Getting a vintage amp to work - Page 2

anatech · 16th July 2007, 09:29 PM

Hi DeadSpeaker,
This is a really nice amp. It will do what you want. However, it uses tubes, a pair of 6L6's for outputs. This means high voltage so you must be careful. This is worth keeping and fixing up.

Things that come to mind are all those capacitors. Especially the smaller coupling capacitors. This will require patience, but you can do it if you are careful. Step one, take it apart and take a few digital pictures. Pictures of the tp of the chassis, and many good ones of the underside where the wiring and parts are. Two, download and print out the schematic. Download a full resolution one, this attachment is a lower resolution. We will be here for questions.

If you were to buy a good DVM, it would serve you well for many, many years. Buy as good a meter as you can afford. You'll use it for everything. A Fluke is a very good brand.

-Chris

poynton · 16th July 2007, 09:30 PM

Quote:

Originally posted by DeadSpeaker
Thanks for the reply. That is a lot of information. So what should I do in order to get it running?

Hi.

The first thing I would do is to open the case and see if there is a foreign body inside which could be causing a short.
(obviously with the amp unplugged!).

Next, after noting where the tubes go, remove them all, replace the fuse and plug in. Does the fuse still blow?

Andy

DeadSpeaker · 16th July 2007, 09:34 PM

Well I looked inside the thing pretty well. I don't know if the reason that the meter did not respond to some resistors is because they are blown or if the meter is not powerful enough. What is my next step now that I've seen inside and have a diagram. Also, is there a way to test the tubes? I know I posted this in the solid state section, but that was before I opened it up and realized that there were tubes in it. Thanks for the help everyone.

Edit: Sorry I posted this after you guys put a bunch of messages up. I'll post more picture soon. The Ohms meter says "woods 1304" on it. Should I really power it on without the tubes in it? What will that tell me?

anatech · 16th July 2007, 09:44 PM

Hi DeadSpeaker,
Okay, we are in the right forum now.

You may need a better meter, and also get comfortable with it.

Do not apply power to this until the coupling caps have been replaced. If you don't follow this advice, you may cause enough damage to make this amp not worth fixing.

Smell the transformers. Tell me what they smell like before you start.

-Chris

DeadSpeaker · 16th July 2007, 10:27 PM

The transformers don't smell smoky or bad or anything. I'm glad that i wiped it down before I did that though. Are the coupling capacitors all the yellow ones in the picture? Here are some pics.

anatech · 17th July 2007, 02:00 AM

Hi DeadSpeaker,

Quote:

Are the coupling capacitors all the yellow ones in the picture?

Yes.

The next job would be to replace the filter capacitors. The brown one with three wires sticking out is one, the others are cans mounted on the chassis.

My feeling is that one or more diodes shorted.

Quote:

The transformers don't smell smoky or bad or anything.

The smell to watch for is a burnt, sweet smell. That's bad! Once you smell it once, you will always remember it. It's not an unpleasant smell, just means bad things happened.

Do not power up this unit until these things are done.

If you want to do a really good job, measure the resistors. Replace the ones that are far away from the marked values. I find that parts like the 220K ohm tend to drift a lot (red-red-yellow-[gold/silver/none]). Others too, but try to measure some of those to get an idea how your meter is working.

-Chris

w5jag · 17th July 2007, 03:22 AM

Quote:

[i]Originally posted by anatech

My feeling is that one or more diodes shorted.

-Chris [/B]

On something that old and not used in a long period of time, I'm thinking filter caps.

Win W5JAG

DeadSpeaker · 17th July 2007, 03:40 AM

Alright well the brown filter cap is 100/50 volts, and the one next to the little transformer is 450 volts, and then I think that the can thing next to the big transformer is one too (maybe 10-500 volts from what I can see). From what pictures i've posted, is that all of them?

Where do you recommend I order these parts from? I'm trying to come up with a parts list and an estimated total cost. The meter and the soldering iron I'm going to borrow from a friend but he doesn't know that yet.

How do you know if the tubes and transformers are still good? Is it possible to test them?

Thanks for all the help.

hailteflon · 17th July 2007, 04:30 AM

I don't mean to rain on your parade, but you may be disappointed with the results.

