Recycling Organ Amp Transformers...help?

[DenaliJoe]

Hi All...

Long time lurker/learner and posting my first time now that I'm graduating myself from tweaking amps to kits to a full-on grounds up amp project...so let me start by thanking everyone who has spent so much time putting such valuable information online for guys like me. Truly amazing stuff that is appreciated.

My question is...I hope...relatively easy and straightforward. I have a PT/OT set salvaged from an old Baldwin organ and am hoping I can just get a thumbs up/thumbs down as to their usability for what I have planned.

And the plan? Building an Atlas Tweed (2x6V6 version of the M@tchl&ss Spitfire).

My PT/OT set was originally the main amp in the organ and ran 2x6L6gb's, a 5u4g, 2x12ax7, and...well...a zillion other triodes.

PT:350-0-350, 12.5v tap, 4v tap all approx as it was measured unloaded.

OT: Here is where my math might need double checking since the PT is an unknown and I had to determine the impedance.

The only low voltage AC source I had on hand is an oddball 20VAC transformer which puts out an actual 26.1VAC.

I applied that to the primary side, which gave me 1.2VAC on the secondary.

So, 26.1/1.2= 21.75, or approx a 22:1 turn ratio.

I square that 22*22= 484, so I have an impedance ratio of 484:1.

Against an 8 ohm load that makes 484*8= 3872/4K

Against a 16 ohm load it's 484*16=7744/8K

So there is the math...and I *think* that I can use these for an Atlas Tweed if:

- I use a 5y3 rectifier, use the 12 volt tap for heaters and wire the 6v6's in series and the 12ax7's for 12 volt, and...

- I use a 16 ohm speaker load so the 6v6's are seeing the higher reflected impedance from the OT.

How did I do?

If it matters I will likely use jj6v6s for power tubes, but really do not want to go with 5881 or 6l6...I'd like to keep the power down to 6v6 level.

Hopefully that all makes sense, hopefully I've posted correctly and if not I am happy to clean it up, and any/all help or comments would be GREATLY appreciated.

Thanks so much everyone and cheers!
Joe

[PRR]

Welcome!

That iron really wants to be a 2*6L6 amp.

Say I want the performance of a 1963 Falcon Ranchero pickup. But I have the engine from a Chevy 3/4-ton. You are correct that doubling the gear ratio "is" laming a 350 engine to nearly a 170 engine. But it is a lot of iron (like double) to carry around.

The 350VAC will spike to 490V, FAR above 6V6 ratings. Yes with bottle rectifier it will sag, and millions of recent 6V6 amps live with 400V on the plates.

I'm also not seeing a 5V winding for this bottle rectifier. 4V plus a finger-slip??

[Paul1453]

I think you will like the sound of your Atlas Tweed better if you get a true PP 6V6 OT.
That should be quite cheap if you are an Ebay scrounger, like me.  Or?
Even a new OT from Doug, isn't too expensive.

You can save this OT for a 6L6 build.

Once you make a great sounding tube amp, you will likely want to do it again and again and again.   

[DenaliJoe]

Thanks for the welcome PRR! Though welcoming a newbie by...you know...throwing reality in my face...that's not really what I'd call warm. And I am of course just kidding. You're absolutely giving me the feedback I'd hoped to hear and your point is well taken. And you're right. I'm trying to dumb down what these were designed to do. (The 4v was probably more my friend's ultra cheap DMM since I measured these at his place where I helped him tear the organ down...those wires were indeed attached to the 5u4g before I clipped them)

Paul thanks to you as well...and I'm with you on cheap. Part of the challenge I'd given myself was "parts on hand"...but a different OT might be the way to go. 

So short of a new OT...and knowing I'm after a really simple circuit and would like cathode bias...I found the Tweedless Current circuit around here. It looks like a Bassman meets M'less Lightning thing, but I can't find any info about this beyond a schematic. Anyone familiar with this amp being actually built successfully?

I'd have to think it would be crushingly loud before getting a little distortion off those 6l6's though, and the individual bias R/C's for each tube are interesting.

Any other suggestions for a lower powered 6l6 circuit with cathode bias? I'd rather not build a Bassman. I suppose I could do a single channel 5E3 with 6l6's and maybe parallel the first stage and stiffen up the filtering to get in the neighborhood of where I wanted to be.

Any thoughts or suggestions are welcome. Thanks gentlemen.

[Paul1453]

My pleasure Joe, and welcome to the forum!

I also have some vintage organ amps I want to convert into excellent guitar amps.

Tubenit, a well respected tube amp designer here, recently posted one of his new 6L6/5881 designs.

The HoSo56, and here are links to those threads:

http://el34world.com/Forum/index.php?topic=20016.0

http://el34world.com/Forum/index.php?topic=20017.msg209452#msg209452

I am hoping to build one or more of these with my organ parts.
It doesn't use a high B+ so I can use my old metal 6L6s or 6L6GAs that I have the most of in my tube stock.
It uses 2 5879 pentodes which you might not have, but they are not that expensive on Ebay.
I also had to get a GZ34 rectifier, which with careful shopping I was able to get for less than $20 delivered.

I would certainly like to have the company of another builder working on Tubenit's design.
Maybe then I wouldn't be the only one asking all kinds of silly questions.
I'll probably still be asking too many questions.
Tubenit and Dummyload have been very generous with spending their time to help me.
Your organ PT and OT may be able to be used on this design.
Those guys will be able to tell you for sure.

Maybe check it out and see what you think.

Best regards,
Paul

[DenaliJoe]

Thanks Paul that's really interesting...I'll go read a bit and see. I'm actually sitting here doing more research and homework on a good 6l6 design right now so great timing...I'll let you know what I think.

I've been scribbling on a 5e5 Pro circuit for a little while...maybe stiffening up the filters, etc to tighten it up...but just not convinced...

Thanks again...more to come...