by bassybeats | Dec 4, 2019 | Amplifiers
A nice quick fix and flick project. A very cheap find on Trademe was the JTM60 3 x 10. Very similar to the 1990’s JTM30, it was loud and the reverb was horrible.
I didn’t end up taking many photos of this build but essentially I brought the amp faulty with the idea that I could fix it. Unbeknown to me, these things had a design flaw which saw the output tubes ( EL34’s ) mounted directly under the filter caps. The heat that dissipated off them went straight up and killed the caps.
I ended up giving the amp to Clarry at 34Audio and he remounted the new caps out of the way. I also found out that the amps effects loop plugs were prone to corroding and making a lot of noise. So a bit of contact cleaner fixed that.
I ordered some new JTM45 grill cloth as the other stuff had overspray all over it. Grill cloth is always a two person job.
Materials:
- New caps from Clarry
- New grill cloth from Mojotone
by bassybeats | Dec 4, 2019 | Amplifiers
I always wanted a big Marshall but could never find the one I liked. Then I discovered Ceriatone. They had a hand wired JCM800 dual volume schematic for a hand wired amp. After doing the math and finding some bargain deals the project was a go!
Finding a speaker cab
First part was finding a speaker cab to use. I was trying to find a cheaper but bad condition cab that I could re-condition and save some cash on freight. Trolling Trademe I picked up a 4 x 12 ( or so I thought ). On arrival it was pretty obvious that the cab was NOT a 4 x 12 but actually a 2 x 12. I said to the guy “if it has the half the speakers i’ll give you have the agreed price.” He agreed.
Unbeknown to him, I had noticed a little badge and some strange colours inside. It turned out to be a Marshall 50th anniversary Jubilee cab. Someone had spray painted the silver tolex black, but when I took the back off the cab I could see the silver inside, as well as little badge on the front.
The wood working
I stripped the cab and made a head to match. The whole setup is actually the size of the 2550 Marshall instead of a proper JCM800, so the whole build was going to be a one of a kind. The head had to be double layered around the front and back to give it that Marshall chunk. The whole thing was made from solid pine boards, i’m not a fan of MDF and ply was too big to fit in my car.
Parts collection
With some phone calls and some trading of skills I got some chassis’ made up from Monaghan Sheet Metal. And because I hate getting just one of something, I got 8. I ended up selling the rest and paying essentially nothing for mine ones.
The tolex, transformers and parts came from Triode Electronics, when the shipping to NZ was reasonable. Because I was going for a 1980’s rock / metal thing I went all out and go red tolex, which I never regretted.
Putting it all together
This part took forever as it was only the third amp I had done and it was the first I had done by myself. With lots of calls to dad and lots of googling I got it all wired up. I ended up purchasing some chassis punches to get the tube socket holes ( boy are those handy! ) With a bit of test fitting I was ready to cover it all up. I also snagged some laser cut badges and faceplates through my mates at uni to replace the broken ones on the cab. Also randomly the mesh for the back is cut down gutter guard, the stuff you put in the gutters to stop leaves blocking your gutters.
Firing it up
I was almost ready to fire it up. I ended up going for 6550’s instead of EL34’s as I the samples I heard were more to my liking. I picked up some valves from VintageAudioValves, where I started a great personal friendship with Paul and continue to get valves from.
When I fired it up and I ended up modifying it and adding in external bias tests points with an external bias pot. Still running too hot with the 6550’s I had to change the bias resistor. After a few weeks I also ended up changing to CTS volume pots as the alpha ones went scratchy fast.
Man does she sing! and I haven’t touched this thing since. One of the most reliable things I have ever built.
Materials:
- 2 x 12 Jubliee cab
- Tolex from Triode Electronics
- Transformers from Triode Electronics
- Chassis built by Monaghan Sheet Metals
- Valves from Vintage Audio Valves
- All components from Triode Electronics
- 19mm Pine boards for head
- Laser cut faceplate and badges
- Gutter guard mesh for back panel protection
by bassybeats | Dec 4, 2019 | Amplifiers, FX Pedals
With the Jansen Bassman 50 done I needed a way to use my Marshall cab with both the Bassman and the JCM800. I was too lazy to keep unplugging stuff all the time so I started building the Aiken Amps head switcher.
I had downloaded the schematics from Aiken Amps a long time ago as the site was often going down, now it’s gone forever by the looks! The general idea of the project was to have the unit switch the guitar signal as well as the main load of the heads between the cab and a 200W dummy load. Heres the schematic if you need it.
Finding the Parts
The Aiken schematic uses a make before break concept using 5 volt relays. Surplustronics had a bunch of these laying around so I grab enough to make 4 or 5 of these units incase friends wanted one and I couldn’t get parts anymore. I had ordered some 100W wirewound resistors a while back as well.
I also had some leftover alloy chassis from Monaghan Sheetmetals nicely corner welded. A bit of drilling and test fitting the wirewound resistors I got on eBay and it all seemed like it was going to come together.
Test fitting
There was some old computer CPU heatsink paste laying around to use for the resistors and the I could wire them up. I did the rest of the wiring on stripboard with solid core wire. I will most likely make a PCB for this and swap it out or make a V2 and sell this one, one day.
