Tube Amp from Hammond Organ Remains?

[timd]

I know this is a stompbox forum, but what are the odds that I could make a cool guitar tube amp from the tube amp section of an old Hammond organ?

Is this a worthwhile task, or just futile? I also don't really want to get killed from making a mistake with possibly lethal voltages.

[crane]

This is 100% doable.
PT and OT are ususally the most expensive parts in a tube amp build - here you have them both.
you should start by checking PT voltages and determining how many and what output tubes this the amp you have has. This would narrow down your possibilities to few guitar amps you can build from it (at least the power amp. in preamp you can vary quite a lot).
BUT I would like to remind that tube amps contain LETHAT voltages and if you don't feel confident - don't try.

[Cliff Schecht]

There are safe ways to test the power transformer and output transformer if you are equipped to do so. The first thing to do is identify what the ratings of each are. A function generator, oscilloscope and some simple ratio calculations will tell you the PT. For the OT you can measure it but it's not so straightforward IME unless you have an ESR meter for the secondaries. Since they are usually an Ohm or two at most your typical DMM is tough to use, instead I just hook up each tap to a 16 Ohm speaker and see which one is the loudest, middle and quietest (this gives you 16 ohms, 8 Ohms and 4 Ohms respectively for a properly loaded primary winding).

Usually if the transformer set was running a pair of 6V6's and a few preamp tubes then I will choose or design an amp that matches the original tube compliment. The transformers are high quality made in the USA stuff but if you push it too hard you are going to cook something or run into problems. You get all sorts of strange problems (note ghosting, crackles, bad smells) when you push a PT too far past its limit.

With pretty much any old Hammonds that I've seen they need to be gutted and rebuilt from scratch to truly be safe and gig-worthy. Some people like to try to recycle the guts but I find the typical point to point layouts they used in these to be terrible practice and unreliable. I used to like doing point to point stuff when I started because I could crank amps out quickly but 30 or 40 odd amp builds later I find myself thinking through every detail before I drill a single hole. This is especially fun for recycled projects as I tend to build with what I have laying around (admittedly a lot of stuff ) and try to reuse as many holes in a chassis as I can.

There's a whole lot to be said here but if you aren't aware of the safety aspects of working with tube amps like Crane pointed out then you need to familiarize yourself with these first. Then go and study other peoples work and READ before you start throwing stuff together. Amps aren't something you want to screw up a few times before you get them right, it can be especially dangerous if you aren't familiar with wiring up a power transformer to modern safety standards.

I highly recommend www.ampgarage.com as a good place to get started and ask questions. I'm a regular over there along with a large group of some of the most knowledgeable guitar amp builders in the world. We've even got John Suhr and Dr. Z posting over there, as well as the occasional troll by Merlin (). There are tons of threads to read with all of the guitar amp related info you could ever want.

Edit: I take back my comment about most Hammonds being point to point. These were usually on short/long turret boards and aren't such a headache to reuse. I'd personally still strip down the amp and use NOS carbon comps and double check the signal caps for leakage. Also the PT's are wound for 117V instead of 120-125V like we see from modern wall sockets so I use a 3A, 6.3V filament transformer to buck down the wall voltage. If you don't then the heaters and B+ are too high and you cook your tubes. If you use a SS rectifier then you can actually use the 5V tap to buck the wall voltage down a smidge too (learned this trick from RG many moons ago!).

[lowvolt]

^^ Before I say a word, know that I am a confirmed idiot, with a brain running in the nanovolt range .. so forgive me if I say something contaditory to known good logic.  That said ....

Aren't most of the things made for US use rated at "+/- 10%" ??  I'm speaking of the 117vac rating for input power you spoke of vs the 120/125vdc that's being used these days?  (My knowledge of this comes from two decades of working on industrially rated equipment like generators and welding machines .. NOT audio gear .. so I may be all wet in that regard ... Just sayin ..).

I have a couple of vintage Hammond organs and they run just dandy off straight wall current .. in fact I don't know of anyone that plays a vintage Hammond that uses a buck/boost trxfrmr to regulate wall voltage down to 117vac.  And I know a lot of vintage Hammond owners/players.

** just to do the math ...  117vac less 10% tolerates down to 105.3vac .. +10% tolerates up to 128.7vac.  Most of these old Hammond battleships are pretty tolerant of "end-user issues" in my experience, such as a little different input voltages. Hammonds are about as tough as a truck!

1962 Hammond A102 console.
1955 Hammond M3 spinet.
1965 Leslie 251.

I may have misread your post .. chances are that's what is going on here.    It's my forte!    Haahaa!

