Gulbransen Organ Amp....Ideas for a Guitar Amp?

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...MEWN:IT&ih=001

18W sans trem.

Quote:

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Originally Posted by Kap'n

18W sans trem.

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Good call, Kap'n!

That's providing I put about 50 dollars worth of tubes in it.
I wonder just what the 18 watt sounds like?

From what I've seen...the EL84's would give off a characteristic Marshall midrange "snot" that I don't like. Even the SEL's I build...I modify to get rid of that tone. I go for a clear low, with gain on the high end.

I could be completely wrong about the 18 watt properties. I never have played one...what about Vox?

Depending on how you build & preamp it the 18w can sound like almost anything, not just Marshall-Snot (I love that). I'd think with 6SN7 or maybe 6SJ7 in the preamp instead of the power section you could get an outrageous Tweed-Snot out of it. :biglaugh:

If you like the EL84 sound but not M.S., maybe go for something in the Vox family of sound. 2xpower, 2xpream & tube rec leaves you a lot of options to explore - really, a LOT!

Hit the 18watt.com message board for ideas. Those guys know the myriad variations in the 18W family like nobody else including some leaning toward Fender, Marshall, Vox, TW, Dumble & a lot of others. It's also very friendly over there so you don't need asbestos pants if you ask something a little off-topic or something that's been asked about 100 times before.

If you can find a schematic for your donor amp, it can go a long way toward helping you figure out what kind of output your transformers can deliver under load. Chances are the organ's PT is WAY more than you need just to get by and should deliver more current that you'll likely need for a small guitar amp. Remember that organs usually have all kinds of non-amp items running off the PT as well. Everything from motors to lights and even external units are often wired to leech power from the same iron doing the heavy lifting for the audio. Most salvaged tube organ iron makes for great guitar amps with tons of punch & clarity. The tradeoff is that they sometimes weight more than the loaded chassis, cabinet and speaker combined.

Not like that's a bad thing! :salud:

BTW: Copper chassis - COOL! Polish that baby up and clearcoat it!

Your rectifier is all over the 'bay for not a lot of $:
http://tiny.pl/svlj
If you search for EZ81, you might get better (and cheaper) results.
You can also use this :: http://www.jj-electronic.com/pdf/EZ81.pdf :: to help you find alternatives.

Cheers,
- JJ

Thank you, JJ!

The amp crawlers around here have probably noticed I have an identical post on several amp forums. I'm getting a lot of great ideas.
Turns out if I order enough (over 100 dollars) from Antique Radio Supply, I can grab the tubes I need for around 40 dollars.

I will have to make a drawing of the current layout. No hope of getting the schematic, unless I post Gulbransen (if they are still in business). I Googled everything I could think of.

Looks like I can stick with what it was designed for, and push it a bit.
Great stuff...keep it coming!

And remember...it HAS TO BE point to point.
No room for anything else.

IIRC Gulbransen was ultimately bought out by Fender. If'n you have a point-of-contact within FMIC mebbe one of the "older hands" there might point you in the right direction for a schematic and/or other info regarding this organ amp.

HTH

Quote:

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Originally Posted by phantomman

IIRC Gulbransen was ultimately bought out by Fender. If'n you have a point-of-contact within FMIC mebbe one of the "older hands" there might point you in the right direction for a schematic and/or other info regarding this organ amp.

HTH

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Ahem.

I used to live in Scottsdale...you are a lot closer than I am.
I'll check with the new guys, to see if they can get in touch.
:smile:

I "know" some new hands, not any old ones.
Thank you, PM.

i know you're not too keen on the marshall, but the 18 watter is pretty sweet. it does get gritty like a marshall, but at the same time it sounds sort of like a vox ac15, not exactly mind you, but sort of. the break up is nothing like either a vox or marshall, but a happy medium. i have one, and my buddy mark has a combo, both with mercury mags... they are oh so cool. try out one of the newish marshalls, you might like it.

Ihave that same amp, just swapping in a 12ax7 gets you a bunch more gain.
I moded the amp and added a tone control for now, but I may mod it again with just a cap for the needed tone.
With good outputs the little baby will churn out 10 watts RMS.

Well, I ordered the rectifier tube, and 2 EL84's for it.

I have to figure out what these connectors are for...there is a 12 pin in which 10 are wired. Another couple of two-pinned. One for power, the other for a standby I guess?

I am going to skip the tube rectifier and bring it up with a variac slowly. The can caps look ok, but I would rather form them back than shock them outright.

I would have to check which model I have, but if you have all crap on one end of mine unit as I did( SS rectos, relays and plugs and all) all that crap can just come off, but I do recall one place where I did thave to mod the original power supply wiring other than the primary end of the PT to get a on/off switch in it, but I can not recall waht it was.I will post my amps model number so you can see if its the same, then may be I can help.
One things for sure, if your model is the same as mine, you end up having that big PT to just power a 5 tube circiut so the plate voltage is quite stable!

