AB763 high voltages help

[joesatch]

'93 Concert converted to FWB rectifier Super Reverb. I have the variac set at 117volts. Well getting some pretty high voltages. 

Have the (2) 6L6 tubes at 34ma.

As follows:
Plate  530V
Negative Bias -57.2v (at pin5)

B+ voltages:
A 534v
B 532v
C 518v
D 473v

[shooter]

A 533vB 530vC 530v

are the tubes installed?  there should be a 10's of volts volts difference
measure the VDC on the corresponding pre tube's Cathode's to verify current is flowing

[joesatch]

i updated voltages measured. i got one wrong. all the tubes are installed. no issues with the amp sounds good but these voltages are very high. I'm afraid if i take it off the variac something will blow.

v1 302v plate
v2 309v
v3 reverb driver
v4 315v
v5 515v
v6 348v

[pdf64]

What does the 6.3V heater circuit measure? ie one probe to pin2, the other to pin7, of an output valve socket.

[joesatch]

What does the 6.3V heater circuit measure? ie one probe to pin2, the other to pin7, of an output valve socket.

7.18 vac

Doghouse (B leads are soldered underneath):

[PRR]

....I have the variac set at 117volts. ...

Set to 117V. What is is actually putting OUT?

[joesatch]

....I have the variac set at 117volts. ...

Set to 117V. What is is actually putting OUT?

i think you're on to something my man. With the variac set at 117v it's actually putting out 130+ volts!



My wall is putting out 121 volts so i set the variac there and re-biased. i think everything is happy now. 

[PRR]

I don't trust those Watt-O-Kills half as far as I can throw them. *Carefully* use a proper meter.

But it does suggest that the "117V" was wrong.

[joesatch]

I don't trust those Watt-O-Kills half as far as I can throw them. *Carefully* use a proper meter.

But it does suggest that the "117V" was wrong.

Checked it with my Fluke. It's off by 1 volt. Not terribly inaccurate. But you helped me tremendously

[sluckey]

Checked it with my Fluke. It's off by 1 volt. Not terribly inaccurate. But you helped me tremendously

What's off by 1 volt? The 117V reading or the 130v reading???

[joesatch]

Checked it with my Fluke. It's off by 1 volt. Not terribly inaccurate. But you helped me tremendously

What's off by 1 volt? The 117V reading or the 130v reading???

The 130v reading from white box. It's actually 131v . The variac dial is way off, having it set to 117v is putting out 131v

[sluckey]

The variac dial is way off, having it set to 117v is putting out 131v

You may want to read this topic...  Add a meter to your variac

[joesatch]

i wasn't aware the variac had the ability to increase voltage.   I assumed the variac at full would equal the wall outlet direct. Thanks!

[sluckey]

i wasn't aware the variac had the ability to increase voltage.   I assumed the variac at full would equal the wall outlet direct. Thanks!

It's an auto transformer, not a rheostat. Mine will take the output up to 140VAC.

[PRR]

i wasn't aware the variac had the ability to increase voltage...

There's two ways to wire it. Boosting the line is a perfectly reasonable use; it may be why they were so popular in the 1940s.