Fender Bassman Ten, first time modding

[Yuehfei]

First and foremost I'm new to this forum, I'm a 26 year old guitarist/singer looking to learn. Nice to meet everyone.

I have recently found a 70's Fender Bassman Ten for a reasonable price (trading a Marshall 4 x 12 cab with road wear and $100 dollars) and after doing considerable research have decided it would be a fun amp to learn how to mod. I've never done any sort of modding, tweeking, etc. to any amp I've ever owned. I am fairly adept at most things technical and have very basic electrical knowledge. My question is, what would be the best way to learn what I am doing and what would be a good basic starting point? I understand of course that its best in most cases to have an experienced tech do these things, but if I'm gonna learn, I have to start somewhere. Any help or info on this amp would be greatly appreciated.

[Chuck H]

You sure found a good place to ask Q's. If that speaks at all to your trouble shooting I think your on the right track.

A good place to start would be to get the amp in ideal working condition. That will familiarize you with some basics. After that you can start tweaking it to your tastes without wondering if any problems that arise are just because it's an old amp.

Lots of info on line. Look into discharging the power supply so the amp is "safe" to work on. Look into "filter caps" or "power supply filters". They should typically be replaced in older amps if they haven't already been. Look into how to tell if tubes need replacement. and then look into biasing that amp. All this should be easy to find by searching here or Google.

Also clean and retention tube sockets, jacks and pots. Test resistors for spec. (old carbon resistors can drift with heat and age).

Once the amp is up to snuff you'll have already learned much of what you need to make circuit adjustments and we're here to answer Q's. You can make then taylor the amp for your personal tastes.

Chuck

[Yuehfei]

Thanks, I appreciate the help. This sounds like plenty to keep me busy for awhile. I'm sure I'll be popping in with questions.

[loudthud]

To get started you will need a Digital Volt Meter (DVM), a soldering iron, and a general array of hand tools. Next, figure out if there is any place locally that you can buy parts. Resistors, capacitors, diodes, wire, plugs and jacks. Radio Shack is not a good source for most things but find the nearest store and look around and look on their website. The one thing you can find at The Shack is bags of assorted resistors. Buy one or two, they'll come in handy. They can order stuff from Allied but you can deal direct with them. Look for a surplus store. The large distributors that cater mostly to industrial accounts usually won't want to sell to you. Ask around to anybody who does repairs locally. Where do they get parts?

[Yuehfei]

Hey thanks for the advice. Any specific features I should look for in a DVM? I have an old school one but its nothing fancy. I'm in a small town so finding a surplus store will be tough, but I will definitely look around and see what I can find.

[loudthud]

Most of the really cheap (often less than $10) DVMs only have 2 ranges for AC volts, 200VAC and 700VAC. It's nice have the lower ranges down to 2.000 VAC.

It can be tough finding parts in a small town. Check around to see if there are any retired old guys that are hoarding parts. Sometimes they will just give you parts. When they die, you can usually buy the parts for what it costs to haul them away. Check if there is a "Ham-Fest" in your state. Usually held once a year, consider making the trip. Get there early and ask around at the flea market.

[Ronsonic]

Good fun amp to play with. They have little cash value and contain all the ingredients of an interesting Fender so it is good mod bait. Despite the piles of amps I own, a modded BM10 is pretty much my main amp these days. It's simply the most interesting sounding amp I've owned.

As already suggested, get it running well first. Everything clean, good electrolytic caps, solid solders like that.

Then decide what you actually want to change. If you just want a good jamalong and practice bass amp, change nothing. For guitar, this is what I've done, in rough order.

Plug the ports in the speaker cab. pull a speaker for access and use blocks of wood glued in place with RTV for easy removal. Without the ports the tuning is much more guitar friendly.

Mine had a winding on the power tranny and a hole half-punched in the chassis for a tube rectifier. I couldn't resist.

Installed a filter choke in place of the big resistor that was in there.

I replaced the Master Volume with a PPIMV.

Modded the second channel to approximate some black/brown era circuit I don't even remember. Just that it was a more or less standard Fender guitar tone stack and gain structure. I think it was a brown era Concert, but don't recall, it was a bit of an improv.

Some day, I'll try a tweed pre in channel one. Should be interesting.

Got ahold of a bunch of Emminence speakers very, very cheap, like almost free a pair of Ragin' Cajun's and a pair of Patriots and put them in X pattern, wired series parallel to get the 8 ohms the amp wants to see. Very good change.

Some or all of these I can recommend.

Have fun, but do get it running well first. Don't try to hot rod something that's burning oil.

[The Kirbster]

I replaced the Master Volume with a PPIMV.


For us uneducated souls.....what is a PPIMV? I see it in this forum often enough to know it's something to do with a Master Volume.

[Chuck H]

A PPIMV (Post Phase Inverter Master Volume) is a master volume placed after the phase inverter so that any additional clipping the phase inverter may contribute to the tone isn't lost as it would be with a more common master volume placed before the phase inverter.

[Ronsonic]

The result is one full tube stage closer to a cranked amp, so it is that much more "realistic." Doesn't replicate a cranked amp perfectly, but it helps. Some amps don't really benefit from it as much as others.