• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

$1 AMP find

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Hello, I'am new here and was told from other cites that you may be able to help me.
I found this western electric 100f loudspeaker set at a garage sale and wat to know if i can put it to use as guitar amp.
here's the pics
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

and here's a link to a ebay sale with better picshttp://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3073214388&sspagename=STRK%3AMEWA%3AIT&rd=1
 
Bump for you. Glad to see you made it.
Can someone offer him some advice on where to find the schematics for this please. It is not original. Seems the back is missing and someone wired an input to the volume control so as a collectors piece it may not be that great.

Doug, do you have access to a tube tester. Before you do any mods you should get it working stock. I will help if needed. But you need to test the tubes first and find a schematic. Was it you who said your dad had some electrical background? That would be good if we get to the stage of testing voltage and/or soldering.
Chances are the caps are dried out. After tubes, caps are a likely problem. What is under that mesh screen next to the tubes? Looks like it is mounted in another tube socket. What does it say it is, I cannot make it out on the pic.
Also post that pic of the model #. That may help someone get us a schematic.
Check you later.

Adam
 
I should also ask if you intend to fix it for what you payed for it?
Haha, cause that is not likely;)
Hopefully we can get it working stock and that will be enough for a bit of guitar. It depends on weither it was designed for line level input or a phonograph. The tone would not be ideal for guitar but you should get some sound out of it. I hope it is line level. This way you could get a guitar preamp or booster pedal and not need to mod it.
 
at the end of my picture there is a link to a ebay auction with the exact same amp mine was spray painted gold, he has a nicer camera and includes the label on the back cover which i have but just removed to take the pictures. my picture of the label won't link but it is the same.

And you are right that someone wired a instrument cable to the volume control. the tubes do light up but will not drive a guitar when hooked up but it it did work when i pluged the cable into the headphone jack of a stero, it has a little approx. 4 inch jensen speaker. There was also two extra wires on the little speaker so someone was fooling around with this before i got it.

I do not have a tube tester, can this just be accomplished with a volt meter, is there still somewhere you can take them to get tested i live in cleveland ohio.

under the cage i believe there is no tube but it is labeled R5.
from left to right the labeling on the chasis is R5 , 25z6gt, 25l6gt, 6sl7gt, .

I could spend $50 to $100 bucks if it would be possible to get a decent guitar amp in the end. Would definetly want to have at least a 8 inch speaker added to it. BY decent i mean from clean to at least a slight overdrive and at a loud conversation volume would be fine.
 
dougv said:
JUst noticed that was you adamamp, thanks for pointing me here lot of other good info about little amp kits here.

You are most welcome. It is a fair bit slower than HCAF(most BBs are) but the knowledge base is bar none. I really think that if we can get it working stock you could use a clean boost pedal to get your guitar rawking. Have you any pedals? Tube testers used to be everywhere. When I was a kid the corner drug store had one. Today most techs(TV or Amp) should still have one. Phone around your area and find one that will do it for cheap. Some may even show you how it is done and let you test them. Even if you do not get the amp perfect I hope this experience will help you learn about tubes in general. So was that you that has the father with some electrical background? If so he prolly has some testing equipment, like a good VOM.
For now we have to get the tubes tested. Those and the caps are the most likely suspect. R5, that is prolly a series R for the series heaters. 25+25+6=56 not 115 Volts. One thing about series connected heater amps. They can have a hot chassis. I will explain to you how to check for a hot chassis after we get going on some other stuff. In the mean time do-not try it you could get hurt:dead: Please read all my questions and suggestions. I love to help but hate writing stuff twice;)

Anyone please help us find a schematic
 
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Joined 2003
Bin it.

I suspected that the thing under that cover would be a resistor. You are dealing with an amplifier that doesn't have a mains transformer. That means it potentially has a live chassis, making it very dangerous. What makes it even more dangerous is that you don't know precisely what you are doing and don't even have the benefit of a diagram.

Just because it was made by Western Electric does not mean that you have to fall down and worship it - it looks like an extremely cheap piece of kit to me, which would be fine if it wasn't dangerous.

I would not tolerate such a thing on my bench.
 
Yes my dad is a retired electrcian and we do have various amp/voltage meters. I will pass all the info to him since he understands all the electrical terminolgy.
I remember going to radio shack to test tubes for an old TV about 25 years ago.
I have a digtech rp80 modeling pedal don't know if this would help.

So after i get the tubes tested and find a schematic i'll be back with more info. I pass a couple of tv stores/repair shops on my way to work so i'll start their.
Thanks again.
 
dougv said:
I'am done tinkering, I read enough warnings about high voltage dangers with amps. Just gathering info now.

Great, I will check with you later. What the above poster & I said about the hot chassis is true. That is why there is no exposed metal parts on the amp stock. Ask your Dad if he has an 1 to 1 isolation transformer. Make sure it can handle the power requirements.
This is the easiest way to insure you do not hurt yourselves!
 
I hope my remarks prove to be useful.

The 25Z6 is a dual diode rectifier with separate cathodes. It is probably wired as a voltage doubler.

