Morley Power Wah Questions

[Andrew M]

I recently got an older AC powered wah. It worked fine for a while and then stopped. Easy enough to fix, the light bulb was burned out (for the LDR part of the circuit). I noticed that the power transformer did not look original so I checked the DC voltage and it is 42 volts at the light bulb (which is a 28 volt bulb). It also has some 35 volt caps in the power supply, so I am guessing that whoever fixed it put in a different transformer.

1) Does anyone know what the DC voltage is supposed to be? I guess a 24 AC transformer would get me in the ballpark for 28 VDC.

2) Should I replace the two prong power cord with a three prong one?
(As it is now the power cord is attached to the power transformer with wire nuts (marrets?), it one came off it would make the case live.

3) Does the current safety standards allow a two prong plug with a metal case? (seems kind of dangerous to me)

4) And lastly, a schematic of this would be nice it anyone has one.

Andrew.

[cjlectronics]

You can find the schematic for your Morley pedal here http://www.morleypedals.com/downloads.html and here http://www.schematicheaven.com/effects.htm

Morley has been very generous with providing service information to their customers.

The schematic at http://www.schematicheaven.com/effec...hboost_pwb.pdf shows a secondary voltage of 28VAC. If your transformer is center tapped, you can use one half of the secondary and I think this should do the job. If not, you may want to consider replacing the existing transformer with a 24vac/100ma transformer. I believe Stancor has a line of power transformers in that form factor as well as that VA rating.

Adding a ground terminal is always a good idea. You could crimp the ground wire onto a ring terminal and them secure it at one of the fasteners on the transformer.

I believe, for most consumer devices, a safety ground in the form of a green and yellow striped wire is required for all equipment powered via mains line voltage, in the USA. Although, I have not researched this fact but I do believe it to be true???

The schematic question was answered above.

I have repaired a few Morley power wahs and they sound real cool... I would recommend putting a trimpot on the lamp so you can adjust the light intensity. Some musicians like a gradual sweep and some like a fast and freaky sweep...its up to you.

Good luck,
CJ

[Andrew M]

Thanks for your advice, the trimpot sounds like a cool idea. I like the wah, but it is not subtle, it might be nice to tone down the effect sometimes.

Andrew.

[benoitxvii]

Morley bulb

Excuse , I don't speak and write english pretty well
I had 3 Morley pedals in seventies(I ,got a very long and white beard)
the bulb was allways a problem.Each time I was moving with my Morley, each time I had to remove the bulb off, because they don't like shocks and vibrations, and in France the price was 12-15$ for one bulb, and it wasn't easy to find
24V was normal in Morley , the problem is not here
Good pedal, but not really easy to adjust, chieftly the progress of lightning on LDR, if you want a good progress in the bass frequencies

[Mark Black]

If you have the old "PWO" model the correct schematic should be this one: http://www.morleypedals.com/pwoes.pdf

The power supply is a little unique in that it actually uses the pilot lamp (through a 150 ohm resistor) to ground-reference the (non center-tapped) transformer secondary. I actually had to re-draw that portion of the schematic to realize it due to the interesting way Morley drew the original.

Anyway point is you would probably need the lamp actually installed to get a meaningful voltage measurement there.

Also due to the unorthodox arrangement only one of the caps (C2) would see anything higher than 35V under normal operation (they show 55V across that one).

According to these guys http://www.bulbconnection.com/ViewIt.../387/item.html
the lamp is 28V, 1.12W, 40mA, which gives a hot resistance of about 700 ohms. Therefore you could probably sub a resistor of something around that or a little higher for testing if you don't want to risk a lamp. Probably a couple 470 ohm 1/2W in series would get you close enough for some voltage measurements (might get a bit warm though over lengthy testing...).

[Andrew M]

Thanks for the schematic, that is the one I have. I found a bulb for a couple of dollars at a local electronics shop that meets those specs (28v, 40mA). I think I was measuring the voltage with the bulb out of circuit so I should double check that.

Thanks.

[Enzo]

The standard Morley bulb is just a #387. This is an industry standard number just like #47 for a fender pilot light. Every decade or so I get a box of ten from somewhere.

Mouser sells them for 47 cents. ANyone selling them for dollars and dollars is either ripping you off or ignorant of what they are. $12?????

Andrew, listen to Mark, without the bulb the voltage readings won't mean anything. This is similar to the voltage at the plate pin of a 12AX7 socket. if you remove the tube, the voltage rises to the power supply voltage. Put a bulb in it and the voltage will fall into place. That 150 ohm resistor will soak up some volts as well, but only with the bulb in place.

[Steve Conner]

AFAIK, those lamp numbers are only industry standard in America, and the original poster is in France. You can probably get the same bulb for 47 Euro cents from the French equivalent of Mouser, but it won't be called a #387.

[Andrew M]

A two pack of the bulbs sell for $3. Yeah it is a rip-off for as you say a 47 cent part, but most of the local electronics suppliers have closed shop in the last few years, and the options are limited. My choices are either pay the money and have the part that day or wait until I have enough parts I need to warrant placing an order online.

[Enzo]

So a #47 is not #47 in Europe? What system do they use?

I am aware of the 12AX7/ECC83 differeing tube numbering systems. But things like semiconductors tend to be universal. For example a 2N3904 is not called something else in Japan. If they make something quite similar it still gets its own number in the 2S system. So what other common component types have differing number systems?

I am interested in such things.

[Steve Conner]

I think it's just called a 28V 40mA midget groove bulb. Maplin has it for £0.49:

http://www.maplin.co.uk/Module.aspx?...20Groove%2028V)

or a "T-1 3/4" if the words "Midget groove" make you expect a tiny Marcus Miller.

I think the American lamp numbering system is actually the General Electric part number. It's only one of many things that Americans take for granted that don't exist in Europe, like EIA manufacturer codes on components, and the RETMA colour codes for equipment and transformer wires.

[Enzo]

You're probably right, though my 1957 Philco Field Engineers Data Handbook charts the types as industry numbers, so the system was well entrenched at least 50 years ago. I guess noting the difference betwen a 387 and a 385 equivalent would be a matter of the spec sheet. (candle power and life)

My Shogyo Lamp catalog uses the number system, but in the front does refer to "US and international globe and envelope sizes."

I love my Philco book. I still have it from high school electronics classes a lifetime ago.

I do take transformer color codes for granted. It still bugs me every time I look in a MArshall and the OT wires are not blue, red, and brown.

[Mark Black]

By the way here is an opportunity to stock up on the #387 lamps (apparently USA shipping only - sorry Andrew & Steve):

http://cgi.ebay.com/ebaymotors/Lamps...spagenameZWDVW