Fender '59 Bassman Reissue Rewire Mods Question

[Walterj]

Hello, I am new to the forum and am on my second amp project. I have already built a 5E3 clone with some mods from a Mojotone kit.
My current project is rewiring a 1959 Fender Bassman Reissue amp. I pulled the PCB and am replacing with an eyelet board and new 355V power transformer from Mojotone. I also want to incorporate a number of mods listed on Rob Rob's site, including:
1. 3-Way Negative Feedback Switch: Normal / 5E3 / JTM45 selectable feedback.
2. Adjustable Balanced Bias: Adds a second bias pot to the Adjustable Bias circuit to evenly bias unmatched power tubes.
3. Voice a "Lead" Channel: Tighten up and modernize one channel's clean and overdrive tone.
4. Master Volume: Trainwreck Type-3 Post Phase Inverter Master Volume (PPIMV) - 1MA pot connect to the two phase inverter outputs between the coupling caps and grid stopper resistors.
5. Cut Control Mod: 250KA pot (audio pot wired as variable resistor) and .0047uF 200v cap connect the two phase inverter outputs between the coupling caps and grid stopper resistors.
6. Add an FX Loop: between the volume pot wiper and the following phase inverter coupling cap.connect to the two phase inverter outputs between the coupling caps and grid stopper resistors.
7. Channel Jumper Switch: Leave your patch cord at home.
8. Gain Boost Switch: Add more preamp gain for more dirt.
9. Pentode / Triode Half Power Switch: Cut your output wattage in half.

My question is with the mods 4 and 5 listed above. Both the 250KA and 1MA pots connect to the same points on the eyelet board - (the two phase inverter outputs between the coupling caps and grid stopper resistors). Do these defeat each other? Do I need to put a switch between them and only use one at a time or can I use both the cut control; and master volume at the same time?

Any comments or advise are appreciated!

[sluckey]

or can I use both the cut control; and master volume at the same time?

Yes.

[Walterj]

Thank you Sluckey for your response. I will proceed with no switch.

[romberg]

I also want to incorporate a number of mods listed on Rob Rob's site, including:
[snip]

Any comments or advise are appreciated!

Depending on how confident you are in your ability to pull off all these mods on the first go, it might not be a bad idea to consider just building a stock bassman circuit first. You can mount any new switches/jacks/etc you will use. Just leave them disconnected. This way you start with a know working circuit (which others can help you with).

Then add all those mods one at a time.

All depends on how comfortable you are with all this and your ability to debug things if something does not work the first go.

Mike

[pdf64]

Vox schematics show a well engineered means of greatly improving the type 3 master volume characteristics, as well as also including and isolating it from the tone cut control.
eg R105 and 112 of https://el34world.com/charts/Schematics ... ac30c2.pdf

[ChopSauce]

Well, I know that was not your question but are you aware that the triode-pentode switch will not cut the noise by half at all?

[bepone]

triode mode doesnt sound right in guitar amp.. missing too much presence IMO

[bepone]

good build doesnt need any mods.. maybe only master volume..

[sluckey]

good build doesnt need any mods.. maybe only master volume..

I consider adding a MV a mod. What do you call it?

[pompeiisneaks]

good build doesnt need any mods.. maybe only master volume..

I consider adding a MV a mod. What do you call it?

Isn't that what he means that it doesn't need any mods... except the master volume mod? or did I misunderstand?

~Phil

[ChopSauce]

Afterwards I am a bit sorry I opened the Pandora's box and I've been willing to start some joke about the interest of being able to bias non matched tubes - those days ...

... but frankly - to those willing to criticize tweed modders: who does need a normal channel as is / full stock on tweed amps?
(etc)



NB : the "lead channel" mod seems to be pretty popular, but Marcus "Norburybrook" & FredViolleau's "hi-plate" mod. (R_a=220k, R_k=2k2, C_k=5uF) for the normal channel (of their tweedle dee deluxe-s) is another interesting alternative. I've tested it and I am thinking about lowering a bit the cap values around but you can find more informations easily here, if you want.

[bepone]

Isn't that what he means that it doesn't need any mods... except the master volume mod? or did I misunderstand?

~Phil

about jtm/ bassman types you can find many mods, a lot of infos.. but lets keep it simple, this is good pedal platform, so when you build good jtm/bassman amp, you need only master volume (also this can work against the tone if the slider is positioned less than 70% of rotation because of lack of presence, life, and problematic trancking on the pots between the channels) and maybe to tame bass on Normal channel (but i dont even do that because bassy normal channel is useful for many pedals sometimes i put 100pF peaker over the normal volume pot)

i have also Metroamp with mercury magnetics iron inside, stock, very good unit... so no need to much.

[Walterj]

I finished the 5F6A build from the RI Bassman. Used a Mojotone 355V power transformer. Added all of the mods that I mentioned in the original post.
I ended up putting the controls for the mods on a hinged aluminum plate that I created and attached to the chassis. I then built a wooden back panel that was thicker than the original so the amp can be laid on its back and the controls are protected.
The amp sounds great. I have gotten some intermittent static that I have not yet sourced. Annoying but infrequent. I did not see the post that suggested building the original circuit and then adding in the mods.
I have attached some pictures of the amp with the hinged plate on the back.
The presence knob does not seem to do anything. I have been running it with no pedals.

Thanks for the info!

[Walterj]

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