Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on November 04, 2021, 05:03:11 pm
-
'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
(https://i.ibb.co/pnrJ2Pp/20211104-180337.jpg)
-
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
-
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
-
What does the 6.3V heater circuit measure? ie one probe to pin2, the other to pin7, of an output valve socket.
-
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):
(https://i.ibb.co/bK6HbZx/doghouse.jpg)
-
....I have the variac set at 117volts. ...
Set to 117V. What is is actually putting OUT?
-
....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!
(https://i.ibb.co/k5zgJtv/variac.jpg)
My wall is putting out 121 volts so i set the variac there and re-biased. i think everything is happy now. :laugh:
-
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.
-
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 :icon_biggrin:
-
Checked it with my Fluke. It's off by 1 volt. Not terribly inaccurate. But you helped me tremendously :icon_biggrin:
What's off by 1 volt? The 117V reading or the 130v reading???
-
Checked it with my Fluke. It's off by 1 volt. Not terribly inaccurate. But you helped me tremendously :icon_biggrin:
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
-
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 (https://el34world.com/Forum/index.php?topic=25028.0)
-
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!
-
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.
-
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.