Double-ODS project planning - opinions requested

[DonMoose]

So I've got a donor chassis and iron (100W Univox with 6 preamp tube slots) and a set of concentric pots by CTS of appropriate values, so I'm lining up my ideas for this project. Being a feature creep, I'm looking at a two full preamps into one power amp, and maybe a Dlator in a sub-enclosure elsewhere in the head box.

This is a tubes-up format chassis, so I need to build the boards 'from behind'.

I'm bent enough to be thinking about two radically different preamps - an HRM and some non-HRM (skyline? High plate? Low Plate?), but stuck on the PI/Power amp choice. Thinking BM for big cleans, but have lately been confused by a couple of threads suggesting that the BM is for _lower_ headroom - the opposite of what I want.

Probably going to start with one preamp, reserving space for the second.

Gotta read more and get some decent speakers hooked to this 'puter.

[David Root]

You want big cleans, use the standard 820/24K/12AX7 PI. If you want even more headroom use a 12AT7 PI.

And for "Total Maximum Thumpage" assuming your Univox can summon up 500 Vp, you need a quad of NOS Sylvania 7581As, not cheap, but HiTest guitars has 'em and www.vacuumtubes.com in Florida has Mesa STR 415s which are also Sylvania 7581As, both same price $320.00.

Oh, and put the D'lator on the main board or a small separate one, it's real easy to do, does not require a separate box, unless you're duty bound to duplicate the original.

[heisthl]

You want big cleans, use the standard 820/24K/12AX7 PI. If you want even more headroom use a 12AT7 PI.

All true, but bear in mind you'll lose most of the bloom and a lot of the nice overtones when you use a 12AT7

[JD0x0]

I've been interested in a EF86 clean channel that cascades into a non hrm OD. The EF86 should give more "Hifi" and brilliant cleans due to the extended frequency range compared to the 12ax7

[gary sanders]

Cool to see some one else gutting an amp and doin the Dumble to it.Could you post a pic of the chassis? Im just curious of what your working with.Mine used to be a Carvin X amp 112 with the slant face.Hey we are recycling!Our amps are earth friendly.

I also use the 12AT7 PI in mine,it just seems to sound better to my ears than the 12AX7.Ive actually been considering trying a 12DW7 just because it was recommended against.Im a rebel

[DonMoose]

All true, but bear in mind you'll lose most of the bloom and a lot of the nice overtones when you use a 12AT7

But I can still get the bloom with an AX and those values?

[DonMoose]

Ive actually been considering trying a 12DW7 just because it was recommended against.Im a rebel

The DW is, IIRC, pne AX triode and one AU or AT triode. Talk about an unmatched PI!

[DonMoose]

Cool to see some one else gutting an amp and doin the Dumble to it.Could you post a pic of the chassis?

Photos will come shortly. This is a tubes-up head with 6 novals (all Mullards!) pretty tightly spaced and a quad of GE 6L6GC in a square, not in a row.

Adding a box for the Dlator is more about having room for more tubes than slavishly aping HAD.

One of my sillier ideas is to do this as a pair of 50W amps in a single box - I think I see a way to squeeze in a second OT.

Need to dig up those eyelet layouts and do a left-right flip - got 'em in my pile somewhere.

[gary sanders]

Ive actually been considering trying a 12DW7 just because it was recommended against.Im a rebel

The DW is, IIRC, pne AX triode and one AU or AT triode. Talk about an unmatched PI!

Wow,didnt know that!Still gonna try it.hehe......

Forget where I read it was used.Think it was on the valve wizard page.

[DonMoose]

Photos

Thinking more about the dual-50W approach as that lets me try and compare two complete circuits. That way I can work my way through the variants A/B-ing as I go until I hit one I don't want to give up.

[Structo]

Man Don,
That actually is a pretty cool looking amp.
Is it really a dog or does it sound decent?

Looks like it needs a cap job but you sure you want to destroy it for a donor?

Definitely has some beefy looking trannys in it.

[DonMoose]

Man Don,
That actually is a pretty cool looking amp.
Is it really a dog or does it sound decent?

Looks like it needs a cap job but you sure you want to destroy it for a donor?

Definitely has some beefy looking trannys in it.

The cleans are nice, but to get it to crunch you really gotta crank it - and then it's just crunch, no real OD, no singing sustain.

I'll admit to being torn on this. For what I paid, I couldn't get anywhere near a set if iron, chassis and cab this nice. And did I mention the all-Mullard preamp?

Maybe I'll build a ShakaBraddah and see how it likes pedals.

Dumb-ish questions -

- is a 50W #124 still a 124?
- if I do the dual-50W power amps, maybe one classic and one BM, do you think I'll get the 'girth' of a 100W?

Hope this helps!

[Structo]

I'm thinking that you won't notice a lot of difference between the two.
Why not build a 50 HRM with the HRM controls on the front panel.

[DonMoose]

Why not build a 50 HRM with the HRM controls on the front panel.

Because 'the non-HRM amps are easier to play' and I need all the help I can get. Besides, my reading suggests that for my relatively soft picking style, the HRM is probably a poor fit.

This is the relative advantage to the dual-circuit approach. Pick two candidates and A/B them until a preference is clear. Scrape out the failure and try another variant. Wipe hands on pants. Repeat.

I do appreciate the input - helps me understand myself more clearly.

[bluesfendermanblues]

Why not build a 50 HRM with the HRM controls on the front panel.

Because 'the non-HRM amps are easier to play' and I need all the help I can get. Besides, my reading suggests that for my relatively soft picking style, the HRM is probably a poor fit.

This is the relative advantage to the dual-circuit approach. Pick two candidates and A/B them until a preference is clear. Scrape out the failure and try another variant. Wipe hands on pants. Repeat.

I do appreciate the input - helps me understand myself more clearly.

Don, I recently did a 50watt (EL34B) amp with a preamp combo with a skyliner V1 into either a NON HRM OD or HRM OD.

The Cleans were great right out of the box, but (as always) the OD(s) needed some tweaking to sound right.

Being able to switch between NON HRM and HRM, I must admit that you don't really hear a lot of difference in sound between the two preamps. IME you can dial in the HRM to sound pretty much like a NON HRM.

My point is that just becuase a HRM has a set of tone controls after the OD, like a Marshall, it doesn't turn the amp into a marshall and you don't have to play the amp harder than you play a NON HRM. The difference in sound and feel between the two preamps is not that severe, IF you dial in he HRM to sound NON HRM'ish, but there's a lot of tonal options in those three trimmers

Based on my findings, I'm going to take out the NON HRM od section, which will drastically cut down on the number of realys and make the amp more simple and gig worthy.

My points being, great idea about trying out different designs of the same amp platform and don't believe that a HRM is harder to play.