The 25L6 is an 11 W. power "pentode" O/P type. For guitar, think in terms of the sound levels a SE 6BQ5 or 6V6 produces. Don't expect the same tone.

The tube complement suggests either 2 cascaded triode gain blocks or a gain block plus a cathode follower and the "final".

The "standard" recommendation to "automatically" replace ALL electrolytic capacitors applies.

The Carbon composition resistors have probably drifted out of spec. and need replacement. Xicon currently makes Carbon comp. resistors that are available from Mouser (www.mouser.com).

I make the dropping resistor in the series heater string to be 200 Ohms. That resistor is dissipating 18 Watts. It is possible to replace the dropping resistor with a capacitor and save some energy. Let's see; 200 Ohms at 60 Hz. works out to be 13.3 muF. Michael Percy stocks a 13 muF. 250 WVDC Axon part that combined with a 10 Ohm surge limiting resistor should be OK, given today's higher mains voltage.
 
I thought I'd better correct this in case anyone tries it - a series capacitive reactance and resistance (like the tube heaters) DON'T add arithmatically - the effective series value is the square root of the sum of the squares. So actually you'd need closer to 400 Ohms of capacitive reactance to sub for 200 Ohms of resistance. It works out that 7 uF is about the right value for a capacitive voltage dropper for 0.3A series string tubes.

It appears that this box has an INPUT transformer too, so it may be safe to use once it's buttoned up. Otherwise NO WAY! Non isolated guitar amps are too dangerous to even THINK about - your next encounter with a mike stand could be your last!
 
This is no joke! Back in the day, high school electronics class to be exact, one of these unisolated amps almost cost one of my classmates his life. Much like you, he was trying to salvage an amp and when he was working on it in class the instructor made him plug it into an isolation transformer. Well he got the amp working and brought it home. He plugged the amp's 2 prong plug in backwards, putting 120v directly on the chassis. Luckily, he touched it with is right hand, but it stung him good. He was lucky and learned a valuable lesson. If there is no power transformer, do not under any circumstances use it for a Guitar amplifier and for heaven sake if you work on it get an isolation transformer. If you have no electronics experience, sell it to a collector and get something else.
 
I thought I'd better correct this in case anyone tries it - a series capacitive reactance and resistance (like the tube heaters) DON'T add arithmatically - the effective series value is the square root of the sum of the squares. So actually you'd need closer to 400 Ohms of capacitive reactance to sub for 200 Ohms of resistance. It works out that 7 uF is about the right value for a capacitive voltage dropper for 0.3A series string tubes.

Right you are Tom; I got LAZY. The standard value near 7 muF. is 6.8 muF. I compute that 129 V. mains are needed with a 6.8 muF. part for 300 mA. If the power company lowers its voltage below 120 V., the heaters will be "starved". Paralleling the 6.8 muF. part with a 0.68 muF. part works out to be nearly perfect. Add a 1 Ohm surge limiting resistor and call it done.
 
Thanks everyone for your responces! The input trafo I suspect is a coupling device and not for the mains power. Not sure unless we find a schematic. Any ideas on that? I do have a fair bit of knowledge(mostly practical) on tube amps. This is why I asked Doug to see if his father has a isolation trafo. Also, please correct me if I am wrong, but to my knowledge a line powered amp is only hot on the chassis if it is plugged in wrong. I was hoping to explain to Dougs dad that hooking a modern polorized plug to the cord after determining which position is right would be a safe alternitive to the isolation trafo.

Doug real busy at this end. Just signed a super guitar player to provide clips for my new amp line when it is ready for release.
Check with you later. Maybe ask any of the techs you check with for a tube tester if they could help us find a schematic. I will also check all my Sams photo facts and Audio Anthology copies for it, when I have time as there is binders of stuff, but no real index. Another idea(the best maybe) would be to just use the output trafo, 6SL7, chassis and tube sockets but add a 6V6 for output, proper power trafo to make a Champ like clone. If we go this route I could scan a schematic and post it here for feedback. Can your dad read a schematic? That will be very important either way. Most of the sybols he should be familar with. Have you talked to him yet? Will he have a fair bit of time to help us?

Cheers all,

Adam

PS. Sorry for the typos, too much work and not enough sleep makes me a very lazy typer:eek:
 
The input trafo I suspect is a coupling device and not for the mains power.

I agree. Still, that trafo isolates the amp from whatever is driving it. That's good for both safety and ground loop control.

In addition to the polarized plug, a wiring tweak in the voltage doubler B+ supply can increase safety. A full wave doubler connects 1 leg of the AC being rectified to the center of the filter cap. stack. Make that leg the "hot" side of the AC mains. That way, both the signal ground and B+ in the unit are associated with the "neutral" leg of the AC mains.
 
Adamamp, my dad will have no problem reading and following the schematic. I only see him on the weekends since he lives over an hour away so there is no hurry. If it ends up being a very involved or risky project the amp will goto ebay, but if it can end up like a champ clone that would be worth it. And again no hurry this would just be a weekend project doing alittle at time.
 
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