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

Moderators: Slowy, Capt. Black

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BY Cdog
#812249
sizzlingbadger wrote:Photos in the previous post aren't working for me.

Ohhh... thanks. Tried again, do they work now? I've started experimenting with google photos, but having teething problems
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BY Bg
#812255
not working for me either, I suspect I need to be signed in to view them maybe?
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BY Cdog
#812265
Bg wrote:not working for me either, I suspect I need to be signed in to view them maybe?

Thanks. Tried moving the pics to a shared folder and embedding from there... if no fix, I'l have to go back to imgur. :(
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BY Bg
#812267
first few are still fubar'd, last post of previous page is good :)
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BY Cdog
#812274
Facebook hosted

Cdog wrote: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.

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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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User avatar
BY Cdog
#815903
Time for a progress report. A couple of hiccups, and the Christmas New Year disruption have caused delays.

Hiccups:
I received the wrong layout fibreboard, and the kit was missing chassis straps. Mistakes happen, it's how they're put right that counts. No points lost for Mojotone there. Fibreboard arrived, chassis straps haven't yet but have been shipped.

Musings:
* I fitted an IEC power socket with internal fuse instead of the fixed cord and separate fuse 3AG holder. :thumbup:
* It is going to be very heavy! No chance an alloy chassis could handle those transformers, steel is a must.
* Difficulty on this one is definitely 5/5 (as advertised). I'm going to have to heavily annotate the schematic and layout, they're pretty minimalistic. (attached)
* Having a little grumble about eyelet fibreboards in general... flimsy and wretched things, I was spoilt with turrets on my last build. My current issue is trying to predrill the mounting holes for this fibreboard. I'm grumbling because there's not really much space to put mounting screws in the best places, and the board is so flimsy it'll need several. Most of the holes were predrilled, just not the eyelet boards mounting holes... obviously due to different layouts etc, the chassis is also for other kits. I've had to assemble the Filter Cap board and premount it in the set position to check for hole placement compatibility. Plopped a dab of RTV under each of the caps to stop them rattling round. The chassis is quite busy on both sides, so it's going to a sod, but not impossible.
* I assume placement of the eyelet board is about correct... i.e as about as far as pos from the PT?

While this post sounds grumbly, I am having fun. Grumpy fun! Any thoughts or tips always appreciated! :)


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BY Cdog
#816448
el byrdo wrote:Very cool man. Do you have any comments on your tweedish tourist pedal? I just bought it off trademe. Haven't tried it out yet as I have all my speakers out of my amps...

It's a lavache. Aint played through one in ages. Compares to Les Lius from memory
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BY Cdog
#845421
A long time coming... Progress pics! ♥

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Yoiks. There's still a lot of chassis left to fill! :shock:

Comments:
Took some time for me to figure out the back panel. Holes have changes, things have been moved.
No standby switch!
Fused all PT taps except Bias
MOV on IEC input
100nF filter across AC line, and a NTC Thermistor to soften the startup. Backup diodes to pre-rectify for the 5U4GB
Power tubes will be 5881
Installed a 3-way impedance switch for different speaker loads. The 50w OT does 2, 4 and 8 Ohms
Power-amp star ground has wandered out into the wilderness a little, hoping this wont be an issue
Little pcb on the dual pot is will be a Trainwreck 2 MV, it replaces the 220k grid leak resistors. The onboard resistors are for safety, pot wiper fail-safes... this mod is from Rob Robinette's excellent site.
Decided to build stock first then rewire in the MV after its work... because that's a much better idea! :roll: :thumbup:
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BY GrantB
#845431
Tidy work!
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BY Cdog
#851936
Alrighty... this has gone on long enough.

No thanks to an ongoing back injury I've had very little time for fun things over the last 10 Months. There was one final hiccup at boxing up-time... the chassis mounting holes in the head-cab were in the wrong place! :lol: Mojotone have been good about it, and quick respond... we reached a solution. No points lost as far as I'm concerned, overall it was a great quality amp kit :thumbup:


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Preamp tubes are a mix of TungSol and JAN. Power tubes are TungSol 5881s, the rectifier is a 5AR4, no standby switch, added a Master Volume but otherwise it's a reasonably stock AB763 Super Reverb circuit. It sounds absolutely outstanding. The reverb is drippy and cavernous, the Vibrato is pretty decent. Master Volume was well worth doing. Cab (a repurposed Spider-Valve) has 2x 10" 4-Ohm Jensen Alnicos, wired in parallel for 2 Ohms, the same impedance as the original 4x10 to match the NFB.

There's still some finishing touches to do, especially on the speaker cab, but she flies for now and I'm very happy to be playing this thing. Think I'm gonna need a compressor pedal haha
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BY kdawg2a
#851997
Corey, what is the speaker ohm output of this amp?

Edit: just seen it, 2 ohms. Bugger. I would have liked to try my 2x10 Weber 16 ohm cab on it!