Ampeg SVT or other 200-300W bass amp?

[M Fowler]

Isn't the PA100 going to need an extra gain stage to get some volume out of it?

In stock configuration running a guitar or bass guitar through the amp it is not very loud used all new tubes in place.

My project will add 1 extra tube to channel 1 & 2 which will be Ampeg Bass circuit and Fender Bass circuit. Leaving channel 3 & 4 stock for guitar use with the reverb.

Without adding the extra triode for gain I don't see how I could possibly get the amp louder.

Mark

[David Root]

I had a '75 SVT for several years, overhauled it, great amp, and just sold it before Xmas.

I think 100W is OK for bass, I had a '74 V4B that I sold too, it depends I think on how big the room is. OTOH, the guy that bought my SVT put it in his studio because he wanted that sound, and the guy that bought my V4B was a gigging pro musician, so YMMV.

The V4B has a pretty flexible tonestack, so does the SVT, they both have an inductor.

www.fliptops.net is the place to go for Ampeg stuff, including repro iron, he has it all.

[selloutrr]

It's going to all depend on the PA. If they are running IEM (in ear monitors) you don't even need a bass power amp. A preamp into a Direct box or even a Direct box with active elctronics will get a fantastic result.

If the PA is struggling to even do Vocals without distorting or being washing out in the mix of the live instruments you will need well over 100watts to keep up and not turn mushy when you play a scale fast or in a low register. A lot of the power needed will also be determined by how loud your drummer plays.

The SVT, Sunn, Hiwatt, etc. all large wattage bass amps were designed to play large arena were you would run them full out and play multiple amps until you had the volume needed to fill the mix. The PA was reserved for vocals.
The B-15n with the altec speaker is the most recorded bass amp of all time. It's not loud however it is smooth and true. With a professional recording chain it can give the "IT" sound. The runner up to the B-15n is the Dual Showman pushing a 2x15 JBL D15" speaker.

I would think as long as you build an amp with a great preamp and way to break the signal chain pre the power supply so in the event you need more power you should be golden.

A 2 ch preamp with a B-15 (S and N mod) and Dual Showman (alembic mod) ch. with FX send. Isolated tuner, Transformer balanced Direct out, bypassable EQ, and preamp out, power amp in. foot switchable ch selection, fx loop in/out, tuner mute. Possible a selectable Fet input for string bass.
I would make it a rack mount style build then build a seperate rack mount power supply that way it would be very versital. Light weight for studio recording, small power amp for small gigs, big power amp for large gigs. add multi amps for more power. Possible build a half power switch into the power amps. to give the best of both. A korg rackmount tuner and it's a bass rig to be taken seriously.

[Cliff Schecht]

Been working less than diligently on this amp lately but it is moving forward. I've got all of the parts minus the correct board standoffs and (maybe) the switch. The board standoffs I ordered were #8 instead of #6 and so they didn't fit at all. That's an easy fix, just order the right standoffs. But I'm having a helluva time finding the right switch for the impedance selector.

I guess the problem originates with the iron I chose, a Hammond 1650T output transformer. Unfortunately I got the one with a weird secondary that requires some switch finagling to work with. I've figured out a schema using a 4P3T switch but it seems I can't find a beefy enough version of this switch. I did order the biggest thing Mouser has (http://www.mouser.com/Search/ProductDet ... A40315RNZQ). I don't like it. It's rated at 125V at 2.5A (5A continuous at lower voltages) and the solder lugs can't really even fit the gauge of wire that Hammond uses on this massive OT.

I'm expecting the amp to put out about 250W and going into a 4 Ohm load this is nearly 4A of current. According to the datasheet this switch is marginal at best as far as being able to handle this kind of current. Am I overthinking this? Can somebody point at an affordable alternative to the switch I've already chosen?

[Cliff Schecht]

As per usual, I figured out a solution immediately after I asked for help here. I have a bunch of these old Centralab heavy duty rotary switches that are always *close* to being right. Tonight I pulled one apart and recycled some of the solder lugs into a 4P2T to make it a 4P3T. All I need to do now is figure out how to notch the insides of the casing so that it stops after three clicks(right now there is no start or stop detents to prevent the from moving past three throws). Anywho, I'm certainly happy with this switch over the C&K unit. I'm sure I'll find a use for the C&K in a lower wattage build though, it's by no means a low quality switch.

