Anyone here heard of "too much B+ voltage to use a SS rectifier"?

[JubileeMan 2555]

I'm in discussions with a guy that I think is in the "know" and he mentioned that he couldnt use a SS rectifier with his super reverb because with a tube rectifier he was pulling 485v in his B+...

... this makes no sense to me and I want to hear from other guys that may know little more deeper knowledge. This seems odd to me.

[Leonc]

Interesting...but clearly a tech question.

[s2amps]

There is probably some truth to what he is saying. Some old Fender amps have 500V filter caps and/or chokes. My Furman is telling me my wall voltage is 129VAC right now. I imagine my amps would run well above the normal 460VDC for a Fender amp. If I were to plug in a SS rectifier, I'm sure my B+ would exceed the max rating of my filter caps.

Remember that a SS rectifier takes the AC voltage of one leg of a center tapped PT and multiplies it by 1.414. Tube rectifiers vary by design, but none approach a B+ that high.

So a typical Fender PT that runs at 320VAC would yield 452VDC B+ assuming a 110VAC primary. You get the idea...

[Toggle]

He may have meant that using a SS rectifier will result in a too-high B+, since he's getting 485VDC on the plates with a tube rectifier already.

-Tom

[TheAmpNerd]

The last super reverb that came though here had about 489 B+.
It is a 64 Blackface.

In his own words it sounds "F***ing Amazing"!

He's gig's and tours with it....oh yeah I did all the work on it
and it is pretty much bullet proof too.

Just make sure the electrolytics are new...it started to sound
like shit, so it was time to replace the blue mallories with better
caps.

Yep it sounds even better then it did too.

[jjasilli]

. . . a SS rectifier takes the AC voltage of one leg of a center tapped PT and multiplies it by 1.414. Tube rectifiers vary by design, but none approach a B+ that high.

So a typical Fender PT that runs at 320VAC would yield 452VDC B+ assuming a 110VAC primary. You get the idea...

Yes: with PT putting out 325 volts, after rectification:

Rectifier SS; 5Y3; GZ34 ; 5U4B
Multiplier 1.4; 1.13; 1.3; 1.2
Voltage 455; 367; 423; 390

[Blue Strat]

I'm in discussions with a guy that I think is in the "know" and he mentioned that he couldnt use a SS rectifier with his super reverb because with a tube rectifier he was pulling 485v in his B+...

... this makes no sense to me and I want to hear from other guys that may know little more deeper knowledge. This seems odd to me.

The bottom line is that with a solid state rectifier, your B+ will increase by approximately 25 volts compared to a 5AR4/GZ34 and more compared to 5U4s, etc. If that new, higher, B+ is higher than the maximum rating of the power supply capacitors OR the plate voltage for your power tubes, that's a problem.

You have to look at the whole picture not a fragment of the picture. Generalizations are worthless.

[Old Tele man]

FWIW -- my late-69 SF/SR runs +485Vp with ss-diode module.

[JubileeMan 2555]

This seems like a pretty freaking important problem that I've never read before. There has been LOTS of tube rect. to SS threads and all anyone ever does is say to put in a copper cap as a replacement... If it has a risk of blowing up one's filter caps, I think this should be massive warning to anyone putting in SS rectifiers.

...is it possible that SS rectifiers like the copper cap are designed NOT to raise the voltage of the amp, but because my rectifier is a home-made 6-diode thing, it does?

[TopBooster]

There has been LOTS of tube rect. to SS threads and all anyone ever does is say to put in a copper cap as a replacement...

I thought Weber Copper Caps attempt to simulate the voltage drop of tube rectifiers, so using these wouldn't be the same as plugging in a straight-up diode bridge...

[jjasilli]

C'mon guys Google! There is not A weber copper cap. He sells a large variety of them ea designed to replace a specific rectifier tube. So you can't go wrong if you pick the one that replaces the standard tube in your amp.

You can pick differently, or Weber will make you a custom copper cap so you can tailor voltage, etc., as you like. But this of course is at your risk; and you should not alter the power section of an amp without first acquiring the knowledge and confidence to do so in a way safe to you and to your amp. But no warning is necessary to do a straightforward, plug 'n play, copper cap substitution.

(This is not an endorsement of copper caps, and I personally do not use one.)

[Blue Strat]

I thought Weber Copper Caps attempt to simulate the voltage drop of tube rectifiers, so using these wouldn't be the same as plugging in a straight-up diode bridge...


True. To help clarify things a bit, a solid state rectifier contains diodes only. A copper cap is a solid state TUBE RECTIFIER SIMULATOR which can be bought in several versions that immitate an actual tube rectifier (5AR4, 5U4, etc.) The B+ change with a Copper Cap is negligible or zero.

[jjasilli]

True. To help clarify things a bit, a solid state rectifier contains diodes only. A copper cap is a solid state TUBE RECTIFIER SIMULATOR which can be bought in several versions that immitate an actual tube rectifier (5AR4, 5U4, etc.) The B+ change with a Copper Cap is negligible or zero.

Yes, the copper cap is solid state diode rectifier AND a resistor. The resistor drops B+ voltage (and also limits the onrush of current when the amp is turned ON).

After (full wave) rectification, the the voltage from the power transformer is multiplied by a factor: SS diode, 1.4X; 5Y3 Tube, 1.13X; GZ34, 1.3X; 5U5B 1.2X. These are substantial differences. E.g.: 325 volts from the PT, yields after rectification: 455, 367, 423, and 390 volts respectively, depending on which rectifier is used.

Because the copper cap has SS rectification it yields a higher B+ voltage than a rectifier tube would. So Weber adds a resistor of the proper value and wattage rating to drop the voltage, to match the voltage put out by the rectifier tube.

[rooster]

Keep in mind, though, that the first filter cap stage in a Fender amp is about 700VDC, as there are (2) 350VDC caps in series (with 220k resistors in parallel). I just recently had to re-cap a Fender head that had been heavily modded back in the day with a HUGE PT that put out about 560VDC and a HUGE OT to handle it. I ended up using (2) 350VDC caps for the power plate stage and (3) 16uF @600VDC caps (all Sprague atoms) for the rest of the circuit. Works great, but I have to increase the dropping resistor between the screens and the rest of the amp, as this amp is running WAY too hot, and is making some crackling.

rooster.

[Blue Strat]

Keep in mind, though, that the first filter cap stage in a Fender amp is about 700VDC, as there are (2) 350VDC caps in series (with 220k resistors in parallel). I just recently had to re-cap a Fender head that had been heavily modded back in the day with a HUGE PT that put out about 560VDC and a HUGE OT to handle it. I ended up using (2) 350VDC caps for the power plate stage and (3) 16uF @600VDC caps (all Sprague atoms) for the rest of the circuit. Works great, but I have to increase the dropping resistor between the screens and the rest of the amp, as this amp is running WAY too hot, and is making some crackling.

rooster.

The are lots of Fender amps that DON'T have the 2-350V caps in series for the B+. Deluxes, Vibroluxes and several other models.