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DIY Stompboxes => Building your own stompbox => Topic started by: sarakisof on February 12, 2020, 12:46:23 PM

Title: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 12, 2020, 12:46:23 PM
Hello everyone, i found a Farfisa Compact organ (uses 2xECC83s for spring rvrb and preamp) that needs recap and some electronics troubleshoot. But before going so, i want to clean the PT first. I opened it and found this situation inside. The previous owner was a painter and seems something like a paint or similar was spilled because i found some paint stains on the top cover above the PT too. It is a weird material though, like an old sticky dried powder dirt. Like wall plaster or smthng. And a bit rusty. Found that the long screw that holds the two bells together and gets inside the laminations hole, has also some of that white plaster stuck. Do you thing it could damage the laminations inside, as it is passes and get screwed through them? The organ plays perfect in terms of PT and voltages are all fine.

Mostly i wonder how i can get this plaster dirt out of the bell, as you can see in the pic is like a mess. I don't want to unsolder PT so to extract bells and do a total job.
What do you guys would do if you were in my place. It doesn't affect smthng obviously, but you know, i d like to clean it a bit. Maybe cover top chassis and try brass wire brush or sandpaper and then paint clear with clear rustoleum varnish as long as the laminations too?

 

(https://i.postimg.cc/xNSZZszB/86266701-2527207740724529-7094502854425051136-n.jpg) (https://postimg.cc/xNSZZszB)



(https://i.postimg.cc/TpNzdcM5/PT2.jpg) (https://postimg.cc/TpNzdcM5)
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: GibsonGM on February 12, 2020, 01:06:41 PM
It really looks like a drink spill, to my eye.  Not a paint substance (I'm a painter...), tho it could certainly be joint compound/plaster.  It could be anything! lol     I'd remove what I easily could...wouldn't dig too much into the trafo guts, not at all.   

Just, a toothbrush (nylon etc - non metallic!), maybe evaporative solvent on a rag, just get it off the bell.   Water & rag alone would clean it if it's joint compound. And I'd leave it at that, wouldn't introduce anything new like poly.    Use rags to keep the gunk out of the rest of it as you work, vacuum it up, then blow it out before power-up...

Just my 2 cents!  Nice rig.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 12, 2020, 01:22:51 PM
Nice input, yeap i ve thought of all those too. I will try with a rag and isopropyl alcohol first, but from my experience isopropyl alcohol doesn't clean dirt so i maybe try some baking soda first or warm water green soap.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: GibsonGM on February 12, 2020, 03:07:02 PM
IMO, you'd want to use a DAMP (not WET or dripping!) rag....then allow it to FULLY dry, of course  ;)   Even apply a hair dryer....you know the routine...
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: ElectricDruid on February 12, 2020, 03:30:54 PM
IMO, you'd want to use a DAMP (not WET or dripping!) rag....

...and make sure the caps are discharged at that!

Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: antonis on February 13, 2020, 06:46:50 AM
I just wonder if it's a spill of battery leakage..  :icon_cool:
(in such a case, use medium copper brush & vaccum hood..)
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: tubegeek on February 13, 2020, 10:49:39 AM
Just a reminder - you don't necessarily want to clean all the rust off of a power transformer. The laminations are intentionally oxidized a bit to insulate them from each other and enthusiastic cleaning can introduce a short between them. This will increase eddy currents/reduce efficiency. Definitely a small effect to be sure but something to know before attacking.

What I'd do: wire brush the part of the bell that's completely outside the laminations (after borrowing Antonis' vacuum hood perhaps?) and avoid the lamination edges as much as possible.

There's a spray-can product that is meant for converting rusty metal to a paintable surface - it may be useful in this situation, I'm not sure.

Then cry cry cry now.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: antonis on February 14, 2020, 05:51:12 AM
(after borrowing Antonis' vacuum hood perhaps?)

