Fender Bassman Servicing (w/ pics)

cobascis · Post by **cobascis** » Thu Jan 28, 2010 3:01 am

Yay!

This thing was filthy, cobwebs, dirt.... dirt. I just spent about 1.5 hours cleaning it. I took it apart, in the chassis it was dated Dec, 1, 1971.

It has a variety of tubes, RCA, Fender, 2 different 6L6s. The electrolytic caps looked original, brown, and chewy.

It works fine, but I heard the caps will need replacing. It is a 3 prong cord but its pretty worn.

What should I tell the amp dude to do?

Thanks.

PICS TO COME, CAMERA DEAD.

Haze · Post by **Haze** » Thu Jan 28, 2010 3:32 am

I'd tell him to change the electrolytic caps (bias cap aswell)
it's already 3-pronged so that's always a plus, if it is frayed anywhere you might consider fixing it
maybe some matched tubes, if you're going to replace them anytime soon you might aswell do it now so it can be biased with the new tubes

cobascis · Post by **cobascis** » Thu Jan 28, 2010 3:41 am

Scratchy EQ pots, are these entirely fixable by compress air or some contact cleaner people put in? If not I could replace those myself..

Haze · Post by **Haze** » Thu Jan 28, 2010 3:46 am

It's more than likely to be a dirty pot that can be fixed with compressed air. Make sure you let the tech know though it should just be a 2 second fix

robroe · Post by **robroe** » Thu Jan 28, 2010 3:46 am

i would wait until you find your sweet spot on the amp before you go switching out scratchy pots. chances are you are just going to leave them 80% of the time anyways

cobascis · Post by **cobascis** » Thu Jan 28, 2010 4:21 am

How much will a cap job set me back? There is a kit on ebay for 75.. so about $100-150?

Haze · Post by **Haze** » Thu Jan 28, 2010 4:56 am

Depending on the individual I would say 150 is a good ballpark (including caps)
another 60 ish on tubes depending on what you get. The tech should have to bias the amp anyways so new tubes shouldn't add anything on to the repair cost

cobascis · Post by **cobascis** » Thu Jan 28, 2010 1:59 pm

Huh, I think I'll call him today. Priority: Tubes or Caps? I can't do both right now.

cobascis · Post by **cobascis** » Thu Jan 28, 2010 10:19 pm

The guy said itd be around 130 for caps. He also said people replace them if they look bad, it doesnt need to happen necissarily. What do old caps do to tone? I'm thinking of getting some new tubes for now and replacing the caps IF needed.

Also 12AT7 vs 12AX7 does it matter? The tube diagram states in V1 is the 12AT7. I'm looking just to replace V1 with a nice TAD 7025.

Post by **Mike** » Thu Jan 28, 2010 10:23 pm

Ts have less gain than X's

NickS · Post by **NickS** » Thu Jan 28, 2010 10:35 pm

In my experience, electrolytic caps may
(a) dry out with no visible symptoms, resulting in hum if the smoothing caps dry out, poor bass if the signal caps dry out*
(b) suffer from failed/perished seals, potentially resulting in electrolyte dripping onto other parts of the circuit as well as (a)
(c) once in a blue moon, go short circuit causing all sorts of nasty results.

If the amp is working well, no excessive hum, no funnies in the bass and no excessive noise from the valves, I wouldn't bother to spend money. But I'm a tight git generally.

*actually, if they dry right out/go open circuit you'll lose gain too.

Haze · Post by **Haze** » Thu Jan 28, 2010 10:53 pm

My caps are ground-hoggin it, last time I powered it up it made a sound like a semi tire blew. Literally, like pressurized air was being released. It might not be 100% necessary but if you plan on keeping it for a while I'd make the small investment.

cobascis · Post by **cobascis** » Thu Jan 28, 2010 11:00 pm

The thing is its not too noisy and the bass is fine. For now at least until I get the money, I'm:

-Replacing the power cord, as it has HOLES in it.. fire!(it is already three pronged, so I should just be able to solder a new one in without mods, yes? Did some bassmans have 3 prongs or is mine modded?)
-Replace a missing tube cap
-Replace a few 12ax7s, the powertubes seem fine (Mesa STR 115 and Lifetime Reality... 6L6)
-Crackly and popping Deep/Bright switches

I'm ordering from a store near me (partsisparts) and they only have Sovtek and EHX 12xa7s. EHXs seem to have decent reviews.

Thoughts? Anything else?

I realize the recapping is important, but at a normal noise level right now I don't see the immediate need, and I can't afford it, so...

The caps looked original, but they could of been replaced, I have no experience in this sort of thing.

Haze · Post by **Haze** » Thu Jan 28, 2010 11:07 pm

I'm certain yours has been modified since 76 doesn't have a 3 prong. Logic would say that your 71 wouldn't have came with one either. However those early CBS years had some oddities

cobascis · Post by **cobascis** » Thu Jan 28, 2010 11:46 pm

This is sort of a stupid question, but I though I'd ask. Are some caps more effective than others? Meaning, can I replace a choice few, with noticeable improvement?

paul_ · Post by **paul_** » Fri Jan 29, 2010 12:09 am

uh-hu-hu-huh hu-hu-huh, you said "nad" hemhehemehe, YEAH YEAH mehehemehehe I HEARD IT TOO

cobascis · Post by **cobascis** » Sat Jan 30, 2010 9:07 pm

I'm going to replace the power cord. Can I just cut off the end of one of my current power cords? (it has the computer-like plug in).

Then it should just be solder and go? Thanks.

paul_ · Post by **paul_** » Sat Jan 30, 2010 9:25 pm

cobascis wrote:I'm going to replace the power cord. Can I just cut off the end of one of my current power cords? (it has the computer-like plug in)

Yep. I did this for my '73 Marshall Superbass to have a longer cord, and when I was building my white SuperLead metroamp kit (they come with one of those and instruct you to cut it) and also my Digitech XP-100 Whammy/Wah pedal's adapter when the AC jack broke (just snipped the jack off and wired it to the PCB).

cobascis · Post by **cobascis** » Sun Jan 31, 2010 12:10 am

I've been working on the bassman and I just ordered a new power cord.

GUT SHOT: All original?

PROBLEM

How do you unsolder this? It is where 2 of the wires coming from the power cord go into. But it seems the wires are soldered from essentially the inside? I have no Idea how to get them out of the metal prongs... HALP?

Here's 2 pictures:

I cut the end of a power cord I already had to test out how it would all work out. Because I could unsolder, I just soldered it on to the existing wires. It looks like this:

I realize it's a shite job, but I was just making sure I could do it before I tried with the actual cable. The amp powered up when I turned it on with this, so I figure it worked. Look alright to you guys?

Chewy caps are chewy:

avj · Post by **avj** » Sun Jan 31, 2010 12:38 am

I believe those are just crimped ring or slotted terminals that are screwed into the external outlet. You could either just snip the yellows and solder the new power cord's ends to their respective positions on the yellows thereby totally bypassing the external outlet (which hopefully you aren't using anyway), or you can find some new terminals to crimp the new cord leads and the yellows into.

If you go with the terminals, just make sure and add some more solder after crimping to make sure the connection is all wonderful.

I realize I'm not a usual supplier of this sort of information around here, so no offense taken on waiting for someone else to chime in.

Fender Bassman Servicing (w/ pics)

Fender Bassman Servicing (w/ pics)

Bassman Servicing Help

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