Welcome to Solid State Guitar Amp Forum | DIY Guitar Amplifiers. Please login or sign up.

June 20, 2024, 09:12:03 PM

Login with username, password and session length

Recent Posts

 

Peavey 45W PA-100 Tech Says Junk It !!

Started by Andy54, April 07, 2013, 01:36:30 AM

Previous topic - Next topic

Andy54

#30
Had no intention of plugging it in until I got some feedback  :tu:

I know I have *no* idea about electronics and not the first clue about how to draw a proper circuit.

BTW Please excuse the quality of the drawing. Can do better but just dashed this one off.

J M Fahey

#31
Just chimed in to post the redrawn 240V transformer wiring.
I'll check your drawing, hope the two of them match :)

EDIT: just checked your drawing.
*Almost* there.
You connected the 240V primary (2 x 120V primries in series) properly, if you plug your amp into 240V it *will* power on,  :dbtu: , but you are not using the glass fuse or the thermal switch (which you labelled as fuse) which are necessary safety features.
You should remove the death cap C27 (.022x125EVL) *now*.
I'll edit the drawing to include the thermal switch, which is originally not shown.
Start getting ready for the Champagne of Victory. :lmao:

Andy54

Thanks JM

Yes I had a gut feeling that the way I have the 1.5amp fuse & thermal fuse wired is unsafe  :duh   One reason why I wasn't going to plug the amp in.     How should they be wired ?

The ominous sounding "death cap" is the second of two that were in the old "stepdown" wiring. I did remove one. The schematic shows two, #26 & #27. So am I right in saying just one should be in the "240V" circuit. If so where should it be in terms of between what combination of colour code wires ?

J M Fahey

Oh, I missed one.
Remove both C26 and C27 .
C21, which also performs some line noise filtering, can stay because it's on the low foltage side.
As of the wiring, let me draw something, better than words.
There's also some issue with the "power on" light.
You draw it as a filament lamp, but I think (and hope) it's a neon lamp, probably direct 125V or something, please confirm.
Check here in 12 hours.
Won't say "tonight" because although somewhat close, measured in KM, we are on opposite time zones.

g1

Quote from: g1 on April 10, 2013, 07:47:52 PM
Quote from: Andy54 on April 10, 2013, 03:47:36 AM
The attached pic I think shows the transformer in question. It has three red wires attached to the board.

  That is the power transformer.  It is not "stepping down" 240 to 120V, it is transforming the 240V to the voltage the power supply uses.  You plug it in to a 240V outlet, yes?  So it is already wired up for 240V operation.
  It is the same size/weight as a north american version of the amp would use, you can't downsize.  Yes, new amplifiers deliver more power and weigh less, like modern cars do.  :)

Sorry about that post, the picture showed the power transformer and I did not realize there was another "step down" transformer in the cabinet.
  Sounds like you are getting it sorted out, good luck.

Roly

Quote from: J M FaheyChampagne of Victory.

Which is like a Lap of Victory, except you do it sitting down.   ;)


Oh duuur!  :duh   I've been looking at the circuit on high magnification and have only just noticed that the required connections are shown below-left of the power transformer - "primary connections for export models 240V 50/60Hz".  (kicks self)

"Death cap" - while this is named with typical dry Aussie understatement, it isn't going to actually rise up and smite your firstborn; it's just something Americans have to do that we don't, and is of dubious merit.

(This arises because the American power system was "economical" and originally didn't have a third safety earth wire as we do.  After innumerable deaths and places burning down Americans have decided that perhaps, after all, a third safety earth wire isn't so wasteful after all, however for various reasons the "death cap" between one side of the mains and equipment chassis lingers on.  It was never needed here because of our green+yellow safety earth wire, so they get clipped out).

Now I can see them clearly they are both rated for only 125VAC so BOTH caps should be REMOVED altogether.

