My new/old Bassman 100 Head - Tube and Check-up Questions

moishelichtfuss · #1 05-10-2011, 01:48 PM

Last week I got this old Bassman 100 that I want to groom a little before using it on a regular basis:

Soooo....I have some questions:

I will replace the preamp tubes on this one, since one of them has turned microphonic. I think I will be able to handle this.
The power tubes look and sound alright so far. I didn't have the opportunity to really crank the amp up and play it a while, but since I have no idea how old these are, I might think of replacing them sooner or later.
I'll probably have this done by someone who knows his way around tube amps, but theoretically:

This is, afaik, a fixed bias Silverface Bassman 100 from 1973. I wasn't really in the mood to take a look inside so far. What does one have to do about the bias?

Are there any other things that should be checked with an amp this old? It seems to behave quite normally.

BassmanPaul · #2 05-10-2011, 02:47 PM

Quote:

Originally Posted by moishelichtfuss

It seems to behave quite normally.

Then leave well enough alone and play!

moishelichtfuss · #3 05-10-2011, 02:52 PM

That's good and easy advice! I'll just replace the ringing preamp tube, then.

(Seriously, though: I guess I'm just spending so much time thinking about that kind of stuff, because rehearsal got cancelled this week and I haven't been able to play it "the way I want to play it". Will still have to wait until Sunday. It's close to unbearable.)

JMac4strngr · #4 05-10-2011, 02:54 PM

Quote:

Originally Posted by BassmanPaul

Then leave well enough alone and play!

I am with BassmanPaul on this one. If You dont know what You are working with, You could damage Your amp or risk life and limb.
As much of a tinkerer as I tend to be and wanna figure out what makes things go, I try to keep My grubby paws out of amps, as I am not an amp tech.

moishelichtfuss · #5 05-10-2011, 03:22 PM

Well...my questions was mainly theoretical...I wasn't planning on rummaging throuhg the amps innards myself.

jastacey · #6 05-10-2011, 07:18 PM

I you feel the need to look inside the amp, the only thing I look at would be the filter caps, they are in the rectangle metal cover, if you see those caps bubbling or leaking, get the amp serviced ...... if you have no experience poking around a tube amp, just don't do it, pay a pro to do it

thefaceofbass · #7 05-10-2011, 07:45 PM

I have 2 1968 Fender Bandmaster heads that I've tinkered with for years. If I had just purchased the amp you have, I would replace all filter caps, completeley retube and bias, and replace all 100k resistors (they snap crackle and pop- this will make the amp quiet). This should keep that head running great for years, and will give you peace of mind while gigging that a random power tube won't go up in smoke. Should be a great sounding tube head, enjoy!

moishelichtfuss · #8 05-15-2011, 04:04 PM

Sooooo....

I played the amp in a band setting for the first time tonight and will have to say I was a little irritated by it...

had the bass channel on at around 7....master volume at 5 or 6 and the bass (mia p) sounded a little dull and distorted...

Is that usually a level at which the amp starts to give up or fart out or does it sound like i need new power tubes?

JimmyM · #9 05-15-2011, 04:09 PM

it's really hard to tell without being there for sure, but yeah, old fender amps do break up right around that point. nothing wrong with having the tubes checked on a tube tester. and honestly, it's never a bad idea to have a tech look at your amp if you buy it used and you don't think it's performing as needed. but i don't know that it's going to do much better than that, even if you replace all the tubes.

moishelichtfuss · #10 05-15-2011, 04:21 PM

one thing i forgot: i also played my little höfner shortscale bass through it, which has a hotter output than the p bass, that one didnt really distort...i'm quite puzzled.

moishelichtfuss · #11 05-17-2011, 08:41 AM

So I just got a call from the amp guy, who replaced the power tubes and checked the circuits. He confirmed that the tubes were pretty much shot to hell and told me that it sounds much more juicy now. I'm eager to hear it.

will33 · #12 05-17-2011, 09:27 AM

If you want a little thicker sound plug into the bass channel then run another cable from the 2nd input on the bass to the input on the normal channel and use both volumes. The deep switch on those is your "mid suck" switch, I leave mine off.

moishelichtfuss · #13 05-22-2011, 03:25 PM

So just to give this little story a happy ending.

After last week's 'disappointment' I played the amp with its new set of power tubes for the first time during a rehearsal just now. Apparently the old tubes were really old, because now it sounds just beautiful...it rocks...I love it. And for my taste it's more than plenty loud enough for our little band. Still got enough headroom. Even with the odd odd Fender 4x12 cab.

Problem solved.

P.S.: I also did the bridging thing, which yielded pleasing effects. Thank you all.