Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bigsbybender on December 27, 2011, 12:09:03 am
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I'm repairing a near perfect (Cosmetically) 1957 Magnatone 213 Troubadour for a customer.
I ended up having to rebuild the entire vibrato circuit which had failed. I have it working but it's very intermittent. It won't work right away, but it kicks on after about 3-5 minutes. It will work for about 10 minutes and then stop. My assumption is that it's not oscillating all the time. I replaced the (ungodly expensive) Varistors and have substituted known good tubes. I've also cleaned and retensioned the tube sockets.
This is only the second Maggie I've ever worked on so if any of you guys have any more experience with these than I do, I'd appreciate any help and insight..
Schematic:
http://www.el34world.com/charts/Schematics/files/magnatone/magnatone_213.pdf (http://www.el34world.com/charts/Schematics/files/magnatone/magnatone_213.pdf)
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What about making new solders on the vibrato circuit ?
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My assumption is that it's not oscillating all the time.
I agree. Monitor the oscillator output sine wave at the top side of the intensity pot with a scope or analog voltmeter. There should be a healthy signal when the circuit is working and I bet it disappears when the vib quits. You can also monitor the plate voltage with a scope or analog meter. If all you have is a DVM, then monitor the plate. It will be a steady voltage if the oscillator is not working and it will just look like random numbers (constantly changing voltage) when it is working.
Check all the resistors in the osc circuit, especially the plate and cathode resistors. Maybe just replace the 3 caps between the plate and grid. If still no go, put a 22µF cap across the 1K cathode resistor. Still no go, then put a jumper across the 1K cathode resistor (make it look like the M10-A oscillator).
Hang on to the old varistors. They are probably good.
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Steve, You're a life saver! This customer wants this amp for rehearsal 3 hours from now!
I actually tried the bypass cap first and it made the vibrato sound a little more full and it didn't cut out. I actually did run into another problem though. When I put the amp back in it's cabinet the Vibrato would cease to function. On the bench it would be perfect.
What I discovered is that I had to bend the chassis slightly to fit in the chassis....and as this is a point to point wired amp, there were a number of components that moved when I'd do that. So I re-flowed any potentially loose solder joints, it still didn't fix it. Ultimately I discovered one of the leads to the old wax Astron .01uF cap would bend at a very strange angle. I chopsticked it and saw that this lead was barely hanging on to the cap. I replaced it with an Orange Drop and we're in business. I replaced the others too as I've had bad luck in the past with this type of wax cap.
This thing sounds heavenly. It's very tweed like in topology but it sounds more clean and refined. I may just have to build myself a copy.
Many thanks, I couldn't have done it without your help!
j.
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The 213 has become very popular and expensive. Take a look on ebay.
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Good for you and your customer.
So the varistors were still good?
Brad :icon_biggrin:
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Good for you and your customer.
So the varistors were still good?
Brad :icon_biggrin:
Good question. The customer wanted them back so I have no idea. I would have liked them to make a clone.
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Warbler muse has dropped his price...
http://www.ebay.com/itm/2-Magnatone-Esteys-NOS-VARISTORS-Closeout-Sale-/170754073441?_trksid=p3286.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D3%26po%3DLVI%26ps%3D63%26clkid%3D5199788764083512436 (http://www.ebay.com/itm/2-Magnatone-Esteys-NOS-VARISTORS-Closeout-Sale-/170754073441?_trksid=p3286.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D3%26po%3DLVI%26ps%3D63%26clkid%3D5199788764083512436)
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I see that. It may be time to clone!
Actually I feel an ethical dilemma by doing this, as I feel these parts should be used to fix vintage pieces.
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Warbler muse has dropped his price...
Wow... I'd feel ripped off if I paid him $10 per pair. Then again, maybe I'll never have the magic mojo of the varistor tremolo.
No matter. I have a $10 Hammond AO-41 just waiting to be turned into some gadget with an unimaginative name... :laugh:
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I've never heard/played through, in person a Maggie vibrato, but have heard many a Lonnie Mac recording, and I like that sound.
And I've heard what sluckey did/built with the "SR" circuit from a Hammond L (I think) series. I think I like this sound much more, smoother.
It's just what you like sound wise I guess? :dontknow:
Our NZ friend tubeswell just built one and loves it.
No matter. I have a $10 Hammond AO-41 just waiting to be turned into some gadget with an unimaginative name... :laugh:
Hum? :think1: How about ---- "The Warbler" ----
(Hey, that other "Warbler" guy can take a walk, not the same thing. )
Brad :l2:
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I maintain a couple Magnatones for a friend in a working band. Well actually just one now (a 260) since he sold the 213. The 213 was a backup for him, but after I overhauled both amps, they never failed anymore and both sounded great, so he sold his least favorite one and kept the 260 since it sounded slightly better. Both amps are pretty damn cool though! Great sound and the vibrato circuit is to die for. I used both amps live several times while waiting for him to pick them up. They aren't super loud and don't break up a lot, but are perfect for some laid back blues or cleaner things. I have a stash of original Magnatone varistors here that I got from Zack at Vibroworld before he closed up shop. I plan to build them into something at some point. I think I have enough for three 260 style amps, or one 260 and one 280. Someday I'll get to it.....
Greg