Belated cool NAD - Magnatone 613 Custom

[mortatone]

Btw I found another Magnatone M7 and gonna pull the trigger on it today.

[Tortuga]

Just looked up the tube data for 6av6 and it's calling it a duplex diode triode, where as a 12ax7 is a dual triode. The 6av6 looks kinda like a single triode with 3 grids. No idea how that works. The two tubes have the same amplification factor though.

It's a good habit to reference tube data regularly. I don't though so if I ever learned anything it's been forgotten. But I know where to go to remember

https://frank.pocnet.net/sheets/093/6/6AV6.pdf

https://frank.pocnet.net/sheets/049/1/12AX7A.pdf

Thanks Mort!

Looks like there are 3, 6, and 12V variants, too... wonder why they didn't just go with the 12? I'd almost be afraid to put in a 6V replacement. Hoping I don't need to replace that one, but have been wondering about it, as the vibrato seems a bit weak.

[Tortuga]

Btw I found another Magnatone M7 and gonna pull the trigger on it today.

Hells yes! Can't wait to see what you find.

[Tortuga]

Forgot to mention... I photo'd the fuck out of the amp last night - hoping I can do some more comparisons to the schematics and see what else I can dig up.

[Tortuga]

...and I just realized (and confirmed, as I can't really be trusted at first take ) that the heaters on these amps are actually 6V, making that 6AV6 the only triode in my amp that's actually rated at what it's being fed

All is well again

[mortatone]

A little something I had never noticed before, as I've always just taken for granted that heaters get 6.3v and are always wired in parallel.

But that's not always true.

On the 12ax7 are 2 heaters, rated at 6v if they are wired in parallel and rated for 12v if they are wired in series with one another. Same tube can be used either way.

But since the 6av6 is only one triode with one heater, you would need a different tube for each heater voltage supply. I'm assuming the 3av6, 6av6, and 12av6 would be identical except for how the heater filament was designed.

[Tortuga]

It's amazing how much I forgot all about this shit in the time since I stopped working on the Bassman (back when my whole life was just about to turn upside down)... Just finished reading this document, and it brought SO MUCH back.

http://www.musicandengineering.com/lect ... es_v18.pdf

Highly recommended refresher. Gonna check out more of this guy's lectures on effects pedals, MIDI, and more: http://www.musicandengineering.com/

[mortatone]

Here's the one I just bought. He had it up as local pick up but agreed to let me send him a shipping label and schedule a UPS pick up.

https://reverb.com/item/21008184-magato ... 60-s-black

Recently played one, absolutely loved it, and had a trade set up for it and some effects. We discussed the trade over several days. I had already gone to his house the 1st day and played it. A few days later we came to an agreement. I went over there, we jammed a few songs together, then when it came time to do the deal he said he was keeping his amp and effects and tried to switch the trade over to a Hartke 4x10 cab, a broken indoor/outdoor speaker, a cardboard baffle with several 3" speakers on it and some other random junk(actual worthless junk that belongs in the trash) from his back porch

It was all I could do to not cuss the guy out. I would have totally understood if he just said hey look man I know it sucks but I changed my mind and want to keep. But instead he tried to see if he could fuck me with some garbage. Fucking asshole

[Tortuga]

Love it!

That new amp looks really cool. I have a feeling the IEC jack isn't stock, though

[mortatone]

It's stock alright, but odd. I'll probably install a typical modern 3 prong one though.

The way it is a person can just plug an extension cord in it

[Tortuga]

New discovery when I unshielded and looked at V1... turns out to be a 6EU7

...and that's different from either of my schematics

Gotta love non-standard (for today) tubes with unique pinouts

[Riffraff]

Happy belated new amp day!! That's a really cool one.

I agree with do maintenance and not mods on that amp as far as changing the circuit goes. Replace the power cord and lose the death cap, replace the filter cap can (disconnecting the original cap can and installing separate caps under the hood to match the values is ok if you have trouble finding a can with the same values & dimensions...differences like 22uf in place of 20uf and higher voltage ratings is no problem but you know this). Only change components that aren't working or have drifted so far out of spec they are causing problems. Clean the pots and jacks.

The only "mod" I do with mine is to mount a little 90 degree steel bracket inside the cab that use to mount an output jack. I connect the OT to that and add a cable & plug to the speaker so I can run the amp through bigger cabs or the stock speaker. Pulling the stock speaker and trying some of the speakers you have on hand could change everything too.

