ampeg V4 voltage question

[methodofcontrol]

was just doing some preventative maintenance on my early 70's V4. i replaced the dropping resistors (R51, R52, R53, R55 among others)
anyway...my work is neat and i put in all correct values, but to be safe when i was finished i turned the amp on w/out any tubes and checked out the voltages at points A, B, C, D and E.
A is supposed to be 545v, i measured 540v so i figured i was off to good start. B is supposed to be 535v, i measured 538v. (usable but not in sync w/ the previous voltage)
now at points C, D and E the voltages get dropped WAY down to 400v, 360v and 325v (respectively). all of these were measuring around 540v which made me start wondering about the quality of components i just installed. so i turned on my ohm meter and tried measuring the dropping resistors in circuit w/ the amp still on, all of them measured 0 ohms. no wonder my voltages didn't drop at all!
once i turned the amp off i remeasured the resistance of said resistors and everything checked out OK.
now the question is....should i be checking this out w/ my tubes installed, i don't want to blow anything up.
also i kept hearing a really subtle noise coming from my can cap in the C17 position. (although i recapped the amp w/ some caps tucked inside the chasis, so i think specifically i'm talking about the cap between D5 and point C in the amp.)

so....does this sound normal at all w/ the voltages given the amp has no tubes in it?
either way...does that mean the noise i was hearing from the cap was the 540v slowly cooking the 500v-rated-cap?
i don't want to explode my tubes or amp w/ excessive voltage. so i'd like some clarity if anyone's got some.

[Enzo]

VOltage readings in a tube amp without tubes are mostly meaningless. You made a couple errors.

First, you ran into Ohm's Law. The voltage across a resistor is directly proportional to the current through it. Since there are no tubes in the amp, there is very little to cause current to flow - nothing draws current. No current through a resistor means no voltage drop across it. So the voltage at one end will be the same as the voltage at the other end. SLight differences are due to the resistance of your meter itself, and also leakage currents in the filter caps.

When you install the tubes, current will flow, and there will be voltage drops through the resistors. FOr example if a couple 12AX7s draw a total of 5ma and their B+ is coming through a 4700 ohm resistor, then there wil be a 23.5 volt drop across that resistor. ( V = I x R )

Next thing you did was try to make a resistance reading with an ohm meter in a live circuit. The ohm meter works by sending a tiny current through the probes and measuring the voltage difference between them. It is the same Ohm's Law again. The tiny leakage currents and what all in the live circuit interfere with the meter, so you get funny readings. SHorted resistors would be an extremely rare phenomenon. You could just as easily gotten infinite readings, or a "negative resistance" indication.

I don't know what the noise was, but it shouldn't be there. Please install your tubes and take real readings. The voltages will drop into place and you can test the circuit properly.

[methodofcontrol]

thanks for the help enzo!
i put the tubes in and, "viola!", everything is as it should be.

i have an unrelated V4 question for anyone who happens to have one they can check out for me...
my V4 is an early 70's, but i when i got it, it was a wreck. two years later i've tracked down every part i was missing and now i have a whole functioning amp.
however, my top panel and reverb tank came from a post '76 model. and they used different reverb tanks at that point. so i have a ground/hum issue when i use the reverb. the tank i have is stamped 4FB2D1C which is code for all of the specs of this particular tank. if you go to accutronicsreverb.com/prodspec and scroll down past the pics you'll see how to demystify the reverb pan numbers.
anyway...if anyone has an early 70's V4, i would love to know what the code on your reverb pan is.
better yet....if anyone has an early 70's reverb pan for sale..let me know!

[J Martin]

I checked a customer's V4 in my shop and it has the same number tank that you have.

[methodofcontrol]

hey j martin,
thanks for the info! are you sure the V4 in your shop is from before '76?
if so, that's all i need! thanks!

[J Martin]

I don't know the year, but its an early one with the blue control lettering. Should be the same build as yours.