[Richie]

If your looking for a bass amp,never overlook these 2 amps. Fender PS 300 and PS 400. Power/sound/tone/loud! they have it all.
http://mhuss.com/PS300/index.html

Now days you can build your own. They also have some new KT120 tubes out now. 60w tubes! You could probably install a grill on the back to cook fried bologna sandwiches between sets..


The Sunn, Traynor, Hiwatt,Marshall, SoundCity, are also good sounding amps and powerfull. These were the tube amps.

The old SS amps were Acoustic,and Sunn. Now Days they have all kinds of huge power bass amps in SS That weigh less than your guitar..

[bb5000]

The Weber AB200 uses the same PI concept as the Fender 300PS & 400PS, a power tube in class A driving an interstage transformer PI. A loud amp with tons of headroom.

[Cliff Schecht]

Thanks guys, I have a solid schematic already drawn up for this amp. Part Ampeg B-15, part modified 5F6A style pre, all the way loud .


I'm having so afterthoughts on what I want to do for a standby switch on this amp. While I typically leave standby switches off of my amps now, this is going to be much higher wattage and more B+ than I typically use in my amps. I also don't know how well the KT120 quad I'm using will hold up to cold starting (especially from a toroid feeding a SS rectifier). I was thinking a switch that breaks the ground connection to a two diode FWB rectifier would do the trick.

OTOH, I'm doubtful that these tubes will be greatly harmed from starting without a SB switch. I've had more problems with these switches dying than tubes themselves dying from not using a standby switch (I've actually never had the latter happen). I was thinking some sort of simple "mute" switch on the front of the amp would suffice for what any (knowledgeable) user would use a SB switch for..

[renshen1957]

I'm not a big fan of the Marshall 200W amps simply because they have the lame passive tonestacks. I've read great things about the Hiwatt bass amps but I haven't seen anything for one of these yet.

Hi,

The Marshall Major's Tone Stack wasn't passive, might be worth a look. The Traynor Super Custom Special might be worth a look. Rumor was it was the basis of Ampeg SVT (including the speaker cabs).

JJ was a 8 pin version of the EL509, 4 tubes would produce close to 400 Watts with the right power supply.

Best Regards,

Steve

[xtian]

Hey, Cliff, what happened to your build?

Was prompted to search for "Ampeg SVT" here because this 1980s beast with 6x KT88 landed on my bench. Needed a new, TEN AMP fuse. Has a medium loud hum, but the fan almost covers that. Has microphonic preamp tubes, too. But otherwise, it's obscene power has frightened every living creature in my 'hood.

[Cliff Schecht]

I finished it and it's off with my buddy. Even drew up a schematic and some basic layouts that I might eventually post someday. The one thing I still feel is missing from that amp is a fan, those KT-120's cook! I also need to add some sort of retainer as the 120 bases are too fat and don't work with normal Fender power tube retainers.

Also I'm glad I kept the plate voltage relatively low (~560V and 170W before distortion theoretically) for that amp because the thought of it being much louder hurts my ears. There's definitely shit that I would do differently (higher plate voltage, no effects loop, maybe add tremolo ) if I were to build another but this thing turned out really cool in the end.

[M Fowler]

I want to build with a pair of KT120's but I figured the plate voltage should be a lot higher then 550v what voltage were you thinking of going with Cliff?

Mark

[TUBEDUDE]

If cost is not an issue, maybe a plitron toroidal output xfmr. If you can add a tube you can have active tone controls. The radiotron designers handbook has a schematic to adapt.

[Cliff Schecht]

I want to build with a pair of KT120's but I figured the plate voltage should be a lot higher then 550v what voltage were you thinking of going with Cliff?

Mark

Well it was originally designed for a quad of 6L6's, but the PT had so much more potential that the KT120's (in a fixed bias configuration) could better utilize the amount of current on tap. I adjusted the plate dissipation to 70% of the KT120 spec and with those tubes it is putting out more than the amount that is calculated by the square of the plate voltage divided by the OT primary resistance. Much more really. I never measured it because of the amount of time I had to start spending on my thesis work at the time.

[selloutrr]

Hey, Cliff, what happened to your build?

Was prompted to search for "Ampeg SVT" here because this 1980s beast with 6x KT88 landed on my bench. Needed a new, TEN AMP fuse. Has a medium loud hum, but the fan almost covers that. Has microphonic preamp tubes, too. But otherwise, it's obscene power has frightened every living creature in my 'hood.

That is one huge complaint I have about the SVT is the Fan noise. It's easily 70db and can over power a wimpy drummer's ghost notes.