My Silvertones are also kind of dark on their own. Like you I discovered that makes them really OD friendly. That's where you do your tone chasing with these. One of my favorites with my amp is an old Visual Sound Route 66 & M108 combo. I run the M108 after the OD and set it mostly flat except for a slight bump in the upper mids. I started flat then adjusted frequencies a slider at a time to find which frequencies enhance the bark without adding flub. I later found the amp loves boost pedals of all kinds and threw everything in my collection at it. The pedal that shocked me the most was one that absolutely sucks with everything else in my collection, a Bogner Uberschall distortion. It's nuts but my 1482 loves that pedal.

You've got yourself a really cool recording tool there.

[Tortuga]

Good info, Riffraff - and yeah, after doing a bunch more research, I'm definitely going to leave this amp unmodded - at least for now. I'm a bit concerned about the irregular V1 tube and the other one in the vibrato circuit, but will leave those as-is for the moment. The good thing is that those tubes are still available, so will probably get another one or two to keep me (probably for the lifetime of the amp - or at least my lifetime ). I believe it's pretty trivial to rewire the V1 socket to take a 12AX7, so that could be a future task.

Did some work on the amp last night. Got the death cap removed and new power cable installed so the amp is properly grounded now. Thing is surprisingly quiet as fuck, too - at least in the bedroom testing I've done this morning. Still planning to get the caps replaced, but it's lower priority for now.

Starting point:



In progress:



All done:



Pretty cool that a bunch of the caps inside this amp are the same (?) blue "molded" components that Fender was using in the 60s. The death cap turns out to be in perfect condition, and will get repurposed somewhere else

[Tortuga]

Did some organizing in my new space this weekend, and got the amps set up so I can use them. The more I play with it, the more incredible it sounds. Really thick in the midrange, and saggy as I need or want it to be. And, it's still quiet as hell. Not even sure I want to change out the filter caps, even though everything I've read and heard tells me that the caps *MUST* be long-past expired. Gonna chew on this a little longer. For now, here's a couple pics of "Maggie" in her new home.





Will try to get some clips together this coming weekend. Still setting things up, and I'm seriously fucking rusty right now.

[mortatone]

One mantra I live by, which isn't scientific at all, is "if it sounds good it IS good". I tend to leave stuff alone until it becomes noisy, weak or unsteady.

Additionally, "if it looks bad, it is bad" concerning parts. If you can tell something has seen some heat then it's not a bad idea to replace it preventatively.

Another good general rule is to pay the most attention to the stuff that does the most work. Filter caps see alot of work that is generally juuust underneath their rating. Cathode bypass caps can cause weak/intermittent operation as they dry out and are generally not rated very high. Like 25v and even though they're usually seeing 1-15v they still are little work horses that wear out. PI components see alot of work too.

Since yours is in good working order and you have an interest in tinkering, it might be a good idea to do your maintenance one step at a time so you can hear the differences incrementally and learn a little something along the way rather than replacing all the electrolytics at once and not really knowing what made the most difference audibly.

[Ostinato Rubato]

The only upgrade you need are some gold pin JJ’s

[Tortuga]

Not sure they make 'em for my V1, unless I rewire that socket for the 12AX7 (or build an adapter )

[Tortuga]

One mantra I live by, which isn't scientific at all, is "if it sounds good it IS good". I tend to leave stuff alone until it becomes noisy, weak or unsteady.

Additionally, "if it looks bad, it is bad" concerning parts. If you can tell something has seen some heat then it's not a bad idea to replace it preventatively.

Another good general rule is to pay the most attention to the stuff that does the most work. Filter caps see alot of work that is generally juuust underneath their rating. Cathode bypass caps can cause weak/intermittent operation as they dry out and are generally not rated very high. Like 25v and even though they're usually seeing 1-15v they still are little work horses that wear out. PI components see alot of work too.

Since yours is in good working order and you have an interest in tinkering, it might be a good idea to do your maintenance one step at a time so you can hear the differences incrementally and learn a little something along the way rather than replacing all the electrolytics at once and not really knowing what made the most difference audibly.

Yeah, I'm definitely liking this advice...

No cathode bypass caps in this amp.

Probably should check out the PI components to see if anything turns out to be out of spec, but everything I've checked so far seems to be in good working order. I'm wondering if this amp has really had that much use in it's 61 years.

[iff]

First draft of updated schematic. Note: there is a slight difference in the cathode wiring for the tube in the vibrato section in the lower left. I drew the cathode resistor on the right of the other leads, due to the way it works in the designer software. I think it's right, though.