Your excellent macro "PA Switch.jpg" shows that the incoming mains active/brown is *frayed* where it solders to the switch.  This is because the cable clamp around the mains lead stops it pulling out, but hasn't stopped it rotating, and over time it has flexed this joint until it is now in danger of breaking off.  Unsolder this wire, clip the damaged bit off the end, then strip a few mm and resolder firmly to the switch contact.  (The blue+yellow will have to come off because it has to be fed via the fuse and thermal cutout as well - see diag).

It is almost certain that the front panel pilot light is a 110V type and was intended to remain across a 110V portion of the primary winding, so that is how I have drawn it.  It's the safe option and the worst that can happen is that it will light only dimly or not at all.

For your first power test you need to make up a Limiting Lamp - see;
http://www.ssguitar.com/index.php?topic=2093.0
This is your insurance in case you (or I) have made a mistake.

See attached diagramme.

{and chill the Champagne}
If you say theory and practice don't agree you haven't applied enough theory.

J M Fahey

QuoteI've been looking at the circuit on high magnification and have only just noticed that the required connections are shown below-left
+
QuoteNow I can see them clearly

May I humbly suggest a couple of THESE?:



.
.
.
.
Oh, I see, you want a SS, electronic, DIY, high tech version?
.
Ok, I'll mail you the schematic of THESE:



Can't attach it here because it's a 1597Mb PDF :(

Roly

If you say theory and practice don't agree you haven't applied enough theory.

Andy54

Roly, thanks for the revised wiring diagram. I'm going to carry out the rewiring and then make a Limiting Lamp.

Re: the Lamp Limiter I read where JM feels the simplest circuit is the best but I'm having trouble sourcing a bulb. Also seeing this amp is 45W is a 75W bulb suitable ?

I can't get my hands an incandescent light bulb, only thing on the shelves at the Burringbar general store are tungsten globes are these I assuming this would work. But being a neophyte { a what ? :lmao: } I could be wrong.

As a teetotaler I won't be opening a bottle of champagne if this works, but maybe a bottle of the finest mineral water  :dbtu:

J M Fahey

Yes, 25W to 100W is fine.
Of course, the smaller one will stay brighter even with idle current, while a larger one will be all but invisible, but the basic idea is the same.
Don't know what happens in ANz but here in Argentina, after my initial worry about filament bulbs (I still treasure a small stash just for that) now I can buy anywhere the "high efficiency" version (which is actually a scam), which has a small halogen lamp floating inside a standard sized globe.
It's the same as before, as inefficient as any and with a 4X price tag, but at least it satisfies the official watchdogs.
So these are fine for amp testing.

Andy54

JM: thanks for the good information.

As for filament bulbs, I think they've all but disappeared from the Australian market. We've been told that the tungsten and fluro replacements are more energy efficient and with the cost of electricity, Australians have accepted that premise.

I have completed the rewiring for 240V and removed the .022uF caps.  I've also removed the large convertor transistor from the cabinet. I had to rig up a block and tackle to get it out  :cheesy:

Roly

Quote from: Andy54Please excuse the quality of the drawing. Can do better but just dashed this one off.
As you can now see from mine there is nothing wrong with that; more than clear enough and tells the story.  :dbtu:   I get some mud map tracings of amp circuits I have to decode and redraft that look like a demented spider fell in an inkwell.

Quote from: Andy54I had a gut feeling that the way I have the 1.5amp fuse & thermal fuse wired is unsafe
And your gut feeling was correct.  The amp would actually work okay like that, no smoke or anything, it's just that the overload and thermal protection are wired in a loop and would be ineffective.

Quote from: Andy54tungsten globes
This is another name for incandescent or filament globes, so I assume your store only stocks the new Compact Fluorescent Lamps - CFL's - and no, you are right, these are not suitable, however there are still a range of lamps with filaments available from hardware and lighting stores for non-standard applications, including 240V Quartz Iodine - QI - lamps as used in "Downlights", and others for ovens and fridges, and in strange shapes and bases, but anything with a *filament* is suitable.

The point here is that of there is a short in the amp all that will happen is the lamp will light to full brightness - no dramas.

