Pentode/Triode mod

[Telenut62]

I have put this in my DR build and I was wondering what you guys think of it, is it worth it and are there any downsides to it? I found the volume drop was pretty disappointing for the amount of work installing it. Seeing there is already a Channel 2 which cuts the volume anyway, I'm thinking of pulling it out.

[Omiewise65]

There's a switch for the pentode / triode option in my Bugera V22 .
Don't use it too often but i think it gives a nice sparkle to the sound using it after the amp has warmed up and has been played for about 30 minutes . I like it .

[tubeswell]

I've done Merlin Belncowe's morph control in a couple of amps - definitely a worth-while thing (but you need a conveniently accessible space to put the pot)

[Telenut62]

Oh ho...that's a new one to me

[tubeswell]

Here's my "6H3". Based on a 6G3 but with a switchable parallel/single stage in V1, and EF86 with the triode-pentode morph control as the tone stack recovery stage, and a whole tube for a 5G9 style bias-vary trem. For 6V6s its quite a loud amp when dimed

[printer2]

Originally Posted by tubeswell

Here's my "6H3". Based on a 6G3 but with a switchable parallel/single stage in V1, and EF86 with the triode-pentode morph control as the tone stack recovery stage, and a whole tube for a 5G9 style bias-vary trem. For 6V6s its quite a loud amp when dimed

Think it was the output tube in question. So with the morph, does it put the tube in triode mode or reasonably close? I would like to do this but followed with a cathode follower and run triode in a Bassman circuit. Also how do you like the tone control?

[Keyser Soze]

Tubeswell, that looks like a very nice design, and I just happen to have pretty much everything necessary to build one.

You wouldn't happen to have a layout for that one too?

[tubeswell]

Originally Posted by printer2

Think it was the output tube in question.

I did come up with a schematic idea (attached) for trying the morph in an output stage but haven't implemented it yet. You could use a dual ganged pot, or for more tonal experimentation, two individual pots.

Originally Posted by printer2

So with the morph, does it put the tube in triode mode or reasonably close?

In 'triode mode' it ties the screen to the plate 'at AC' so its like using a switch to do the same thing (except the cap keeps DC off the pot) . There are some interesting subtle tonal variations in between that and 'bypassed screen pentode mode'.

Originally Posted by printer2

I would like to do this but followed with a cathode follower and run triode in a Bassman circuit.

Yes I've done that as well and its definitely better with the CF when driving a tone stack, but you need to adjust the g2 resistor (IIRC I used 680k instead of 560k in that circuit)

Originally Posted by printer2

Also how do you like the tone control?

The tone control part is reasonably effective, there is quite a wide range and the mid-scoop/hump brings out the upper mids when dimed. But its completely different from a BF stack

[tubeswell]

Originally Posted by Keyser Soze

Tubeswell, that looks like a very nice design, and I just happen to have pretty much everything necessary to build one.

You wouldn't happen to have a layout for that one too?

I usually do layouts with a pencil and rubber so I don't have anything worth posting, but I'll take a few picks of the guts and stick them up in the weekend.

[Keyser Soze]

Originally Posted by tubeswell

I usually do layouts with a pencil and rubber so I don't have anything worth posting, but I'll take a few picks of the guts and stick them up in the weekend.

Same here.

And it's not like it is so different from a brown deluxe that you couldn't just tweak the existing layout. But, given how detailed and thoughtful your design was I had hopes that you'd have something super easy...

Gut shots would be greatly appreciated, thanks!

[jefrs]

Originally Posted by Telenut62

I have put this in my DR build and I was wondering what you guys think of it, is it worth it and are there any downsides to it? I found the volume drop was pretty disappointing for the amount of work installing it. Seeing there is already a Channel 2 which cuts the volume anyway, I'm thinking of pulling it out.

You're right. There is not much volume drop and the pentode mode sounds better

My Epi BC30 (Bassman clone) has the pentode/triode switch (2x6L6GC). I don't use it. I added a master volume instead, and a couple other tricks. Just turn the volume down.

[Telenut62]

Interesting information for a future build...I can see someones face when they ask..What's that knob for?....It's a Morph control!! lol