What software did you use to draw that schematic? Just wondering since it looks more pleasant to quickly mock something up than EAGLE.

[Tortuga]

The DigiKey website has a free portal for creating schematics that I've been using for a while... it's called Scheme-it. Their components library is pretty good and the ability to reconfigure symbols (flip/rotate/etc) handles a lot of my needs. They do have basic tube symbols (triodes, pentodes, etc.), but I have created my own for several of the tubes (rectifier, the weird V1 in this amp) and transformers so that they can be configured more to my liking. Once I "favorited" the basic stuff (resistors, capacitors, fuses, speakers, jacks, and the like) I'm using, it became fairly quick to put together new schematics. Haven't found anything else I like as much for doing this.

https://www.digikey.com/schemeit/project/

let me know what you find, and if you need any help

[Tortuga]

One mantra I live by, which isn't scientific at all, is "if it sounds good it IS good". I tend to leave stuff alone until it becomes noisy, weak or unsteady.

Additionally, "if it looks bad, it is bad" concerning parts. If you can tell something has seen some heat then it's not a bad idea to replace it preventatively.

Another good general rule is to pay the most attention to the stuff that does the most work. Filter caps see alot of work that is generally juuust underneath their rating. Cathode bypass caps can cause weak/intermittent operation as they dry out and are generally not rated very high. Like 25v and even though they're usually seeing 1-15v they still are little work horses that wear out. PI components see alot of work too.

Since yours is in good working order and you have an interest in tinkering, it might be a good idea to do your maintenance one step at a time so you can hear the differences incrementally and learn a little something along the way rather than replacing all the electrolytics at once and not really knowing what made the most difference audibly.

Yeah, I'm definitely liking this advice...

No cathode bypass caps in this amp.

Probably should check out the PI components to see if anything turns out to be out of spec, but everything I've checked so far seems to be in good working order. I'm wondering if this amp has really had that much use in it's 61 years.

Mort/RiffRaff (and anyone else who might want to chime in...) - I have that basic ESR tester for caps, and thinking maybe I should at least test the filters to see if they're at least in-spec. I'm pretty sure I'd have to desolder one side of each cap before testing, but if they all tested good that might give me some more peace of mind that I'm not gonna wind up with a down amp all of a sudden?

[iff]

The DigiKey website has a free portal for creating schematics that I've been using for a while... it's called Scheme-it. Their components library is pretty good and the ability to reconfigure symbols (flip/rotate/etc) handles a lot of my needs. They do have basic tube symbols (triodes, pentodes, etc.), but I have created my own for several of the tubes (rectifier, the weird V1 in this amp) and transformers so that they can be configured more to my liking. Once I "favorited" the basic stuff (resistors, capacitors, fuses, speakers, jacks, and the like) I'm using, it became fairly quick to put together new schematics. Haven't found anything else I like as much for doing this.

https://www.digikey.com/schemeit/project/

let me know what you find, and if you need any help

Thanks, I'll check it out.

[Tortuga]

One year (and 3 months) later...


Decided to get the cap can replaced while I'm in amp mode (and waiting for the parts to finish up the JEL mod on my 2204 build). Started with the schematic diagram I'd been working on, and found that it was still a bit incomplete on the filtering and power sections. Still verifying things a bit with the amp and keep finding strange inconsistencies, like the 4.7k dropping resistor (instead of 4.2k), 40/30/20/20uf cap can (instead of 20/20/20/20uf), swapped pin 8 & 2 wiring on the rectifier, and the aforementioned 6EU7 V1 preamp / 6AV6 vibrato tubes.

I *think* I'm very close to having this diagram spot-on for this particular amp as-built:



For anyone still with me here (and in-the-know), I've found that first dropping resistor way out of spec (reading over 7k now), so I'm going to replace it. I'm wondering if a 4.7K was subbed in for the 4.2K to handle the difference in cap can? And, should I replace with the 4.2K as called out on the drawing or the 4.7K as was actually put into the amp?

And, is there any reason pins 8 and 2 can't be swapped as I found in the amp? I'm guessing it's ok, since the thing lived for 60 years this way, but just want to make sure.

More pics of the progress will be posted later tonight. Thanks in advance for any help!!!

[Mike Oxhuge]

I don't know how I missed this thread, but that is a badass souding amp! Love it!

[ajaxlepinski]

Yeah man!!!!