Fender BASSMAN 100 ALIVE!!!!!

[Andre Oliveros]

Hey guys its been a lot of years since i last wrote, i used to have a Fender Bassman 100 and a Marshall JCM 800 2210 which were bad, i tried a lot to fix em back then but couldnt  be successful, so i kept them and move on, a month ago i was cleaning my stuff and found the amps, and i remember that i did buy almost all new (Caps, sockets, filters, tubes), so i think why not give em a last try, so i decided to go with the bassman 100 first, and voila after some ours of reading, working and soldering the amp is alive, i have a few questions since i read about the amp, its supposed to has a lot of headroom, which leads me to my question,


1. The Normal channel seems to have a lot more volume and headroom, how can i archive the same thing on bright channel?


2. Its something i missed? both has same Groove tubes in pre amp both new also, according to what i read bright channel should be loud and clear.


i own a Vibrolux Custom, which i modified myself with fromel kit, and both channels has same "volume" just different color, i would like that with the bassman


thanks !

[sluckey]

That amp doesn't have a bright channel. It has a BASS channel that is voiced for bass guitar and it has a NORMAL channel (which has a bright switch) that is voiced for guitar. If you want the two channels to sound the same then pick out the one you like and modify the other preamp channel to look just like it. It's mostly just changing the tone stack.

[Andre Oliveros]

True about the names, sorry, what should i look specifically for more headroom in the "NORMAL" channel, im not into the color or tone of the bass channel but more into a even headroom in both since the bass channel does has a lot more right now ?

[sluckey]

A properly working normal channel should have plenty of volume and headroom. I suspect a problem. Try a new tube, check tube voltages and compare to schematic voltages. Post your voltages here so we can have a look.

What have you done so far to repair the amp? Be specific.

[Andre Oliveros]

i swapped pre tubes, and put other set of power, no change, but i observed the "bright" switch is not working, i don't hear any tonal difference, so ill be checking that, also i will change when arrive sockets since i ordered new ones, and two new .01uf 1KV Z5U RMC Ceramic, apart from that already did caps on pre amp section, phase inverter, filter caps, and re solder some stuff that were kinda old or messy, add a 3 prong cord, and re wired the heaters tight em, and put some new 100ohm resistors from pilot lamp to ground, the amp is super quiet and clean right know,i have never listened one of these guys, only twins , vireos  deluxe reverbs, but i do suspect that this normal channel should have more headroom, not only because bass channel has it but also because its a 100W, ill check all that and see what happens, thanks Sluckey

[Andre Oliveros]

So i have news, i finished to change all in the amp, so is stock to schem, sounds great i mean im happy with the tone and the volume in the channels are even but and a big BuT, i have the chance to bring a silverface twin reverb, and i compared both in the same cab of the twin, and just happened what i suspected the bassman has faaar inferior headroom, correct me if im wrong i was looking for both schems and i found they are virtually the same amps with the difference of vibrato and reverb, so the question : what could be causing a massive difference in headroom? And how can i make the bassman 100 to even the twin? Thanks for reading and  to any input

[pompeiisneaks]

Did you try what sluckey suggested?  His pointers seem correct to me.  The bassman should be very clean in that model to know what it was 'a lot alike' would need you to clarify which model bassman you have? is it the AA864?  Is it the 5F6A etc?

~Phil

[Andre Oliveros]

https://schematicheaven.net/fenderamps/bassman_100_schem.pdf


This is the one, the amp sounds great, is just i dont feel like its giving like full headroom, is quiet compared to this Twin Reverb 100w mv, i mean its quieter than a vibrolux custom 40w that i own,

[pompeiisneaks]

Have you tried swapping the 7025's to see if the tonal change follows the tube? Also as sluckey added, it's a different tone stack, that could be impacting it depending on the channel.  The schematic also shows expected voltages with the designated input, if you can give it that.  Make sure you get similar voltages as expected, if not, something is amiss in that section, either a dropping resistor right before isn't doing the needful, or maybe a transformer issue etc.  The only other subtle differences I see are the normal channel bright switch vs the bass channel's deep switch.

~Phil

[Andre Oliveros]

Ill do the readings, some weeks ago i remember i revised the amp vs the schem since i did all stock, and didnt find nothing wrong, however my specific model its a international one, so the only thing different its the power transformer vs the schem, also did tried a bunch of different tubes, but didnt find any difference output wise, wich is what is lacking, different tone yes, What really amaze me is, the twin reverb i have its a 100W, and lets say if i put in Normal chanel pre 8 and master 5 its a huge big and loud amp, but if i do that for the bassman same speakers, the volume and headroom is almost like 60% less, thanks phil ill keep looking and comparing schems

[Andre Oliveros]

Update ok, so before checking things i decided to try something simpler as i notice the bassman has bigger output trans i tried it with a cab loaded with a 12' EVM 200W and boom, the headroom its almost as big as the twin, so i can figure out two of them would make the amp a full blaster, as i read it was designed to run four speakers so ill call them even, thanks for the help