I picked this one up from a friend.
Copper chassis, 6CA4 rectifier, 2x12AU7, 2xEL84.
Physically large PT, small OT.
Problem is, I don't have that rectifier tube, nor any EL84's to fire it up.
I'm thinking of making a low watt guitar amp project out of it.
I'll most likely end up putting octals in, and using 6SN7's for the power stage. 12AX7's for the preamps. I don't know what to do about the rectifier, I might have to spring for the 6CA4.
Another issue...there is no room for a board!
This has to be point to point. It has a bunch of can-caps (4) on it.
Any ideas for a point to point mini shredder? or miniature TW...4-4-0
maybe?
And another thing...identifying these transformers.
PT is #343PF-649-1
OT is #343A0300-1
Link to the ebay auction showing pictures:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... :IT&ih=001
Gulbransen Organ Amp....Ideas?
Moderators: pompeiisneaks, Colossal
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CaseyJones
- Posts: 856
- Joined: Fri Mar 17, 2006 1:29 pm
Re: Gulbransen Organ Amp....Ideas?
It's junk. 
Sorry. Toss it in a box, send it to me and I'll dispose of it for you.
Go with what you got. It's PERFECT for a cheap-o Spitfire clone, chopped AC-15, 5E3 w/EL84s, etc. Any number of circuits will work in there.
I'd figure out the signal path, stock.
Either track down a 6CA4 rectifier or yank the filament leads off the socket and stick a couple dirt cheap 1N4007 diodes across the socket lugs. There's yer rectifier!
Next, if you figure out the signal path and even without a schematic it ain't rocket science... I'd plug a couple 12AX7s in there, (install the 6BQ5s of course) plug a guitar into the front end and see what I had. I'd expect I could juggle a couple parts, add a volume and tone control and end up with a point to point Spitfire or similar that will make the hair stand up on my neck. Hell, burn a faceplate, dump it in a cabinet... all of a sudden it don't look so "homebrew" anymore!
Sorry. Toss it in a box, send it to me and I'll dispose of it for you. Go with what you got. It's PERFECT for a cheap-o Spitfire clone, chopped AC-15, 5E3 w/EL84s, etc. Any number of circuits will work in there.
I'd figure out the signal path, stock.
Either track down a 6CA4 rectifier or yank the filament leads off the socket and stick a couple dirt cheap 1N4007 diodes across the socket lugs. There's yer rectifier!
Next, if you figure out the signal path and even without a schematic it ain't rocket science... I'd plug a couple 12AX7s in there, (install the 6BQ5s of course) plug a guitar into the front end and see what I had. I'd expect I could juggle a couple parts, add a volume and tone control and end up with a point to point Spitfire or similar that will make the hair stand up on my neck. Hell, burn a faceplate, dump it in a cabinet... all of a sudden it don't look so "homebrew" anymore!
Re: Gulbransen Organ Amp....Ideas?
Ya kill me, CJ!
Yes...I was thinking of a SS recto.
Since I'll have to go and actually BUY the 6BQ5's, I might as well just spring for the 6CA4 recto. ("Orders over 100 dollars=no handling fee").
I'll likely go through this with a fine tooth comb and draw up the layout in Autocad. I can tweak it there and plug all the whatnots into a Tubecad type program.
This thing is loaded with Illinois, Ajax, and Mallory caps!
And carbon comp "mojo" magic.
Clean as a whistle throughout.
Yes...I was thinking of a SS recto.
Since I'll have to go and actually BUY the 6BQ5's, I might as well just spring for the 6CA4 recto. ("Orders over 100 dollars=no handling fee").
I'll likely go through this with a fine tooth comb and draw up the layout in Autocad. I can tweak it there and plug all the whatnots into a Tubecad type program.
This thing is loaded with Illinois, Ajax, and Mallory caps!
And carbon comp "mojo" magic.
Clean as a whistle throughout.
Re: Gulbransen Organ Amp....Ideas?
