Today's Haul

[Toxophilite]

Today I picked up an older somewhat defunct organ, though the power amp was good
Giant PT the size of a babies head! 5U4gb rectified 2  7591 output tubes and a Nice big OT, Easily as big as some I've seem on 2 6L6GC organs
A pair of Quam 12" alnico speakers
pilot light, on off switch, fuse, and a host of other parts,sockets, bits wire etc
Thanks organ donor!

I have another 7591 amp and it sounds pretty sweet(ex sherwood mon hifi)
I've heard I could use this Transformer setup for 6L6s if I set it up properly for the build

Also I know there's some cool 7591 amps out there(Ampeg etc?)

Any recommendations on a build?

[TIMBO]

ARRRRRRR NICE

[HotBluePlates]

I've heard I could use this Transformer setup for 6L6s if I set it up properly for the build

Also I know there's some cool 7591 amps out there(Ampeg etc?)

Any recommendations on a build?

I'd use it largely as-is. 7591's are like a 19w metal 6L6, but they have much higher Gm so require much less driving voltage to hit full output and start distorting.

Model? Got a schematic?

If it were me, I'd try to leave the power supply as-is, and also keep everything from the phase inverter input through to speaker output. The preamp might stay the same or be slightly altered to be guitar-friendly.

Depending on what the schematic shows, there may be feedback around the output stage, which could stay, be removed, or be adjusted for less feedback. No way to say without amp-in-hand or a peep at the schematic.

[Toxophilite]

THe preamp is on another piece of chassis
And If I was to use this as is where is I'd have to cut a big hunk off of the unit as it's about 3 ft long and most is useless, That or remove it and rebuild the same thing elsewhere

[HotBluePlates]

I see.

What I believe you'll come to find is that the power and output transformers (as well as original tube type and power supply topology) generally work best in the original circuit. As soon as you think, "I'll just cannibalize this bit to re-purpose into a model XX amp...," then you run into headaches of one sort or another.

Common issues tend to be the power transformer having odd voltages or taps that only really work well with the original power supply format.

Also, if you have an OT that had 19w 7591's, it probably has no "meat on the bone" to really be used with higher dissipation tube types and still pass full bandwidth at a higher power output. That said, pushing "too much power" through an OT generally shaves the top and bottom, and might sound good with distorted guitar (and maybe an organ had wider bandwidth than you need).

Anyway, it's hard to say how re-working this stuff will go unless you (or someone else) has already done it with the specific model you're working with.

[DummyLoad]

respectfully suggest: reuse PT, choke(s), & OT. scrap the rest. keep the output stage and PS as stock as possible (use 7591). graft whatever preamp type "x" to it. redesign the phase inverter or use the original plan. in other words, reverse engineer the power supply, output stage, and phase inverter.

take pictures - lots of them, close ups with good direct lighting and at several angles.

was that a lowery organ? 

whatever path you choose, happy hacking... 

--pete

[6G6]

I don't know about that one, but some organs use a large herd
of 12AU7s, etc for tone generators.
Without them there is some extra headroom on the PT.

[eleventeen]

I've salvaged numerous amps of that sort.

My general comments: Most of the time, unless you have great sheet-metal tools available, the time & effort you might spend mechanically re-working a completely outsize chassis would be better spent buying a Mojo or other chassis or one from China on ebay with tube socket holes pre-punched, and the corners spot-welded, so that thing is sound, the holes are nicely aligned, etc; Not so much so for your electrohome chassis, that is workable as is.

A lot of the time, these things have a choke that is bigger than the OT, LOL. Irritating. +8 lbs. Takes up more room than you can spare on most amp layouts.

Probably the PT and OT are perfectly adaptable to a 6V6 or 6L6 Fenderish circuit and will work fine. It is wise to evaluate the B+ possibilities of the power trans by pulling the 5U4 or other rectifier and measuring (carefully) your AC just to see what you might expect. Or you could stay with 7591's, they're just generally more expensive and a tad less available than 6V6/6L6. Sometimes you get into a situation where the B+ is apparently not enough for say a high-powered pair of 6L6, and some times you can fix this by going with a SS rectifier which usually adds 30-50 volts to your B+. Sometimes you can't. The bad outcome is when you can't really power 6L6's the way you would want so you go with 6V6 but are stuck with a 12 lb power trans, way oversize. Works fine, wish it were lighter.

