Mini-Major build

I usually don't do build logs because I never know how long I will take to finally finish (and clips are always expected). But I'll give it a go.

Inspired by MichaelR/Ts awesome modded Major threads I decided to try building a 2xKT88 version. I could have used a Marshall chassis but it looked like a Hiwatt chassis was a perfect fit so I chose that. Always gotta be different for some damn reason.

As I was sourcing parts I came across the TGP fusionbear build, which then led me to an EL34World thread from ~2014 about mini-Major builds. Always nice to have resources like this.

Still waiting for a few parts, mainly transformers. Transformers are from Merren Audio. He makes a mini-Major OT (with UL taps and all) and then you just use a 100W PT. Thanks to RT I was able to get a new pair of Gold Lion KT88s for $75 and I have a pair of new JJ KT88s (not sure how I acquired these).

EDIT: My plan is to not even connect the NFB. The Major injects the NFB back into the preamp at V2a cathode and is essentially absent at low MV settings. Plus, the ultra linear power amp already has NFB as it's part of the deal with UL. It's a super easy addition if I decide to add it. So I'll have to devise an alternate Presence circuit (prob just a bleed at PI input).

I have a tentative layout drawn and the main board is mostly populated.
I'm including spots for split cathode but intend to initially wire it shared.
Updated pic:


Updated pic:


Decided to try these Vintage Tone caps. They are not Mustard clones, more like early Fender (per description that is).
Updated pic:

Looks great...

stephen sawall":3ecspjjp said:

Looks great...

Click to expand...

Thanks!

This chassis has a front control panel but no back panel. So I decided to paint the chassis and apply labels to the back panel. Not the most professional look but not quite Trainwreck-like either.

I think about building one occasionally. I need to rebuild my silver face Champ. I think the black looks good.

stephen sawall":21bmq42t said:

I think about building one occasionally. I need to rebuild my silver face Champ. I think the black looks good.

Click to expand...

I have several old builds that need to be redone. But something about a new build gets me way more interested.

Makes sense to me. I usually prefer big tubes. KT88 and KT66 probably my favorites.

-love the dynamics the big bottle tone monsters bring, a played through a DIY amp kit that had just one KT88, thing was awesome, I tried to low ball him, figuring no one would buy it, called a couple days later poof!! Gone!! I keep looking for THD FLEXI to fall into my lap dirt cheap, don't seem to be happening thou,

-back to the mini major talk

I have KT66 in my Flexi, KT88 in the Bivalve and EL34 in my THD Plexi.
Flexi has a lot bass compared with a JMP.

OK, I got the transformers and of course an endbell got damaged during shipping. I removed the bolts and tried to flatten it from the inside, looks way better but not perfect (the pic is before I flattened it). The Ultralinear OT is a monster!


And now everything except the main circuit board is mounted. It's going to have Hi/Lo inputs, a Clean/Dirty switch, and either a Bright switch or a Fat/Tight switch (TBD after listening). Dirty will be the one-wire mod and Clean will be stock Major. Fat/Tight would be a V1 cathode adjustment; Fat would be the stock shared 820R//220uF and Tight would be a shared 1k5//.47uF. 1k5//.47uF shared is close to 2k7//.68uF split so that's the idea here. This will be accomplished by having the 1k5//.47 pair always ON (i.e. always grounded) and then the ground for a 1k8//220uF pair will have a ~100k resistor in series that is bypassed by the switch (so no pop). 1k8 in parallel with the 1k5 is real close to the stock 820R.


I think I'm gonna like these chrome chicken heads.


I'll have to change the bias circuit a little. No center tap for the bias winding (I should have foreseen this) and I want the bias circuit full-wave rectified so I'll have to use a bridge.


I think I have a name for it. Caiman, the animal that looks like an alligator. What would be so cool is if I could find a logo for the Porsche Cayman; cut the "y" such that when glued back together would make an "i" and use that as the logo. I'd have to dot the "i" with something extra cool (like maybe a tiny metallic gator head, just might be able to find such a thing here in Florida).

Some progress. Pretty much just installing/connecting the main circuit board left. Time for a beer.

Remember this thing? I first had hum issues so I back-burnered it for a while but finally fixed that. Then I had oscillation. Back-burnered it again but just this past weekend got that figgered out. I completely rebuilt the preamp circuit board (I made a hand-drilled/hand-staked eyelet board from G10). The way these Majors run with a PPIMV, the PI tube/circuit is SCREAMING. I had located the PI tube too far away from the associated circuitry on the preamp board. So I had to relocate the PI tube one spot over (see pic above) which made the PI wiring much, much shorter. After a few initial tweaks it sounds really, really good. I'll take some better pics and make a shitty clip (only kind I know how to make). But I might wait a few days to make the clip...I should have a new Chubtone to make it with. Here's a crappy pic. I like the chrome chicken-heads. Kind of a 'leather-and-chrome-biker' type of look.



FWIW, I'm running it open-loop. No nfb although running it UL, the screens provide some nfb. So since there's no nfb loop, the regular Presence won't work. But since there is no nfb loop, a Vox-style Cut control will work. And it works beautifully! You can really tame any high-end harshness/fizzies (which it doesn't really have in the first place) with this control since this control occurs after the distortion. I have it wired backwards from the typical Vox Cut control so it acts more like a regular Presence (i.e. turn up for more highs).