Amp tinkerers and people who aren't afraid of 700 volts or so in here....

Moderators: Slowy, Capt. Black

User avatar
BY Cdog
#812010
Finally arrived, right before Christmas! :D

The Mojotone Super Reverb head kit, ordered at the end of October, took about 3 weeks for them to build the head cab and a further month to get here via Youshop. Maybe only saved about $100NZD over shipping direct, to be honest might be worth paying extra to ship direct next time. It became fiddly as it was shipped in 3x big boxes, which Youshop charged separately to ship to NZ. (Too big to consolidate). In all shipping was about $470. Customs was about $250.

Anyways, the Super Reverb circuit is a blackface AB763 variant, interesting comparison of the different models here. Those trannies weigh a ton!

Head cab is basically a stock Mojotone cab, but has big rubber feet instead of the vintage steel slides, and the Mojotone aged grille cloth. Bought some extra cloth for the speaker cab. Grabbed a couple of 2nd hand reissue alnico Jensen's, the type used with these back in the day. May go with 4 speakers, not sure.

Tubes: Haven't ordered tubes yet. Last time it took a few months to build and by the time I put the tubes in to test, one of the was badly microphonic and out of warranty. (JJ ECC83S). I'll order closer to completion this time.

These kits come with a schematic drawing and a layout diagram ready to go! Inventory check is OK :)

I'll update this thread with progress pics as it happens... Here's the first couple

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The build threads I have seen online are littered with problems, so I'll not going to be rushing things. I do have a couple of questions for the experienced builders out there...

1/ Where to start? It's looking like a complicated build, quite a bit going on in that chassis. :shock: :lol:

2/ The kit came with carbon comps, I experienced noise introduction and drifting from these in my last build... Is it worth getting film resistors instead?

3/ Any other advice?

Woo! :D
Last edited by Cdog on Sat Dec 22, 2018 9:29 am, edited 2 times in total.
User avatar
BY sizzlingbadger
#812014
1) Does the kit provide step-by-step instructions or do you have to work it all out yourself ? I would try and dry-fit as much as possible to start with to make sure everything "lines up" as expected, you can also tweak the layout slightly if you see a better way to do it.

2) I'd use modern resistors, for the same reason you have already discussed. Carbon comps do have an effect on tone but its minimal and really only in places with large varying voltages, like plate resistors.

Ask yourself if you're trying to build an exact replica, as close as possible to the original, or if you are re-creating the amp as a modern version, this will help with some of the decisions you may have to face. Read up as much as you can on other builds of the amp, see what problems they faced and how they solved them before you start.
User avatar
BY Molly
#812018
There are various SR mods I read about when I had mine. Some were simply pulling tubes for xyz reasons. Often it was guys chasing SRV tones.

Pete Thorn does a great demo of a fantastic sounding old SR. Might be worth a listen (assuming you like it and there's something specific to its year).
User avatar
BY Kris
#812019
Just my experience,but you shop seem to try split orders up into separate packages all the time.even if it makes no sense.
User avatar
BY Cdog
#812022
sizzlingbadger wrote:1) Does the kit provide step-by-step instructions or do you have to work it all out yourself ? I would try and dry-fit as much as possible to start with to make sure everything "lines up" as expected, you can also tweak the layout slightly if you see a better way to do it.

2) I'd use modern resistors, for the same reason you have already discussed. Carbon comps do have an effect on tone but its minimal and really only in places with large varying voltages, like plate resistors.

Ask yourself if you're trying to build an exact replica, as close as possible to the original, or if you are re-creating the amp as a modern version, this will help with some of the decisions you may have to face. Read up as much as you can on other builds of the amp, see what problems they faced and how they solved them before you start.



Thanks for the suggestions!

I'll do a dry fit too, good call. Missing a few bits of hardware from the kit, but I already have a big selection of M3 and M4 fasteners so no worries there. Thanks for your comment on resistors, that confirms my decision.

This wont be a vintage replica, but it will hopefully look like one. I'll definitely be fusing the HT and all PT windings. Probably go crazy with MOVs in there too ala RG Keen's Immortal Amplifier Mods, but no mods until it's working stock first. Maybe a VVR too, eventually.
User avatar
BY Cdog
#812023
Molly wrote:There are various SR mods I read about when I had mine. Some were simply pulling tubes for xyz reasons. Often it was guys chasing SRV tones.

Pete Thorn does a great demo of a fantastic sounding old SR. Might be worth a listen (assuming you like it and there's something specific to its year).

Yeah saw that, added a bit of weight to my decision to choose this model 8)
User avatar
BY Bg
#812053
I love those jensens, they're by far my favourite alnico - mojo at work with them :D
User avatar
BY Cdog
#812173
Heavy pics content... and lol at end! :rofl:

Started with the SPEAKER CAB... using a donor Spider Valve ex TM (Will be repaired and converted to head at some stage)
Bonus is that is comes in (ratty) black tolex, and a suitable profile. Let see how it goes :P

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18mm Ply and some circles to cut out:

[img width=1000 height=500]https://scontent-syd2-1.xx.fbcdn.net/v/t1.0-9/48421692_10156224643133403_4669177840766287872_o.jpg?_nc_cat=111&_nc_ht=scontent-syd2-1.xx&oh=84612e09f92e8ae5cd9269f98be9ddc8&oe=5C8C7D7B[/img]

Some angle cut tricks with a skilly, finally made the baffle.

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Couldn't resist

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Filled, sanded, painted

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Now the tricky part... using Mojotone Aged Fender grille cloth.
Tough Polyester stuff, will be durable, but not very pliable in assembly.


[img]https://scontent-syd2-1.xx.fbcdn.net/v/t1.0-9/48421479_10156224643358403_7006591677104128000_n.jpg?_nc_cat=111&_nc_ht=scontent-syd2-1.xx&oh=42ffd07958ef2ada36cdf235727ccd89&oe=5CD311B8[/img

Well we got there

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It's Jensen Time!

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And fits together rather well:

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Wired in series for 8 Ohm.
May rewire to 2 Ohm once the SR is complete... apparently that's part of their 'sound'

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And now the handsome pair, looking like they were made to be together...
But wait... something's not quite right... :think:

See if you can spot it :lol:

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OMG... easier to redo the head, I'll sort that later :oops: :lol:
Last edited by Cdog on Tue Dec 25, 2018 10:42 am, edited 1 time in total.
User avatar
BY Cdog
#812246
Sorry more spam.

Check out the differernce in size of the transformers between the Spidervalve and the Super Reverb!
Interestingly, both are rated 40W and use 2x6L6 power tubes. The Mojotone trannies are pretty much double the size and weight.

PT
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OT
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I read that the Super Reverb version of the AB763 came with bigger Trannies that the other 2x 6L6 versions.
Scuse me while I geek out.

Spidervalve gutshot for more geeking: I suspect it needs new 6L6s, this will be a project for another day :)
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Last edited by Cdog on Tue Dec 25, 2018 10:46 am, edited 6 times in total.