Baldwin organ guts often have lots of 12AX7's, which is great. Conns usually have mostly 12AU7, a far less useful tube. Boo.

Assuming they work, the power and output trannies can almost certainly be worked into a working geetar amp of some kind, and with careful circuit selection, a nice one.

Take some time to evaluate what you have and what you would like to end up with, and ponder the feasibility of what you want to do. Instead of starting out enthusiastically and finding yourself walking into a blind alley later. *It will patiently wait for you to decide*.

My belief is that once you have determined feasibility, the easiest and cheapest way to turn the entire project into something useful, especially if have a grossly oversize chassis as you say, is to find a dead solid state combo amp for really cheap, $10-$25, gut it, and build your new amp on the old chassis. Yes, you will struggle with certain things. But your cabinet, tolex, corners, grill cloth, maybe or maybe not a usable speaker and handle will all be present and you could spend $200 or more buying those things and some number of hours assembling same.

Amp built upon CONN organ chassis. (Work in progress)

There were so many holes in the top surface in places where I really did not want them that I fabbed a sheet to cover almost all of the top surface and remade the holes for the sockets, etc;

IF YOU DO THIS: Be VERY SURE you drill all the holes you will need for transformer mounting, parts board standoff mounting, anything you can think of, because when you have two pieces of sheet metal "permanently" sandwiched together (eg; after you have mounted all your tube sockets, etc; etc;  should you drill any new holes, the drill will generate a burr between the pieces of sheet metal and bulge the two pieces of metal apart and you will NOT be able to fix it.

[Toxophilite]

Thanks for all the replies
I'm not at all adverse to using the power amp circuit as is , i was just saying it's not really possible in situ. Rebuilding it into another chassis is entirely possible and a good idea.
Strangely (and sadly) i don't belive there are any chokes, but the PT is certainly going to add a pile of weight to any amp due to it's massive size.
I traded a PT away recently because i thought..That thing is waaay tooo big for a 6V6 amp
I'm currently working on a deluxe lite so it's not going anywhere. i was just doing some pondering in advance.
I have plenty of decent speakers and even a couple of likely cabinets.
I do these things on cheap.My man expense is caps and resistors..though I did pay $75 for a D130 lately..but heck, it was a JBL!
I think looking for a hooped SS chassis is a good idea. The preamp piece for these amps is almost workable as a potential  chassis as well as it has the right amount of large socket holes(for plugs) down one edge..might have a look at that.
Much to think about further!

[eleventeen]

"Much to think about further!"

And much cheaper to do so than to start out and hit brick walls. I learned the "1 inch setback" thing the hard way, as you might imagine. On my second pix, you can see that there was a nice cutout for the original power transformer that would have made my life a lot easier, but you can also see that if the PT was mounted in that hole, then the front edge of the laminations would be flush with the front of the chassis so it would kill that "setback" thing. OK, you say, enlarge the hole and move the tranny towards the rear of the chassis. Nope, then there would not be room for the pair of 6V6 in back of the tranny which are already about as close to the PT as I would want them. OK, no problem, find a different PT. Ahhh, but now I am mounting the new PT over the big cutout for the original one, and it is tough to mount a transformer to AIR. So now this forces me to make the adapter plate that this tall tranny sits on. No problem, spend more time hacking and drilling up more metal, right?

Another problem with scrounge organ chassis, especially Hammonds, is that sometimes they are so narrow, front to back, that there is no room for a horizontally-mounted parts board...you want to have some room for the front panel pots, some room for circuitry, R's and C's, and then some room for tube sockets, and with any luck, room to be able to get your soldering iron in there.

Until you build lots of things, you will never be able to foresee all the potential mechanical interferences, and it is still a tricky thing in some cases to be looking at a schematic diagram and run into issues with the physicality of the parts and their sizes. Lots of times you can't (neatly) mount a .1 ufd cap in the space normally taken up by a 1/2 watt resistor.

