Adding a second (tube) rectifier

Eoin · Post by **Eoin** » Mon Dec 06, 2004 9:56 am

I'm mostly just curious, but how exactly would you wire a tube rectifier into a Plexi power supply? Is there any reason why you couldn't add a tube rectifier (with a tran for the heater, I guess) and wire both it and the original bridge rectifier through a switch?

I think I actually prefer the sound of solidstate rectifiers in general, but I thought it might be an interesting project to expand an amps range of sounds.

Obviously, it's not an original idea... but I won't mention the M word here.

flemingmras · Post by **flemingmras** » Mon Dec 06, 2004 12:18 pm

Here's your schematic for the switchable tube/solid state rectifier. You must use 2 rectifier tubes for a 100 watter since one rectifier tube is only rated to handle between 150-200mA.

If you want just a tube rectifier, eliminate switch S2 and the 4 1N4007 rectifier diodes.

Right click the "Download" link and select "Save Target As", then save it to your desktop. This will give you a better view than Internet Explorer.

Hope this helps.

Jon

Eoin · Post by **Eoin** » Mon Dec 06, 2004 1:08 pm

Thanks Jon, you're a gent.

Could you switch from one rectifier to the other while the amp was on, or would that be dangerous?

The solidstate part isn't the same as the rectifier in the Superlead schematics I've looked at - what difference would this circuit make?

And one last question

: has the diode rectifying the bias supply (in amps in general) always been solidstate, or is there a tube alternative?

flemingmras · Post by **flemingmras** » Mon Dec 06, 2004 1:12 pm

I don't think it will be dangerous to switch between the rectifiers with the amp on since as it switches it goes into standby for that split second.

And yes the rectifier in the bias supply has always been solid state as long as I can remember.

There shouldn't be any tone difference between the dual voltage doubler and the full wave center tap circuit since both circuits yield the same voltage out.

Jon

Eoin · Post by **Eoin** » Mon Dec 06, 2004 1:35 pm

flemingmras wrote:There shouldn't be any tone difference between the dual voltage doubler and the full wave center tap circuit since both circuits yield the same voltage out.

Jon

Is there a reason why a full wave centre tap won't work with this switching circuit or does it make a difference? I can see how it could be changed to suit that instead (I trust you that there's no tone difference, I'm just curious!

).

Is there a calculation for the change in voltage across various types of rectifier? Thinking of that... is it safe to switch rectifier type in any tube amp?

Hope you don't mind all the questions.

flemingmras · Post by **flemingmras** » Mon Dec 06, 2004 1:51 pm

Yes it's safe to change the rectifier type in any tube amp.

The solid state rectifier circuit used in the diagram I gave you is a full wave center tap type. The stock one is a dual voltage doubler type. In order to build this design with a dual voltage doubler type, you'd have to use a transformer with hald the B+ voltage, so when you switch over to the tube rectifier, the B+ would be so low that the amp wouldn't sound all that great.

Jon

Eoin · Post by **Eoin** » Mon Dec 06, 2004 2:32 pm

Sorry, my mistake.

In that case, to change the rectifier of an amp with a dual voltage doubler you'd have to change the transformer as well?

flemingmras · Post by **flemingmras** » Mon Dec 06, 2004 2:52 pm

Yes, the tranny will need a transformer that puts out half of the required voltage since the dual voltage doubler will double it anyway. If you tried to use a voltage doubler on the kind of tranny used on a full wave center tap circuit, your B+ would be WAY too high.

Jon

Eoin · Post by **Eoin** » Mon Dec 06, 2004 3:09 pm

Why 4 diodes in the full wave rectifier instead of just 2?

I can see how an output transformer can directly affect the tone of an amp... but how much difference do you think the power transformer makes? I'm not planning on butchering my 76 Superlead btw, just thinking about useful mods for a replica.

If you were just using one rectifier tube in a smaller amp, do you put one side of the transformer into 4 and the other into 6... or how does it work?

flemingmras · Post by **flemingmras** » Mon Dec 06, 2004 5:02 pm

OK, the reason for 2 in series is to increase the voltage handling. The 1N4007 is a 700V diode, but with 2 in series the circuit will see it as one 1400V diode. Just for extra reliability.

Yes, power transformer will have an effect on tone. Not as much as the output tranny since your signal actually flows through the output tranny to the speakers, but it will have some effect.

And yes, in a 50 watt amp, one side of the transformer would go to pin 4 and the other to pin 6. But since it's a 100 watter, you're gonna need the rectifier to be able to pass more current. By putting both halves of the rectifier in parallel, then putting one on each side, each rectifier can now pass twice the current.

Jon

Eoin · Post by **Eoin** » Mon Dec 06, 2004 6:16 pm

Hmm... if a tube rectifier in a Superlead can only be accomodated by changing the power transformer completely, it would seem to be a fairly futile exercise.

Thank you for your time once again, Jon.