Basic Simple 50 watt Bass Head

[big_teee]

Line 6 with headphones...

That ain't even Right!

[J M Fahey]

Then build a stripped B15.
Designed specifically for Bass, the most popular Bass sound in the World (all others are compared to it), **can be set flat** (try that with a Fender and even worse, a Marshall) and tone controls are not interactive like in those just mentioned, where raising treble cuts bass and turnover frequency varies too (just simulate all 3 types in Duncan's TSC )
You can even play music through it !!!! (add a tweeter to the cabinet).
It also has simple treble and bass boost switches.
Midrange would be nice, of course, but will complicate building.
So build 1 channel (both are the same), PI, power tubes.
jm2c

[big_teee]

Then build a stripped B15.
Designed specifically for Bass, the most popular Bass sound in the World (all others are compared to it), **can be set flat** (try that with a Fender and even worse, a Marshall) and tone controls are not interactive like in those just mentioned, where raising treble cuts bass and turnover frequency varies too (just simulate all 3 types in Duncan's TSC )
You can even play music through it !!!! (add a tweeter to the cabinet).
It also has simple treble and bass boost switches.
Midrange would be nice, of course, but will complicate building.
So build 1 channel (both are the same), PI, power tubes.
jm2c

Thanks JM.
What would I use for a layout and schematic for a stripped down version?
Any Ideas to point me in the right direction?
Thanks

[Chuck H]

I was thinking the same thing as Juan. A single channel B15. Two preamp tubes, two power tubes. You can skip the rectifier tube and just use a big resistor if you want the sag. As to layout.?. I don't know about the actual layout but it shouldn't be hard to create something stable, actual layout not withstanding. For a bass amp I think getting THE tone would be more about getting the voltages and circuit correct. If you tell me what size chassis you'll be using I could mock something up.

EDIT: If it wouldn't disturb your sensibilities I would probably change some things. Like using more common preamp tubes, possibly change to a LTP PI and redesign the power supply so that the bias isn't dependent on the standby switch.

[big_teee]

I was thinking the same thing as Juan. A single channel B15. Two preamp tubes, two power tubes. You can skip the rectifier tube and just use a big resistor if you want the sag. As to layout.?. I don't know about the actual layout but it shouldn't be hard to create something stable, actual layout not withstanding. For a bass amp I think getting THE tone would be more about getting the voltages and circuit correct. If you tell me what size chassis you'll be using I could mock something up.

EDIT: If it wouldn't disturb your sensibilities I would probably change some things. Like using more common preamp tubes, possibly change to a LTP PI and redesign the power supply so that the bias isn't dependent on the standby switch.

Thanks, let me take a pause, and look things over.
I'm trying to load a new laptop, and nothing is cooperating!
T

[wyatt]

I agree with the B15N suggestions. Good, modern 6SL7's are commonly available.

It gave birth to the "modern" bass amp, instead of just a re-purposed guitar amp. The reason you can strip it down is because the channels are redundant...they are identical; and you may want a SS rectifier and heavier filtering to keep that low-end tight and punchy.
http://www.webphix.com/schematic%20h..._portaflex.pdf

There is some discussion about a stripped-down B15N here (I have cannot vouch for the layout in the thread, you'll want to do some due diligence)...
http://music-electronics-forum.com/t15809/

There are also resources on this TAG thread...
The Amp Garage :: View topic - Ampeg B15 layout and cabinet plans

Another thread, a build at Hoffman's forum...
Ampeg B15 build report (schematic with mods added) - Hoffman Ampifiers Guitar Tube amp forum

I can't think of any proprietary parts you would need to DIY a B15N, but will list this handy resource for renovations anyway...
Fliptops Home of Parts for Ampeg Lovers

[hylaphone]

Can't go wrong with the B15, I've build a few versions of it now and each has been a wonderful amplifier.
I'd suggest sticking with the 6SL7's, they are noisy but worth the trouble IMO.
The humdinger pot works pretty good

[J M Fahey]

Just checked a few online schematics.

Plus I have actually custom built some for customers, the same way I suggest here

The original ones are built around octal preamp tubes, more modern ones are 12AX7 based but on the power amp "upgraded" to non mainstream 7199, 7027, etc. which today are a PITA

Yet all of them sound like Ampegs so what I did (doubly so because I live in Argentina and had to work with "standard" stuff) was to mix and match.

They are all Ampeg B15 anyway

I wanted the sound, not to please some fussy collector so:

I used one of these preamps:



Coupled to a simple Fender Power amp:

This is a standard one, most are practically the same.



Only difference to "Ampegize" it would be to :
a) lower feedback from Fender very tight 8:1 (820 ohms : 100 ohms) to much looser Ampeg .

