New Caps and Tubes for the Bassman: HELP!!!

Haze · Post by **Haze** » Fri Mar 26, 2010 5:07 am

So i've decided against buying a new modern amplifier and just fix up the Bassman. Its been crapping out far too often on me and its just not predictable. Not ideal for gigging! I was going to jam with some friends this saturday and i don't even feel comfortable doing that with this amp after these last few days of it cracking, popping, and motorboating. So its discharged for the time being until i get some basic maintenance out of the way.

New electrolytic capacitors, new pre-amp and power amp tubes, convert to 3-prong [usa] power chord

Here is a list of tubes.
3x 12AX7A [7025]
1x 12AT7
2x 6L6GC

And the electrolytic capacitors
1x 16 MFD, 475 VDC
3x 20 MFD, 500 VDC
2x 70 MFD, 350 VDC

Here is where YOU can help, people like helping people right?
Where can i get all of these from one place [less shipping] And does anyone have recommendations for different brands of tubes and variations [ax7, au7, ect]

Haze · Post by **Haze** » Fri Mar 26, 2010 7:22 pm

Badside of Harmony Central has been super helpful, http://acapella.harmony-central.com/sho ... st39411904

He's pointed me to the german made F&T brand for the e-lytic caps. They're smaller and most importanly CHEAPER!

So far i have everything in a cart from Tubes and More for $104.75
This includes all of the power filtering caps and the bias cap, a 12' 3-prong cable and a matched set of JJ tubes.

ONE QUESTION LEFT
My Bias caps reads "80 - 75v" is it safe to use an 100uf 100v cap for the bias circuit?

Sloan · Post by **Sloan** » Sun Mar 28, 2010 2:28 am

Haze wrote:
ONE QUESTION LEFT
My Bias caps reads "80 - 75v" is it safe to use an 100uf 100v cap for the bias circuit?

Get the capacitance (.uf) value as close as you can, the voltage can be higher, but don't go lower. The voltage rating is basically the highest the cap can take, so having it higher is always good, but more expensive.

Power cable:
Just cut the end off one your not using or someone else's, like from an old computer.

Also:
Tubes and more is good. yes!

Haze · Post by **Haze** » Sun Mar 28, 2010 2:37 am

Thanks for the answer. I found a 80uf/100v that i'd use BUT FIRST - Possibly something else you can answer, Sloan. Turns out this is an AA371 circuit. Great for bass apparently but considered the worst for guitar. I haven't had too many problems with it sound wise and i've always thought it was a solid platform to expand upon with pedals and such. Just knowing it could be better [aa864/ab165] for not much more kinda sucks!

I've found a few results in searching for aa371 to aa864 conversions like this one - http://forum.metroamp.com/viewtopic.php?f=10&t=29174
does this seem a bit extensive/expensive for something i could sell for $300 as is and put toward something else? I'm already looking at spending $100 on caps and tubes and now i'm reconsidering trying to get it up to par and leave that for someone else and move on.

Will · Post by **Will** » Sun Mar 28, 2010 5:18 am

If you like the way it sounds, who the fuck cares what circuit it is?

Anyway, looking at the 2 schematics on Ampwares it looks like the preamp sections for the normal channel are identical. The difference is in the power section. Only real major thing, just giving these a cursory glance, is the 2 capacitors running from the phase inverter to each power tube. Basically, they get bigger in each subsequent revision (from .022mf to .1mf). You're version is at .047, so closer to the original AB165 (which I used to have and sounded fantastic.) The bias section seems to be the same, so I wouldn't expect a dramatic difference in the feel. There are little things, like added caps to control oscillation, but no big topological or part value differences.

I wouldn't worry about it. It seems like as the revisions went on they tried to optimize it more for bass use, but I don't see anything dramatic in the guitar channel's path.

Haze · Post by **Haze** » Sun Mar 28, 2010 6:19 am

Thanks, Will. I was thinking the same thng tonight - it sounds good to my ears so who really cares. I'll put new caps/tubes in it and WORST case I keep it as a killer bass amp. I've even used the bass channel to run my microphone for rehersals with decent results. I could always look into changing the bass channel closer to the jtm specs and use an a/b switch to change from fender cleans to marshally goodness.

James · Post by **James** » Sun Mar 28, 2010 10:24 am

Will wrote:If you like the way it sounds, who the fuck cares what circuit it is?

+1

Whilst I have and love the 'full mojo points' circuit, I imagine a lot of the talk comes from people who don't consider Mustangs to be proper guitars and who think having orange drop caps and cloth wire improves your guitar tone.

You've spoke of loving the tone, and you've recommend the amp to people looking for a guitar amp. So you obviously like it for guitar. It'd be silly to start thinking of it as a medicore guitar amp and a great bass amp and then feel like you're not quite where you should be in terms of your speakers pushing out the right direction mojo arrows.

Don't worry what the internet says, do repairs (you're going to have to do them even if you sell it), give it some time with fresh ears and fuck the hyperbole. Don't mod the amp when you've only had it a couple of months. You'll be doing it for the wrong reasons.

Sloan · Post by **Sloan** » Mon Mar 29, 2010 12:05 am

I agree, i think I would go ahead and replace those caps and stuff. I did a cap job on a Super Twin Reverb and it totally made the amp sound so much better.