Next 4-ish builds and Magnatone 210-410 discussion

[andyfromdenver]

Hi all. Here's what I'm thinking:
I bought these 9.5" x 6" (super cheap from Watts Tube Audio Facebook) little chassis to do 4 different Single Ended designs. Maybe one parallel single ended, but not sure. All will be head only and I'm going to really trick out the chassis art like my "White Worm" (to be rebuilt eventually...). I included a pic of the White Worm amp to show about the amount of room we're talking (that chassis is 9" x 6").


The first will be a Magnatone 210 or 410. The 410 only differs in having a bright switch and a bigger cab with two speakers.

Next (possibly):
A Fender Reverb Unit, that would just hook up to an external spring tank.

Next (possibly):
A Marshall-y build. Cascaded first preamp gain stage volume and additional volume. Cathode follower TMB to????? Single El34? 6V6? Paralleled el84s?
Solid state rectifier

Next: ? Totally don't know. I was thinking Fender VibroChamp??

So, I'm open to suggestions and I'll work on these as time and $ permits.

 

[andyfromdenver]

Here's the Magnatone 210 schematic I redrew from actual pics I took while at a friends.
And a link to the documents and more schematic info.

http://www.magnatoneamps.com/210.html

I forgot to draw a 22k resistor on the cathode of the 12DW7 tube (and forgot to label those tubes)

 

[andyfromdenver]

Here's a video of the Magnatone 410


You can hear it's pretty low powered, and I kind of want to discuss that.

If you look at the schematic from the 210, The B+ is around 355. on The 410 schematic it's like 335 or something less.

I'm going to definitely shoot for 355-360, more in-line with a Champ.

Also, you can see from the scheme that the 6v6 screen gets it's voltage much lower than the Champ, after two dropping stages one of which is fairly significant at 22k. I am sort of wondering if tweaking the power section more inline with the Champ will be a good thing??
I'm not sure though, and plan to build it stock first because I had a chance to play one and basically you just turn both the volume and vibrato to max and enjoy it's "One Trick".

Also, the inputs are weird because there's no 1meg and it looks like when you go through the low, it's like a 100k pot set mid way?
Is the input section holding the amp back? I kind of want to do that Fender style too.

 

[andyfromdenver]

I'm already very excited to paint this chassis in a homage to the original 210 Chassis and try to match it's look which I really like.

Next step, i'm going to make a decent layout and order transformers.
Any transformer advice is appreciated, I kind of want to do stand up Power cause i dread cutting a big a hole for the Transformer.
I want to hit my 360 B+ target, without any shenanigans, from a 5y3.

I'm also planning on using a can cap to save space.

 

[jipp]

its cool you have the skill to take on such projects. i like the idea of a tube reverb where you can try different tanks.

the mag magnatone sounds fantastic.

im not sure what other amps you could build. seems like maybe go back to the 60s for some of them odd balls. just for the giggles.

good luck.
chris.

 

[andyfromdenver]

its cool you have the skill to take on such projects. i like the idea of a tube reverb where you can try different tanks.

the mag magnatone sounds fantastic.

im not sure what other amps you could build. seems like maybe go back to the 60s for some of them odd balls. just for the giggles.

good luck.
chris.

Thanks Chris.
Yeah, the magnatone 210 I played and photo'd went for sale shortly after for $500 and like a fool I waited for a possible price drop... The old mojo-y cab and original or old speaker just added such a nice vintage touch and sound. I feel pretty sure if I build the circuit though, it will have that sound still.

I kind of want to make one (or more someday) little 8" speaker cab from old wood, uncovere,d and either a sandblasted/shabby white or robin egg blue, to run these little guys through.

I'll make sure and post a layout when I get to that and Transformer info so someone else can do it.

There is still much research to do on the two key parts to the Magnatone Vibrato, Varistors. It seems there are suitable new parts, pay an arm and a leg for old parts, construct a similar device from components (Thank goodness for Engineers ). I may choose the last route and incorporate it into the layout.

 

[andyfromdenver]

Desperately seeking Susan, wait no, NOS Magnatone Varistors. Willing to pay $$$.

*come on, many of you guys knew it'd come to this*

Sigh.