I´d replace the 820 ohms one by , say, 2K2 or 4K7 .
Pick by ear.

b) increase power amp input cap from bass killing 500pF to, say, standard .022uF

The amp will not be an *exact* clone of any other but will definitely sound and behave like an Ampeg and will be easier to build and maintain.

As of a layout, maybe some kind soul will help, or you draw your own and post it here for friendly revision.

Use standard, off the shelf parts, meaning Fender type iron and some proper gsemi-generic chassis.

Or maybe you can cannibalize and recycle some stuff you already have and spend peanuts.

[Chuck H]

bt already mentioned that he has enough guitar amps, but looking at the B15 schem I think it might actually work well for guitar too. It's a notorious bass amp already. I've never had the honor of playing one so I dunno.

I was thinking along the same lines as Juan (again). 12ax7 preamp, 12at7 PI, a pair of 6L6's at around 450V with a 6.6k primary load and about 15:1 NFB ratio. With a good, efficient 15" speaker in a slightly oversized cabinet it'll beat your brains out and you'll actually enjoy it!

Then you can plug it into a lower efficiency 4x10 cab and play a club gig with your guitar!!! Looking at the EQ curves I'm sure of it. A mid heavy preamp driving a LTP PI into a pair of 6L6's. What's not to love?

[big_teee]

What advantage would a 6.6k OT be over a 4.2k for 6L6s.
Was thinking if I went with the 4.2 I could have more tube choices?
I'm probably not correct on that?
Also If I ran the 2 input tubes single chan?
I would prefer to stick with the 12 family, 12ax7, 12ay7, etc.
Without getting overboard with High voltage, what would be wrong with running an inexpensive marshall style 100 w PT.
With it I would expect around 500v and might could run a pair of 6550, like marshall did in the US JCM800s.
It wouldn't cost much more than the 6L6 layout.
Just bouncing ideas!
T

[big_teee]

Update!
After Doing Some trading with ChuckH, I now have a nice Marshall 50 watt set of Iron.
I took The PT I got from Chuck and swapped it with the one in my 2204.
The output of the one from the 2204 produces around 500v Loaded.
So I think I will go with EL34s instead of the 6L6s.
Still not decided on the preamp circuit.
Still gathering parts, will build it on a blank JTM45 Chassis.
T
Edit** Probably use the Preamp like Juan suggest in post 23.
One tube 12AX7 from B25 Schematic, and then use Marshall 1986 Schematic for PI, and Power section.

[Chuck H]

I can't speak about the alternatives, but I'm not sure EL34's are the best choice. I've had some trouble with a couple of different EL34 products in a recent build with 470Vp. This is just my isolated incident but it sure caught my attention when a second, and then a third different brand of newly manufactured tubes failed. All parameters were checked and rechecked. Bias, drive voltage, heater voltage, connections, loads, grid current conditions that might cause bias shift, etc. The amp is currently working well with a pair of Ruby EL34 BHT's (though they exhibit some microphony). I know that the spec for all the EL34's on the market tends to regurgitate those on vintage data sheets, ie: max anode 800V and max g2 500V, but I'm not convinced that newer tubes meet this spec in real world conditions. A bit more expensive, but perhaps 6550's might be a better choice.

[big_teee]

Thanks Chuck.
Yes I have run them on that PT for 3 years and I blew a JJ KT77 right out of the Gate.
I have a set of the E34Ls that have survived, and a set of EH34s that do fine with it.
Was thinking of trying the TAD 34s I get a pretty good price on them through Mojo.
I can also get some China 6550s on the Cheap.
This is just gonna be a bass test amp sitting in the shop to test bass pickups.
Also the OT, would it be OK for the 6550s, it I think is in the range of 3.2-3.6k primary?
T

[Chuck H]

It's not an ideal distortion figure primary for any big bottle for a bass amp, but Marshall seemed fine with selling those amps loaded with 6550's for 6 string guitar.?.

Any EL34's you have that are already known to work at that voltage with a similar primary Z should be fine then. I would make the effort to design the bias circuit to supply different tube types should it come up in the future.

[Leo_Gnardo]

Terry, if you haven't already committed to a preamp design I'd like to point out the "white" Fender Bassman of the early 60's. Essentially it sends your bass signal thru one gain stage then a cathode follower, then into EQ. Cuts out a needless gain stage & yields a clearer more authorotative bass tone. I suspect SVT's designers may have had a peek at this, then added their fancy midrange control to create their preamp. You could do that, or substitute a pot for Fender's midrange-setting resistor for simplicity. We PM'd about this awhile back.