A bludged vacuum hood should be a non-negotiable spousal casus belli..!!  :icon_frown: :-\
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: duck_arse on February 14, 2020, 08:44:30 AM
(after borrowing Antonis' vacuum hood perhaps?)

.... bludged .....

sometimes you surprise me, antonis. also - transformer bells, carry on.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 14, 2020, 11:53:01 AM
haha thanks guys. So i managed to remove the white material mess, it can be dissolutted and be removed with a bit hard proccess, but it had left a brown spot in underneath - probably rust from the material - that it is hard to remove. I will try though.

Also, something related, antonis and others, please have a look at this thread too: https://www.diystompboxes.com/smfforum/index.php?topic=123852.0

Most people suggest the product Fertan or any similar Rust Converter based on tannic acid, not phosphoric.
What do you think of using AmbroSol Rust Converter instead of Fertan? Talked with local dealer and told me it has no "etching/corroding warning", only the usual "danger warning". He also compared it with another can of Rust Remover and told me it has both "danger and corroding/etching warning" sign.

https://www.ambro-sol.com/wp-content/uploads//I260_EN_rev.0.pdf
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 14, 2020, 12:05:24 PM
And smthng more: all people mention the "appropriate" common Rustoleum for painting/coating their transfos, but heh, which one is the "appropriate" for this use? Rustoleum produces a generous number of products out there.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: GibsonGM on February 14, 2020, 12:47:07 PM
I'd leave it alone.  Just my impression...thing is vintage, it's expected to have seen some use, and have some wear.  I wouldn't paint it.  I don't think it'll go thru any inspection...   

If I did paint it, I'd get a small bottle of Testor's model paint, silver, and just do that end after you clean it up.   But I wouldn't, so that's moot  :)

I think they mean simple "Rustoleum" spray paint.  Original...basic....nothin' fancy.  If you go to the trouble, probably should prime it first, too.  Mask everything.   I'd leave it alone tho, let its age show.

Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 14, 2020, 01:18:56 PM
yeap i will apply rust converter first and then rustoleum. So you think smtgng simple like that woyuld be ok right?

(https://i.postimg.cc/TyQ920hL/e85f96df-a13b-49c8-bf4e-6d87b72d2d7c.jpg) (https://postimg.cc/TyQ920hL)
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 14, 2020, 01:53:27 PM
Also look at the specs from datasheet of the AmbroSol product i m going to buy. It says "Temperature of exercise +5C / + 75C"

https://www.ambro-sol.com/wp-content/uploads//I260_EN_rev.0.pdf

Do you think 75C is OK for transformer use?
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: GibsonGM on February 14, 2020, 03:05:14 PM
Well - in the picture, that's just clear coat.  It has no color! Only for protection as a top coat.   

I truly believe if you simply clean the bell off, and leave it alone, it will be fine!   It is a vintage piece - painting things reduces their value, EVEN if they are a little bit scarred by their 'life'.  Nobody will mind if it is not perfect!  If you do this incorrectly, you could damage it, cause it to short out and so on...ruining it!

To properly do this, you should remove the trafo from the enclosure so you can access all of it.  I don't think you should get into that.   You would need to disconnect it and that is work that seems unnecessary. 

Can you post a pic of it now that you have cleaned it off?
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: Rob Strand on February 14, 2020, 04:23:17 PM
Quote
I truly believe if you simply clean the bell off, and leave it alone, it will be fine!   It is a vintage piece - painting things reduces their value, EVEN if they are a little bit scarred by their 'life'.  Nobody will mind if it is not perfect!  If you do this incorrectly, you could damage it, cause it to short out and so on...ruining it!
Agreed.   There a lot of opportunity to make things look worse or even damage the transformer. 

There's guys out there that pull stuff apart, re-plate metals, and the final job looks like a million dollars.  The thing is those guys have done it all before, have had many fails, and have learnt from their mistakes.   I guess you have to ask yourself is it worth the risk of failure for a one-off.

