Need help restoring/rebuilding a Rickenbacker M11

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Need help restoring/rebuilding a Rickenbacker M11

Postby (milo) » Sat Mar 30, 2013 1:12 pm

Several months ago I snagged what I think is an M11. I have looked through the Registry and it comes up as being an M11 (it was already entered in there twice I believe) and I have found the one single article on it by Dave Hunter that also calls it an M11. This is the version with the rounded top that spells RICK across the grill slats and has the upward facing controls, though the one I bought was missing the back panel to mount the chassis.

I'm not amp illiterate, especially with a schematic, but I also really need to do research to work my way back up to how these things really work if I'm doing something beyond a small mod, recap, or just tracing down a problem. I assumed that this amp would just need some bad parts replaced and now I'm finding that whoever touched it before it got to my house probably didn't just replace parts, but also didn't replace them in the right spots...at least not if the circuit used the tubes that the Hunter article refers to.

I guess to start out I'm wondering if anybody at all has any gut shots of one from this era, and then if anybody can at least tell me whether the preamp tube should be grid leak or cathode biased and what type of phase inverter this would most likely have had. I can find the M11 on the Rickenbacker site with a pair of 6SC7 tubes, but this one has a 6SJ7 pentode preamp and (supposedly) a 6SN7 phase invertor. It came to me with a 6L6 in one power tube slot, a 6V6 in the other socket, and another 6V6 in the PI socket.

I have compared the PI to a few old schematics from the '50s with octal tubes and part of it seems to wired correctly where connecting to the output section except that those components are shifted one pin off which doesn't fit with any of the octal twin triode tubes I've found data on. I could theorize that somebody accidentally moved these over one pin except that I have no heater filaments and the heater pin that would have gone to ground seems to have at least on original component and solder joint so I'm at a bit of a loss. The power tube section looks right to me except for one oddball capacitor between the two tubes. Any kind of pictures, or at least some knowledge of what "basic" circuit design each tube used would be greatly appreciated. I could rewire it to match some other circuits, but would prefer to get closer to original if it was something unique.

I don't know if there are enough experts here to help me or not, but if nobody is familiar enough with these circuits maybe somebody can at least point me to some good research sources that may show some example circuits for these tubes or a forum that delves into the older or developmental stage circuits.

Thanks.
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Re: Need help restoring/rebuilding a Rickenbacker M11

Postby (soundmasterg) » Thu Apr 04, 2013 4:47 am

Looking at the M11 schematic which I found here >> (http://www.el34world.com/charts/Schemat ... er_m11.pdf) it looks like the power section should be two cathode biased 6V6's. It looks like they are using a paraphase phase inverter using a 6SC7, and the inputs look to be grid leak biased. The schematic isn't drawn very well...at least not to convention. It is missing the dots to show connections, but if you know the circuits you can figure out where things are supposed to go. There aren't any voltages on the schematic either, which would be helpful to at least be able to check if things are working correctly.

It sounds like someone has mucked around in that amp so I wouldn't trust the condition you found it in and the tubes that were in use. They are somewhat of a rare amp and I personally haven't seen any Rickenbacker amps in for repair, and I don't know anyone who has locally either. Sorry I can't help you any more than that directly, but you may try posting at the Hoffman site where I found the schematic, or perhaps at Ampage too and see if anyone has an idea.

Greg
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Re: Need help restoring/rebuilding a Rickenbacker M11

Postby (libratune) » Thu Apr 04, 2013 5:25 am

Here's something for comparison: a Pro 12: "The Pro 12 is an upgraded version of the M-11 with a slanted back control panel and a heavy-duty 12” speaker."

Some Pro 12 innards pics:

RAMP003011.jpg
RAMP004009.jpg
RAMP003002.jpg
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Re: Need help restoring/rebuilding a Rickenbacker M11

Postby (milo) » Thu Apr 04, 2013 10:17 pm

Thanks,
I just came back to post that I got it up and running this evening and found your post. Nice amp!

The Dave Hunter article had a typo as far as the phase inverter tube. The article said SN7 and with some searching everything that came up was a 6SN7 so I bought a couple of those first and had no luck since the socket appeared to be wired wrong. I had also found a Rickenbacker schematic for an M11 using a pair of 6SC7s so I was trying to compare the pin outs and the wiring just didn't look correct. My amp had the cathode bias resistor on pin 8 and had come with a 6L6 in the PI so I figured it had been messed with, but a couple of those solder joints looked original so I was baffled and suspicious.

The article also mentioned that it was ahead of it's time and that the mid-50s Fender tweed Deluxe bore a striking resemblance to this amp and that Leo probably saw a few of them in his radio repair shop before he started making his own amps so I started with the 5C3 Deluxe and worked my way backward all having the same PI tube either with or without negative feedback. On a whim I started searching for information on the Woody amps that Fender first built and these showed a 6N7 phase inverter tube with the wiring to the plates and cathode matching the wiring of my amp. The volume and tone are completely different, but I could sort of see that they may work and the wiring to those seemed untouched except for a cap.

I bought a few 6N7s off of Ebay and since I got four of them, had extra fuses, and a safe way to fire the amp up I figured it was worth blowing a tube or fuse. Rigged a phone jack to the speaker wires, plugged into the cabinet from my '62 Fender Super, and she's alive! Not extremely loud with single coils, but not too bad. Clean all the way up the dial as it currently sits with low/medium output pups. Maybe a cathode bypass cap across the power tube resistors will add a touch of gain, or maybe some of the original resistors are way out of spec. Have to ad a three-prong cord this weekend, too.

I kind of doubt that the choke is original, although a 1946 Fender Woody Pro does show a choke (with 6L6s) and this one does happen to exactly match the hole pattern across the top of the power transformer bolts.

The biggest bummer is that the original cabinet was broken and repaired once before I bought the amp, and then the yahoo who shipped it just threw it in a box and the loose chassis broke the top off of the cabinet again. At least that was a clean break across the poorly glued original repair so now I need to make a back panel and glue the cabinet back together properly.

I'm going to try to steal an AutoCAD license at lunch whenever I get some free time and draw up a schematic for it, at least as it sits right now. Is there an easier way to create a schematic with free software at home that may already have the symbols in it?

Thanks again for the post. I'll throw better pics up when I can take them and resize them. The knobs and faceplate are original and in fairly good shape.

Image
Image
Image
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Re: Need help restoring/rebuilding a Rickenbacker M11

Postby (jps) » Thu Apr 04, 2013 10:27 pm

:shock:

DSC00698.jpg

Thermador!.jpg

:mrgreen:
(Insert famous quote here)
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Re: Need help restoring/rebuilding a Rickenbacker M11

Postby (milo) » Thu Apr 04, 2013 11:46 pm

That must be the deluxe Thermador...it has way more knobs. Pre-cursor to the Transonic possibly? :lol:
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