Transformer Re-Winding

[bigsbybender]

Hey fellas,

This isn't guitar related but is related to an antique tube musical instrument amp.

I'm in the process of restoring an amp from a 1936 Hammond Organ model A-20 tone Cabinet (Amp and Speaker Combo). I got the amp when I found the Model A Hammond sans cabinet and speakers. I found a cabinet in St. Paul, MN. on Craigslist. Since then, I got pretty lucky yesterday and found a stash of good condition Jensen field coil speakers with the correct part numbers for free in the attic of a very old local music store. I got some a few years ago, and recently found more.

So to make a long story short(er), I put it all together and fired it up through a light bulb limiter with all tubes removed, and the thing glows brightly. I'm afraid the PT is done for. It looked like it had been pretty hot in the past judging by some of the drippy wax and darkened lead wires.

Since this amp uses a 5Z4 Recto and a pair of '56 tubes driving a push-pull quad of 2A3, (and remotely sends B+ to the '56 and 57' in the organ console) finding a suitable replacement is nearly impossible. None of the names that I know of make a 525-0-525v with 5v and 2.5v heaters. I know some of the hifi guys use 2A3 but the transformers they use tend to be impossibly expensive and wouldn't fit anyway.

Is anyone here capable of rebuilding this PT or know of anyone who is?   I don't want to spend a fortune as the value of the tone cabinets aren't that high (Only Leslies bring the bucks.) I went through a painstaking process of finding correct parts for this restoration so I think only an original replacement or re-wind of the xformer will do.

Any help is greatly appreciated!

j.

[DummyLoad]

kind of buckish... but, maybe a donor amp? maybe a complete replacement?

http://cgi.ebay.com/vintage-webster-electric-hammond-tube-amp-2A3-tubes-/190471203376?pt=Vintage_Electronics_R2&hash=item2c58f7ea30

still thought, a replacement/donor amp may be a less painful time-wise and on the wallet with a rewind.

[Tiny_Daddy]

With a little luck you may be able to find a new Hammond transformer that is the same size and swap out the end bells.

[PRR]

The problem isn't the tubes. Problem is that Hammond clung to Choke-Input filter which nobody else in audio has used in 70 years.

Hammond (no relation) *probably* has something that will work.

[bigsbybender]

The problem isn't the tubes. Problem is that Hammond clung to Choke-Input filter which nobody else in audio has used in 70 years.

Well, she's 75 years young in February....so she was still in fashion in her day.....

I looked over Hammond MFG's line of PT's (The Canadian Transformer and box company) I found a plate supply transformer that would come close but then I'd need to add separate heater supply transformers.... all in all an ugly hack.
Hammond/Suzuki (The US/Japanese Keyboard/Organ company) doesn't support any of their old tone cabinets, so no luck from them.
 
It looks like Heyboer does rewinds... though I have no idea what they or other people are charging.  I did a google search and found a site where it looked like $150-200 for most rewinds. This is certainly a skill that I wish I had at this point. If anyone out there has had some rewinding done, I'd be interested in some testimonials. Though generally in the guitar racket, suitable replacements come easy so this may not be the best venue to find folks with this experience.

ISO, Thanks for the heads up... That's actually a newer amp (by a couple years) than the one I have, it's very similar but not the same. I think the PT is the same, however I can't swing $250 on that... without the intention of restoring it too.   

Below I have a picture, the cabinet work on the front is beautiful, but I can't get enough of these big old bottles so I photographed the business end......


j.

[Ritchie200]

Hey BB,

Check out this post on DIYAudio.  The poster is DCGillespie, the third to the last post.  He has an A20 amp - who knows, maybe he will part with it for cheap?  It's an old post tho...  http://www.diyaudio.com/forums/tubes-valves/166332-using-old-hammond-iron.html

And here on AudioKarma about halfway down posted a few days ago by HornHead - maybe cheap?  http://www.diyaudio.com/forums/tubes-valves/166332-using-old-hammond-iron.html

I can't imagine what a rewind would cost...

