Bass Amp OT and tubes

[GainFreak]

Hi,

What specs should a bass tube amp OT have? Does it need to go down to 30-40Hz or this is too low?
Also according to your experience which tubes are a better choice for a bass tube amp - 6L6, 6550 or KT88?
Thanks.

[Albert Kreuzer]

Hi GainFreak,

Low E on bass is 41.2Hz, low B on a 5string is 30.9Hz. If you go that low, you'll need a cabinet that can reproduce these frequencies too.
Personally, I like KT88s best (think Hiwatt DR405).

Cheers,
Albert

[EETStudent]

The choice of tubes might depend on your needs. The popular Ampeg SVT-Classic uses 6550 tubes, six of them for a very punchy and monster tone. However, many older "bass" amp designs used 6L6s at lower wattate, for a more relaxed, vintage tone. On another hand, even some modern designs use six or more 6L6s, maybe for availability reasons. Maybe someone with expertise can shed more light on this.

As for your OT, 30-40 Hz is NOT too low. Your OT will need to deliver that low of a frequency, seeing as it IS a bass amp. If your going loud and powerful with your amp, you want something that can handle a lot of current while putting out the desired wattage. The Hammond 1650TA, 1650WA are solid choices intended for multiple tubes with high power ratings
(approx. 300W).
http://www.hammondmfg.com/1608A.htm

[GainFreak]

Low E on bass is 41.2Hz, low B on a 5string is 30.9Hz. If you go that low, you'll need a cabinet that can reproduce these frequencies too.

As far as I know the famous Ampeg 8x10" cab for example doesn't go that low.
I read somewhere that the fundamental tone is at -3dB or -6dB for punchier tone.
For 30Hz one will need a car battery type of Hammond indeed

[Steve Conner]

Correct, bass tone is in the harmonics, not the fundamental. The SVT 8x10" was made with what were essentially radio speakers that delivered huge amounts of harmonic distortion, and this was considered to be a good thing at the time. (You wouldn't even hear bass guitar when tracks were played on the radio otherwise.)

For low-powered amps with cabinets small enough to be portable, you don't even want to waste power trying to reproduce the fundamental. If you want to be heard over a rock drummer with, say, 100 tube watts, the thing to do is roll off the bass and bark your way through the mix with midrange, as if you were a rhythm guitar.

I have a 300PS OT, and according to the data I got with it, it only goes down to 50Hz.

[GainFreak]

I have a 300PS OT, and according to the data I got with it, it only goes down to 50Hz.

300W at 50Hz makes it much more easier to design and it wouldn't look like a car battery

[Steve Conner]

Yes, it "only" weighs about 14lbs, compared to the 28 that Hammond quote for their 1650WA

[GainFreak]

Maybe if you cut the fundamental appropriately even the 1650TA could do the job considering it's rated to go down to 30Hz at full power.

[mac1amps]

I've re-tubed a number of [70's] SVT's, using KT88's with some excellent results. Not to say that a decent made 6550 isn't also a good choice, but the KT88's were definately an upgrade. One of these days I want to install a set in my own ['73] SVT, but since I'm not a "performing" bassist, I can't justify the $$$ right now.
There is also a certain "school" of bass players that like to have a moderate level of [tube] break-up in their sound. Since 6L6's will 'clip' sooner/'easier' than 6550's or KT88's, that would be the only situation I would consider using them (although NOT in an SVT)....you also have to consider what kind of volume level you're working with. If you're up against a couple of high gain stacks (especially if we're talking Metal players), you'll need all the headroom and power you can get, whereas if we're talking about a typical Blues band (for instance) you can get away with alot less power.

[GainFreak]

So if you have to choose between Sovtek, Electro Harmonix and JJ which KT88s would you prefer for a 6x 300Watt amp and why?

[HTH]

So if you have to choose between Sovtek, Electro Harmonix and JJ which KT88s would you prefer for a 6x 300Watt amp and why?

I've tried Sovtek KT88s and they were very midrangey, but not very deep in the bass - not a typical KT88 tone imo. Sounded ok in a guitar amp, but there were others I liked more...

EH 6550 - much nicer tube, good bass end and a fairly smooth top end, but not as good as...

Svetlana 6550s - very nice indeed, good solid low bass - my fave.

ain't tried the JJ KT88s, but JJ's stuff is generally very well made so you'd not go far wrong with them.