Going through my revibe now. Wonder about ecap voltages.

[Mike_J]

Going through my revibe and noticed the B+ and screen ecaps are 100uF @ 350VDC but the reverb and vibrato circuitry have 500VDC caps and that is after they have gone through dropping resistors. Guess is the 47uF caps on hand were 500V so that was what was put on the schematic.


My reason for asking this is it is time to replace the ecaps in this unit and I have 47uF @ 350VDC radial ecaps but none in the 500VDC range. Can't think of any logical reason not to use the 350s. If these are not suitable then the B+ and screen caps should be upgraded to at least 500VDC.


Suggestions would be greatly appreciated.


Thanks
Mike

[acheld]

Not having the schematic in front of me limits my response, but my guess is that there is sufficient margin in your caps.   And if it is truly working well, I think the increased margin for failure (of the new caps) is less than the potential downside of a) new, untested parts, and b) mucking about in a working circuit.

I'm not saying you're mucking about, but any time anyone works on a circuit there is a chance of screwing it up.  It's happened to all of us here, except sluckey.  And maybe shooter.

If it ain't broke, don't fix it.

 

[Mike_J]

Not having the schematic in front of me limits my response, but my guess is that there is sufficient margin in your caps.   And if it is truly working well, I think the increased margin for failure (of the new caps) is less than the potential downside of a) new, untested parts, and b) mucking about in a working circuit.

I'm not saying you're mucking about, but any time anyone works on a circuit there is a chance of screwing it up.  It's happened to all of us here, except sluckey.  And maybe shooter.

If it ain't broke, don't fix it.

[/c]

I think the answer is to hook power to the PT. Run it through the 1000v - 3 amp bridge diode and see what voltage

comes out. Doubt it will be significantly more than that, certainly after going through a drop down resistor.

[Bieworm]

Why not parallel 2x 22uf 350V? That gives you 700V rating combined.

[Mike_J]

Why not parallel 2x 22uf 350V? That gives you 700V rating combined.

I may be wrong but if I remember correctly I think when you parallel them it gives you twice the uF rating but doesn't change the voltage rating. I gave that some thought with two 22uF/500v which I have plenty of. If you run two caps in series then the voltage is doubled. Could take two 100uf/350v in series and end up with 50uF/700v but don't think it is necessary and there isn't a lot of room on the board for doubling up caps. My guess is they had more 47uF/500v caps to sell than 47uF/350v. Could be wrong but I doubt it.


Got an answer to how much voltage is coming out of the bridge diode which is 276VDC with 125VAC coming out of the wall outlet. Didn't see any voltage doubler circuitry in there so I am going to presume the voltage would probably be less going into the reverb and vibrato circuitry since the 276VDC is being passed through drop down resistors in both cases. Going with the 350VDC caps because I really don't see much risk in it. If the board had a lot of room on it I might increase the voltage of the B+ and screen voltage caps to 500VDC but would need to order and wait on them and I don't see the necessity for doing so.


What I am going to need to figure out is how to install a 220k resistor to bleed voltage out of the system when the power is shut down. Probably just run the resistor from positive to negative on the B+ ecap is my guess. Will have to look that one up unless someone comes up with an answer before I get around to doing that.


Thanks
Mike

[Bieworm]

Why not parallel 2x 22uf 350V? That gives you 700V rating combined.

I may be wrong but if I remember correctly I think when you parallel them it gives you twice the uF rating but doesn't change the voltage rating. I gave that some thought with two 22uF/500v which I have plenty of. If you run two caps in series then the voltage is doubled. Could take two 100uf/350v in series and end up with 50uF/700v but don't think it is necessary and there isn't a lot of room on the board for doubling up caps. My guess is they had more 47uF/500v caps to sell than 47uF/350v. Could be wrong but I doubt it.


Got an answer to how much voltage is coming out of the bridge diode which is 276VDC with 125VAC coming out of the wall outlet. Didn't see any voltage doubler circuitry in there so I am going to presume the voltage would probably be less going into the reverb and vibrato circuitry since the 276VDC is being passed through drop down resistors in both cases. Going with the 350VDC caps because I really don't see much risk in it. If the board had a lot of room on it I might increase the voltage of the B+ and screen voltage caps to 500VDC but would need to order and wait on them and I don't see the necessity for doing so.


What I am going to need to figure out is how to install a 220k resistor to bleed voltage out of the system when the power is shut down. Probably just run the resistor from positive to negative on the B+ ecap is my guess. Will have to look that one up unless someone comes up with an answer before I get around to doing that.


Thanks
Mike

Owww... my mistake. Been parallelling caps lately for testing and tweaks.  That's why I said that 😀

[d95err]

Going through my revibe and noticed the B+ and screen ecaps are 100uF @ 350VDC but the reverb and vibrato circuitry have 500VDC caps and that is after they have gone through dropping resistors. Guess is the 47uF caps on hand were 500V so that was what was put on the schematic.

My reason for asking this is it is time to replace the ecaps in this unit and I have 47uF @ 350VDC radial ecaps but none in the 500VDC range. Can't think of any logical reason not to use the 350s. If these are not suitable then the B+ and screen caps should be upgraded to at least 500VDC.

Have you measured the actual B+ voltage at the 350V caps?

I guess, if the 350V caps have survived long enough to warrant replacement as part of general pre-emptive maintenance (rather than failure), that's pretty good evidence 350V will be sufficient for another cap lifetime.

[Mike_J]

Going through my revibe and noticed the B+ and screen ecaps are 100uF @ 350VDC but the reverb and vibrato circuitry have 500VDC caps and that is after they have gone through dropping resistors. Guess is the 47uF caps on hand were 500V so that was what was put on the schematic.

My reason for asking this is it is time to replace the ecaps in this unit and I have 47uF @ 350VDC radial ecaps but none in the 500VDC range. Can't think of any logical reason not to use the 350s. If these are not suitable then the B+ and screen caps should be upgraded to at least 500VDC.

Have you measured the actual B+ voltage at the 350V caps?

I guess, if the 350V caps have survived long enough to warrant replacement as part of general pre-emptive maintenance (rather than failure), that's pretty good evidence 350V will be sufficient for another cap lifetime.

Voltage to B+ is 276VDC as I measured it. I agree if 350 volts was not acceptable the place to upgrade to a higher voltage would be at B+ and the screen but I don't see a need for that. I just think they had 500 volt parts so that is how they documented it. I will use 20uF/500v caps on this and if I drew a schematic of how I made the amp it would show that value even though it wasn't necessary but was what I had that I could readily get my hands on.


Thanks
Mike