APS-4.

Man, I had some of those 6CA4. I hope they weren't in the pile of hundreds I threw out last weekend. Lemme see if I have any left.

Don't discount the wimpy rectifers. The lower voltages oftentimes make for better OD tones. My '57 Silvertone is God-like and it uses a 6X5.

:doh

Yes sir! my silvertone 1482 and both my univox U45B amps are great sounder`s with those 6X5 rectos, but a 6ca4 is even a beefer recto.

I have a rectifier chart...somewhere.

EZ81/6CA4: 1A Heater Current, 150ma, 28V Voltage Drop,
1.3V Voltage increase (plate to plate)

6X5: .6A Heater, 70ma, 22V Drop, 1V Increase.

BTW...what is this little mess that looks like a small inductor?

Yup, mine is the aps-4 model also.
That amp has alot that can come off it,
eveything on the non- tube side of the PT can come but for the fuse holder and the power cord, so like those 3 filter cans and all of the wiring that goes to them can be ripped out.
Your speaker out put wire will come off of the 8 pin black socket on the other side of the amp, you just have to trace the wires from the OT back to the socket and solder on a new lead.

OK, I have the tubes.
Wish me luck...I'm digging in!

Hey Steve, do you happen to know what the output ohms are for that OT?

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?

I figured it out.
(Black/Black of course)

Fired it up...it works!
It sounds pretty good as it is.
Tweaking will be forthcoming...:D

I forget if its made for 16 or 8 ohms, I want to say 16, but I will check mine tonight and let you know in the morning.

I know you've gotten pretty far down the line with this already - and we've had a few discussions about using 6SN7's in P/P - if you use a couple of 'em then the OT will likely be out of whack but if you use a single 6SN7 it's a perfect fit for the 2xEL84 P/P OT - we're now experimenting with an 8K with both 8 & 600Ω secondaries - three guesses where we're headed with that... I'll give you a clue - John's building a 50W power amp with selectable ss or tube rectos, cathode or fixed bias and pentode triode switching... he's mad as a hare and we've no idea yet how/if it'll even work but - hey - that's what's all about :D :D

yankeerob...

Where are you when I need you?
:lmao:

Actually, no problem.
I fired it up, and it awaits further planning.
Nothing has been touched otherwise...yet.

It doesn't need much at all for Kap's 18 Watt idea, or a Matchless Spitfire either. I will probably look at both. Since I haven't played either...well, who really needs 9 different amps, anyways?

Wait...:smile:

Quote:

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Originally Posted by Cygnus X1

yankeerob... Where are you when I need you? :lmao:... It doesn't need much at all for Kap's 18 Watt idea, or a Matchless Spitfire either. I will probably look at both. Since I haven't played either...well, who really needs 9 different amps, anyways?

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I'm usually at the mill... pulling things apart and putting 'em back together... I check my email pretty regular though... drop us a line anytime - oh yeh, having a load of little amps is cool though - they're kinda like children... that you can switch off when you want :D

The OT in that organ amp is looking for a 16 ohm load. Sorry it took so long to check mine.

Quote:

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Originally Posted by steve25

The OT in that organ amp is looking for a 16 ohm load. Sorry it took so long to check mine.

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Good!
That's how the cab is wired.
:smile:

I forgot to mention to you that with out that PT powering the rest of the organ the plate voltage on those el84s rides up to some 360 volts and thats too high.
What you have to do is change that 130 ohm 5 watt resistor on the recto socket to a 560 ohm10 watter to get that plate voltage back down to around 300.
The 10 watt is too long to solder across the recto scoket again, so just place it from the recto to the next filter connection( other end of red wire) on the other side of the chassie and insulate the leads, as that connection on the amp chassie wall of the the recto scoket is real close to shorting out!

Thank you, steve25, I didn't even check it.
I just ran it long enough to see if it works.

I have another organ amp coming to me.
A Hammond M2.
Things are piling up a bit.
:D

Its always good to have things stacked up to play with on a snowed in weekend!

Dumb Q:

What is this "EXP Control" hooked up to pin 1 of the the first preamp socket?

It also has two very large brown disks (they don't look like caps, just brown with a coil of wire encased in them) in the same circuit. Some sort of external volume control connection?
The "volume" pot is actually connected through the input to pin 2. So it simply restricts the signal.

I'm going to remove this "EXP" mess. It doesn't fit anything I am about to do.

Bump to announce the birth of a newborn!

It is now a Spitfire clone.
Quietest build yet...but some tweaking needed to contain the farty distortion. Official word and pics will come in the Amp Section later.

Very Vox-ish to my ears.

Expression pedal? :D

Yeah, Rob...who knows?
It's out of the equation now...it must have been part of the volume looking at the way it was connected. I ended up stripping everything and built the Spitfire circuit in it.