To me it doesn't look like rust.  It looks like something has attacked the outer plating.   My guess is it's zinc and the white stuff is zinc oxide (doesn't look like cadmium plating from that era.)
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 15, 2020, 08:35:38 PM
It was a hard day today. I fully unsoldered it and disconnected it from chassis. Things were a bit bad there. When i unscrewed the long screws which hold laminations together the two "I"s from both side edges landed to the floor. All the other laminations seem pretty solid as they should be. So i started searching and found old videos i ve been watching in the past for glueing laminations. I saw again this video from D-lab etc etc
https://youtu.be/dtOwewfqucI
In meanwile i managed to clean all that rusty stuff out from the bell and the power enclosure chassis. Dremel wire brush could not do the job perfect, so i dipped those metals into Hydrochloric Acid for 2 minutes and job was done totally. The material was immediately disolutted. Seemed it was spilled battery leakage, as some areas and a ground bare wire had been corroded getting that "blue-green corroded salt".
Now i will Zinc plate them and see how it goes.
I was out all day searching for rust converter (non abrasive-nin phosphoric acid, but tannic acid based) , varnishes, clear coats, oil based wood paint etc but it is really hard to find those dedicated products in my area. You can only find simple acrylic varnish, strong rust removers and wood varnish water based  :(

So i will wait and ordered Fertan rust converter, a wood varnish oil based and rastoleum black.
Here is why.
I am planning to convert first the remaining rust from laminations, as you can see there is rust on top lamination. I want the Fertan for other transformers i have too, that have some "grey" little areas (black coat has been slightly gone off in some little areas).
Then i will glue the two "I" laminations with oil based wood varnish like in the video. I found a simple one and another that contains a bit wax. Do you think this with wax would be better?

Finally, i will apply rustoleum black paint to laminations to look like new. You will ask "why don't get an oil based wood paint black"? That's because i want to get a spray can, as i told you above i have some other transfos that i want to do a similar job, but without disconnecting them from chassis. I will cover chassis and spray them.

So rust converter(tannic), wood oil varnish to glue the two "I"s and rustoleum black paint.

Tell me what you think of.
(https://i.postimg.cc/8fkvwwYQ/IMG-20200216-015901.jpg) (https://postimg.cc/8fkvwwYQ)

(https://i.postimg.cc/3WhFdFnZ/IMG-20200216-024345.jpg) (https://postimg.cc/3WhFdFnZ)

(https://i.postimg.cc/75J2B5K6/IMG-20200216-024453.jpg) (https://postimg.cc/75J2B5K6)

(https://i.postimg.cc/BX6DKYD2/IMG-20200216-024556.jpg) (https://postimg.cc/BX6DKYD2)
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: GibsonGM on February 15, 2020, 09:57:05 PM
It looks very good.  As I said...it looks good enough for me.  (ha ha!).

If you want to paint, Rustoleum is basically oil-based.  It is close enough for your purposes.  They do add other things to make it into an aerosol, but that's probably not an issue here.   
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 16, 2020, 02:38:41 PM
Is it OK to use simple water based wood varnish instead of oil based PRR suggests to glue the two "I" laminations ?

https://youtu.be/dtOwewfqucI
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 19, 2020, 04:06:34 AM
After a loong but beautiful research journey i managed to do it guys  :)
As you know from previous posts i had already get all the dirt and rust (battery leakage/white strange material) off from the bell and upper chassis. After that i just coated them using 3 layers of simple acrylic metal spray varnish.

