What is the best Bassman design for bass

[Danelectron]

Chuck H, What do you mean by "bias arrangement"?


I like the idea of just one channel. That'll keep it really simple. If I'm going to redesign this design for different tubes or output, is there a better tube for sound for bass? I was looking at KT88, 6550 and 6L6s. Thanks, Dan

[Chuck H]

KT88's are waaay to expensive IMHO. 6550's are good performers for bass (as many, many bass amps will evidence) and eminently more accessible. Changing the bias arrangement would be a matter of locating the voltage divider in the bias circuit and changing the resistor values to provide a little more -V. 6550's usually need a tad more -bias V for a given voltage than 6l6's. The bias arrangement for the Bassman 135 may already be accommodating. I don't really know. I do know the OT requirements and the power tube component values are already suitable to plug in 6550's. So why fret about a special 6l6 tube type or lowering voltages when, for bass, a 6550 will do an even better job and is redily available.

JM2C

[imaradiostar]

You should probably use larger transformers than Fender used. Here's where I'd start:

EDCOR Electronics Corporation. CXPP100-MS-2.5K for the output

and:

EDCOR Electronics Corporation. XPWR127-120

for a power transformer...at least as a starting point.

jamie

[imaradiostar]

Let it also be said- if you really want to make the best of 6550's you can also use a split supply with 600 volts for the plates and roughly 300-350 for the screens.

The Edcor output transformer I linked should be capable of about 200 watts of output (4 6550's) at 40Hz using this arrangement. An Antek Inc. toroid could be used to make a center-tapped power supply with about 640 volts B+ and half that for screens.

jamie

[Chuck H]

Jamie,
The OP is not a tech but a builder. The finite details of using toroids or split supplies goes too far. Witness the Q about the bias supply suggestions from my post. If you could post a complete layout and schematic of your plan it would be fully do-able for the OP. Otherwise I think we need to stick with easier mods and accomodations. I do agree that oversize trannies would be a +. this is easy since original Bassman 135 trannies won't be available and there are many over the counter models that will fit the bill but excede the specs of the original iron. Mr. Fahey's suggestion of the 135 is a good one. The only change I would make is switching to 6550's instead of high end 6l6's or lowering voltages to accomodate common 6l6's.

[imaradiostar]

Thanks Chuck, I should have read more carefully. I'd hesitate to use 6550's with Fender iron because of the difference in filament current by going to 6550's. The Edcor PT would give an extra amp or two which could help.

It would be easy enough to use the Marshall bias arrangement since the Edcor lacks a bias tap- we could point him to a schematic with this design so he could copy it.

As much as I like a slightly more complicated preamp, I have to agree that a simple Dual Showman with 6550's would be a neat amp.

jamie

[HTH]

why all this talk of 100w output stages and 6550s ????, the OP said that the guy will be using the amp at home. I've used my little Champ 5C1 build (SE 6V6, 6SJ7 pre) for home guitar and bass use and it can get LOUD for home use. Surely even a SE 6550 is overkill for home use?

[J M Fahey]

Dear HTH, the OP asked for "the best", and didn't restrict it for home use at all.
In fact he started speaking of 50W, and finally settled for 100W, I bet *he* has a pretty good idea about where it will be actually used.
Doesn't say it in so many words, but at least playing with a guitar player and a drummer can be hinted.
To play alone at night, a SE amp may be enough to annoy the neighbours, but to play along a drummer, 50 up is more realistic.
Well, that's how I see it.

[Danelectron]

Clarification.

This will be for my brother for home use. I originally thought a 50 watt Bassman would be fine, but changed my mind when it was suggested 50 watts for bass is not much and the relative increase in cost to 100 watts is small. I like power, but as HTH has put it back into the original perspective, 50 watts may be fine or may even be too much. This will be used in a living room and bass can even at low volumes be annoying to a neighbor that is already looking for something to b***h about. I'm looking for a good design from the many available. I know this is vague and subjective, but if Bassmans truly suck for bass then maybe a showman or what?

