Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on September 01, 2011, 10:58:50 am

Title: voltages on a schematic
Post by: dude on September 01, 2011, 10:58:50 am

When voltages are posted on a schematic are they with or without tubes.

I know maybe a stupid question, without tubes some points won't have voltage.

al

Title: Re: voltages on a schematic
Post by: jjasilli on September 01, 2011, 11:05:19 am

Schematic voltages are stated with tubes in = loaded.  This is true generally -- that voltage is stated under load. 

Title: Re: voltages on a schematic
Post by: stingray_65 on September 01, 2011, 02:52:08 pm

By load JJasilli means tubes in sockets, NOT under load with a signal present.

Always have a speaker or dummy load plugged in also.

While it would not hurt if no signal was present to not have a speaker installed, there is a chance that oscillation may occur, then send a signal through the amp and the OT will likely suffer.

I was often confused myself until I asked.

Ray

PS, Don't forget, you got a + or - 20% tolerance on those stated values. eg. if the schemo states 100V, 80 to 120 V is acceptable.

The only place I REALLY try to keep dead center is the 6.3V heater supply.

Title: Re: voltages on a schematic
Post by: stratele52 on September 01, 2011, 02:58:19 pm

Yes with all tubes AND proper bias. No signal at the input . Voltage can vary to 10 %.

A colder bias will gave you more voltage specialy at the output tubes plate and center tap of power transformer / power supply. A very very hot bias = lower voltage.