About the two de-attached laminations now, after many hours of reading, thinking and asking many people, i finally talked with a guy that makes his own tube amps and transfos from scratch. Being experienced in coils, he suggested me to call a company that sells raw materials for making transformers to customers and large companies. Coils, motors, laminations, varnishes and all that kind of stuff. The engineer guy there was kind enough saying to avoid any common wood varnishes and told me to go straight for Electrical Insulated Varnish, Polyester based. You know, industrial pro stuff like Dolph's AC-43 Varnish for insulatin and potting transfos and coils.

http://www.sinadinos.gr/pdf/ALBESIANO%20AC-43%20ing.pdf

He indroduced me immediatelly to co-operate company that repairs and makes transformers, coils and motors here in my town, i went there with an empty can and in 5 minutes the guys there offered me about 1/2 litre local Clear Air Drying Electrical Insulated Varnish for free ! The varnish is called "Elektrotek 428" and i think it's the local equivalent of AC-43. They use them in large quantities so when i went there handling two small laminations they laughted  :P

https://www.sinadinos.gr/pdf/Electrotek_428_en.pdf

As an answer to my question about "if this will be OK for audio transformers etc." i wa told that it would not be a problem even if i would give a bath to the whole transfo into the liquid, that's what they use for potting.

So i went home, glued the two laminations with it clamped for 12 hours,  then applied another two layers of it to the whole outside laminations and let dry for about two days. The transfo is sealed like never before, having covered any "bare lam areas etc", it is a insulated tank  :icon_biggrin:

The "bad" thing is that i cannot get my hands in it any time in future as it is almost impossible to deassemble the lams anymore. I don't know if it is "bad" but i don't see any reason of doing this, even if there is some small ammount of rust already inside laminations that i cannot see, i mean i cannot do smthng for that (well except for with Fertan that it is said to can acces into lams and convert the rust anyway), this rust could maybe reach the core someday, i couldn't do many things for thisanyway. I don't know if the lams must "breath", but i don't think so, as that's the way they do it from factory, i mean, they seal them right?

In the end of the day, i re-assembled the whole thing back, bells, wires everything, soldered back to chassis underneath, fired it up and all work GREAT !  :icon_biggrin:

Measured power voltages, all perfect, i got 274-275 V. at the first filter cap and 229-230 V. in the second !
Multimeter always moving between "274 and 275" , "229 and 230", it never gets stabilised at "275" or "230", but i guess this 1 V. isn't a big deal right?
Was measuring about half an hour and exactly the same steady numbers.


(https://i.postimg.cc/v4CnLfZZ/COMPACT-VOLTAGES.jpg) (https://postimg.cc/v4CnLfZZ)

What do u think guys ?


(https://i.postimg.cc/VrBN3bB1/86857623-193761808497917-8890584510333190144-n.jpg) (https://postimg.cc/VrBN3bB1)

(https://i.postimg.cc/hfvvhv14/87045608-239601257049314-3889796432235855872-n.jpg) (https://postimg.cc/hfvvhv14)

(https://i.postimg.cc/xXH0bzJQ/87160167-491126868435629-6577029444957896704-n.jpg) (https://postimg.cc/xXH0bzJQ)

(https://i.postimg.cc/N9G944mm/87369304-2426035274374021-3780363757910228992-n.jpg) (https://postimg.cc/N9G944mm)

(https://i.postimg.cc/2bXptkbT/86857605-246622089671659-4983636899294871552-n.jpg) (https://postimg.cc/2bXptkbT)

(https://i.postimg.cc/1fFxWZ9c/87036518-2744362535663001-70315851655413760-n.jpg) (https://postimg.cc/1fFxWZ9c)

(https://i.postimg.cc/KKZdvktJ/87022538-2550388285218677-3240566323914211328-n.jpg) (https://postimg.cc/KKZdvktJ)

(https://i.postimg.cc/qhFYL1S5/84299585-125376945498800-4944465667978952704-n.jpg) (https://postimg.cc/qhFYL1S5)
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: GibsonGM on February 19, 2020, 05:25:44 AM
That is a SUPREME job, sarakisof!!  Very nicely done!  Very good that the trafo company helped you out!

The very slight voltage variation, I would not worry much about.   Your next project, however....is to replace all of the electrolytic capacitors, which are now getting VERY old.  They dry up and degrade with age.   Audiophiles change them in 10 to 15 years, many times.  Yours may be 50 years old, ha ha.   I see from reviewing your original post, you know about this.   Good luck, it should not be a difficult job.

Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: antonis on February 19, 2020, 06:03:02 AM
Does the ancient spring reverb still works satisfactorily, Sofoklis..??
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: duck_arse on February 19, 2020, 09:24:44 AM
Quote
What do u think guys ?

I think it's a good story well told. and a nice outcome. where the hell do you keep finding these organs?
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: tubegeek on February 19, 2020, 11:07:01 AM
What do u think guys ?

I think it's all about the friends we make along the way, and making friends with a transformer shop is as good as it gets!
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: pinkjimiphoton on February 19, 2020, 01:58:12 PM
wondering if the dust was just old dry rotted potting wax from the transformer?
also, old insulation in these sometimes either evaporates or turns to a nasty sticky goo. as the stuff evaporates, the fumes seem to break down other stuff made of plastic in these.

i have a combo compact if ya need parts that needs a home. if interested for a fair price, pm me. the one i have DID work last it was plugged in, tho there's a note "Stuck on" i am assuming is likely a bad cap or something. i was gonna just part it out for germanium, but better to recycle if someone can use it.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 21, 2020, 02:36:33 AM
.....
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 21, 2020, 04:14:28 AM
Your next project, however....is to replace all of the electrolytic capacitors, which are now getting VERY old.
Take a look at my last post's pics, i am already in the proccess of doing this. Have replaced all electros on tube power and preamp section and some others in one or two problematic tone generator cards alongside with some faulty SFT 352 Germaniums - replaced by Soviet ΜΠ20Α PNPs, after having geofex tested them out (thats why u see markpen dots on - i hfe grade by marking them).
I use to repair vintage combo organs, i love them. In the past, i used to make pedals, diy tube amps, vintage condenser mic clones and stuff like that, guitar/bass stuff mostly, but since i found my first combo organ four years ago, the Elka Panther 300, i then felt in love with them. I learned to play keys and blend them into my music, because i was fixing them... Now i play more keys than i play my guitars and basses. That's the amazing world of electronics don't u think?
I do a full repair job on them, meaning internal full electronics and external cleaning and maintenance, trying to keep the original character and shape as much as i can. Even for the simple common 3 prong fix job, i try (if it's possible) to reuse the original prong - cord . I really do care of them and think -amongst others - they are part of our musical history. Never ever a VST or anything similar can be the same with the real thing. But u know they are huge and heavy..

I think it's a good story well told. and a nice outcome. where the hell do you keep finding these organs?

If you are patient and search hard enough you can score some nice finds out there. Local ads and other older musicians mostly.

So far, i am a proud owner of the following monsters: 
Elka Panther/Capri Dual 300, Farfisa Fast 4, Farfisa Fast 5, Farfisa Foyer (rare version one, with 6 voices, not the standard), Farfisa Compact, Philicorda GM 751 full tubes version and two Philicorda's GM 751 transistorized.

As you can understand there is no more free room in the house my 3 year old son to play  :icon_biggrin: Wife warned  "no more combos, just get guitars or basses, they don't take so much room like organs do" mission accomplished: more guitars now  :icon_lol:

Does the ancient spring reverb still works satisfactorily, Sofoklis..??
Yeap absolutelly, it works like a charm! I didn't excpected to, but heh i was lucky this time.
Not like wit my Foyer. I had opened a loong thread here months ago for my other Farfisa the Foyer model (like Farfisa Mini, plus spring rvrb and full tube circuity - 1 rectifier,3 pre's and  2 output tubes), it's a great organ and my most beloved so far, but if you call back in mind this old thread you can see there i finally managed to make the spring reverb functional, but it is a bit weak compared with the loud-full signal in the Compact.
I will be patient, i am sure sometime i will find a Foyer for "Free Pick Up Collection", canibalize it and get the piezo cartridges from inside.
Or maybe pinkjimiphoton
i have a combo compact if ya need parts that needs a home. if interested for a fair price, pm me.
could send me just the piezo cartridges or a substractional power trafo for my Compact who knows  :icon_mrgreen:

So, "no more combos anymore", thank you guys for the discussion, it's a warm place here  8)

What do u think guys ?