[Toxophilite]

All good points!
And much appreciated
That's a nice looking conversion
I've built many things, Done several preamp conversions from reel to reels, Reccapped man amps..including a couple of echolettes ..after that I was ready for brain surgery..no problem! So small spaces don't intimidate me.
I might get into using boards, though I haven't yet, except when working on my super. there's one in this Hammon L-100 amp I have,waiting for attention...Actually it's PT and maybe Chassis might be an option for this build. It's a 5U4 as well . I have a schematic for it too so I might be able to discern some of it's specs..hmmm
Physical layout for space wouldn't be as much of a probelm for me as I'm pretty good with those things.
It'd be the lack of electrical theory and experience, but that's why I'm here.
Hopefully to learn!

[Toxophilite]

Well this might be the ticket..though it is a little bulky on the back end..
Alledgedly defunct keyboard amp head my drummer had, I think he scavemned knobs and a pot from it.
It's an okay size, maybe a little big but solid
Has some possibly usefull resistors and maybe a couple of pots if they're high enough wattage

I might keep an eye out for an actual old SS guitar amp with a smaller chasiss, but ths would do in a pinch

[eleventeen]

Here's a great example of how much of a PITA a re-purposed chassis can be.
1: Chassis 3" tall. Ugh.
2: Power transformer 900 volts CT (!)
3: Choke the size of a Buick

and no, the red 6SL7 didn't come with it, that was mine. 





As you'll most likely find, the sheet metal of zombie SS amps will present some challenges in many cases. But any given one IS the right width, it DOES fit over the baffle board neatly. You will probably find that NONE of the pots are usable in a tube amp, the values are just vastly different SS to tube.

[DummyLoad]

i'll trade you a six-pack of beer of your choice for that red base 6SL7...   

j/k

--pete

[Toxophilite]

"the sheet metal of zombie SS amps "

As of the SS wasn't bad enough..Aiiie! the Zombie SS!!

[Toxophilite]

I'm curious what could be wrong with the sheet metal in the SS chassis..other than all sheet metal is a pain in the @$$, whether cutting, drilling, grinding, welding, slashing your fingers etc etc..though pop rivetting is fun.

I'm not too worried about unconventional shapes as I don't require the amplifiers that I'm building to look like other existing amps. I build my own cabinets, often to fit the amp, I don't mind having controls on the back, so long as I can get to them somehow. I have a little amp like that in a Bell & Howell cab that I've been using for years as part of my stereo rig. It's been trucked around on tour etc etc, it sounds great and looks cooler.

I like to find existing boxes that are sturdily built that have good cabinet/amp case potential too.

I really appreciate you helping to make me aware of the myriad pitfalls possible in such an undertaking, but they don't faze me too much. I like stupid challenges of that sort..How to make it all work!

I think my biggest dislike of this particular unit is the giant PT (there is no choke on this amp)
Unnecessary weight and a zillion unneeded taps)
So I might keep an eye out for a smaller donor unit . I realize as well that there will be difficulties with finding one for the job, but a lot of this sort of stuff passes through my hands fairly regularly

Also despite my limited electical skills with tube amplifiers. I'm really quite handy in other areas

I'm going to let the parts for this one come together and then I'll build it
It'll be fun

[eleventeen]

Wouldn't you be tossing the PT on that particular amp? It is true that sometimes, you can series-connect some 80 volt and 100 volt windings on a weird power trans for a SS amp and through a voltage doubler, obtain a nominal voltage level for some tooobz. Indeed, I am doing that in the first amp I pictured, the CONN, with that tall black tranny has a 126 and a 22 and a 22 volt winding. (Weird enough?) But it *also* has a 6.3 winding, and that makes my life a little easier. Typically, a donor SS amp doesn't have a 6.3 winding, although we know we can change things.
 

[Toxophilite]

Myapologies
I wasn't being specific enough
I was referring to the organ amp PT not the solid state amp PT
Pretty well everything inside that SS chassis will get tossed if I decide to use it.
I was just interested in the chassis

[Toxophilite]

That's a cool idea!
I'll look into that
I know aluminum was a bust as a house wiring metal because of oxidization but do peaople use it for amplifier chassis
My brother is a very accomplished welder and has a metal shop