Voltage check on A4,5,9, B7,8 reads 194V. Problem? [solved]

[geekosphere101]

Hello fine people. Just finished first crack build with my dad. Running checks on it before attempting speedball. Resistance checks were all in range.

Voltage checks were in range until A4, A5, A9, B7, and B8, which all read 194V, instead of 0. The tubes glow as they should.

After looking at the schematic, those terminals are part of the tube heating elements, correct?

We were double checking everything and noticed we had a wire different than the picture. It was the 5/6/10 revision that wired terminal 4 on the transformer to 14U instead of 22L. Would this revision have an effect on the voltages of these tube terminals?

My dad isn't sure we should be worried about these readings. But we're not taking any chances.

Do I have a problem?

Greatly appreciate help!

[geekosphere101]

nevermind, accidentally wen to 15U instead of 14U on that terminal 4 wire.

I will fix it and update if we have any other problems. Sorry!

[Grainger49]

The heater voltages are all AC.  Did you change your meter to read AC instead of DC? 

If they are out of range reading AC volts, post the out of range voltages.

[geekosphere101]

My initial issue was fixed as described and the Crack measured correctly and ran fine for an hour.

Now I completed the speedball upgrade, all voltages check out EXCEPT

T1 60


which is a little low, but I wasn't worried.

Plugged it in to source and I have a hum that goes away when the pot is turned off 0%, but comes back when I turn it back down to 0%. anything above 'off' is buzz free and plays music.

[Paul Birkeland]

What do you get with no source plugged in?

[geekosphere101]

Correction, the buzz is only in the 0% position of the volume pot. When I turn it up a little, I get a crack 'bzzt' and then no sound (at about 1 or 2% vlolume) then above that, music plays fine, buzz free. The buzz only occurs at the 0% position on the volume pot.

[geekosphere101]

What do you get with no source plugged in?

with no source, i get the same behavior, buzz at 0%, a crack when 1-2%, then no noise the rest of the way up to about 90%-100%, where a very feint buzz ( more quiet than the 0% buzz). This buzz at high volume is well above listening levels.

[Paul Birkeland]

Is the buzz in both channels?

[geekosphere101]

Is the buzz in both channels?

Yes, it is, both with input connected and disconnected.

[Paul Birkeland]

What resistance do you get across the RCA jacks when the volume control is all the way down?

[geekosphere101]

What resistance do you get across the RCA jacks when the volume control is all the way down?

107k on left, 100k on right.

[Paul Birkeland]

Sorry, I was thinking one thing and writing another...

How are the resistances between ground and the middle pot lugs with the level control all the way down?

[geekosphere101]

Both lugs are 0. I found another thread with this issue, in which Doc said

This probably means that either the wiper in the pot is lifting at the bottom end of its travel or there is an intermittent connection to one of the ground lugs of the pot.

I will trace the ground and see if there are any issues.

[geekosphere101]

After tracing the ground and checking all resistances according to Grainger49's guide, all measurements were 0 or near 0 as they should be. Could it be a faulty pot? What else can I check?

The thing sounds amazing, my workaround now is to not bring the volume to the absolute 0% position, but if I forget, that buzz is annoying, but should I be worried about it, considering everything measures correctly, except for the T1 voltage, which is  low at 60V. 

[Paul Joppa]

A resistor from the wiper to ground would probably solve the roblem by giving the grid a ground path when the wiper lifts. I imagine anything 100K to 500K will work well; I'd pick 220K (the geometric mean) myself.