70s Ampeg V4B Blows Fuses

[The Dude]

Let me rephrase. One end of C16 shows 2.0 the other end reads OL. Unable to get any other reading except OL at 200 or 600VAC.

If you are getting voltage on one side of the cap that is out of meter range (regardless of what it is) and only 2V on the other side, the cap is bad. Replace it.

Edit- and for clarification: Assuming we are talking about this cap:

[ca7922303]

I should have not posted the title Blows Fuses. I have not had it blow a fuse yet. Guy I got it from told me it blows fuses and in my hurry to get advice on this amp, I prematurely posted it that way. But no, it does not blow fuses, tubes in or out.

[Enzo]

At this point, just to clarify where we are, am I correct that we have basically established that the amp does not blow fuses until the tubes are installed?

Also, crappy filter caps can drop bias voltage severely, it generally results in low bias, not completely absent bias. meaning even after replacing the filter caps, you may have an open rectifier diode or a resistor, or just a broken connection.

[tboy]

About the can I read schematics question, I would say very basic ability, but how bout someone pose me two questions, one easy and one harder about schematic reading and I guess you would have a more accurate answer?

The question that needs to be answered is if you can look at the actual circuitry present in your particular amplifier and determine whether it matches what is shown in the posted schematic. Is the C16 present on your circuit board performing the same function as the C16 shown in the schematic?

[ca7922303]

I appreciate the help. I'll get them ordered.

[Leo_Gnardo]

About the can I read schematics question, I would say very basic ability, but how bout someone pose me two questions, one easy and one harder about schematic reading and I guess you would have a more accurate answer?

Let's put aside the schematic challenge, and get those 3 cheap caps in the bias department changed out, OK?

DO make sure you install the electrolytics with proper polarity. Heck, even I goof that up on occasion.

[ca7922303]

About the can I read schematics question, I would say very basic ability, but how bout someone pose me two questions, one easy and one harder about schematic reading and I guess you would have a more accurate answer?

[Leo_Gnardo]

C16, cheap enough to replace, also absolutely vital to the bias supply. Without which your amp is toast. Sling another one in there and see whether your bias supply revives. I have seen these fail, so cannot rule out that yours might be kaput.

At this late date - 50 or so years on - it's time to replace the two 10 uF bias filters as well. All 3 caps might set you back $5. Not including shipping of course.

Analysis is paralysis. Do the above & let's see whether that bias department comes back to life.

[vintagekiki]

Are you able to read schematics?

Real question

[ca7922303]

Let me rephrase. One end of C16 shows 2.0 the other end reads OL. Unable to get any other reading except OL at 200 or 600VAC.

[g1]

C16 on the schematic I posted earlier does not have a + or -, it is non-polarized.
That means either you are looking at the wrong board, or the schematic does not match your unit. Are you able to read schematics?

[ca7922303]

2.0 on the positive end of c16, OL on the negative end of C16. Unable to get any reading any different than OL on negative end on higher range. Used 200 then went to 600.

[vintagekiki]

Please be more specific with your comments.. Not sure what you are responding to here, or what these numbers mean. If they are response to post #32, you must not be on AC range as AC does not have + or -. And if you get an OL indication, please try the next higher range til you get a number. And specify which range it was on.

Welcome to the machine

[g1]

2.0(+), OL(-)

Please be more specific with your comments.. Not sure what you are responding to here, or what these numbers mean. If they are response to post #32, you must not be on AC range as AC does not have + or -. And if you get an OL indication, please try the next higher range til you get a number. And specify which range it was on.

[ca7922303]

2.0(+), OL(-)