The power is on, the tubes are glowing, the cable is good, NO SOUND.

[nad]

Bought a Sunn Sorado amp from Ebay, hooked it up using cables that are perfectly fine, and I'm getting no sound. The tubes are glowing away, the fuse is good, and I can hear the amp slightly humming so I know it's on... I'm hoping for a stupid mistake or easy solution.

Anything I can look for, or did I get screwed?

[Plain Old Me]

If you are using an active bass, make sure the battery is good.

[savit260]

Originally Posted by nad

Bought a Sunn Sorado amp from Ebay, hooked it up using cables that are perfectly fine, and I'm getting no sound. The tubes are glowing away, the fuse is good, and I can hear the amp slightly humming so I know it's on... I'm hoping for a stupid mistake or easy solution.

Anything I can look for, or did I get screwed?

I know this is going to sound really stupid but, It's not on standby is it?? I once saw a guy flipping out about no sound at a show once before he figured out that the amp was on standby! Just a thought. Anther quick thought.... There is a 12AX7 behind the output transformer on the right side of the amp if you're looking at it from the back. You can't see it, but if you reach around behind the transformer, it's there. Is that tube all the way in? it's socket?

[whacker]

Check the speaker cable. Make sure the standby switch is flipped up (on). If all this is correct, unplug your signal cable from the bass and see if it give you the ground noise when you touch the tip.

[Rock City]

Just because the tubes are glowing doesn't mean they're working. The heaters are most likely what you are seeing, and they'll light up in most cases unless there's a major failure.
Try swapping out preamp tubes one at a time. My old Hiwatt 200 would eat a preamp tube occassionally, and wouldn't pass signal to the power stage.
DON'T open the amp up and mess with it if that doesn't work. Those amps are running about 450 volts DC inside....and they will KILL YOU DEAD if you're not careful.
Corey

[nad]

Standby switch off/on no difference.

Bass and cable fine.

Touched the plug tip, nothing.

Removed preamp tube, inserted as far as it will go.

Still no sound.

[nad]

Originally Posted by Rock City Guitars

Just because the tubes are glowing doesn't mean they're working. The heaters are most likely what you are seeing, and they'll light up in most cases unless there's a major failure.
Try swapping out preamp tubes one at a time. My old Hiwatt 200 would eat a preamp tube occassionally, and wouldn't pass signal to the power stage.
DON'T open the amp up and mess with it if that doesn't work. Those amps are running about 450 volts DC inside....and they will KILL YOU DEAD if you're not careful.
Corey

Right, will try that. I have a spare 12AX7. Also thanks for answering my "if they glow, does that mean they work?" question before I asked it.

No worries, I will NOT be opening up the chassis, don't feel like getting croaked tonight.

[nad]

Originally Posted by savit260

Anther quick thought.... There is a 12AX7 behind the output transformer on the right side of the amp if you're looking at it from the back. You can't see it, but if you reach around behind the transformer, it's there. Is that tube all the way in? it's socket?

I don't know why I'm just seeing this post... selective sight I guess.

Replaced that one (duh), it doesn't seem to be lighting up. Didn't even know that was back there, thanks.

EDIT: It glows, but faintly. Still no sound at all. This sucks.

[i_got_a_mohawk]

Woooooaaaah, stop messing around! If something is up and not working this could be very bad! Take the amp to a tech, as if its not functioning properly you could very easily screw up the transformers aswell as a host of other components!

- Will

[Eric Cioe]

Try changing the fuse. Before I bought my Bassman 100, it didn't work, but the guy at the store thought it was a fuse. Changed it and things are great now.

[savit260]

O.K. Make sure you have the tubes in the right place. The one in the back behind the Transformer is a 12AX7. The one that IS NOT behind the transformer is a 6AN8A (phase inverter, not a pre amp tube) They look about the same, but are very different tubes. Make sure you have the right tubes in the correct places. If that doesn't do... Take it to a tech. Unless you smoked a transformer, it shouldn't cost much to fix.

[BillyB_from_LZ]

Did you try both speaker jacks?