I think it's all about the friends we make along the way, and making friends with a transformer shop is as good as it gets!
co-sign

(https://i.postimg.cc/47m36x6k/4.jpg) (https://postimg.cc/47m36x6k)

hahaha  ;D

(https://i.postimg.cc/XrkX3hjh/3.jpg) (https://postimg.cc/XrkX3hjh)

(https://i.postimg.cc/HjFrtXvS/1.jpg) (https://postimg.cc/HjFrtXvS)

(https://i.postimg.cc/MMTn9D8L/5.jpg) (https://postimg.cc/MMTn9D8L)

(https://i.postimg.cc/R3v6Hmp4/2.jpg) (https://postimg.cc/R3v6Hmp4)








Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: Rob Strand on February 21, 2020, 04:32:49 PM
Great story with a happy ending.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: PRR on February 21, 2020, 07:17:39 PM
> Wife warned  "no more combos, just get guitars or basses, they don't take so much room like organs do" mission accomplished: more guitars now  :icon_lol:

https://www.greatbigstuff.com/products/guitar
http://www.guitarsite.com/news/and_finally/giant_guitar_boat/
(https://live.staticflickr.com/3095/2560804377_2beab0a42a_z.jpg)
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: Rob Strand on February 21, 2020, 08:22:34 PM
The biggest guitar I've seen,

https://www.ecorazzi.com/2012/09/10/man-plants-guitar-shaped-forest-to-honor-late-wife/

Saw this by fluke looking out of the window of the plane coming back from Uruguay.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: PRR on February 22, 2020, 07:57:04 PM
Nazca Guitar, Cordoba, Argentina in Google Maps sky view
https://www.google.com/maps/place/Nazca+Guitar/@-33.8684992,-63.9866841,1238m/data=!3m1!1e3!4m5!3m4!1s0x95cfc846ed52133d:0x4519fb7d7fdc2cc9!8m2!3d-33.8677431!4d-63.9864779
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 24, 2020, 02:02:38 AM
> Wife warned  "no more combos, just get guitars or basses, they don't take so much room like organs do" mission accomplished: more guitars now  :icon_lol:

https://www.greatbigstuff.com/products/guitar
http://www.guitarsite.com/news/and_finally/giant_guitar_boat/
(https://live.staticflickr.com/3095/2560804377_2beab0a42a_z.jpg)

 :icon_mrgreen: :icon_mrgreen:

Just for the record, after full recap the beast.


Pass me the Ketchup please ...
(https://i.postimg.cc/t75WFFv0/7.jpg) (https://postimg.cc/t75WFFv0)

(https://i.postimg.cc/F7CSBNQD/10.jpg) (https://postimg.cc/F7CSBNQD)

(https://i.postimg.cc/XGgGc08K/9.jpg) (https://postimg.cc/XGgGc08K)

(https://i.postimg.cc/nMHQVCF3/8.jpg) (https://postimg.cc/nMHQVCF3)

Something last: Previous owner had replaced original fuse with another one bigger amps (probably just what he got in hand), so i had to replace it too in first steps.
Maybe stupid question, but schematic mentions just "Fuse 0.5A - 250V.", no fast or slow anywhere. I used a slow blow. Is it OK or i shoud go with fast one?