Quote from: J M FaheyI still treasure a small stash just for that
Me too.  And the LED's come marching in.  It's clear here that LED's are already making serious inroads in lighting generally, and with QI downlights specifically, and the latter can't happen fast enough for my liking, very popular, horribly inefficient, and notorious fire starters, while LED's last 20 times longer, give better light, consume 1/20 the power, and best of all you can still touch them after they have been on an hour.  A local pub just refitted their coolroom with white LED's and they've got a tonne more light at a tiny fraction of the power (and heat).

Quote from: Andy54As for filament bulbs, I think they've all but disappeared from the Australian market. We've been told that the tungsten and fluro replacements are more energy efficient and with the cost of electricity, Australians have accepted that premise.

I have completed the rewiring for 240V and removed the .022uF caps.  I've also removed the large convertor transistor from the cabinet. I had to rig up a block and tackle to get it out  :cheesy:
"transformer"

The tungsten QI that JM illustrates is a scam and are sold as "more efficient" but aren't.  The CFL's however aren't a scam ('tho they introduce another issue which is a problem for he suppliers but not an end user concern), but they also contain mercury which is a problem in the waste stream.

BOTH caps gone, good, they are only rated for 125V and could get "interesting" if subjected to 240V. 

Look on the bright side, if you sell the stepdown on eBay you could end up turning a handsome profit on this repair.  Note the VA/wattage rating and Google for 240/110 stepdown prices, you may be surprised what these cost.

Might be an idea to post another pic post-rewiring, just to be sure.

Note also:

- that the front panel pilot light must be wired across half the winding (as I have drawn), not all of it to 240V as you had it, or it will have a very short and exciting life.

- The unused Black+Red and Blue+Red must be well insulated for everything including each other.

Quote from: Andy54a bottle of the finest mineral water  :dbtu:
Just make sure it's a good vintage from the South side of the slope.   ;)
If you say theory and practice don't agree you haven't applied enough theory.

Andy54

#42
Well fellas, with your great amount of help the Peavey PA-100 ia now working !!  :dbtu:

The final push to the summit was made last night and tested with a newly constructed lamp limiter [ thanks JM ]. When the lamp glowed a dull red all those present [ myself and the dog ] gave three cheers and toasted the members of SSGAF. See photo of lamp limiter with 25W bulb.

Wiring as per diagram supplied by Roly was a success. I've attached a photo  [I've been using my Canon 7.1 mega pixel camera set on macro & flash disabled ] which shows the rewiring for 240V as :

Please excuse another one of my wiring descriptions.

From mains switch ~ to fuse 1.5amp ~ to  thermal cutout
: Active Brown / switch / Brown / 1.5amp fuse / black [top LH just out shot]/ thermal [ switch ] / black /  blue with yellow stripe RH tab strip .

From LH to RH on Tab Strip
Tab 1 : Neutral Blue + Black from transformer + Red to "pilot light".

Tab 2 : Blue + Black from transformer + Red to "pilot light".

Tab 3 : Earth Green & yellow

Tab 4 : Blue with yellow stripe + black [ from 1.5 amp fuse ]

Third photo shows insulated red wires from transformer

Fourth photo is of the step down transformer that found it's way into the circuit. Sort of like some alien sleeper waiting all these years to be removed only to take over another unsuspecting piece of electronics.

Now let's see over the next while how amp  will perform.

Roly

Quote from: Andy54the Peavey PA-100 ia now working !!  :dbtu:

:dbtu:

Very professional limiting lamp.

Wiring in the pix looks good.  Is there a star/lock washer under the nut holding the tagstrip?

That stepdown looks like it's about 500VA which is way overkill for this job, not that it should have been used in the first place.

Well done.
If you say theory and practice don't agree you haven't applied enough theory.

Andy54

Thanks Roly, yep I put a spring washer under the tagstrip. The amp sounds the best it ever has.  <3)

Maybe I should get myself an old Goldtone and start another project  8|