 

[Telenut62]

Oh yes indeed

There was a thread from bernardblack on a magna built....search for that.

http://ampgarage.com/forum/viewtopic.php?p=228624

 

[andyfromdenver]

Oh yes indeed There was a thread from bernardblack on a magna built....search for that. http://ampgarage.com/forum/viewtopic.php?p=228624

Thank you for the link, I'm trying to have faith.

Magnatone build...Gotta Have Faith.

So this layout is proving to be a tricky-Dick.

Here's version 2.0, I think I'm on the home stretch.

The little gotcha part is the (I think) LFO section on the 6,7,8 half of the 12DW7 tube. It can kind of exist in it's own space, but then running leads to the pots starts to get spaghetti-y.

You can see I'm going to try wiring the preamp tube way in the corner by the inputs, which has me psyched.

In version 1.0 I tried placing the 12DW7 near the front too, but that started to look like Shinola's (-)

Mini is totally in; lol

 

[Fred Mertz]

Just a thought; rather than using a 12DW7, you could use half of a 12AX7 and half of a 12AU7. The benefits are that there is better tube availability and you would be able to locate the LFO circuit anywhere you want. The down-side is you would use one more tube.

 

[andyfromdenver]

Just a thought; rather than using a 12DW7, you could use half of a 12AX7 and half of a 12AU7. The benefits are that there is better tube availability and you would be able to locate the LFO circuit anywhere you want. The down-side is you would use one more tube.

Dang, sadly that is a big downside, but you're right; thank you.

I hadn't looked around, I guess that's a rare tube type... *edit I see there are plenty o new*

I'm on version 3.0 of the layout, but maybe I'll do one with that in mind too.

 

[Fred Mertz]

A 12DW7 has a high-mu triode section (pins 6, 7, and 8) which is equivalent to one triode section of a 12AX7 and a low mu triode section (pins 1, 2, and 3) that is equivalent to one triode section of a 12AU7. One section of the 12AU7 would be wired in the same manner as pins 1, 2, and 3 of the 12DW7.

http://www.magnatoneamps.com/schematics/magnatone_410rd.pdf

EH has a 12DW7 and JJ has one. That's about it for new production AFAIK. OTOH, there's still lots of NOS 12AU7s and 12AX7s available. Oh and just to keep things interesting, there's at least one version of the JJ 12DW7 that has the triode sections reversed.

 

[andyfromdenver]

Oh and just to keep things interesting, there's at least one version of the JJ 12DW7 that has the triode sections reversed.

Lol I was afraid of something like that! I'm definitely gonna just stick with the one tube and be diligent.

I was gonna post this layout on maybe ampgarage, I've done two versions with the dissimilar triodes circuit swapping places on the board. I'm thinking this version is a winner, but the proof will be in testing.

Any thoughts welcome

*edit, I forgot that the original scheme has the power tube cathode cap and resistor going to the 8ohm output transformer lead, that frees up some more space actually.

 

[jipp]

here some inspiration andy.
i did not realize they came in such a small package too.. big 8" speaker and 5w. i bet it would be a fun amp?

(link removed)

chris.

 

[andyfromdenver]

here some inspiration andy. i did not realize they came in such a small package too.. big 8" speaker and 5w. i bet it would be a fun amp? (link removed) chris.

Thanks Jipp! I actually am "watching" that.
I saw the gut shots, looking for varistors but didn't see them. I didn't look for the scheme on line.

To update my thread, I have ordered all the parts (for the magnatone 2/410) and have a lead on some varistor subs. I'll update with all the info soon.

 

[jipp]

sounds good. just stumbled on to it and thought of your build. so thought id mention it.
chris.

 

[andyfromdenver]

OMG OMG OMG.
So, I splurged on these little guys.
The rare-er than rare NOS composition correct Magnatone Varistors.

You bet your sweet buns they will be heat-sinked and babied

I'll come back to this project soon. Got everything in place to start.

 

[Fred Mertz]

Mmmmmmm........secret sauce! Those little jewels should make the circuit a success. Did you ever decide on a power transformer?

 

[andyfromdenver]

Mmmmmmm........secret sauce! Those little jewels should make the circuit a success. Did you ever decide on a power transformer?

Expensive secret sauce!!

Yeah! I bought the Hammond 272x probably will wire the 125vAC tap to get happy heater voltages, and a bit lower B+

 

[Fred Mertz]

Good choice for power transformer. With a 5Y3, I believe it should put you in the 350 to 360 volt DC range for plate supply voltage to the 6V6.