Figuring out how to wire it up
I had a bit of trouble figuring out how to lay it all out since there was only a schematic. The notes said to physically isolated the two circuits, but I just kept the separate on the same piece of vero board. I will eventually swap it out for a PCB when I get round to it.
I still haven’t got to running it through a pair of amps switching full load yet ( too scared! ) but it all works as it should and switches both signals.
Materials:
- JZC-22F 5VDC and DS2Y-S-DC5V relays
- 18g alloy folded and welded chassis
- Resistors from eBay user abillionstore
- Schematic from Aiken Amps
- Components from Jaycar
by bassybeats | Dec 4, 2019 | Amplifiers
Yet another amp project build. This time it started with dad being given a bunch of old Jansen amps from old trades at the Rockshop. Included in the stash was a 1975 Jansen Bassman 50.
The old girl was looking a bit sad
It was clear that this amp was in a bit of a sad state. The amp seemed to have burnt out the PCB board mounted valve sockets from the heat of the 6L6GC’s. Good thing was, I had access to the schematics and the pcb photos from the original board as well as my dad’s Bassman 75, which are more or less the same with different tubes.
Dad’s Bassman 75 was a good source for figuring out how it was wired originally and what the type of parts was back then.
The planning
First stage for me was to source parts. I picked up a silverface Bassman faceplate off Clary from 34Audio and used the left over tolex and grill cloth from Dave from Southgate Studios’ Fender Blackface build. The knobs came from a NOS box from Surplustronics. Clarry was also able to supply the schematics for the Bassman 50 and 75. Turns out they are almost identical.
Next phase involved tracing paper and ALOT of patience. I manually traced over PCB after it had been stripped and then put it into illustrator. I tidied up the drawing and re-etched the PCB. I kind of failed with the etching, I brought double sided board and the etchant start eating into the traces because of the time it took. But the continuity checked out and the board was ok, even if it didn’t look the nicest.
Populating the board and wiring
Lucky for me, I had a lot of old tropical fish caps and Phillips Mustard caps. So a fair amount of the parts we’re similar or NOS versions of what it came out with. I ended up mounting the valve sockets to the chassis and remote wiring to the board since it overheated and burnt out the last time.
There were a few modifications that Clarry recommended doing before firing it up. One was too wire the heaters as 12.7V instead of 6.3, some protection diodes and replacing the ‘spark gap’ and installing a bias pot.
Firing it up
Due to so many variables in the build I opted for Clarry to fire it up as he had a Variac and had repaired many of these in the past so he could check my wiring. From what I recall he changed some jacks to shorting jacks and rerouted some wires for noise suppression.
Once he fired it up it was apparent that the Output transformer was dead. He hooked it up to a test rig he has and confirmed that the amp runs and just needed the OP transformer rewound. And the amp sat for 1 year and half till I got the money to get it finished.
It puts out a whopping 50 watts ‘clean’ and 65 watts flatout, all with NOS RCA 6L6GC’s.
Materials:
by bassybeats | Dec 4, 2019 | Amplifiers
The amp the started it all. The 1974X is a very popular build amongst DIY amp builders. Some say it holds that classic Marshall tone.
My Build starts 18watt.com and my dad, as usual. During my first year at uni dad started building the Marshall and it just sounded soooo good. Of course I could barely play guitar but I had to have one. That feeling when you are learning, playing through a killer amp and get a power chord right is just awesome.
Re-purposing speakers
Sourcing the schematics and wood was the first task. I ended up building mine to the physical specs of the Marshall Bluesbreaker instead as I managed to find two Celestion G12L-55’s from and old Rivera cheap. The speaker baskets got a gold paint job as they looked pretty rough.
The build
I used the workshop at uni to fold up the chassis for free essentially. The specs for mounting the chassis in these old Marshalls is a bit different where the chassis held captive by two boxed sections built into the cabinet instead of folded and welded ends like modern Marshalls. I also managed to sneak in some time on the laser cutter to get some badges and faceplates cut/etched.
It was a complex build, you have to do most things in just the right order or else it wouldn’t go together right. You need to route under the top vent to be able to wrap the tolex around and you need to build the speaker grill in 3 pieces to be able to get the grill cloth wrapped and the top panel to cover the t-nuts that bolt it all together.
All in all it turned over pretty well.
Taming the beast
After years of lugging it around and realising that it only sounds good when it is at full blast I decided to get a Hall Electronics VVR installed. It worked well but just didn’t sound the same and as you lower the B+ voltage the tremolo stopped working correctly.
In the end I ended up selling it as I just didn’t have the space to play it at volume or store it. I think the guy that brought it ended up putting Greenbacks in it and loving it.
Materials:
- 19mm pine boards
- 12mm ply front and backs
- Mojotone tolex and grill cloth
- Hofner Heyboer transformers
- Celestion G12L-55 speakers
- Hall Amplification VVR kit
- Laser cut faceplates and badges from 3mm perspex
Page 18 of 19« First«...10...1516171819»
Recent Comments