Bassman 100 help !

[Rob Livesey]

Hi Guys,

A bass player friend of mine picked up a "nice" Bassman 100 recently and I said I'd give it a recap and retube for him. Anyway, he dropped it off cheerfully this morning and I've just opened it up.

Where to start !? The pics say it all really. I need a layout for a Bassman 100 if anyone has one and also some idea of how the mains filter cap board should look. I haven't spoken to my friend yet, I don't know how to break the news to him......

[img:800:600]http://personalpages.manchester.ac.uk/s ... man/01.JPG[/img]

[img:800:600]http://personalpages.manchester.ac.uk/s ... man/02.JPG[/img]

[img:800:600]http://personalpages.manchester.ac.uk/s ... man/03.JPG[/img]

[img:800:600]http://personalpages.manchester.ac.uk/s ... man/04.JPG[/img]

Cheers,
Rob

[ToneMerc]

Here's one.

TM

[Gibsonman63]

Schematic Heaven (google it) has the original Fender schematic and layout. They are fairly simple amps to work on. The normal channel on mine is wired like a AB763 Showman and the Bass instrument side is basically stock. I can send you some pictures this evening if you need them. The filter caps are not always shown clearly on the Fender layout drawings.

Mine came with a matching 4 x 12 cabinet. The speakers are mounted in a reverse pyramid configuration. For bass, I have to remove the hold down screws and put a towel between the head and the cabinet or it rattles things loose inside the head. I had to work on the box for a while to get all of the rattles out of it, but it sounds solid now.

[xtian]

"Suntan" caps! That's gotta be worth extra, right?

Anyway, creative use of flying tag strips. I think this is a hall-of-fame nominee.

[Rob Livesey]

Here's one.

TM

Bingo ! Cheers for that! There may be hope for me yet.

[Rob Livesey]

Schematic Heaven (google it) has the original Fender schematic and layout. They are fairly simple amps to work on. The normal channel on mine is wired like a AB763 Showman and the Bass instrument side is basically stock. I can send you some pictures this evening if you need them. The filter caps are not always shown clearly on the Fender layout drawings.

Mine came with a matching 4 x 12 cabinet. The speakers are mounted in a reverse pyramid configuration. For bass, I have to remove the hold down screws and put a towel between the head and the cabinet or it rattles things loose inside the head. I had to work on the box for a while to get all of the rattles out of it, but it sounds solid now.

Gibsonman, yes, any pics you can send of your amp would be helpful, especially close ups of the mains filter board, values of caps and resisters.

Cheers,
Rob.

[gingertube]

That amp has already been re-caped at some time, the caps shown are certainly not original.

The one thing to check on these amps is the 470 Ohm resistors to the screens of the output tubes. They get stressed quite badly and you will find that they often go very high in value. I've even seen amps where one or more of them were open circuit which of-course means that that particular output tube was effectively switched off (no screen voltage => miniscule tube current). I (and many others) routinely just rip out those 470 Ohm an fit 1K 5W wire wound (Rats coffin style) resistors in their place. Does the 1K change the sound? Yes, marginally, it gives a little earlier breakup, that is goes into power amp overdrive sound a little earlier (ears only seeping a little rather than pouring out the blood).

The other thing I normally do, but not everyone does, is to rebuild the bias supply, change all diodes, resistors and caps, including the 1K5 grid stops on the output tubes.

Cheers,
Ian

[Gibsonman63]

Here's some pics. I re-ran some of the pre-amp wiring to clean it up, but there is still a lot more than can be done.

[Gibsonman63]

A few more

[Gibsonman63]

Filter Caps

[Rob Livesey]

Thanks for all the input guys!

GibsonMan, those pics are just what I need, thanks for taking the time to do it, much appreciated.

So, it seems my friend the bass player has not yet paid for this amp. He approached the seller and asked him about getting it put back to stock and he said he would pay for it to be done. So, all is good!

I'll post some pics of the completed amp when I've done it.

Thanks again everyone,

Cheers,
Rob.

[JazzGuitarGimp]

WOW! Did this thing even pass signal when you got it? If so, how did it sound?

[Rob Livesey]

WOW! Did this thing even pass signal when you got it? If so, how did it sound?

It does run ! It just has no balls

[RevD]

Not surprised, looks like it was kicked squarely in the balls by whoever did that to it!

Regards,

Don

[Gibsonman63]

I would not worry about the internal butchery as long as the outside hasn't been hacked up. The circuit is axe-handle simple and that amp has some serious iron in it. I had forgotten how much that one weighs.