Pages 4, 7 and 38.
http://www-personal.umich.edu/~damont/FarfisaComboCompactCompleteUserServiceManual.pdf

Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: anotherjim on February 24, 2020, 04:10:09 AM
Generally, low current fuses will be slow-acting to avoid blowing with a switch-on surge that can be expected to be much greater than the service current - like having a lot of caps to charge up.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: anotherjim on February 25, 2020, 02:16:52 PM
Am I right in thinking that all of the classic divider organs have independent top octave oscillators? How is the tuning stability of those and was there a brand/design that is the most desirable? The reason I ask is that the combo organs in my Nord Electro disappoint me somewhat by being too perfect! I suspect they are only a variation on the Hammond tonewheel modelling which is of course perfectly synchronous.
Additionally, were there any with a master tuning control for all 12 oscillators?


Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: sarakisof on February 25, 2020, 05:17:26 PM
Hmm as much as i can say i don't know anyone to use master tuning control for all the 12 oscillos. At least the most well known  ones, brands like Farfisa, Vox, Elka, Gem etc. use top octave independent oscillos and dividers. By the time you open them up to explore the guts it's like pretty common and straight forward process.
How is the tuning stability of those and was there a brand/design that is the most desirable?
Are u in my mind or smthng?  :P i was about to mention here, that compared to my other combo organs, this one tends to behave a bit worse in terms of tuning stability. Don't know why, maybe it's just in my imagination, but i think the A and G# got a bit tiny out of tune since my last tuning a week ago. Maybe my feeling is a bit false, but i will follow silently and looking for any behaviours like that in near future, take tuning neasurements and compare. In my Elka, Fast's and Philicorda's i didn't noticed that, no de-tuning at all since 1 year now.
Whi knows maybe I'm more "sensitive" and care more about my Compact.  :icon_mrgreen:
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: PRR on February 26, 2020, 12:50:19 AM
> organs have independent top octave oscillators?

An equal-tempered divider is a VERY complex thing. They "did not exist" for much of e-organ's history. 12 oscillators and knobs was much simpler thus cheaper.

I know when top-octave on a chip was introduced the intervals were only "very tolerable", not perfect. I don't know if this improved as the cost of complexity went down. The top-octave-chip era ended when I was not looking.

R.G. has remarks somewhere on the forum about programming low-price PICs for this duty.

Of course some of the "charm" in many organs is their imperfections. Bach never got all his pipes tuned before they started to drift, especially in days before thermostats. Pianos aren't even in tune with themselves. Tone-wheels have charm in abundance.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: amptramp on February 26, 2020, 04:15:04 PM
The National Semiconductor MOS handbook had several different designs of PMOS top octave generators with different divider ratios.  I don't know who their customers were but these have to show up somewhere.

One idea I had some time ago was a tonewheel type divider connected to a phase locked loop and a phase unlock loop just to keep it from getting properly phase locked so it would sound more like independent oscillators.  The only problem with a phase unlock loop is you never know whether it is going to push the frequency high or low and it has no way to go through the fixed tonewheel frequency.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: highwater on February 26, 2020, 11:02:10 PM
R.G. has remarks somewhere on the forum about programming low-price PICs for this duty.

Tom (electricdruid) has an article about top-octave generation (https://electricdruid.net/adventures-in-top-octave-generation/). He turns it a bit sideways, though, using 12 PICs, each generating 10 octaves of one note.
Title: Re: Cleaning Power Transformer Bell Out Of Strange Dirt
Post by: anotherjim on February 27, 2020, 05:32:57 AM
Ah, this isn't really a question about TOG's (in fact, I've coded my own TOG in an Atmega328 and in a slow project to build a string machine with it). I was more interested in the apparent preference for old organs with separate oscillators. Is that because of a particular sonic character obtained by carefully tuning to suit? A little beating between intervals can be good, especially if the frequencies wander a little. When you have an error in a TOG, it's stuck and no getting away from it.
For a combo organ, particularly in rock & pop music, the string type voicings are important and to me, that's what sets them apart from a Hammond sound. The strings are essentially high pass filtered square waves. Tuning error between intervals can sound utterly horrid due to the number of high harmonics interacting. This is especially noticed with a TOG instrument and low pass filtering is also required (string machines are typically limited to 5kHz). It also influences playing style - note the preference for fast chord stabs.