Tube bass amp in a combo cab?

[dynaman1]

Bad idea? 50-75 watts.

[sluckey]

Sunn did a 2 EL34 bass amp combo with a single 15" speaker. It was called Sonora. Looked like and same size as the Solarus combo guitar amp, only just 3 knobs. Amp was same as the head style Sorado.

[HotBluePlates]

Ampeg made the B-15 and B-18 amps, which were about 30w and a sorta combo cabinet (fliptop).

Weight of the final amp is the main limiting factor.

[PRR]

I wuz gonna say.... B15. If that was a bad idea, how did we get through the 70s and 80s?

Depends what you want to do. If you have to rumble the stadium, you will need a forklift built into the back of the combo.

Perhaps a key problem is: a not-HUGE bass loudspeaker needs a closed (or small-port) box, a tube amp needs an open space. Traynor BassMate had the tubes above the box; B15 made you take them out and flip-over. A guitar amp can be open-back, tubes can vent, speaker-chamber needs no top and minimal back.

[dynaman1]

Well, I was mostly concerned with the tubes and vibration.

I've a few options. I have an old guitar combo cab that was equipped with a 15" speaker. The internal volume is sufficient and I've already done a bit of research and came up with a suitable speaker that will get me the required low end with some slight modification to the existing vent/port. However, reusing the existing chassis will require extensive metal work, and the cab is rather light and flimsy. Bracing would prolly be in order.

My buddy also has an old solid state Peavey bass amp with a single 15". I haven't yet taken measurements to see if I can add a tube amp. I'd like to use this cab, as it's already "tuned" for bass. Perhaps I should just make a separate amp and use the cab minus amp.

I did think of the Ampeg, but I figured a relatively low powered amp like the B-15 didn't exactly shake the cab (and tubes) much, plus it's actually operated outside of the cab, no?

I'll check out those other amps you folks mentioned. Thanks for the replies.

[bigdaddy]

Good idea if you have no problem with replacing tubes and your back is OK. Bad idea if you have a bad back, the iron is going to be heavy and the weight of the speaker too unless you use toneless Neo speakers. Vibrations will kill new tubes and the thing will weight a ton. Better off even keeping the head off the cab completely.

The trick to getting the most out of a lower wattage tube bass amp is to use a cabinet with a very high efficiency. Like the old style Perkins bins or scoop bins or W bins. They all made the speaker much more efficient and was able to project the sound. Sealed enclosures for bass are great for recording or small venues. But for a little longer room you need some porting. These round ports and small vents are useless. You need a real horn enclosure to make that 50-70 watt bass amp work. Years ago they used JBLs which really did not produce a lot of low end except for the E145 and E155 models. But they did not have a long XmaX and really compared to todays woofers did not have a lot of lows. Although they were very efficient and the design of the cabinet made up by really producing a lot of low frequencies. Think about making a front loaded cabinet but with a good amount of porting behind it and a speaker with a high enough SPL but long enough XmaX.

Something like this but front loaded and smaller:  http://www.usedprice.com/items/pro-sound/cerwin/pro-sound-reinforcement-speaker/je36c-507098.html?

[Shrapnel]

I've also seen combo amps where the chassis wasn't inverted, as Leo did it, but mounted in the same position as Jim did. That is to say, the speaker cab and head shared a single piece of lumber. It was like a shelf was installed just for the amp chassis.

My grandmother bought an amp off someone once for her electric guitar (She loved music, but mostly played violin) that was built that way. 1-15" speaker, 2-6L6GC's (I think they were GC's), 2-12AX7s, and 1-5U4G recto. Metal front panel, only had a power, and I think it was a "polarity" switch, with a rectangular Neon (color was regular neon behind a clear plastic bezel) and a Volume, Bass, and Trebel control (I think the tonestack was james/baxandall style. The name badge was Supro, and I could have sworn it said it was a Thunderbolt (I haven't seen that amp in years.) This was open backed though if I remember right. (I remember it had a light-blue, almost cyan? and silver/chrome front panel, and the supro plastic logo was written in script. Am I wrong on the model? If so,any clue as to the real model? IIRC, it was claimed to be a bass amp.) There were other brands as well that were set up that way too. Gibson had it's Thor bass amp that way.

Point being, a not too powerful bass rig with that kind of setup of a cabinet, *could* have a sealed cab for the speaker, and a permanently mounted tube amp in the same combo unit.

