bass amp build for a friend

makepeace · #1 04-19-2011, 07:06 AM

ahoy fellows.

i've committed to building a bass amp for a friend who is keen to get started. min ouput would be about 30W, max 50. 2x 12' or 1x 15' driver(s). might go head and cab for a little bit of versatility. if any live work is done, it will most likely be mic'd into a PA, which explains the relatively low power out.

he's decided he will build the cab, baffle etc and i will do the chassis/circuitry. we haven't decided as to whether to to go solid state or tube yet, but most likely tube. does anyone have any suggestions/advice regarding state?

i've been told that it is fairly simple to adopt guitar amps to bass. in this vein, would it be a good idea to take perhaps, a bassman, hotrod deluxe or deville etc design and appropriate the preamp stages to be suitable for bass? if so what would that entail? i would also imagine that the sag present in guitar tube amps would not be ideal for bass, thus, solid state recto, assuming we go tube?

neither of us have ANY experience when it comes to bass tone, playing or amps. what sort of thing do bassists look for in an amp? i think that any design with good tone, regardless of specifics and nuances would be applicable in our case. as he explores the instrument he'll discover what he likes and doesn't like and can make adjustments if possible, or even sell the thing off if he eventually gets to the point where it can't do what he wants (we'll aim to do it very professionally

).

lastly, does anyone have any schematics for bass amps or know where to find some? i e-mailed ashdown and they are very schny with theirs, understandably so. i've found schems for an ac30 bass, bassman, jcm 800 bass power section (although 375W is way too much..) and also an elk viking 100 bass.

thanks

wcriley · #2 04-19-2011, 07:56 AM

Get a copy of "The Tube Amp Book" by Aspen Pittman. It has schematics for almost every tube amp ever built.

BassmanPaul · #3 04-19-2011, 10:41 AM

Quote:

Originally Posted by wcriley

Get a copy of "The Tube Amp Book" by Aspen Pittman. It has schematics for almost every tube amp ever built.

Well not quite.

In the OPs place I would look at a B15 clone. It's such a simple circuit and suitable iron is easy to get. If your friend wants a 50W amp then start with a classic.

John D · #4 04-19-2011, 10:58 AM

Quote:

Originally Posted by BassmanPaul

Well not quite.

In the OPs place I would look at a B15 clone. It's such a simple circuit and suitable iron is easy to get. If your friend wants a 50W amp then start with a classic.

+1 You can't go wrong with a B-15 design.

Bass_Pounder · #5 04-19-2011, 11:17 AM

Quote:

Originally Posted by makepeace

min ouput would be about 30W, max 50. 2x 12' or 1x 15' driver(s). might go head and cab for a little bit of versatility.

Definitely make sure it is a tube head if you are going to do a 50W max amp.

If you build solid stae, 50W would be good for bedroom practice - not gigging.

makepeace · #6 04-19-2011, 01:53 PM

thanks so much for the replies! i will definitely check out that b-15

i have serious gas for some tube books, but living in South Africa, they are a little difficult to come by.. must definitely have a squiz on ebay at some stage..

any other ideas re designs?

also, what are the recommendations re drivers? could one go for a 12' +15' combo? or would that be unsavory?

ddnidd1 · #7 04-19-2011, 03:34 PM

Here's the first thing I found through Google.

Guitar Tube Amp Schematics

BassmanPaul · #8 04-19-2011, 03:58 PM

OP, just as a sop to my concern, do you have any experience with tube and high voltage electronics???

makepeace · #9 04-20-2011, 04:50 AM

i've done some reading, and i think we'll be going with a design similar to the heritage b-15, with the 1964 and 1966 channels (1964: tone stack between gain stages - cathode biased, 1966:tone stack before phase inverter - fixed bias) with some power supply mods. btw bassmanpaul, i have a little bit of experience. i built a 5E3 deluxe from scratch, but thats all really. i have a very knowledgeable tube man close to where i live, which is very useful. i know of the dangers associated with hv.

Vintage-Blue · #10 04-20-2011, 06:11 AM

You might find some useful information at CtG electronic's website. Keith has done a couple projects similar to what you are thinking about.

makepeace · #11 04-20-2011, 01:38 PM

thanks vintage blue, great reply. some excellent documentation there! also checked out your restoration project. awesome! i'm also toying with the idea of running KT88's for higher output. would a beefier transformer be all i would need to swap them in?

JimmyM · #12 04-20-2011, 01:44 PM

Quote:

Originally Posted by makepeace

thanks vintage blue, great reply. some excellent documentation there! also checked out your restoration project. awesome! i'm also toying with the idea of running KT88's for higher output. would a beefier transformer be all i would need to swap them in?

don't ---- with a good thing

Vintage-Blue · #13 04-20-2011, 04:32 PM

Quote:

Originally Posted by makepeace

thanks vintage blue, great reply. some excellent documentation there! also checked out your restoration project. awesome! i'm also toying with the idea of running KT88's for higher output. would a beefier transformer be all i would need to swap them in?

From a philosophical point of view I agree with Jimmy. From a technical point of view I don't have a clue! My B15NC project was meant to be a learning experience for me, which it was, but I am still very ignorant about the electronics of these things!

makepeace · #14 04-21-2011, 05:49 AM

Don't get me wrong, I am all for designs that stick to vintage specs, but there are certain things that you have the option of doing when building a custom amp that are just plain useful. for eg, on my 5e3 i substituted the 'normal' channel with a blackface spec'd tonestack. the versatility it gives you is incredible whilst still providing the classic tones. plus, jumping the stacks gives you something very unique.

i think we will go with 6L6's in the mean time for a classically referenced sound, but i definitely will try 6550/KT88's at some stage in the future..

anything ideas regarding speakers? looking for something decent, but not too expensive. companies such as weber and warehouse guitar speakers spring to mind. not sure about 1x 15', 2x 12', 3x 10' or combinations (1x 15' + 1x 12' or 1x 12' + 2x 10'). also any other suggestions re manufacturers?

cheers

BassmanPaul · #15 04-21-2011, 11:03 AM

Quote:

Originally Posted by makepeace

i'm also toying with the idea of running KT88's for higher output. would a beefier transformer be all i would need to swap them in?

Not really. Installing KT88s would be a redesign of the output stage AND the power supply. Changes that will affect how the amp sounds and responds. You could get 100W watts out of a pair but your B+ will have to go up a hundred or so volts making the project more dangerous. Both power and OPT will need to be changed.

BassmanPaul · #16 04-21-2011, 11:07 AM

Quote:

Originally Posted by makepeace

i think we will go with 6L6's in the mean time for a classically referenced sound, but i definitely will try 6550/KT88's at some stage in the future..
cheers

Per my earlier pos,t maybe not such a good idea. You also have to factor in the increase in heater current from 0.9A for the 6L6 family to 1.6A for the 6550 or KT88.

BassmanPaul · #17 04-21-2011, 11:10 AM

The other thought that came to me is the question of whether the previous stages would be able to swing the increased drive voltage needed by the larger tubes.

KramerBassFan · #18 04-21-2011, 12:36 PM

It's just not worth it.

If you really want a B-15 with KT88's, then build one from the beginning.... trying to adapt something mid production or later just opens more stuff to trouble shoot.

And dropping them in wouldn't really give you any more power/headroom, unless you put bigger transformers and a power supply capable of handling them.