#183 B+ Voltages

[Jhyatt2012]

Is there a chart for the #183 with the B+ voltages and what they should be? I'm including a reverb and internal loop and I'd also like to know what the B+ voltages for those would be. Anyone know where I would look or where I would find these values?

[ToneMerc]

See the #183 layout in the "Files" section.

TM

[Jhyatt2012]

I don't see anything on the layout or the schematic about what the B+ voltages should be. I've run an LSpice simulation based on the schematic and from the simulation am getting:

B+3 = 460
B+4 = 440
B+5 = 439

Am I close?

[vibratoking]

Like ToneMerc said...look on the layout. It's there.

[Jhyatt2012]

Thanks, guys I appreciate your help. Looking at the layout I'm seeing B+ as 465.

I also see "Voltages after screen resistors 463VDC". A note about the "Bias was set to 30.3mA@465.5 DC plate voltage".

302V, 307V and 58V to pins 1, 6 and 3 on V3.
207V, 1.67V, 204V and 1.78V on pins 1, 3, 6 and 8 on V2.
206V, 1.51V, 207V and 1.67V on pins 1, 3, 6 and 8 of V1.

Other than that I don't see anything else about the voltages for B+3, B+4 or B+5. Is it the way I'm looking at the layout or should one of these be read as B+ voltages?

[vibratoking]

I also see "Voltages after screen resistors 463VDC". A note about the "Bias was set to 30.3mA@465.5 DC plate voltage".

302V, 307V and 58V to pins 1, 6 and 3 on V3.
207V, 1.67V, 204V and 1.78V on pins 1, 3, 6 and 8 on V2.
206V, 1.51V, 207V and 1.67V on pins 1, 3, 6 and 8 of V1.

Other than that I don't see anything else about the voltages for B+3, B+4 or B+5. Is it the way I'm looking at the layout or should one of these be read as B+ voltages?

It takes a little thought and calculations on your part to find the voltage at every node. For instance, the current through the triode with 1.67V on V1-pin 3 can be calculated as 1.67/2.2k = 759uA. So B4 is about 207V + 759u*150k = 320V. This will get you a good approximation with errors due to component tolerance, etc...

[Jhyatt2012]

I think I see, thanks.

[Structo]

Also different tubes of the same designation (12ax7) will draw different current amounts, thus the voltage will differ as well.

Once you get the amp going, don't change any voltages (unless dangerously high) until you have rolled some tubes through the sockets and checked voltages and tone.

In fact I'm sure a lot of us are guilty of making changes too soon in the life of a new amp.
Best advice is to get stable voltages and play the amp for a few hours to let things settle in.