A switch for toggling between solid state and tube rectifier

[gnugear]

Is this something that is possible? I like the idea of being able to flip between the two ... especially since the Komet uses a rectifier.

[rhinson]

hello there, it's easy to do (obviously assuming you have the 5v winding on your trannie for the rect. tube). just parallel run the h.v. sec. wires to the solid state diode strings and to the tube rect. socket---usually pins 4 and 6. then run the output of each one to the outside lugs of a good quality spdt toggle switch( rated at 10A or better is good), and then the center lug goes to the rest of the amp. you'll probably want to pick an in between bias point because if you bias from operation with the tube when you switch to the diodes it will probably be too hot (and too cold the other way 'round). this depends on the tube you use as well----the 5ar4 has almost no voltage drop compared to the other rect. tube types, it's almost like a tube solid state rect. to get the most effect from this switch use a 5u4 or a 5r4---both have a big voltage drop and will give lots of sag. good luck. rh

[LeftyStrat]

I've even thought about using a dpdt switch, and run the bias supply (pre bias-setting pot) to the other center lug, and then each end to a different bias pot. That way you could set the bias for ss and tube rect.

Of course a better way might be to have one leg go directly to the pot and the other go through an internal compensation trimmer. In theory, the trimmer would only have to be set once for the voltage differential.

Or is this idea totally wacked?

[Omar]

I put a rectifier switch on the first version of my Express. I didn't care for the tube rectifier since it made the amp sag too much and became 'squishy' for lack of a better word. See the attached .pdf I found.

Omar

[Rocket Roll]

That Torres' version is OK, but what about mounting diodes directly on the DPDT - could anyone draw a layout for that, please?

[M Fowler]

Rocket Roll,

Anything is possible but directly mounting the diodes on the switch in my opinion is not a good choice. Use a small board so the diodes are supported as In4007 are not very sturdy to begin with and with the high voltage wires dangling of the diodes without the board to help support is not good.

Mark

[Rocket Roll]

Thanks, I'll take your advice and mount the diodes on the GZ34 socket (one side) and on a small piece of tagboard (other side).

[Firestorm]

I've even thought about using a dpdt switch, and run the bias supply (pre bias-setting pot) to the other center lug, and then each end to a different bias pot. That way you could set the bias for ss and tube rect.

Of course a better way might be to have one leg go directly to the pot and the other go through an internal compensation trimmer. In theory, the trimmer would only have to be set once for the voltage differential.

Or is this idea totally wacked?

You don't even need a dpdt switch to do the diode switching; with parallel high voltage connections to the tube and the diodes a spst would work -- the diodes offer so little resistance to current flow that once they're engaged the current will almost completely ignore the tube. So if you used a dpdt, you could have one side switch the recitifiers and the other side switch the bias supply (either the dropping resistor or the load resistor).

[Rocket Roll]

OK, would this work?

[paulster]

That'll work in terms of actually switching between solid state and tube rectification but you'll need to watch out for the voltage rating of your diodes since you've only got a single diode per leg (rather than the usual two in series which doubles the voltage rating) and also that you find a bias point that will be suitable for the two differing B+ voltages.

[Firestorm]

Also make sure the first filter cap can take the higher voltage of the metal diodes. The way you show it wired, you can use the switch while the amp is off, but if you do while it's on, it will be noisy (and you'll want a big switch to ensure adequate insulation). If you want to be able to switch rectifiers on the fly, you'd want a SPST switch. Kevin O'Connor shows this in TUT 1. He also has a 10K resistor between the hot side of the switch (the junction of the diodes) and the input to the cap to supress transient noise. The text says 1W flame proof, but the graphic says 10W flameproof. The resistor doesn't really carry much current because when the switch is closed, it's out of the circuit and when the the switch is open the 10K resistance makes the current go through the tube instead.

[Rocket Roll]

Thanks! It's actually a Matchless Lightning build (cathode biased, 2xEL84, 280-0-280 PT secondary), capacitors are 450V rated and diodes are 1N4007, so I hope I'm on the safe side as far as this kind of switch/diodes/caps combo is concerned?

[ER]

3 position switch with off in the middle, up for SS, down for tube B+?

I'd have to think a bit to figure a wiring diagram, but seems doable...

-ER

[Rocket Roll]

3 position switch with off in the middle, up for SS, down for tube B+?

I'd have to think a bit to figure a wiring diagram, but seems doable...

-ER

Use the same wiring layout as I've posted above, but use on-off-on switch and you'll have a "tube rectifier - standby - diode rectifier" switch.