At some point in time I promised myself I would never waste any more time on a PA amp. It is for pumping midrange through a store speaker system. It may have filters and/or a special output transformer that keeps the lows out of the output. This is to maximize screamablility through a department store, car dealership, etc.

It probably was not intended for high fidelity audio. It also looks corroded: not a good specimen for a beginner. Lots-O-Luck, Mark

DeadSpeaker · 17th July 2007, 04:40 AM

I don't know about department store tube amps, but I got this out of my grandfathers basement. It had belonged to my uncle who owned a music store and was a musician. Because of the that and the XLR plugs on the back, I have assumed that it must be a decent vocal amp.

16th July 2007, 09:29 PM	#11
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi DeadSpeaker, This is a really nice amp. It will do what you want. However, it uses tubes, a pair of 6L6's for outputs. This means high voltage so you must be careful. This is worth keeping and fixing up. Things that come to mind are all those capacitors. Especially the smaller coupling capacitors. This will require patience, but you can do it if you are careful. Step one, take it apart and take a few digital pictures. Pictures of the tp of the chassis, and many good ones of the underside where the wiring and parts are. Two, download and print out the schematic. Download a full resolution one, this attachment is a lower resolution. We will be here for questions. If you were to buy a good DVM, it would serve you well for many, many years. Buy as good a meter as you can afford. You'll use it for everything. A Fluke is a very good brand. -Chris __________________ "Just because you can, doesn't mean you should" © my Wife

16th July 2007, 09:44 PM	#14
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi DeadSpeaker, Okay, we are in the right forum now. You may need a better meter, and also get comfortable with it. Do not apply power to this until the coupling caps have been replaced. If you don't follow this advice, you may cause enough damage to make this amp not worth fixing. Smell the transformers. Tell me what they smell like before you start. -Chris __________________ "Just because you can, doesn't mean you should" © my Wife

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16th July 2007, 09:34 PM	#13
DeadSpeaker diyAudio Member Join Date: Jul 2007	Well I looked inside the thing pretty well. I don't know if the reason that the meter did not respond to some resistors is because they are blown or if the meter is not powerful enough. What is my next step now that I've seen inside and have a diagram. Also, is there a way to test the tubes? I know I posted this in the solid state section, but that was before I opened it up and realized that there were tubes in it. Thanks for the help everyone. Edit: Sorry I posted this after you guys put a bunch of messages up. I'll post more picture soon. The Ohms meter says "woods 1304" on it. Should I really power it on without the tubes in it? What will that tell me?

16th July 2007, 10:27 PM	#15
DeadSpeaker diyAudio Member Join Date: Jul 2007	The transformers don't smell smoky or bad or anything. I'm glad that i wiped it down before I did that though. Are the coupling capacitors all the yellow ones in the picture? Here are some pics.

17th July 2007, 03:40 AM	#18
DeadSpeaker diyAudio Member Join Date: Jul 2007	Alright well the brown filter cap is 100/50 volts, and the one next to the little transformer is 450 volts, and then I think that the can thing next to the big transformer is one too (maybe 10-500 volts from what I can see). From what pictures i've posted, is that all of them? Where do you recommend I order these parts from? I'm trying to come up with a parts list and an estimated total cost. The meter and the soldering iron I'm going to borrow from a friend but he doesn't know that yet. How do you know if the tubes and transformers are still good? Is it possible to test them? Thanks for all the help.

17th July 2007, 04:30 AM	#19
hailteflon diyAudio Member Join Date: Sep 2006	I don't mean to rain on your parade, but you may be disappointed with the results. At some point in time I promised myself I would never waste any more time on a PA amp. It is for pumping midrange through a store speaker system. It may have filters and/or a special output transformer that keeps the lows out of the output. This is to maximize screamablility through a department store, car dealership, etc. It probably was not intended for high fidelity audio. It also looks corroded: not a good specimen for a beginner. Lots-O-Luck, Mark

17th July 2007, 04:40 AM	#20
DeadSpeaker diyAudio Member Join Date: Jul 2007	I don't know about department store tube amps, but I got this out of my grandfathers basement. It had belonged to my uncle who owned a music store and was a musician. Because of the that and the XLR plugs on the back, I have assumed that it must be a decent vocal amp.