70's fender bassman 100 head recap?

[BonesMachine]

Newbie question. I'm going to be replacing all electrolytic caps and buying spare caps for everything non electrolytic. hopefully wont be swapping out much as far as non electrolytic. not going to be too picky about tone stuff i just want some good quality spare caps to have on hand that are appropriate replacements. i have 2 questions:

1: would it be a good idea to use Cornell Dubilier 150's to replace anything non electrolytic? I think i might have to use something else for the 120pf bright switch and the 250pf, 500pf treble since those values arent available in the 150's. but everywhere else non electrolytic 150's, yeah?

2: i haven't gone through to see where these caps are in the actual amp. just looking at the schematic. should i be concerned with the 150's fitting or just assume there's plenty of room?

[Stevem]

I have a question for you.

Will you be using this amp for guitar or Bass, and if for guitar and considering that it’s 100 watts can I then also assume that it will only be used for clean tones with guitar?

This will matter in terms of a suggestion for non stock values for as you say non electrolytic ( coupling and tone ) caps in the amp.

[mojotom]

I would only replace all electrolytics on the amp (filter caps, bypass caps and bias cap) then put new tubes in after a good checkup (especially power tube and PI tubes) and go from there. The stock caps you would like to replace by 150m should all be ok and great sounding so I would leave them as is and check for leakage.
Especially important on that one are the Power resistors. I did have a big cement one (5 or 10W) almost done (but it was a Bassman 70) and need replacing and I have also replace all filter resistors with metal oxyde resistors and besides safety the noise floor was lowered.

You could also replace screen resistors (should be well worned out) and maybe also rewire the bias for a bias control and not bias balance.

With all of this done and good properly tuned power section tubes the amp was working perfectly as it should without messing with the audio signal caps and resistors.

Once in good condition and well set and biased you should have very little noise floor (still a vintage tube amp) and good and defined bass. Then you could try some mods if that’s not what you’re looking for.

I think you can have a worst sounding amplifier if you change all those audio caps compare to NOS vintage ones (at least not an improvement). You may have to change one or two if leaking but I would recommend only to change what’s necessary.

[Ten Over]

Board right to left viewed from rear. On center in inches.
0.1uF: 2 1/16
.047uF: 1 7/8
.047uF: 1 13/16
500pF: 7/8
0.1uF: 2 1/16
.047uF: 1 7/8
250pF: 3/4
.022uF: 15/16
.01uF: 1 1/4
0.1uF: 2 1/16
.01uF: 5/8
0.1uF: 2 1/4
0.1uF: 1 3/4
2000pF: 5/16
2000pF: 5/16

Faceplate
.0047uF: 1 1/2
120pF: 1
.047uF: 1 1/2

Fender Bassman 100 Layout 1.png

[Ten Over]

A later version and schematic.

Bassman 100 Schematic '75.png

Fender Bassman 100 Layout 2.png

[BonesMachine]

I play guitar and plan to use the normal channel for clean and distortion pedals... Thanks for the schematics and info I haven't seen those!! ... Again I ONLY plan to replace the electrolytics. While I'm placing orders online I just want to have everything else on hand just in case you know. I will only replace non electrolytic caps if I absolutely must. So that said. Are the CD 150's an appropriate replacement cap for everything NON (tone, coupling and electrolytic) assuming I can get the value/voltage?

[BonesMachine]

Might seem like an overly obvious answer but I'm a newbie and not 100% comfortable buying components for anything I haven't read about. Not much info on any of the components in question. A simple yes/no appropriate would be just fine. Thanks...

[BonesMachine]

Also I'm not talking about component size I have info now to make that judgement easily. Thanks again! Just wondering if the CD 150's are an appropriate replacement for the parts in question.....

[pompeiisneaks]

Cornell Dublier caps are great, also the CDE Orange drops are another option. (I assume you're talking about the CDE yellow ones?)

Usually the non electrolytic caps last almost indefinitely unless they were a specific time range that I don't recall... I.e. you'll likely be fine but having some on hand can't hurt and they're usually a dollar or two per cap at 600V rating.

~Phil

[Phil_S]

...A simple yes/no appropriate would be just fine...

Old amps are like old shoes. When you resole them, sometimes they are ruined. The same applies to changing the tone caps. I don't think anyone can say if you'll like the 150's. They are nice caps. If you feel the urge to buy them, go ahead. It's just that it isn't a simple yes/no question.

Part of the problem is that values may drift over time. The other part of the problem is, with an amp this old, the manufacturing tolerance spec when it was made was pretty loose. The stuff being made today is to a much better spec. So, you think you are replacing a .01uf with a .01uf. In reality, it may be something else. This affects tone.

[BonesMachine]

Ok good to hear they should be ok I definitely understand what's there is probably best. I'm going to pick up some extra CDE 150's to have on hand. the amp is not working right now it was turned on without a load plugged in and fried 2 tubes possibly an OT and screen resistors. It's a complete pain for me to recieve orders placed online and I have 1 chance to get everything I need so yes I want to get every damn replacement part possible even if I don't necessarily need it right now. I have absolutely ZERO spare parts at the moment. Thanks for the help!

[gui_tarzan]

I have one of these. I am putting Mallory 150s in place of the turd caps that came with it. The picofarad caps you mentioned are typically the old reliable disc caps. They rarely go bad. The 100K plate resistors have been prone to causing static noise in a lot of the Fenders I've worked on so I replace them. One thing you should do when you replace the 1500 ohm resistors on the power tubes is to leave the leads longer and get them up and away from the hole in the tube socket where heat comes up through. Don't forget about the bias circuit 80/75 electrolytic cap, it's easy to overlook those. I use 100/100 replacements.

[BonesMachine]

I have both blue and brown blobs. I think I'm gonna get some CDE silver micas for the (120pf, 250pf, 500pf) caps. "Just in case".... So what about the 2x 2000pf caps attached to the grids of the output tubes? Anyone try clipping these? I read they are possible "tone suckers" put in to stop self oscillating?

[Matthews Guitars]

Blue Paktrons and the similar blue blobs are good capacitors. As are molded blue suppositories. (They look more like that than bullets.) I don't replace any of those if they aren't bad.

Actually I save them and add to my stash of them when I can get them. I don't like the brown blobs as much. The amp sounds better with the other types in it.

Own a capacitance meter that measures ESR. It'll earn its keep very quickly.

[BonesMachine]

Yeah I'm looking into the Anatek blue esr meter..... Looks like those 2x 2000pf are disc. I probably should have mentioned them with the other pf disc caps in my initial post I knew about em must have forgotten