Author Topic: 1200S for a bass rig  (Read 15625 times)

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Offline rp

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Re: 1200S for a bass rig
« Reply #56 on: October 14, 2006, 12:12:48 pm »
I wouldn't mess with rectifier tubes, particularly using the amp for bass. I would go this way;
http://www.webervst.com/ccap.html
Cheaper and less voltage drop - more potential for your power tubes, and they drop right in.
I'm guessing the capacitors are the silver fixed tubes behind the 6550's??
Those are likely the original can caps, maybe replaced, maybe bypassed, who knows? If they are original, they are almost definitely bad (have I mentioned to get a qualified tech?) and need to be replaced - actually they should also be upgraded from the spec on the schematic. (have I mentioned to get a qualified tech?) There are capacitors throughout the chassis, but those big filter caps have the most potential to ruin your day.
He asked me for a schematic, but have had no luck in locating one. I wouldn't feel safe messing around in there...
I have a factory schematic, I can PDF it to you.
I have to admit I didn't know it could shock you unplugged.
Not just shock you, it can freekin' KILL you!
Those are awesome...and not that expensive. Maybe I'll just pick those up, and if they solve the problem
that's that. If not I'll just make the drive to a tech. I never really intended to dig in it too much...just check the tubes
and see kinda what was making the fuse blow out. I was worried it might be a transformer.

Thanks, more than likely whoever I take it to will need that schematic. :-D

The tubes read 6550A RCA that are good....should I swap these out also...or at least get a spare?


Offline EdBass

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Re: 1200S for a bass rig
« Reply #57 on: October 14, 2006, 07:25:55 pm »
Robin - the whole point of capacitors is that they store charge. Filter caps store HUGE amounts of electricity.  Getting shocked by one of those would be the equivalent of licking a live plug that runs to the wall outlet in your house.  It could (and probably would) kill you most quickly.
Well, let's not get crazy here. The potential exists, but to actually get offed by a filter cap would take a "perfect storm" kind of scenario that would likely involve using both of your hands to complete a circuit with your heart in the middle. My high school electronics teacher made us put one hand in your pocket while you poke around the guts of a chassis, I mostly still do that to this day.
They will knock you on your ass pretty quick though.
Those are awesome...and not that expensive. Maybe I'll just pick those up, and if they solve the problem that's that.
Maybe that will work, but it could be a number of things. My money's on the filter caps. Regardless, IMO those Copper Caps are superior to tubes in respect to a clean, strong bass application. For guitar some like a little more sag, it's pretty much personal preference.
If not I'll just make the drive to a tech. I never really intended to dig in it too much...just check the tubes and see kinda what was making the fuse blow out.
Good thinking.
I was worried it might be a transformer.
You have just hit on the worst case scenario. If you need a tranny it's gonna cost you some money, maybe half of what the amp is worth in excellent condition.
The tubes read 6550A RCA that are good....should I swap these out also...or at least get a spare?
Have you tested them on a tube tester? If they are matched and test strong, that set of USA RCA 6550's are gold. You don't need a spare, if you blow one or more you should get another matched set of 6550's or KT88's.
I won't even speculate on what brand of new tubes, it's a personal preference. I think that's like telling a player what string gauge that you think they should be using.

Offline rp

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Re: 1200S for a bass rig
« Reply #58 on: October 15, 2006, 10:39:18 am »
Should I try a pair of those WZ68's? Or stick with the WZ34? As far as I can tell by using fuses the 6550's are ok.
Is there anything I can do to test if the transformer is bad without going inside? Caps?


Offline EdBass

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Re: 1200S for a bass rig
« Reply #59 on: October 15, 2006, 04:13:36 pm »
Should I try a pair of those WZ68's? Or stick with the WZ34?
You got me on that one! I got a bunch of the WZ34's and use them instead of GZ34's wherever I need them in my tube rectified Sunns. You probably only need one of those WZ68's to replace both of your rectifier tubes. You can actually run your amp on just one GZ34, but it will starve for current and break up quickly. You should email Ted and ask him;
ted@webervst.com
he will be glad to help you out.
As far as I can tell by using fuses the 6550's are ok.
I have no idea what that means.
Is there anything I can do to test if the transformer is bad without going inside? Caps?
No you can't. Again, find a tech. Or learn about electrical engineering. A tech will probably be quicker and cheaper than a few years of school or home study.

Offline rp

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Re: 1200S for a bass rig
« Reply #60 on: October 15, 2006, 06:04:41 pm »
I e-mailed him, as soon as I get an answer I'll order a couple of whatever he recommends...and
then go from there.

Offline rp

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Re: 1200S for a bass rig
« Reply #61 on: October 16, 2006, 02:16:45 am »
Thanks for the pdf file, Ed!  :-D

When I get her going I'll post some pics. This head is way bigger
than the marshall cab it sits on...looks huge. :evil:

Offline rp

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Re: 1200S for a bass rig
« Reply #62 on: October 24, 2006, 05:00:42 pm »
Well I'm going to see a tech tommorrow...I e-mailed him the schematic and
told him kinda what I'd like to do. However he did ask me what kind of caps/cans
he would need to order to replace the old ones? Anyone know?

Offline EdBass

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Re: 1200S for a bass rig
« Reply #63 on: October 24, 2006, 07:53:40 pm »
Well I'm going to see a tech tommorrow...I e-mailed him the schematic and
told him kinda what I'd like to do. However he did ask me what kind of caps/cans
he would need to order to replace the old ones? Anyone know?

I sent you an email with some ideas. If you or your tech has any questions about it, let me know!
Good luck, and keep us posted!

Offline rp

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Re: 1200S for a bass rig
« Reply #64 on: October 25, 2006, 04:09:30 pm »
Well I'm going to see a tech tommorrow...I e-mailed him the schematic and
told him kinda what I'd like to do. However he did ask me what kind of caps/cans
he would need to order to replace the old ones? Anyone know?

I sent you an email with some ideas. If you or your tech has any questions about it, let me know!
Good luck, and keep us posted!

Well we chatted today about it and I think it went pretty well. I had a couple of burnt small tubes....
The rect tubes were actually not burnt, but by the time I left he hadn't checked the 6550's.
The rect tubes were mullards from great britain btw. He reversed himself on the copper caps though but
only because I was considering putting in kt90 tubes with them. He's also going to do the can cap mod
to handle that extra power....by running them together he said their handling can be increased to 800 (watts,volts I forget)
instead of the five something they were before. He thinks it should increase watts up to about 160-180.
A few components had gone bad also, but he said they would be a dollar or two to replace.

 :-D
« Last Edit: October 25, 2006, 05:35:42 pm by rp »

Offline EdBass

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Re: 1200S for a bass rig
« Reply #65 on: October 25, 2006, 06:04:29 pm »
Should be a rockin' rig. Get your tech to switch your output tranny to the 8 & 4 ohm taps while they are in there, it ought to sound great through your Hartke cabs.

Offline rp

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Re: 1200S for a bass rig
« Reply #66 on: October 25, 2006, 06:13:45 pm »
Should be a rockin' rig. Get your tech to switch your output tranny to the 8 & 4 ohm taps while they are in there, it ought to sound great through your Hartke cabs.

I can post pics when he's done if guys like. He also builds custom cabs with weber speakers, as well as custom tube heads.
I may try having him build me a 6x12 cab with some high end weber speakers. I need to look around for some specs of the original cab
for ideas. Those 6550's were all good but one, so I'm going to sell them back at him for hi-fi applications towards
a quad of kt-90's. :-D