The 135 may not be such a good choice if the "special " tubes needed are unavailable. I'm not totally electroilliterate and can do reasonable changes. Terminology sometimes escapes me so a bias arrangement may be (to me) interpreted as physical layout as much as component value so that puts me in the builder category.

If a 5c1 is fine in a home environment maybe I should be asking what makes a bass amp design different from guitar.

Thanks for your responses and hope your Turkeys came out moist and meaty!

[HTH]

Hi Danelectron,

Since it appears that you want an amp that your brother can play at home, then 5w is plenty. I'd go with an Ampeg B15 preamp into a SE 6V6 - that will give him some tonal variation while keeping the volume sensible. 5w cranked is still loud for home use, but thats what the volume control is for

If you want an amp that can be gigged, then 100w minimum is what I'd be thinking with the screens run at half the plate voltage for max clean headroom.

Cheers, Ian
p.s. J M Fahey, this is just a friendly discussion about amps, don't get your nose all bent out of shape, settle down eh.

[J M Fahey]

Dear danelectron, trying to balance cost/flexibility/ease of build maybe you could consider something based on the Bassman 50, but using only one channel, the "Normal" one which is basically the Normal Showman channel too.
You will profit from the advantage of having the layout already solved, standard tubes and transformers, and probably even original-spec ready made chassis and cabinets if you wish so.
You can play it in a bedroom , of course, since you are not going for power tube overdrive, *and* you can jam with your friends too, in the garage or at some club.
If you build two normal channels, guitar and bass can jam on the same amplifier, at home.
The Bassman 50 in all its glory:
1964-1967 "Black Face" Bassman
Schematics:

You might compare what I suggest with Bassman 20, which is practically the same , only in a 20W version:

[Danelectron]

J M Fahey and HTH,
Veeeeery interesting! I'm leaning toward either the Bassman 20 design or Ampeg preamp with some kind of output section. They both have different preamp component values and tubes so I may do both for comparison. I think he might like to be able to drive the power tubes a bit and the 50 would probably have some limits for him. He has an old Hot Tubes effect that he uses occasionally, but he might be surprised at a driven power tube sound. I don't think he has ever been able to drive either of his amps hard. I have a bass amp at my house he uses and I haven't been able to get him to drag his Trace Elliot over. I get burned out network switches from work that are great for cabinets. They are rack mountable and are big enough for 20 watts. It seems I've seen a 6V6 design that uses 2 power tubes paralleled out single ended. I think he will want a bit more than 5 watts. I'm trying to imagine the output. I built a 5F2 that would be plenty loud for guitar at his house. I love it for guitar, but it probably wouldn't be enough for bass.

Thanks for these suggestions. You've both given me a good starting place.

Edit: I was just reviewing this thread and realize I've been around in circles so it's no wonder you guys were confused about what I was looking for. My fault for over thinking.

Imaradiostar, Your suggestions didn't go unheeded. You've inspired plenty of curiosity to keep my R and D division busy for a few months.

[imaradiostar]

Thanks, best of luck. Everyone has an opinion, make sure you don't lose sight of your goals!

One more thought- I've gigged a church worship gig with an under 20 watt tube bass amp. While not super clean, it was doable and I had fun. I still would favor a 50 watt 6L6 or 6550 based design as the difference in build time and effort is minimal. Think B15...lots of great tonal mileage there!

I would never ever try to use a single ended amp with bass for anything other than bedroom practice. Once again- just an opinion!

Jamie

[ThermionicScott]

Cedar Rapids, eh? Neighbors!

I think the 5F8A Twin might be a cool build. Just like the classic 5F6A tweed Bassman, but with four 5881's and bigger iron for 80 watts (allegedly). One could build it with Twin Reverb iron and a Weber WZ34 Copper Cap to simplify the parts selection.

In fact, I've got some Baldwin organ guts that are patiently waiting for me to do that very thing!

- Scott