2xEL84 Liverpuddle

[Fischerman]

Just about got everything.



It will go into a chassis just like my 18W Lightning-inspired build with the cap can where the rectifier is.

[Fischerman]

Not the prettiest control panel but works for now. That’s the Lightning faceplate reversed. I hope to get a nice pro looking faceplate for this and the Lightning (with added Cut control).

I decided to add a post-PI Master Volume.

[bcmatt]

Nice!
I didn't know you could get a 3-position switch that's not "off" in the centre. What kind is it?
What sort of volume control are you using? VVR or a PPIMV?
Did you change the 25W resister from a 1K to 1.7K for a pair of EL84s like Mark Abbot's schematic suggests? I ask because I just realized that I have pulled a couple EL84s on my Liverpool a few months ago and it just occurred to me that maybe I am supposed to alter the circuit and not just switch the speaker load.

[Fischerman]

[Fischerman]

Nice!
I didn't know you could get a 3-position switch that's not "off" in the centre. What kind is it?
What sort of volume control are you using? VVR or a PPIMV?
Did you change the 25W resister from a 1K to 1.7K for a pair of EL84s like Mark Abbot's schematic suggests? I ask because I just realized that I have pulled a couple EL84s on my Liverpool a few months ago and it just occurred to me that maybe I am supposed to alter the circuit and not just switch the speaker load.

Sorry for late response. I think I got the switch at AES. There are only 4 lugs total. PPIMV. I used a 1k5/20W ‘choke’ resistor. The amp is running at 317vdc plates and 300vdc screens, 9.3vdc cathodes across a shared 120ohm resistor.

It’s pretty hot, I will likely install shielded wire to both V1 grids but I wanted to see how wild it was without it first. Unfortunately I finished it late yesterday and finished the evening watching football. And I left town this morning.

[maxkracht]

Nice looking build! The enamel resistors are classy.

[Fischerman]

This thing screams but it's a bit too focused in the midrange. I originally used 1M Treble/Bass/Volume pots but reduced the Treble to 500k. I'm going to try 47n output couplers and then play with that coupler preceding stage 3.

I have that Stage 3 grid leak adjustable with a 39k resistor in series with a 50k trim pot. I started at 56k total resistance and turned it down to 47k. It seems to me that coupling cap and that grid leak resistor form a filter that cuts lows. So if the Express uses a 2n2 coupler and 150k grid leak then you'd have to increase the cap to compensate for the 56k grid leak in the Liverpool. 2.2 x 150/56 = 5.9 so approx 6nF with a 56k to get the same frequency response. Maybe that's why these amps sometimes have two caps here...because he had to dial in the gain via the grid leak resistor first, then add caps to dial in the frequency response using that chosen grid leak resistor. And it was sometimes a weird cap value.

I'll probably start with 4n7 since I have the grid leak at 47k.

EDIT: I should also add that this Master Volume works fantastic. The 'best' tone is with the Gain up high (say 1:00-2:00) but with the Master between 11:00-1:00 which is still loud but not nearly as loud as full up and better/tighter distortion. There is plenty of distortion on tap so getting 'more' distortion is never an issue. It's just a 250k dual gang pot but with 1M resistors in parallel, still mounted on board. So the effective resistance to ground is 200k.

[Fischerman]

10nF was too much. That spot is really sensitive to coupling cap changes. I put in a 4n7 and turned the grid leak up to 54k. That vocal-mid-focus is gone but geez it has a ton of gain.

Then it occurred to me that I never turn the Presence up to 3:00, which is where it really starts to ramp up. Most of the sweep from zero to 3:00 doesn't do much. And the amp is already bright so I would never turn it past 3:00. So I ripped out the Presence circuit and installed a Cut control. The MV already in place adjacent to it made it super duper easy. 250k pot, 4n7 cap and a short piece of wire. Then I grounded the PI thru a 470R resistor and left the NFB wire and NFB resistor intact so it technically still has a tiny bit of NFB but not really. Previously it had the typ 4k7 resistor from 25k Presence pot lug to ground (100k NFB resistor from 8ohm lug). This is 1/10th that.

Much better! A much more useable control. The amp is still a wild beast and doesn't sound all that different except now I have the option of cutting a bunch of highs if I want. And it still sings and breaks into feedback even with the Cut control cutting a lot.

And it's stable with everything dimed. Before it was not. Not that it was a useable tone but still, I'd prefer this type of amp be stable; but close to unstable, with everything dimed. Like a good Super Lead. That's where its at now.

[Littlewyan]

Done a really nice job on that one! And great you've dialled it in to your liking now. All that's left to do is play....................or start planning the next build

[dorrisant]

Very nice looking build!

[Tone Lover]

So what impedence of an ot did you go with. And does it still clean up when you back of the volume. Thanks Bill

[Fischerman]

So what impedence of an ot did you go with. And does it still clean up when you back of the volume. Thanks Bill

The OT is 5k9 at 2/4/8 ohms but I’m running it at 4/8/16.

Yes it cleans up but I deviated from the Liverpool enough for it to not be apple-to-apples. For me, originally it was just a bright, unruly beast that only did one thing and it wasn’t for me. So I made it no NFB, Cut control, and removed the cathode cap from second stage. Much, much better for me and still tons of gain, touch feedback, all of that.

Also, it does not sound small, middy, or thin at all. Both my Lightning and this (now tentatively called Thunder) have surprising girth and muscle.

[Reeltarded]

You make me do bad things to great circuits that are naturally a little problematic.



I often wish my Liverpool was a Rocket.

[Fischerman]

You make me do bad things to great circuits that are naturally a little problematic.



I often wish my Liverpool was a Rocket.

Here’s my Rocket I built way back during the big RJ Rocket build. I had the cab built to match an old Carvin 1x12 I had. It has evolved into a Matchless DC30.

[Reeltarded]

I love the Baaaawwwaaaaar! of a wound out AC just before it demands too too much supply.

Lovely looking amp there.