4 x KT88 Bass amp ?

[Smokebreak]

I've got a pal who wants me to build him a "200W" bass amp head. He is currently using a Bassman100, and loves it, but wants" a little more power". So I'm thinking Bassman100 preamp into 4xKT88 power section. I've been looking at the Major, the Sunn2000s, and the Hiwatt.
That all seems pretty straightforward, but I could use some input concerning iron and chassis.

1. PT - I've been looking at the Hammond 278CX, 800VCT @535mA, but the 6.3V winding is only 6A, and I'll likely need more than that.

Then there's the Classictone 40-18069 thats 380 or 330-0, FWB @ 500mA. They're calling this a 100W PT, but it seems like it can put out the current for 4 x KT88. It also has a 60V bias tap, and the 6.3V winding is 10A . http://www.classictone.net/40-18069.pdf

2. OT - It seems the Hammond 1650TA is the only affordable game in town, unless I wanted to make a heavy jump to their 300W OT, which I don't. The 1650TA is 1K9 primaries, and rated at 120W, 30Hz to 30 KHz

Anyone been down this road with this iron?

3. Chassis - This seems to be my biggest obstacle.

Does 1/8" thick aluminum sound about right for 30lbs of iron?

I would like to find some sort of pre-drilled chassis to work on, be it a JCM800 or ODS or Twin or whatever I could make work, but I'm game for drilling if I need to.

If anyone has any ideas and/or suggestions I'd love to hear them.

Thanks - J

[sluckey]

Maybe this chassis is of some interest for your project?

http://el34world.com/Forum/index.php?topic=17411.0

[Reeltarded]

Stay away from the Major ideas. Bassman 100... hmm. It's not very loud. Has he ever heard of an SVT? 140w output is a hump. It takes 10/1ths money and trouble for each five of those last 60w.

This is my honest opinion. Make him a 50w magnificent tone machine and use a big cheap assed power amp. It's what I do with guitar. It absolutely works great for bass. It's expandable and shrinkable.

[JoeCon]

Miles is right. I hang with a bunch of bass playing fools (one guy is a bass instructor at Berklee School of Music) and they swear by big ole SS power amps to drive their bass setups. 4 Tens or 15's it doesn't matter they go power amp all the way. Their rigs looks like my stereo system used to look....

[Smokebreak]

Thanks guys. Well, he sounded pretty set in seeing a quad, but i can surely talk to him about it.
Just so I'm clear, you're saying build a 50W amp with a preamp out, then have him pick up a cheap SS power amp? Can you explain the topology of the whole system?

[xtian]

I went down this road with a retired bass player who worked at Gallien Krueger in the Bay Area. I built him a 25-watt SE with KT88, balanced line out, and he runs it into a Class D power amp and big cabinet he made. Very, very cool project. Came out great. The head turned out to be a rock machine, great for guitar, too. Tone stack based on his blackface Bandmaster.

http://ampgarage.com/forum/viewtopic.php?t=22434

[Littlewyan]

Just to confirm how many speakers does he currently use? And could they handle the extra power?

[xtian]

He built two 8x10 cabs. Not kidding. Don't know what drivers, but he's an old speaker vet, so you can rest easy the wattage is covered.

[martin manning]

Aaron you should update the schematic for your SE KT88 to show the final configuration you settled on. I can see where there might be some interest in it, especially if it works well for guitar too.

[bb5000]

I built a Hiwatt DR201 clone in 2011, you should be able to get the correct transformers from Heyboer. The power supply is "dual-rail" using 2 bridge rectifiers so you will need a PT with 2 HV windings. Since I'm in Europe I ordered my transformers from TubeAmpDoctor in Germany, don't know where they get them from but they were pretty close to the Partridges in specifications.

[Littlewyan]

Wow hes moving a serious amount of air with that setup! I think Lemmy (Motorhead) only runs two 100W Stacks, although I suspect hes somehow plumbed into the PA System as well. Your friend will probably not notice much difference going from 100W to 200W, as there is only 3dB in it.

[Smokebreak]

Ok so say I have a 50W Fender head, I've been running into a cab...standard fare head.

I would want to :

1. Be able to run the amp by itself through a cab via it's speaker outs(done)
2. Bypass the amp's power section and run it through a separate SS power amp
3. Run the head through a cab, via it's speaker outs, AND have a jack that allows me to run it to a separate SS power amp.

How would I accomplish this?

I imagine a dummy load would have to be involved for 2 and 3. I'm also unsure of the terms slave out/line out/balanced line out, etc. He also wants an XLR out, to run straight to the house PA. This would be a balanced line out, correct?
What's the difference between this XLR out, and the out for another SS poweramp(besides the jack)?

[xtian]

My Line Out is a tap off the OT secondary, so it includes any distortion from the power tube. Yes, we have a dummy load that gets engaged when you remove the speaker cable.

I'll have to get permission from the owner to detail this stuff, so let me know if there is interest.

[Smokebreak]

My Line Out is a tap off the OT secondary, so it includes any distortion from the power tube. Yes, we have a dummy load that gets engaged when you remove the speaker cable.

I'll have to get permission from the owner to detail this stuff, so let me know if there is interest.

Like this does? https://taweber.powweb.com/store/modkits.htm#balun

[bb5000]

Ok so say I have a 50W Fender head, I've been running into a cab...standard fare head.

I would want to :

1. Be able to run the amp by itself through a cab via it's speaker outs(done)
2. Bypass the amp's power section and run it through a separate SS power amp
3. Run the head through a cab, via it's speaker outs, AND have a jack that allows me to run it to a separate SS power amp.

How would I accomplish this?

I imagine a dummy load would have to be involved for 2 and 3. I'm also unsure of the terms slave out/line out/balanced line out, etc. He also wants an XLR out, to run straight to the house PA. This would be a balanced line out, correct?
What's the difference between this XLR out, and the out for another SS poweramp(besides the jack)?

Traditional tube amp line-out is usually taken from the OT secondaries and will require 1. Power tubes operating 2. A load as you mentioned.

An alternative would be a line-out pre-PI. Some modern tube amps turns the preamp tubes on in Standby, allowing for a preamp line-out signal to be sent to PA/Slave power amp. The power tubes turns on when you switch out of Standby. Or add a separate switch that cuts the cathode connection to ground for all power tubes, that will turn them off.