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

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

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Andy54

Hadn't thought of that. Better still, get off the plane in Patagonia and take the train to New York ! :tu:

J M Fahey

Quote from: Andy54 on April 08, 2013, 07:30:14 PM
Hadn't thought of that. Better still, get off the plane in Patagonia and take the train to New York ! :tu:
Well, believe it or not, it can be done.
Not only that, this guy actually did (and wrote a book):

Whose Amazon comment is:
QuoteThe Old Patagonian Express: By Train Through the Americas
Author: Theroux Paul
Beginning his journey in Boston, where he boarded the subway commuter train, and catching trains of all kinds on the way, Paul Theroux tells of his voyage from ice-bound Massachusetts and Illinois to the arid plateau of Argentina's most southerly tip.

Although, why travel in train if you can do it "our" way, on horseback?
What about riding 10000 miles, from Buenos Aires to Washington DC , in  1925, to be received by USA President Calvin Coolidge at the White House?
Of course, it takes 2 Argentine Gauchos and a couple Argentine stallions to do it:


Maybe they were trained horses?
Not exactly:
Quote29-year-old Tschiffely ignored the legion of critics who told him his quest to ride 10,000 miles from Buenos Aires, Argentina, to Washington D.C. in 1925 was "impossible" and "absurd."
Not only did this brash neophyte propose to attempt this equestrian suttee, he said he was going to do it on two elderly horses, ages 15 and 16, owned by a Patagonian Indian, who were currently unbroken and running free on the Argentine pampas.  In his own words, "they were the wildest of the wild."

Roly

Quote from: phattyou can see the parts and room to work on it all. <3)

You looked inside one of those Aldi Fx pedals?  At first I though it was a blank board, then on closer inspection I saw all that microscopic SMD.  Gak!

Indeedie JM, many moons ago I had a project pulling down SatPix, one of which was a polar view, and I was struck for the first time that South America was "just over there".  Until this route the shortest way to Buenos Aires from Melbourne was via LA!

Let's face it, if something serious goes wrong in a modern airliner you're stuffed wherever you are.

Tschiffely's Ride - ah, they don't breed em' like that any more, not here either.  "This horse has sloppy power steering and no air con!"  I see farmers belting around on giant tractors that have more "mod cons" in the cab than my living room.

The Man From Snowy River - Banjo's Poem  (10mins)
http://www.youtube.com/watch?v=fs_-DKUimeo

Part of Aussie mythology, but on the Northern Rivers of New South Wales the country is even more forbidding and people still work cattle on horseback as the only option.
If you say theory and practice don't agree you haven't applied enough theory.

Andy54

#18
Peavey PA-100 problem seems to be fixed  :dbtu:

Thanks so much for all your patience and input. I'm so glad this forum turned up in a web search and that I didn't spear off and replace all the transistors.

Through the combined effort of members help with fault finding it's been on test for 2 hours without any static. I've put a loop pedal thru all channels and they sound fine. Should I leave it on test any longer to be on the safe side ?

What I did was two things suggested 1) metho on transistors ~ no change in static 2) pushing the board down at various places gave me *heaps* of static around the driver stage transformer. Also wiggling the reverb connections where they join the board with "pins&socket" gave increased static.

Dumb luck fix ~ I re-soldered the "tabs" that connect the transformer to the board along with where the pins for reverb connection are.

So here's a photo of the board. I've marked the re-soldered points with an arrow.

Just wondering if the points I've marked as 1, 2 & 3 which are the red wire contacts from output transformer should be re-soldered as I think they may have made a noise when I was pushed on that section of board. Although they seem ok now.

Check out the date 12/76 almost vintage :lmao:   BTW the *vintage* 240v to 110v converter in this thing is a monster when it comes to moving it around. They sure did make them substantial back then.

Andy54

Roly, Just had a brainwave re the heavy old stepdown transformer in this PA. Couldn't I swap it for a new lighter model ? This amp is rated at 150W. What would you suggest ?

Enzo

What is the power supply voltage in this?  50V? 70V?   Is the existing transformer a single secondary winding?  Like two red wires and that is all?

Rather than buying a smaller step down, why not find a 240v transformer that puts out the same as the existing one, and install it into the amp.  That way there would be no extra transformer.  A 50v transformer rectified and filtered makes about 70v.

