads 109
B6 reads 121.8
B8 reads 0

 

[castelletti]

So after tearing my hair out trying to diagnose this thing and coming up empty, I had the bright idea to roll another tube. 

I took measurements once again before I switched to the new tube and came up with the same frustrating numbers.  Plugged in a new tube and VOILA!!!  Perfectly in spec!

So happy now!  Time to go fire it up and give a listen!

Thanks everyone for your help!

 

[Grainger49]

Don't feel rained on.  Swapping tubes from channel to channel is one of the first suggestions but Crack doesn't lend itself to that.  So we all jump to a bad solder joint.  You won't believe how many problems are solder joints and tubes.