Good luck!
Jim

[PRR]

> I looked over Hammond MFG's line of PT's (The Canadian Transformer and box company)

Contact a human there. Hammond iron+box has been in business so long they probably do have a similar part, just not listed or stocked. Tell them what it's for, also how tall and any winding and tube data you have, link to schematic.

They'll get the old guy in the back room to find the plans for something they did back in 1963, and ask you if that's OK. They can probably change stack size, add/omit endbells, no charge; if a major design/re-design is needed they'll have to add a design fee. But an existing plan means it just goes to the shop and gets run the next slack-time between large runs of popular parts.

Compared to re-winding: no shipping TO a winder, no tricky knocking-apart, you save a few bucks. OTOH you are buying new iron... the cost may be a wash. Either way you probably buy all new copper. The all-new part will be too shiny (unless you can match the endbell size and recycle the old mojo-dusted endbells). The leads will be plastic not cloth. (Look for hollow bric-brac in sewing supply store.) The new part is probably more reliable over the next 75 years.

Be VERY sure the old PT is dead before you go this far. Lift ALL the wires off where they go. Peer inside the endbell holes for bad insulation. Lamp-test out in the open. If still shorted, pry the endbells (it may be hard: the thru-bolts must be insulated and that shellacked paper may not want to let go the bolt) and examine. Gently slice the paper and look at the outer winding. You may get lucky. Or you may find a big ZAP where dozens of turns arced and vaporized, which is at least conclusive.

[bigsbybender]

Be VERY sure the old PT is dead before you go this far. Lift ALL the wires off where they go. Peer inside the endbell holes for bad insulation. Lamp-test out in the open. If still shorted, pry the endbells (it may be hard: the thru-bolts must be insulated and that shellacked paper may not want to let go the bolt) and examine. Gently slice the paper and look at the outer winding. You may get lucky. Or you may find a big ZAP where dozens of turns arced and vaporized, which is at least conclusive.

I did lift all of the secondaries and bulb test them.   It's a lay-down mounted PT so I did try to go in where the leads meet the windings.. the paper is very hard, appears to be 'well done' in places and just disintegrates to touch....  I've been at some other forums and email lists bothering others to see if anyone has a replacement. This is coming down to electronics archeology.

Below I have attached the schematic... I had to shrink it down and convert it to get it to upload so I hope it's legible.  Yup choke input filter.... now I was wondering if I used a Center-Tapped 5v winding and or transformer if I could get the 2.5v filament heat from there? I'll have to look up the datasheet for all those tubes to add up how much current I need.

Thanks for the assistance!


j.

[PRR]

5Z3 is 5U4 with different base.
5Z3 5V 3A = one 5V 3A winding

2A3 is 2.5V 2.5A, you have four
'56 is 2.5V 1A, you have two
one 2.5V CT 12A winding

HV is 1,050 V CT, to deliver about 400V 0.25A DC through 2-diode rectifier and choke-input filter (0.163A AC rating)

5V 3A = 15VA
2.5V 12A = 30VA
1,050V 0.163A = 175VA
==========  220VA total load

This suggests an X14 or X15 formfactor, see table here:
http://www.hammondmfg.com/300series.htm
X14 and X15 are the same laminations, X15 is stacked higher.

Ah, Hammond's custom work is $500 minimum. So ask if they can modify a suitable stock item (it seems likely), then try EdCor which is IIRC $25 custom charge (plus the part).

The 382X seems like a suitable base unit, DEPENDING on your existing hole spacing (not given for many of these parts; you have to ask; the overall lam size is rough guide):
382X -- 283VA 1,000VCT@230ma. 50Vbias 5VCT@3A 6.3VCT@6A
CHANGES:
1) Lay-down style (all leads on one side)
2) omit bias-tap (if convenient)
3) change 6V winding to 2.5VCT 12A
4) change 1,000VCT to 1,050VCT (not essential)
5) 115V-only primary acceptable(?)
The base 382X is a $160 part.