Andy54

#21
Quote from: Enzo on April 10, 2013, 02:52:28 AM
What is the power supply voltage in this?  50V? 70V?   Is the existing transformer a single secondary winding?  Like two red wires and that is all?

Rather than buying a smaller step down, why not find a 240v transformer that puts out the same as the existing one, and install it into the amp.  That way there would be no extra transformer.  A 50v transformer rectified and filtered makes about 70v.

Gee Enzo now you're asking me hard questions  :-[

The attached pic I think shows the transformer in question. It has three red wires attached to the board.

If that transformer is changed won't I have to re-wire the back of the metal cabinet to take the step down transformer out of the circuit ?

J M Fahey

If that's the original Peavey power transformer, which it seems to be, it can be rewired for straight 240V primary, with no need for an external stepdown. :cheesy:

Andy54

Quote from: J M Fahey on April 10, 2013, 04:36:51 AM
If that's the original Peavey power transformer, which it seems to be, it can be rewired for straight 240V primary, with no need for an external stepdown. :cheesy:

I wonder why Peavey used the step down transformer if they could have just rewired the power transformer to suit 240V ?

Sorry, but I'm so far behind the 8 ball on terms like "240V primary" that I don't understand what you mean. I'm really at a monkey see monkey do level  ;)  I wonder if you'd be able to give me a basic run down on what I would have to do rewire it ?


Roly

+1 to Enzo!  :dbtu:

Quote from: Andy54Dumb luck fix

Do you mind!  That's how real technicians do stuff.   ;)

Perhaps you can see why we all reacted to "replace all the transistors".  He does all that transistor replacing for $400 with his blunderbuss "technique", and he's still got the fault!  You should perhaps leave sleeping dogs lie, but if it were me I'd be up his shirt for a refund.

Looking at the copper side, if you push or flex the board there should be no signs of movement at all in any solder joint.  If there is it's fractured and needs resoldering.  If you have good soldering technique then do it anyway if you're doubtful.  My guess is that the mass of the driver transformer on the board has led to flexing over time and fractured some nearby joints, the ones you found.

Now JM says that these PA's were originally fitted with a power transformer, the one internally on the back panel, that has dual primaries allowing it to be connected to 120 or 240 depending on how it is wired.  If that is the case (and that power tranny looks original to me), then somebody encountered a similar  :duh  tech back in the history of the amp and has needlessly been lugging a stepdown tranny ever since.

From your back panel pic it certainly looks like it has a bunch of wires coming out colour coded consistent with the coding on the circuit, and looking at the circuit it appears in fact to have a multi-national primary allowing operation of 110, 120, 220 and 240V.  {There is a cap C26 0.022uF that we call a "death cap" that should be removed for Aussie service}, but apart from that the wires are colour coded and it should just be a matter of rearranging the primaries.



Power transformer primary (mains side) wiring.  UNPLUG from the mains.

Concept:
Pull up the circuit and look down in the bottom-right.  The mains comes in and is shown going to two windings that are connected in parallel for 120V.  We need to reconnect these so they are in series for 240V operation.

First check;

According to the circuit there is a 0.022uF cap between the black and ground/chassis - this should be disconnected and/or removed if not already.

As you are using a 240/110 step down then currently the blue and black should be connected together, and the black+yellow stripe and blue+yellow stripe should be connected together to make a 120V primary. 

Before you do anything you should check that this is the case.

It's hidden behind one of the white connectors in your pic, but it looks like all the transformer primary wires already go to a single tag strip, and it should be a fairly simple matter to do the required rewiring there (as I am sure Peavey intended).

If so, then;

The black wire (the bottom of the primary winding) should go to one side of the mains infeed (blue, neutral).

There is a black+yellow stripe, and a blue wire.  These need to be disconnected from wherever they go and connected together.  These are now the middle of the primary winding or 120V point.

The top of the winding is a blue+yellow stripe.  This needs to be disconnected from wherever it goes and connected to the other side of the 240V mains (brown, active) via the power switch.

The black+red and blue+red should not connect to anything (these are the 110 and 220V points).