Also, having rebuilt a few of the preamps myself, you'll find that most of the electrolytic caps are pretty well gonners by now.  While I've never redone any of the POWER amps, the same holds true with them as well.  So make sure that you use good quality caps .. Nichicon, Vishay, etc ...  The Xicon/Chinese type caps have low load life ratings (below 1khours) and not only that they often times don't even live up to their ratings.  A 1k hr Xicon may only actually live half that .. or it may live twice that!  I've found that good quality caps will live at least ot their rated load life.  Try to use caps rated at 2k hours minimum if possible. 

There ... I've dumped my entire box of knowledge on this .. that's all I got on this. 

Thanks.

In any case I'd like to know more about this input voltage issue .. I A.D.O.R.E my vintage Hammonds and don't wish to do anything to harm them.

PS:  This is my very first post here at DIYStompboxes and I see we have the dreaded "flickering-edit-screen-issue" in this forum .. once a post gets below the viewable level the screen starts jumping around.  It won't stay scrolled down to the level I'm posting at either .. it keeps jumping "up".  It's hard to describe but I know other folks have observed this as well.  Dunno   INFO:  Using Internet Explorer as a browser .. byoc does this as well.  Dunno what's up with that.  No other forums I particiapate in do this except here and byoc.  Just sayin'.

Thank you for tolerating my nonsense. 

[Cliff Schecht]

^^ Before I say a word, know that I am a confirmed idiot, with a brain running in the nanovolt range .. so forgive me if I say something contaditory to known good logic.  That said ....

Aren't most of the things made for US use rated at "+/- 10%" ??  I'm speaking of the 117vac rating for input power you spoke of vs the 120/125vdc that's being used these days?  (My knowledge of this comes from two decades of working on industrially rated equipment like generators and welding machines .. NOT audio gear .. so I may be all wet in that regard ... Just sayin ..).

I have a couple of vintage Hammond organs and they run just dandy off straight wall current .. in fact I don't know of anyone that plays a vintage Hammond that uses a buck/boost trxfrmr to regulate wall voltage down to 117vac.  And I know a lot of vintage Hammond owners/players.

** just to do the math ...  117vac less 10% tolerates down to 105.3vac .. +10% tolerates up to 128.7vac.  Most of these old Hammond battleships are pretty tolerant of "end-user issues" in my experience, such as a little different input voltages. Hammonds are about as tough as a truck!

1962 Hammond A102 console.
1955 Hammond M3 spinet.
1965 Leslie 251.

I may have misread your post .. chances are that's what is going on here.    It's my forte!    Haahaa!

Also, having rebuilt a few of the preamps myself, you'll find that most of the electrolytic caps are pretty well gonners by now.  While I've never redone any of the POWER amps, the same holds true with them as well.  So make sure that you use good quality caps .. Nichicon, Vishay, etc ...  The Xicon/Chinese type caps have low load life ratings (below 1khours) and not only that they often times don't even live up to their ratings.  A 1k hr Xicon may only actually live half that .. or it may live twice that!  I've found that good quality caps will live at least ot their rated load life.  Try to use caps rated at 2k hours minimum if possible. 

There ... I've dumped my entire box of knowledge on this .. that's all I got on this. 

Thanks.

In any case I'd like to know more about this input voltage issue .. I A.D.O.R.E my vintage Hammonds and don't wish to do anything to harm them.

PS:  This is my very first post here at DIYStompboxes and I see we have the dreaded "flickering-edit-screen-issue" in this forum .. once a post gets below the viewable level the screen starts jumping around.  It won't stay scrolled down to the level I'm posting at either .. it keeps jumping "up".  It's hard to describe but I know other folks have observed this as well.  Dunno   INFO:  Using Internet Explorer as a browser .. byoc does this as well.  Dunno what's up with that.  No other forums I particiapate in do this except here and byoc.  Just sayin'.

Thank you for tolerating my nonsense. 

Lowvolt......Dude.........

First off, WELCOME!!

I think everyone hops into forums a bit intimidated but you asked some great questions. Since I didn't thoroughly explain my reasoning behind the bucking transformer you asked "THE" question to ask...Why!

The answer is an easy one but I know I won't be able to quickly dig up the graph I have showing why. Somewhere in my tube literature (or the intarwebs tube literature) there is a graph that displays overall tube life vs. heater voltage for a 6.3V tube. What you see is a bell-shaped curve showing that the closer the AC voltage on the heaters of a tube is to its nominal rating (i.e. nailing 6.3V on those AX7 heaters) the longer the tubes lifespan. Now if you are using new manufacture tubes then whatever, you can just go buy more tubes. But I don't use new manufacture tubes, nearly at all really, I use old pulls and NOS tubes a good 98% of the time in my amps. I also use old 117V iron which typically puts 6.3V heaters well above 7V on your modern high wall voltage. This dramatically reduces tube life and has no audible benefits, so instead of burning through my not-so-humble collection of old tubes I aim to get everything dead-nuts on. Otherwise I wouldn't be able to afford an otherwise very expensive habit (tube collecting CAN still be done cheap if you know where to look ).

