Rectifiers and max capacitance

[imo1]

I’ve been toying around with a few Dumble based circuits.
I’m really digging a 50w version that suits my playing well.
The one thing I haven’t tried is a tube rectifier, and I wanted to try that.

The standard Dumble 1st stage capacitance is the 2 220us for this circuit. That(110u) is almost double the max recommended capacitance for the GZ34

The two routes that I can see would be either using 1 GZ34 , and lessening the first stage cap to 2 120u or using
Dual rectifiers in parallel, which I think doubles the max capacitance.

I would love to hear real world thoughts on what this does to the response. I’m assuming the dual rectifiers would greatly reduce the sag. I’m kind of wanting to experiment with a little more sag.

I would probably put the tubes on a switch for now, but wanted to get some feedback as it’s just an idea at this point, and I really like the amp with the silicone diode rectification as is

[xtian]

If sag is what you're after, avoid all the trouble of using a tube rectifier, and just add post-rectifier resistance.

[WhopperPlate]

If sag is what you're after, avoid all the trouble of using a tube rectifier, and just add post-rectifier resistance.

Curious, do you have any experience comparing a sag resistor vs a comparable tube rectifier circuit ? I am actually about to implement this in a build , probably switchable .

[pdf64]

Per se, GZ34 don’t have much of a significant sag effect. There’s probably more sag from the requisite transformer equivalent series resistance.

Compared to a GZ34, silicon diodes feeding a sag resistor of about 80 ohms (sag resistor between rectifier output and reservoir cap) provides about the same idle HT voltage.
At max overdriven output, the sag resistor value is about 20 ohms.
This might seem counterintuitive but when I measured it, that’s how it worked out.

[imo1]

Per se, GZ34 don’t have much of a significant sag effect. There’s more sag from the requisite transformer equivalent series resistance.

Compared to a GZ34, silicon diodes feeding a sag resistor of about 80 ohms (sag resistor between rectifier output and reservoir cap) provides about the same idle HT voltage.
At max overdriven output, the sag resistor value is about 20 ohms.
This might seem counterintuitive but when I measured it, that’s how it worked out.

That might be what it is then..Maybe its the variable resistance, depending on pull, that does the thing I'm looking for.
Having played countless Fenders over so many shows, I feel like I can definitely hear a pretty strong difference between a GZ34 and a silicon rectfier, even with similar adjust voltages.
I'm trying to chase the last 5% of a feel thing that always seems to bug me with "tighter" amps. So much that I love, and a couple of things I miss

[xtian]

Do you play loud? That’s the only way to get the HT to dip.

[imo1]

If sag is what you're after, avoid all the trouble of using a tube rectifier, and just add post-rectifier resistance.

Ive tried that before, using the resistance( i think in the form of the weber part many years ago)but the post below may be hitting what I am looking for; a variable resistance that depends on current draw. I think it does a sonic pull that may be one of those mojo things that players like.

[Stevem]

Just do it the easy way, add the 80 ohm 5 watt resistor and then change over to UF5408 diodes to get rid of the switching noise hash like a tube recto would.

Also if you do not have a 1/2 amp fast blow fuse on the center tap of the OT, now would be a good time to add that.

[imo1]

The fuse on the center tap is a good idea!
As far as the resistance, I know a lot as a player, and a decent amount as a builder, so, if we were really trying to emulate a tube rectifier wouldn’t we want a variable resistance that reacted to current draw? There is a definitive sound to different rectifiers. To me, a gz34 does a thing where there is a sag that happens immediately when you hit a big note. It’s quick and less dramatic than a less powerful rectifier. I can hear it in my playing and always liked it in really soulful players.

Do you mind elaborating on how those diodes affect the sound? I understand the theory, but I’m curious to know how that translates into the actual sound itself