The last step is to replace the 3 amp fuse with a 1.5 amp fuse.  This is a 3AG type, standard blow (not delay).

Inspecting the central tag strip you may find that the required rewiring is actually much simpler than the description.

Check;

You should end up with;
- brown infeed to mains switch,
- switch to blue+yellow,
- transformer blue to black+yellow,
- black to blue mains infeed.

And of course green+yellow mains infeed safety earth to chassis.

If for any reason any of this does not make sense, or you can't find wires with these colours - stop and ask; post another of your excellent macros of the tag strip.

I assume that the two white three-way screw terminals are where the stepdown currently wires in.  These and their stubby wires will be redundant and can be clipped out.

The tag strip at the opposite end to the transformer looks like a ring-in and is now redundant.  The mains neutral (blue infeed) should now go to the central tag strip, and and green+yellow mains earth can also be reterminated on the grounded tag of the central strip - keeping in mind that a solid safety ground is vital.



This stepdown mod wasn't done by Peavey, by their local agent, or indeed anybody who had any real idea of what the were doing.   :loco

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

Enzo

Three red wires, not two, right.  Sorry, I had the wrong transformer in mind.

Let's get some terms straight.  The existing transformer in the unit does indeed take the mains voltage and step it down to 50 volts or whatever, but we don;t usually refer to that as a "stepdown."  We just call it a power transformer.  WHen you say "stepdown" to me it means an external transformer that takes 240v and steps it down to 120v so a 120v amplifier can plug into it. 

So when I suggested eliminating the stepdown, I was assuming you had am external stepdown unit for your 120v amp to plug into.  I am still not exactly sure what you have.

I am looking at the schematic now, and I see this one has a split supply, but the transformer puts out 50vAC center tapped.  The three red wires.  What I was suggesting was to replace it with one with the same 50 volt secondary, but instead of 120v, get 240v.

But now looking at the schematic, it appears the stock transformer already has primary side windings so it can be used on 240v directly.  WHich was just discussed above.

g1

#26
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.  :)

Roly

While we await @Andy54's response; the two three-way screw terminal blocks in the rear panel pic are certainly not original Peavey, and I'm reading this as as where an add-in 240-120 volt "stepdown" tranny has been installed ahead of the original power transformer.  This is not that uncommon here with imported American gear that doesn't have "international" primaries as this seems to.  It certainly looks to me like the 240V infeed is taken to the far side connector block, and 110 comes back in on the one near the power transformer.  (or perhaps I'm misreading the situation)

I think a similar (same?) "tech" in the OP "converted" this to 240V by adding a stepdown tranny instead of re-linking the primary.   :duh
If you say theory and practice don't agree you haven't applied enough theory.

Andy54

#28
Ok guys once again I *really* appreciate your eagle eyes on my amp.

Just to make it clear in the bottom of the cabinet that this amp is housed in a *huge* transformer that I've always believed was there for two things.

1] As I was told by the guy that I bought it from in the early eighties, when I asked why it was so heavy, that he put it in there so it would run on *Australian* power because *American* power is different. :duh

2] To herniate the discs in my lower back. These days I need the help of another person to get it into the wagon.

Work carried out today....... see attached photos. Please criticize this wiring.

a) Brown mains wire to switch blue / yellow stripe to other side.

b) Remove blue .022uf cap #26 ............ ??? Of course this photo is during the stage when I was removing the stepdown transistor wiring. It was connected between the earth and black wire.

c) Following Roly's instructions on how to diffuse this thing is the 3rd photo  :lmao:
Mains earth is connected to the chassis.

Mains blue is connected to black from transformer.

Black/Yellow Stripe and Blue from transformer are connected.

I 'm not sure if the fuses are wired correctly to the circuit.

The two red wires with blue masking tape connect to the pilot light. I did this as they were like that in the stepdown configuration wiring.

Please be hyper critical on this one.

Tab strip with new wiring configuration to be riveted to chassis.



J M Fahey

Words are nice, but please make some kind of hand drawing of what you just rewired, and post it here, *before* plugging that amp into 240V mains.
Label carefully all wire colors.
Remember some are dual color (background+stripe).
*Just in case*, make a lamp bulb limiter and plug the amp there, better safe than sorry.