Alright...I dug up a couple of Spitfire soundclips.
Meh. To my tin ear, a cranked Tweed Champ sounds better.
Not unless they were just bad clips.
Help?
Meh. To my tin ear, a cranked Tweed Champ sounds better.
Not unless they were just bad clips.
Help?
Re: Gulbransen Organ Amp....Ideas?
OK...this thing has an absolute rat's nest on one side of the power transformer around the primaries. I clipped off this side and have to identify
which wires are the primary for the 120V input.
It has 2 black wires, 2 brown, and one striped.
The secondary is no problem.
Is it the two black?
which wires are the primary for the 120V input.
It has 2 black wires, 2 brown, and one striped.
The secondary is no problem.
Is it the two black?
Re: Gulbransen Organ Amp....Ideas?
I figured it out.
(Black/Black of course)
Fired it up...it works!
It sounds pretty good as it is.
Tweaking will be forthcoming...
(Black/Black of course)
Fired it up...it works!
It sounds pretty good as it is.
Tweaking will be forthcoming...
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CaseyJones
- Posts: 856
- Joined: Fri Mar 17, 2006 1:29 pm
Re: Gulbransen Organ Amp....Ideas?
A Spitfire is "one of those things". Same circuit, different voltages, different amp. Similar circuit, stick "Dr. Z" on the front, everyone wants one.Cygnus X1 wrote:Alright...I dug up a couple of Spitfire soundclips.
Meh. To my tin ear, a cranked Tweed Champ sounds better.
Not unless they were just bad clips.
Go figure!
Cygnus X1 wrote:Fired it up...it works!
It sounds pretty good as it is.
Re: Gulbransen Organ Amp....Ideas?
Hey! I've got the same amp! One of a small collection of potential "organ donors" kicking around 
I've never plugged mine in because there's some crazy thing going on with high voltages exposed on one end of the chassis, and all those spooky looking old filter caps, I think at least one is physically broken on mine via UPS.
I did spec out the OT though, I think it's 10K:8 ohms. That PT is just way too big for me to want to deal with, I've been thinking of using the OT for a 6AQ5 amp some day, as they like the 10K load a little better than do EL84's.
Anyway, there ya go, small world. I do appreciate the Gulbransen-labeled Amperex EL84's and Mullard 6CA4 that mine came with.
I've never plugged mine in because there's some crazy thing going on with high voltages exposed on one end of the chassis, and all those spooky looking old filter caps, I think at least one is physically broken on mine via UPS.
I did spec out the OT though, I think it's 10K:8 ohms. That PT is just way too big for me to want to deal with, I've been thinking of using the OT for a 6AQ5 amp some day, as they like the 10K load a little better than do EL84's.
Anyway, there ya go, small world. I do appreciate the Gulbransen-labeled Amperex EL84's and Mullard 6CA4 that mine came with.
Life is a tale told by an idiot -- full of sound and fury, signifying nothing.
...in other words: rock and roll!
...in other words: rock and roll!
Re: Gulbransen Organ Amp....Ideas?
Double post.
Re: Gulbransen Organ Amp....Ideas?
Cool, Alexo!
I ended up taking nearly everything off one side of the power transformer.
The three large can caps can come out if you would like. The selenium rectifier board...remove it. Take off everything except the red/red/and red/orange striped wires that go to the rectifier tube. The only wires you'll need on the primary side of the PT are the two blacks for 120VAC.
That 12 pin connector comes out, also.
Removing those three large canister caps gives an opportunity to put another rectifier in, and using the current rectifier slot for another preamp tube.
I ended up taking nearly everything off one side of the power transformer.
The three large can caps can come out if you would like. The selenium rectifier board...remove it. Take off everything except the red/red/and red/orange striped wires that go to the rectifier tube. The only wires you'll need on the primary side of the PT are the two blacks for 120VAC.
That 12 pin connector comes out, also.
Removing those three large canister caps gives an opportunity to put another rectifier in, and using the current rectifier slot for another preamp tube.