You aren't going to hurt your organs by running them on 125V but you most likely will ruin the tubes faster than if you stepped things down a bit.

IME the Xicon caps aren't bad at all. I agree 100% that people should spring for Nichincon or other higher quality parts where they can afford to but I'm yet to have a Chinese wonder-cap fail on me in-situ. The important thing to do (that most people don't) is calculate and make sure that the capacitors you are using (especially post-rectifier) can swallow the ripple current you expect it to. Nine times out of ten the caps can but if they can't then they heat up internally (high ESR*ripple current = HEAT!!) and wear themselves out quickly.

[lowvolt]

Hammond amps are set up VERY conservatively.  It isn't uncommon to find them with SIXTY YEAR OLD tubes that are still is great shape.  And just imagine how long they've been running at modern voltages!  The design voltages are pretty conservative and most everything is rated at really conservative levels.  They're designed to be in someone's home for literally decades with little or no maintenance.  My M3 is 57 years old and it still has the STOCK tubes in it!  And I've found no reason to change them either, it's still plenty loud and none of them are showing any signs of wear.  So the variations in input voltage are really kinda not an issue.  I don't see why you couldn't put a bucker in front of it .. I mean more protection usually isn't a bad thing on an old "anything" ... y'know whut I mean Vern?  Heheh ..

But seriously, they are designed with so much over-engineering and so conservatively set up that overvolting them by .. what .. 5% like that (125 vac instead of 117vac) really won't even make the things blink!  It's been a while for me .. as well as having had more stinkin' "VA pain meds" pumped through me than Charlie Sheen (I'm disabled) .. so my memory of some things is a bit flakey ... but if I remember correctly anything in the USA that has a UL listing on it is rated 20% plus or minus.  So an old organ rated at 117vac should be ok all the way down to 93.6 volts, and all the way up to 140.4 volts .. give er take.

I know that when I owned my industrial repair shop the variation on generator output voltages (when setting up a newly installed voltage regulator on a generator repair) was 20% ... and that came from the generator manufacturers ... and they were LIABLE for the stuff people were using the gens to power!

Would I run an old Hammond amp at 93 volts?  Oh hell no!  No sooner than I would run one at 140vac!  I'm just saying that +8 volts on a Hammond ain't gonna even get a giggle out of it.  And the tubes will probabaly just flip you off at 125vac with a smart-assed "is that all you got homey?"  

Again .. the protection you're suggesting is just plain old PRUDENT and probably pretty danged solid workmanship as well .. but it won't won't hurt one of them things at all to run them at 125vac for ten years or so .. jsyk.  

OH .. and thanks a lot for the compliments and the hearty "Welcome!" too.    I'm usually not so bold.  

(THIS DANGED FLICKERING SCREEN IS MAKING ME NUTS!)

[lowvolt]

And not to be a contrarion punk about it here .. but I just did a Nichicon price check on doing a Hammond preamp ....

All 8 electrolytic caps = $7.80 total.  That's seven dollars and eighty cents total cost (Mouser)  

So they just really don't cost that much!  All of them are two thousand+ hour load-life ratings too!

[digi2t]

(THIS DANGED FLICKERING SCREEN IS MAKING ME NUTS!)

(Guessing at what is bugging you here...) If you`re running IE 8, this sites text boxes has a problem with IE 8. This might be because your IE 8 is not running in Compatibility View. I had the problem with IE 8, the text would start jumping up and down when I would get past the bottom of the text box. Go into the Compatibility View options, and check the box that says ­­``Display all websites in Compatability View`` (or something like that). Restart IE, and you should be fine. That cured it for me.

DO NOT CLICK THE COMPATABILITY VIEW BUTTON NEXT TO THE REFRESH BUTTON, AFTER YOU HAVE TYPED IN YOUR TEXT, IT WILL ALL DISAPPEAR. The screen refreshes, giving you a nice new... empty... text box. Also, it only works once, and you have to click it every time you come here. Major PITA.

I hope this helps.

Cheers,
Dino

[timd]

Thanks so much everyone for all of this info!

[PRR]

> I A.D.O.R.E my vintage Hammonds and don't wish to do anything to harm them.

As you say. 60 years of hard use and neglect in church didn't kill them, often did no harm at all. Nothing a casual guitarist does is any worse. (If it's booked for a 200-stop world tour, it would be wise to go through carefully OR buy some spares while they are common.)

I'll dis-agree with gutting. While not Fender/Marshall flavor, many of these amps are quite musical dead-stock. Fix what's broke, adapt the connectors, add a preamp, play. This does tend to be case-by-case: the oldest ones depend on field-coil speakers to load choke-input rectifiers and are not readily adapted to magnet-speaker use. The very last ones were cost-driven and less inspired. But many do NOT need gut-work, just some in/out conversion.

[tubegeek]

As always, RG has some info for you:

http://www.geofex.com/Article_Folders/old2new.htm