Cascading gain stages in a 5E3

[BloozeGit]

Hi folks,

I'm one of those that finds the 2 channels on a stock 5E3 too similar to justify keeping in there, so I'm thinking of using one of the 12AY7 stages as a switchable cascade boost. Has anyone ever tried this before? Would it be as simple as feeding the output of one stage into the input of the next with the standard resistor values?

[Scott S]

Have you tried jumpering the channels yet? Not as much gain as cascading the two, but there is a boost.

JohnnyCrash should be here soon, to answer the cascading gain question.

- Scott

[tubeswell]

Yes cascading the stages is fairly easy to do in a 5E3, but you will want to have separate cathode resistors for each cascaded stage, otherwise you are likely to get unwanted LFO.

The bypass caps also may possibly need to be smaller values than traditional 22-25uF to roll off boominess.

You might want to experiment with different coupling cap values for between the first two stages, (.022uF might be too farty) as well as adding a 10k-100k grid stopper on the 2nd stage (to stop unwanted blocking distortion).

For inter-stage attenuation (depending on your taste) you could use the '2nd' 1MA vol pot as a variable grid-leak/divider in front of the 2nd stage (OD control) or decrease that to 470kA or 250kA. Or maybe possible attenuation in the form of split-load plate resistor(s) and/or different voltage divider options between the two stages.

[BloozeGit]

That's plenty to play with, thanks for that!

[JohnnyCrash]

Originally Posted by tubeswell

Yes cascading the stages is fairly easy to do in a 5E3, but you will want to have separate cathode resistors for each cascaded stage, otherwise you are likely to get unwanted LFO.

The bypass caps also may possibly need to be smaller values than traditional 22-25uF to roll off boominess.

You might want to experiment with different coupling cap values for between the first two stages, (.022uF might be too farty) as well as adding a 10k-100k grid stopper on the 2nd stage (to stop unwanted blocking distortion).

For inter-stage attenuation (depending on your taste) you could use the '2nd' 1MA vol pot as a variable grid-leak/divider in front of the 2nd stage (OD control) or decrease that to 470kA or 250kA. Or maybe possible attenuation in the form of split-load plate resistor(s) and/or different voltage divider options between the two stages.

Took the words right out of my mouth.

I cascaded mine and decided to remove it. 5E3's have plenty of gain, and if more is needed a 12AX7 in V1 is often more than enough.

The couplers on the 5E3 are large - which makes for fat, thick, juicy tones with Teles/single coils. On the other hand, with humbuckers or when cascaded, it can mean too much woof and whooliness. For this, I'd drop the couplers on both stages to 0.022uF and tweak the cathode bypass to no more than 2uF on the 1st cathode.

The 2nd cathode setup is up to you and how much gain you're looking for. JCM800's use 2.7k + 0.68uF on the 1st and an unbypassed 10k on the 2nd. This was my first setup when I cascaded. Bypassing the second will increase gain (and shape freq rolloff at that stage).

When it comes to cascading, sometimes its easy to go overboard... this is especially true with the already gainy 5E3.

As mentioned, that now unused 1M Volume pot can be a Pre/Gain control between the cascaded stages if you'd like a Master Volume.

As far as what to expect - it will completely change the 5E3. It will no longer be a fat blues machine, but will instead be a modern hard rocker. I already had those type of amps, so I put my 5E3 back to normal - if you need a portable 1x12" for hard rock, you might love this mod.

[BloozeGit]

You're right JohnnyCrash, it's a different vibe altogether. I'm making other plans now, perhaps a single triode stage tremolo fed to the output section cathode bias. Not sure how it'll work with the 12AY7, but I'm guessing that phase-shift oscillators don't need that much gain anyway. Whaddyall think?

[tubeswell]

Originally Posted by BloozeGit

I'm making other plans now, perhaps a single triode stage tremolo fed to the output section cathode bias. Not sure how it'll work with the 12AY7, but I'm guessing that phase-shift oscillators don't need that much gain anyway. Whaddyall think?

Actually they need a minimum gain of 29 if you have three RC phase shift oscillators. See:

http://www.freewebs.com/valvewizard1/trem1.html

A 12AY7 has a gain factor of 45, so it should work okay.