[sluckey]

I've also seen combo amps where the chassis wasn't inverted, as Leo did it, but mounted in the same position as Jim did. That is to say, the speaker cab and head shared a single piece of lumber. It was like a shelf was installed just for the amp chassis.

Point being, a not too powerful bass rig with that kind of setup of a cabinet, *could* have a sealed cab for the speaker, and a permanently mounted tube amp in the same combo unit.

That's exactly how the Sunn Sonora is built.

[supro66]

I've also seen combo amps where the chassis wasn't inverted, as Leo did it, but mounted in the same position as Jim did. That is to say, the speaker cab and head shared a single piece of lumber. It was like a shelf was installed just for the amp chassis.

My grandmother bought an amp off someone once for her electric guitar (She loved music, but mostly played violin) that was built that way. 1-15" speaker, 2-6L6GC's (I think they were GC's), 2-12AX7s, and 1-5U4G recto. Metal front panel, only had a power, and I think it was a "polarity" switch, with a rectangular Neon (color was regular neon behind a clear plastic bezel) and a Volume, Bass, and Trebel control (I think the tonestack was james/baxandall style. The name badge was Supro, and I could have sworn it said it was a Thunderbolt (I haven't seen that amp in years.) This was open backed though if I remember right. (I remember it had a light-blue, almost cyan? and silver/chrome front panel, and the supro plastic logo was written in script. Am I wrong on the model? If so,any clue as to the real model? IIRC, it was claimed to be a bass amp.) There were other brands as well that were set up that way too. Gibson had it's Thor bass amp that way.

Point being, a not too powerful bass rig with that kind of setup of a cabinet, *could* have a sealed cab for the speaker, and a permanently mounted tube amp in the same combo unit.

Yep that is what it was Supro 6420 Thunderbolt
I built two go to my site

http://fatbasterdamps.com/

I heard tell Jimmy Page played thru one of these at a recording studio

http://www.thegearpage.net/board/showthread.php?t=296118

[bluesbear]

Fender Bassman 10 had 4 - 10's in a closed box with the amp above in the same cabinet. They weren't light! They were far lighter than the Port-O-flex's, though. Actually, not a bad bass amp. Amazing for Fender!
Dave

[dynaman1]

I've also seen combo amps where the chassis wasn't inverted, as Leo did it, but mounted in the same position as Jim did. That is to say, the speaker cab and head shared a single piece of lumber. It was like a shelf was installed just for the amp chassis.

My grandmother bought an amp off someone once for her electric guitar (She loved music, but mostly played violin) that was built that way. 1-15" speaker, 2-6L6GC's (I think they were GC's), 2-12AX7s, and 1-5U4G recto. Metal front panel, only had a power, and I think it was a "polarity" switch, with a rectangular Neon (color was regular neon behind a clear plastic bezel) and a Volume, Bass, and Trebel control (I think the tonestack was james/baxandall style. The name badge was Supro, and I could have sworn it said it was a Thunderbolt (I haven't seen that amp in years.) This was open backed though if I remember right. (I remember it had a light-blue, almost cyan? and silver/chrome front panel, and the supro plastic logo was written in script. Am I wrong on the model? If so,any clue as to the real model? IIRC, it was claimed to be a bass amp.) There were other brands as well that were set up that way too. Gibson had it's Thor bass amp that way.

Point being, a not too powerful bass rig with that kind of setup of a cabinet, *could* have a sealed cab for the speaker, and a permanently mounted tube amp in the same combo unit.

Yeah, that's how the tube combo amp I was thinking of using is constructed. The friend I'm making this for just informed me that the speaker in his Peavey solid state combo is still functional so I'm thinking of suggesting that he simply use that as a speaker cab. No doubt, Peavey has engineered them to work well together so I'd just as soon make a head in a different enclosure. I hope the speaker is efficient. Obviously this is a budget build.

Initially, I planned on following a Traynor YBA schem. The bass player in my band has a 50W Traynor that's stupid loud when driving a big Ampeg cab. I do have the parts to make either a 50W or 100W version, and possibly optimize one channel for guitar. However, the Sunns look interesting (and really simple). I even have a spare 6AN8 laying around.

I think one of the outputs I have stashed away has UL taps. Is there any advantage to using them? I don't want to do anything that would result in less available power, as I fear that a single 15" won't be nearly as efficient as a multi-speaker cab.