[bigsbybender]

Thanks, PRR!  That's invaluable info!

I saw that Hammond has gone very high $$ in the "custom" area. Edcor has bumped theirs up to an easier to swallow $40 for custom work. I just emailed a guy in Texas that claims to have the right transformer...I'm waiting to see pics before I agree to buying anything.
The original used a 115v primary, so the customary Hammond (Mfg) primary would be kosher. 120v would be closer to what the power company sends to my house on a given day though.


I went through the amp again with an Ohmmeter.  Fortunately the Resistance readings on the Choke and Output transformer look good. The Power transformer reads dead short on the Primaries, it reads 'open' on the 2.5v taps, but the 5v and secondaries seem to give reasonable readings. I'll see if this deal down in Tejas is going to work for me, if not, I now have the info I need to custom order!

On a related note, You have to feed the mains power to the amp from the organ through a cable... (no short in cable fortunately). I unplugged the organ from the current limiter to play it through my JTM45 clone but forgot to unplug the special multipin cable from the
tone cabinet amp.... Man was there a fireworks display from the amp!  I got it unplugged before I blew a breaker in my house, but now only the starter motor works in my Organ, the "run motor" won't spin.....   Uh oh.... hurrying may have cost me big!   I think I can fix the problem, but have a lot of digging to do to get to it.....



Thanks again!

j.

[sluckey]

BB, could you use this?

http://cgi.ebay.com/2A3-TUBE-AMPLIFIER-HAMMOND-2A3-TUBE-AMPLIFIER-/200557328401?pt=Vintage_Electronics_R2&hash=item2eb225f811

[bigsbybender]

Thanks for the link Steve!

That's a different (newer) amp than mine, but comparing the schematics, the PT would work for my Hammond amplifier.

If only I could get it to go down in price........   


j.

[sluckey]

If you're patient you may find one cheaper. I thought the price of that one was comparable to a rewind price.

[bigsbybender]

Yup, it is about the same price...  that big can on that is an oil filled reverb tank which is different than mine.  Mine predates the reverb....actually it may be an upgrade to the amp I have, however it's not original.

As I look, I should be able to find a replacement I think....

Most Hammond players prefer Leslie tone cabinets and I believe Hi-Fi guys just want the 2A3's so these amps may be relatively common for parts.... at least I hope.   

My incident where I left the shorted transformer plugged in killed my "On" switch. It's a common style switch, but I'll have to take the whole instrument apart to get at it..... 

Thanks everybody!

j.

[sluckey]

that big can on that is an oil filled reverb tank which is different than mine.

That can is the filter caps.

[bigsbybender]

Yes, You're right, I should have looked at the photo of the guts underneath.  Mine no longer has this because it had Cap-Cans put in it around 1974. Mine also only has one choke other than the field coils. The transformer specs for that one should be the same however.   

I confused that big can for the oil-filled unit reverb that some of these WWII-era units had. 

j.

[RicharD]

I have an oil filled reverb tank.  It's as tall as a geetar.

[DummyLoad]

ding! ding! ding!   

http://cgi.ebay.com/Hammond-Organ-Rauland-quad-2A3-tube-power-amplifier-/160504303884?pt=Vintage_Electronics_R2&hash=item255ecd510c

BB from what you describe, this seems like a drop-in replacement for your amp.

250 clams + ship - it appears to be in excellent shape though.

[bigsbybender]

I have an oil filled reverb tank.  It's as tall as a geetar.

I want to put that in my TWIN (somehow)! 

I'd out splash Dick Dale!

Thanks for the link ISO...  it's basically the same amp but made by Rauland (which still exists) instead of some company from Racine, Wis. that built mine. Hammond appeared to source their amps from a few different makers. It would bolt in and the parts are interchangeable...but it appears to have a second filter choke which mine doesn't have.....again not a big deal.


j.