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  #1  
Old 12-31-2016, 04:41 PM
clintj clintj is offline
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Default Tweed Bassman build thread

Been a couple of years since I've posted one of these, but now it's time to do it again.

My Mojotone Tweed Bassman kit was delivered today while I'm here at work. This is one of those bucket list amps for me. Been wanting to build this one for a couple of years now, especially after building its English twin brother, the Marshall JTM45, for a friend a while back.

I've been doing a lot of reference book studying, learning, and have learned a ton about tube circuits since my first amp. I've also learned a handful of little tips and tricks from some pros I'll point out as well as I go. I've also bought a lot of upgrades to my tool and test gear collection that make this a lot easier and more fun.

I'll start unboxing and inspecting parts tomorrow and Monday, and do a full inventory to make sure I have everything I should. Pics will start coming then.

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  #2  
Old 01-01-2017, 07:59 AM
stevecuss stevecuss is offline
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Excellent! I built a Marshall Plexi Lite 18 watt a few years ago and am considering jumping in on a 5E3 deluxe sometime down the road. I'm keen to follow your Bassman - one of the finest circuits ever designed
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Old 01-01-2017, 08:12 AM
Darwin Darwin is offline
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I will be following. I just found a 70's oscilliscope this week for checking tube amps and may do a build in the future. The Bassman would be on my bucket list. -- Darwin
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Old 01-01-2017, 10:29 AM
LouieAtienza LouieAtienza is offline
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Awesome... will be watching!
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  #5  
Old 01-01-2017, 11:10 AM
clintj clintj is offline
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Checked inventory this morning, and I seem to actually have all the parts! That hasn't always been the case with these kits, but looks like they tightened up their process for pulling parts for orders since I last bought one. Kudos!

I'll likely load the speakers in, and maybe wire them today or tomorrow. I'm pretty busy the next week or so, then I'll start in earnest. I was figuring on having to get them to send some missing parts, honestly.

To be continued....

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Old 01-02-2017, 06:07 AM
Dru Edwards Dru Edwards is offline
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Looking forward to the progress on this one, Clint. Good luck!
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Old 01-02-2017, 09:51 PM
clintj clintj is offline
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Installed some parts in the chassis tonight, and the speakers into the cab. Nothing to complicated, but I'll probably spend too long tweaking parts later until everything looks nice and straight to me.

Work week starts tomorrow, so this will get picked back up later this week or early next week. I'm ordering a small trim pot in a day or two so I can change the bias to adjustable instead of the stock design.





I'll get a pic of the speakers in the cab when I start installing the chassis and wiring in the speakers.

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Old 01-03-2017, 09:10 AM
Dru Edwards Dru Edwards is offline
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Bright, shiny and clean!
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Old 01-03-2017, 10:28 AM
redir redir is offline
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Sweet!

I'm in on this thread...
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  #10  
Old 01-08-2017, 03:14 PM
clintj clintj is offline
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Drilled the chassis mounting holes in the cab, then mounted the transformers and choke. These are seriously hefty chunks of iron, but remember what this amp was originally designed for: bass guitar. You need a lot of iron to keep the low frequencies from saturating at high power and getting muddy.

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  #11  
Old 01-08-2017, 06:33 PM
clintj clintj is offline
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Easy way to keep flying leads from wiggling around when soldering.



Board is mostly populated. I tested each component as it went in, to verify the right value and to make sure it was a good part. Saves a lot of grief later if something is wrong.

Those caps are Jupiters, and are built to the same spec as the old Astrons that were used in the vintage amps. They're also marked for the outside foil end, which saves me a few minutes. One thing I've learned is that the orientation of caps affects the noise floor of the amp. Connect them the right way, and outside noise gets sent to ground instead of being amplified.

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  #12  
Old 01-08-2017, 06:44 PM
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Gutch Gutch is offline
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Looking good!
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Old 01-08-2017, 07:32 PM
redir redir is offline
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Awesome! Interesting about sending noise to ground.
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  #14  
Old 01-08-2017, 08:55 PM
clintj clintj is offline
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Quote:
Originally Posted by redir View Post
Awesome! Interesting about sending noise to ground.
If anyone is interested in the science side of it, here you go.

http://www.aikenamps.com/index.php/w...-on-capacitors

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"You don't have to be great to start, but you have to start to be great." -Zig Ziglar

Acoustics
2013 Guild F30 Standard
2012 Yamaha LL16
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1991 Yairi DY 50

Electrics
Epiphone Les Paul Standard
Fender Am. Standard Telecaster
Gibson ES-335
Gibson Firebird
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  #15  
Old 01-09-2017, 11:06 AM
clintj clintj is offline
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Heater wiring done. Per Merlin Blencowe's recommendations, each heater pin's wiring stays tightly twisted up to the socket, then jumps straight across to the opposite pin on the preamp tubes. This minimizes the chance of the AC heater wiring radiating hum that is picked up in the sensitive signal wiring. Runs between sockets are pushed up into the chassis corners to maximize distance and shielding for those runs. Done right, this all combines to reduce as much heater hum as practical. Takes a couple of hours, and can it really build tension in your neck and shoulders from the tight quarters in a chassis.

Break time!

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"You don't have to be great to start, but you have to start to be great." -Zig Ziglar

Acoustics
2013 Guild F30 Standard
2012 Yamaha LL16
2007 Seagull S12
1991 Yairi DY 50

Electrics
Epiphone Les Paul Standard
Fender Am. Standard Telecaster
Gibson ES-335
Gibson Firebird
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