VT-212 Carvin amp Rectifier diodes???

[DrGonz78]

So I have found an open diode on this Carvin VT-212, but I am not sure what part to use as a cross reference. The diode says CR-100 and it takes power from the power transformer into the preamp board. I think this part is obsolete and it is rather confusing looking at all the datasheets on this one to decide what it is exactly. Can anyone help point me in the right direction for a part replacement/specification? I have no service manual for this amp either so it makes working on it a bit of a challenge. Thanks for reading.

BTW: This is a 1979 amp just like the one on the Carvin website...

http://www.carvinmuseum.com/decade/i...comboamps.html

Actually the model says VTR 2800 and I did find the schematic just now.

http://www.carvinmuseum.com/pdf/amps/VTR-2800.pdf

[DrGonz78]

Still looking at this schematic I see exactly where it shows CR 100 Diodes X4. However, still very confused as to what these are exactly. I guess they are the bridge or may just regulators of some sort...?

[Enzo]

Plain old vanilla rectifiers, in this case for the B+ supply. Tube amps are all the same under the skin, this is not much differnt from a Fender Twin reverb. It makes about 500v for four 6L6s. In your amp we would look to see what those parts are wired to, the high voltage wires from the power transformer. SO if in doubt, whatever works in a Fender Twin Reverb ought to work here.


If your diodes are bad, replace them. I'd use the generic 1N4007 from my drawer, that's about as vanilla as it gets. Those 1N4007 are 1A 1000v diodes.

[Jazz P Bass]

Please keep in mind that the "CR" designation on the schematic is merely that.
It designates that that component is a diode/ rectifier.
Actually it stands (stood, passe as of the'90's) for 'crystal rectifier'.
Talk about a throw back term.
So if the actual diode part number is not listed on the schematic, then you must look at the actual diode.
There will be a number marked on it. (1Nxxxx)
As Enzo stated 1N4007 is a good high voltage/current rectifier.

[DrGonz78]

Thanks guys. I got exactly four 1N4007 as well in my left overs parts drawer too. Appreciate the the information and the back story too ->Jazz.

[J M Fahey]

You said.

So I have found an open diode on this Carvin VT-212, but I am not sure what part to use as a cross reference. The diode says CR-100 and it takes power from the power transformer into the preamp board.

If so,you are not referring to the +B (or +HV) rectifiers D3/4/5/6 but to either D1/2 which do exactly that.
They are the low voltage rectifiers for the preamp board, derived from the Bias tap.
Please clarify.
Anyway, what's the actual problem with your amp?
I think we should start there.

[DrGonz78]

The CR 100 diodes (x4) are on page 10 of the schematic and are connecting the B+ voltage line. I originally posted it was the preamp "Board" before I had the schematic, and I just called it that since there is a preamp tube on that board. The amp was cleaned up by my cousin a few years back and has very little amount of time on the amp. I basically would turn it on every once in a while to make sure it would still work. Now I decided to replace components that are very old. There was a 50v electrolytic cap that was wiggling free almost. I looked at these diodes and one was open. Right now I am really just inspecting all the caps (gonna replace since 30+ yrs old). The amp has already had some ground issues and now I can see why. My cousin made it sound much better and restored the amp aesthetically. Even then the amp probably needed more done to it.

The clean channel went out first so wanted to check some soldering in there... Which the soldering in this amp is nasty. So basically just trying to do some spring cleaning and check caps etc...

[DrGonz78]

So here is some more information on this amp... I have come across what is supposed to be a 220uf 50v capacitor that has been coupled by two caps. There are actually two caps, both 100uf 50v, connected negative to positive on each leg and fitted into place to be the other 220uf 50v. My question is are these caps coupled together using two 100uf 50v caps to make one 200uf 50v? Which would fit 10% tolerance that schematic allows for and makes sense if this is what is happening in this case. You can clearly see a missing spot where there once was a 220uf 50v cap and they soldered it right to a resistor that is in line w/ where that cap is located. Does this make any sense? I am gonna get rid of those caps and put a 220uf 50v back in there once my parts arrive...

Also, this picture shows the diodes that I had referenced in my original posting and can help pinpoint if I am right thinking they are the ones that are in the schematic as mentioned before. So maybe looking at this picture can help figure if they are the diodes that connect to B+ or are connected as rectifiers for the preamp. That does not seem to make sense to me that since D1 and D2 should have 1N4002 marked on them.

My cousin did some work on this amp and just thought to include his site where all the pics were for the original project. It is all pretty interesting and relevant to my current work on restoring more on this amp.

Prowess Amplifiers - Projects - Carvin VTR2800

[Dave Curtis, dB AudioTech]

The way you describe it, they are wired in series (connected negative to positive), which would make the capacitance 50uF, but would double the voltage rating to 100V. If they were paralleled they would add to 200uF (more plate area), and the voltage ratings wouldn't change. Are you sure they're not wired in parallel?

[J M Fahey]

connected negative to positive on each leg

What does this mean?
Not clear, please post a drawing.

[Dave Curtis, dB AudioTech]

I assumed series, but that may not be the case... the description is a bit vague.

[52 Bill]

I assumed series, but that may not be the case... the description is a bit vague.

If you look at the photo the two caps appear to be paralleled together on the board.

And yes DG78, the four diodes at the lower left side of the board are the main high voltage rectifiers. I suggest that you replace them all, rather than just the single open one.

And it appears that the preamp is all opamp, so if there is a tube on that board it's probably the driver tube.

Maybe it would help you to sit down with the amp and the schematic and try to match up the many elements that make up an amplifier. It would probably help you to better understand signal path, power supply and the other functional circuits.

[jrfrond]

Whenever I am in doubt, or just want to bomb-proof the rectifier circuit, I will use 1N5408, which is 1000V@3A.

[DrGonz78]

Okay yes the two caps are definitely in parallel and to show why there was some confusion>>> here is a picture.

I was looking at the arrow on each side, but made the mistake of not noticing the "+" on one of the arrows. I don't usually see caps that have an arrow or black line and it being positive side. So yes it is in parallel and that makes a lot more sense now, plus I learned some good info about coupling caps too. Sorry to be unclear in my posting but it was not the easiest thing to type and make perfect sense. Thanks for bearing w/ me on that one.

So here is a picture of what I believe to be D1 & D2. Pulled one off and it read 1N4002. So to me the CR100 (x4) are connected to the B+ voltage on the schematic. I am still looking at the board to find D3 & D4... But this is where I am confused mostly now. The four diodes in the bottom left of the picture of the amp are marked as CR100. << So are those main high voltage rectifiers and is that what B+ voltage is...?

So I am very new to all of this and have read some on B+ voltage, but I am confused as to what it does completely so I will read some more tonight. This is turning out to be a good project to learn more about tube amps and finally get to a better understanding of what everything does. Yeah I need to spend lots of time to analyze the signal path and really learn all of these principles/components. Thanks for the help along the way.

[Dave Curtis, dB AudioTech]

"The four diodes in the bottom left of the picture of the amp are marked as CR100. << So are those main high voltage rectifiers and is that what B+ voltage is...?"

Yes. The output tubes need the high (B+) DC voltage to operate. they also need a lower negative (bias) DC voltage to operate within their specification.

Those other diodes are D1 & D2. D1 is the low voltage rectifier for the solid state power supply, and D2 is the rectifier for the bias voltage supply. I don't see a D3 & D4 on the schematic; The 4 CR100 diodes don't have individual designations.