Fender Bassman 10 project

[Blindog]

I'm looking for some advice. I'd like to make this into something a bit more guitar friendly. I thought about a Super Reverb (without the reverb and trem) since it's already in a 4x10 cab. Here is the schematic of my amp.

http://www.ampwares.com/ffg/schem/bassman_10_schem.gif

Mine is a '74, based on the speaker date codes. I already plan on replaceing the filter caps. From what i've read on the web, I don't think this circuit has the funky negative feedback that some Bassman's had.I'd like to lose the master volume, thought about Presence control in place of it.

My novice brain tells me that a cool guitar amp is lurking in here somewhere

Any other ideas you all may have would be appreciated. This is my first mod project. Many thanks in advance!

Mark

[Blindog]

Bassman 10 to Super Reverb conversion

OK, I've made my decision: convert to a Super Reverb (AB763) I'm going to start with rewiring the phase inverter, bias circuit, and output first, should be an easy win, comparing the two circuits. Then, tweak the two input channels so they match. I guess then I'll decide if I will get very ambitous and add the reverb/vibrato circuits. I thought about leaving the power supply alone to make the amp a little more bold. My only thought is should I get a new circuit board, or try to add the eyelets to the current one when I add the verb/vibe section? Any thoughts out there?

Thanks

Mark

[Satamax]

Hi Blindog.

My take on this, get the PI and output to blackface specs. Leave the studio side as it is, just changing the trebles 500pF for a 250pF, and remove the coupling cap between tonestack and volume. I'd say remove the master too.

To get a nicer sound i'd add a 5V filament transformer, and drill for another socket, to use a tube rectifier.

Nother trick i've done on bassmans is to switch the mid cap from .047 to .033 µF that's super reverb and BF bassman values.

On the normal chanel i think i would ditch all the bass circuitry and make a tweed deluxe tone control.

Bye.

Max.

[Blindog]

Hey, Max!

Thanks for the reply ...
I'm with you except for the filament transformer part. This already has a 6.3 volt tap on the transformer, if I'm not mistaken. Can you elaborate a little bit more on the transformer part? I am pretty new to mods ... I know enough to make me dangerous.

The cool thing is, there is already a knockout on the chassis for the rectifier tube that has never been punched, so that's a plus.

Thanks again,
Mark

[chuggy]

BM 10 mods

A BM 10 I recently inspected had unused 5V taps suitable for a tube recto. While some amps use the same 6.3V tap for the recto heaters as well as other tube heaters, I don't think this was done on Fender amps.

Adding verb and trem to your amp will be a big job. Probably need a new circuit board.

Be very careful! Hi voltage in there.

[Satamax]

Hey, Max!

Thanks for the reply ...
I'm with you except for the filament transformer part. This already has a 6.3 volt tap on the transformer, if I'm not mistaken. Can you elaborate a little bit more on the transformer part? I am pretty new to mods ... I know enough to make me dangerous.

The cool thing is, there is already a knockout on the chassis for the rectifier tube that has never been punched, so that's a plus.

Thanks again,
Mark

Hiya! Well, i was saying to add a filament transformer because most octal tube rectufriers have 5V heating. You conect one side of the 5V winding to the filament, and the other end goes to ground, ground onto which is applied the other end of the 5V winding, so the circuit is closed. and you have HT (AC) aplied to the plates of the rectifier, transforming the AC in DC. The filament is heating directly the cathode, (cathode and heater are connected) so the negative side of HTDC is at ground potential again closing the HT circuit. look there, it's pretty clear. http://www.ampwares.com/ffg/schem/ba..._5e7_schem.gif

A BM 10 I recently inspected had unused 5V taps suitable for a tube recto. While some amps use the same 6.3V tap for the recto heaters as well as other tube heaters, I don't think this was done on Fender amps.

Adding verb and trem to your amp will be a big job. Probably need a new circuit board.

Be very careful! Hi voltage in there.

