1959 Tweed Bassman – Part VI

Part 6, Tweaks

Well peeps, I finally had some extra time to finish some more tweeks on the ’59 Bassman clone.

First up I replaced the “orange drop” signal capacitors with SoZo units. These are closely modeled after the Yellow Astron and Blue Molded series of vintage capacitors. Listening before and after the SoZo units was quite revealing. The sound, after putting in the SoZo units became higher in fidelity. The high-end was nicer, more articulate. The bottom-end was tighter and a bit more beefier. Amazing!

SoZo caps

Next up, I modified the bias circuit making it adjustable. I removed the 56k resistor and replaced it with a 50k linear potentiometer wired as a rheostat. I also replaced the ground wire from pin 8 to chassis with a 1 ohm resistor to ground. This will assist you in taking readings with a voltmeter to bias the power tubes. Once you have an adjustable bias control you can really dial in your sound. I started out low in bias voltage and ended up higher than what Fender traditionally has it set at.

At about 18 static dissipation watts per tube, the sound really opened up. The player can no be very expressive in their playing. Using a lite touch sounds nice and clean while a more aggressive touch makes the amp break up just wonderfully. Find out what your output tubes can handle in wattage. The 5881’s max out at 24.

New Cap

1ohm resistors

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1959 Tweed Bassman – Part V

Part 5, Assembly of chassis and speakers into cabinet and final listen:

If you use the MojoTone kit w/cab you will need to have them drill the mounting holes in the 4-10 cabinet to install the chassis. Minor additional charge. Install the 4) 10” Jensen speakers so that the speaker terminals are towards the center of the cab. This will help in wiring and servicing. When installing the chassis turn the cabinet on its side for easier line up of the chassis mounting holes.

There is a time element for the speakers to break-in and loosen up a bit. About 40 hrs. But still, this 4-10 cabinet sounds GREAT! Guitar or bass, this is tone HEAVEN!

If you have found this blog fun and interesting let me know. I had a lot of fun doing it. If you know any guitarists looking for an amp like this I am open to building one out for them.

Great Mix Recording
Great Mix Recording
Great Mix Recording
Great Mix Recording

The previous posts have been opinions from Jacques Sewrey re: the building of a ’59 Fender Bassman clone kit.

Coming up in future blogs will be the modding of and minor circuit changes of the aforementioned Bassman. This will improve the tone options and make biasing for the power tubes easier.

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1959 Tweed Bassman – Part IV

Part 4, Final Assembly and testing of the chassis:

NOTE: The ground switch is not connected. Due to the current power grounding schemes in the US, the Ground switch does not do anything to help in getting rid of hum. You will notice that I used one of the ground switch terminals as a connection point only. The proper way to hook up the power input to the Power Transformer is by connecting the white wire to one of the black PT input wires and the black wire (coming in) going thru the fuse and the Power switch before connecting to the other black PT wire. Great Mix Recording

Tip: For minimum hum, keep all wires as short as possible. FinalLeft

Now, a discussion of tubes is in order. Currently there are less than 6 manufactures of audio tubes in the world. Czechoslovakia, China and the former Soviet Union. I prefer the Russian tubes. MojoTone uses JJ tubes in their kits. While these are pretty good, I have my own ideas on tubes. I picked the Sovtek 5AR4 rectifier based on past experience with Sovtek and reviews of great extension and tightness on the bottom end. NOS (new old stock) tubes can provide better handling of the rectification but I feel that the cost is too much for what you get. For power tubes I decided on 5881’s vs 6L6’s. In general 6L6’s have a bit more gain but I’m going for tone. So, 5881’s by the newly reissued TungSol version built by the Russians. The preamp tubes get more interesting as there are a lot more choices and which ones you put in what stage. As you peruse the internet you will find hundreds of opinions on all sorts of combinations. For V1 I am staying with the 12AY for better tone. I have picked the EH (Electro Harmonix) from “Doug’s Tubes”. No reason for balancing or matching the triode’s as ½ the tube is for the normal channel and the other ½ is for the bright channel. Who cares, its 2 different inputs. Viva la difference. V2 goes before the tone circuit, the first ½ increases the voltage and the second ½ matches the impedance for the tone circuit. Here I chose a NOS 12AX by GE, this is where you want to use a great sounding tube. (Does not need to have matched gain or balanced triode’s). Next up is V3, the phase inverter. This tube creates the plus and minus waveforms for each of the 5881’s. Some also call this the “driver”. This is where you want to use a high quality tube and get it with balanced triode’s and matched gain. I used a reissued 12AX TungSol from Doug’s Tubes.

So, fired it up sans tubes, took some voltage measurements and all was good. Put the tubes in and ran some sound thru it, no issues. Took the amp over to my Guitar buddy Kris and we ran it thru a 2-12 cabinet with v30 Celestion’s. Playing his custom late 2000 Strat, he was grinning ear to ear. That sounds X@X@Xing awesome he says. A few adjustments of the gain and tone controls and he’s loving it.

Where’s the 4-10 cabinet he says. That, I say, is for another day and another blog. 🙂

Great Mix Recording

Great Mix Recording

Great Mix Recording


Stay tuned for more to come on this exciting project!

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1959 Tweed Bassman – Part |||

Part 3, More Assembly:

Next up is the high voltage filter capacitor board. This is a very important part, so make sure it is done correctly.
Great Mix Recording Notice position of the caps on the board and how the minus side of the caps are tied together.
Great Mix Recording

When done and wired go ahead and mount with “cover” to the chassis running the wires thru the grommet into the chassis. I did add some rubber feet to the bottom of the cap board to take up space under the cover so it does not bounce around and put some sticky pads on the chassis for the caps to sit on. Mount so that the caps sit on the chassis. Great Mix Recording

The main circuit board is pretty involved, so take your time. If you are a “righty” start on the left and work your way to the right. If a “lefty” reverse the procedure. Do the underside tie lines first before mounting components.

Great Mix Recording Double check you work constantly. I found myself making a few mistakes and corrected them by comparing the schematic to the wiring diagram. Pay particular attention to the 2 bias resistors (220k) and the 2 screen resistors (470). These need to match very closely in value in order to get the most out of your matched power tubes.

Great Mix Recording Wire all leads going from the board to the chassis components to the underside, as it will give a cleaner look. I also wrote the values of the orange drop caps on the caps to aid in servicing down the road. Dry fit the board to the chassis and drill 2 holes through both boards to mount directly to the chassis. Make sure you do not hit any wiring or components on the other side of the chassis.

Stay tuned for more to come on this exciting project!

. Record . Mix . Master . Music .
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