Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: G._Hoffman on November 28, 2012, 05:26:21 pm
-
So, one of the folks here in the shop just got back a Magnatone M6 amp from a friend. It hasn't been used in probably 10 years, and we want to make sure it is safe to use before we start it up. So, aside from the obvious precaution of using a current limiter when starting it up for the first time, what should I look for first? I've already told her we should replace the power cable with a grounded plug - what else? I'm assuming I should at least check the ESR on the electrolytic caps, right?
Gabriel
-
If you look in the "Archives" folder there is an article specifically called Powering up an old amp for the first time.....it's about ten or twelve titles down from the top....
good luck with your Maggie
-
Some Pictures, if you want to see it. (http://www.flickr.com/photos/27325537@N04/sets/72157632127464332/)
Gabriel
-
If you look in the "Archives" folder there is an article specifically called Powering up an old amp for the first time.....it's about ten or twelve titles down from the top....
good luck with your Maggie
That appears to be about a new amp, and while that is helpful, I'm more worried about what might have gone wrong in the (at least) ten years since it last had power applied to it, and of course in the 30-40 years before that when I have NO idea what was going on with this amp.
Gabriel
-
I would put it on a light bulb limiter. If the light is not full bright then I would plug it straight into the wall and see what happens. Look, Listen, Smell! Be ready to unplug if any danger signs.
I would not bother with ESR. And I would not install a 3 conductor power cord until the amp is working properly. If you don't have a power cord you should be able to use an extension cord to power up.
Looks like it will be fairly easy to work on. That little 'cone' board at one end of the main chassis is the vibrato circuit. I have a schematic if you need one.
-
Nice pics, I love the way they mount the components directly on the sockets. I would like to do a build that way just to see how it would perform.Thanks
-
Well, there is a schematic in the case that appears to be readable, though it is very brittle. I barely touched it, and one corner cracked and broke off. I'll ask the owner if we can maybe pull it out and try to photograph it, and maybe do a bit of preservation on it. It is perfectly clean, if the text is a bit small. If I can't pull it out, I'll try to at least get some close up shots of it (the camera at the shop has a good macro mode, but it still might be a bit close of a set of shots. I'll give it a try. I am very worried, though, that if I try to remove it, it will turn into dust.
Gabriel
-
I put the schematic on my website. It's too big to attach here. I'll leave it there for a few days only.
http://home.comcast.net/~seluckey/Magnatone_Custom_M-6.pdf (http://home.comcast.net/~seluckey/Magnatone_Custom_M-6.pdf)
I replaced the single cap can with two cap cans on my M10A and I also installed an IEC power connector so I could have a grounded power cord. There are two good pics of my power supply on this web page that may give you some ideas.
http://home.comcast.net/~seluckey/amps/magnatone/magnatone.htm (http://home.comcast.net/~seluckey/amps/magnatone/magnatone.htm)
BTW, the entire line of suitcase amps were all built on the same chassis. That's why you see all those extra holes and cutouts on your chassis. The top of my M10A will fit right on your M6 speaker cab and vise versa. I suppose that cut production costs.
-
the camera at the shop has a good macro mode, but it still might be a bit close of a set of shots. I'll give it a try. I am very worried, though, that if I try to remove it, it will turn into dust.
I'd try taking pics and leave the schemo alone. If you can't get good pics you could draw it out, that is if it's different from sluckeys.
Brad :icon_biggrin:
-
I'd try taking pics and leave the schemo alone. If you can't get good pics you could draw it out, that is if it's different from sluckeys.
I think that is going to work. There are a couple areas that are a bit fuzzy, but I think I can get better shots of those areas if I try. They are uploading to the flickr album I linked to earlier as I write. (Might take a while - my camera takes big pictures, and my internet connection here at the shop is SLOOOOOOOOOOOOOW!)
Gabriel