Chuggy, if Blindog's amp has the 5V for the recto, that's perfect. He won't struggle. Besides he's saying that a hole is prepunched I was advising to use a switch to switch from bassman to SR value caps, and forget about adding a reverb, and use the other side as a tweed deluxe (for more grind )

Bye.

Max.

[TD_Madden]

why not just get the Weber CopperCap "doghouse" for that amp......you get the sag, increased reliability, AND no need for the filament voltage....

[Satamax]

why not just get the Weber CopperCap "doghouse" for that amp......you get the sag, increased reliability, AND no need for the filament voltage....

Well, why not, but to me it's not the same, and does the copper cap has the same voltage drop as the big botles, as this amp has big voltages, which would be nice to lower imho!

Blindog, there's nother trick, put a 10K or 100K variable resistor (a pot!) in series with the 820Ω negative feedback resistor. The higher you go on the resistivity, the less NFB, and the more gain. Some call it NFB presence. There's also the 6G6 type bassmans presence which is another option.

[TD_Madden]

I think the drop can be configured however you wish...the CopperCap page allows you to select your own parameters.

[Blindog]

Chuggy,

I have the unused 5v tap! I answered my own question to Max's post about the filament xformer by reading the schematic. I assumed all the tubes used the 6.3 v tap.

Max,

Thanks for your explanation, I learned something I did not know, and that is
always good

I have thought about the Weber Coppercap, but I think I'm leaning to the recto tube.

Spent a lot of time comparing schematics (mine vs AB763). Max is right, with a couple of quick mods the studio channel can be made into the vibrato channel really easy. Don't know what Fender was thinking with that normal channel tone stack!

Another thought, should I elimanate the .022uF cap when get rid of the master volume?

Thanks to all!

Mark

[Satamax]

Yes you can get rid of the 022µ as it serves only the purpose of isolating the master from the DC on the plates, thought, there's two plate caps in the AA763 before the summing resistors. I don't think this is needed.

Well, then you want a single channel with vibrato? You don't have enough tubes! Since there's a recovery stage between vib chanel and PI. I think in this case, IIRC you stated that you wanted a bit more gain, you may be could do the recovery stage and do a single tube "bias vary" oscilator as in some tweeds. http://www.ampwares.com/ffg/schem/vi...5e11_schem.gif

Well, good luck, and i tell you, if ever i get across one of thoses cheap, i'll buy it in a heartbeat.

Bye.

Max.

[Blindog]

Thanks Max, that helps a lot. I think what I want to achieve for right now is to reproduce the Super Reverb circuit without the verb/trem, see how it sounds and then decide what to do next. I realize that you get a bit of extra gain in the vibe channel from the other half of the reverb pickup tube that I won't have in my circuit. I have always wanted a Super Reverb, so that's why I was considering adding the other components to go ahead and finish it off. The holes for the pots are already there, so I would have to punch holes for the other 2 tubes and there is a nice bare space between the PI and inputs to fit everything. I know it sounds ambitous, but I like challenges! We will see what this does to my sanity first! I also thought about dropping a Hoffman board in there. Any thoughts?

I picked this amp up last year for next to nothing at my local music store just for this purpose, and with fall and winter approaching i have renewed my interest in this project.

Mark

[David Schwab]

Don't know what Fender was thinking with that normal channel tone stack!

Maybe that someone would be playing bass through a Bassman amp?

Always thought it was funny how they became such popular guitar amps.

[Blindog]

[QUOTE=David Schwab;5341]Maybe that someone would be playing bass through a Bassman amp?

Touche!

[chuggy]

BM 10 mods/tone stack

The bass player in my band just blue-printed a BM 10. He prefers channel 2 over channel 1. I dropped a brown Concert tone stack into a Bantam Bass (baby brother to the BM10) pretty easily using the original eyelets.

The nice thing about plug-in over hard wired rectos is the easy switchability. Go from solid state no b+ sag to low sag (GZ34) to lots of sag (5R4) with a recto swap and bias adjust. You could do this with plug in Copper Cap rectos also, by why idle those lovely yellow 5V leads? I don't think originality is a great concern with a Bassman 10.