Robinette JCM 800 Bias Problem

[B-Rex]

Happy Sunday all! I hope I have a simple mistake that someone can spot. I am doing startup routines on a Robinette JCM 800 6V6/6L6 and I got to the point of putting the preamp tubes in and checking bias voltage. My 50V Bias from the PT is fine to the 470k 2W resistor doing fine then into the diode and all I am getting on the anode side is -2? I have tested the 470k resistor, the diode, the 50uF100V cap and all read good. I am including the Robinette bias schematic and layout along with pictures and diagrams to clarify the pictures. I hope someone sees the answer and thanks to anyone looking ahead of time. Please let me know anything I can clarify.

[AlNewman]

I don't see a 470k in the schematic, I see a 470R.
I do see a 470k in your picture.

[tubeswell]

Rookie mistake


When you’re starting out it pays to have your multimeter handy to check component values before installing them

[B-Rex]

Your right and I am a rookie. This is my first build and probably way over my head considering the closest thing I have done is make guitars. I did have a multimeter handy and checked all the values before putting them in. I assumed this was to be 470k but if it is supposed to be something 470Ohm or something else can you throw in an answer with whatever insult is neccessary?

[Willabe]

The layout drawings and the schematic all show 470 ohms.

Not 470K ohms/470,000 ohms.

[B-Rex]

Thank you very much, I appreciate the help!

[tubeswell]

470 next to a resistor on a schematic is means 470 Ohms

470k = 470 kilo ohms

470M = 470 Mega Ohms (which you would never see on a guitar amp schematic, 10M tops, mostly 1M, 2M2, 3M3, 4M7 or 5M , which are other ways of saying 1Meg, 2.2Meg, 3.3Meg and so on. Conversely 4k7 = 4.7k etc for kilo ohm notation)


No hard feelings- It’s okay to be a rookie. I was one once upon a time ;-)

[tubeswell]

Another clue, which you might have noticed in other schematics - sometimes the bias supply input resistor is actually in the kilo-0hm range, but this is when the bias supply is taken directly from the high tension winding and you need to loose 300V or so (as is the case for the BF Princeton Reverb where a 100k resistor is used). But when the bias winding/tap is only 50VAC or so, it'll usually be 470R.

[B-Rex]

Thanks for the input and everything helps with this crash course I'm on. Really looking forward to having an amp I can work on and look forward to playing. No more disposable amps.