Fender amps have a shorting jack on the main speaker jack so that turning the amp on without a load won't fry the output transformer.

If you plug in the extension jack first, the amp's output is shorted out and no (or extremely very little) power goes to the cabinet.

If you have two cabinets so much the better.

[The 0x]

Originally Posted by Eric Cioe

Try changing the fuse. Before I bought my Bassman 100, it didn't work, but the guy at the store thought it was a fuse. Changed it and things are great now.

If the fuse was blown, the tubes wouldn't light up at all.

[nad]

Originally Posted by savit260

O.K. Make sure you have the tubes in the right place. The one in the back behind the Transformer is a 12AX7. The one that IS NOT behind the transformer is a 6AN8A (phase inverter, not a pre amp tube) They look about the same, but are very different tubes. Make sure you have the right tubes in the correct places. If that doesn't do... Take it to a tech. Unless you smoked a transformer, it shouldn't cost much to fix.

Yep, that's how they are arranged. I'm going to get a new 6AN8A and try that as well. That particular tube glows REALLY bright, I'm not sure if they are supposed to but it's much brighter than the 12AX7 and 6550 pair.

Originally Posted by BillyB_from_LZ

Did you try both speaker jacks?

Fender amps have a shorting jack on the main speaker jack so that turning the amp on without a load won't fry the output transformer.

If you plug in the extension jack first, the amp's output is shorted out and no (or extremely very little) power goes to the cabinet.

If you have two cabinets so much the better.

Yep, tried both the 4-ohm (extension) and 8-ohm outs, no difference. I have a 4-ohm cab by the way.

[BillyB_from_LZ]

I wonder if the rectifier tube (the GZ34) is good... The filament (heater) winding on the power transformer works independantly of the B+ (high voltage) supply. The tubes could glow but if the rectifier tube is bad and not making DC for the power supply, the amp won't work.

On a separate subject...looking at the schematic, it appears that the 4 ohm tap on the output transformer is only accessed by plugging into the Ext. speaker jack (as the Ext. jack has a switching function). I've never seen the inside of a Sorado to know if that's accurate. Anyone know?

[nad]

Originally Posted by BillyB_from_LZ

I wonder if the rectifier tube (the GZ34) is good... The filament (heater) winding on the power transformer works independantly of the B+ (high voltage) supply. The tubes could glow but if the rectifier tube is bad and not making DC for the power supply, the amp won't work.

It has a plugin solid state rectifier, not sure if that makes any difference. Maybe I should pick up a GZ34 tube when I get a a 6AN8A?

Is it possible for the tubes to be installed incorrectly, yet still glowing? The seller (who is being very helpful) thinks I may have the pins misaligned, but I'm assuming they wouldn't glow at all if not installed correctly.

[BillyB_from_LZ]

The heaters only go to 2 (or 3 for a 12AX7) pins. If a pin got folded over when the tube was being installed in a socket, that would prevent you from getting signal through the amp.

I once bought a guitar amp on eBay, the seller had stuffed the preamp tubes back in the amp before shipping it and managed to fold over one of the pins. One input channel wasn't working and I noticed that switching the pickup selector on my Strat made a noise through the amp like it was switching DC... I measured 300+ Vdc at the input jack (not a good thing). Ultimately it wasn't as bad as I had thought because the DC connection to the jack wasn't direct, the grid of the tube floated up toward the supply voltage because the cathode pin wasn't connected to the bias circuit.

Straightening the pins on the preamp tube solved the problem.

The small tubes have a large space between two pins that lines up with the large space on the socket. The power tubes have a keyway on the base that you have to line up...

Depending on the tone that you're looking for, a tube rectifier will give you a nice sag when you crank it up that a solid state rectifier won't.

[nad]

Checked the tube insertion, everything was fine and the pins don't appear screwed up. I'm going to order 6AN8A, 12AX7, and GZ34 tubes, that's pretty much the extent of what else I can do.

Also I just got the phone number of a local tube amp tech, will give him a ring if that doesn't solve my problem.

Cheers for all the help!

Oh and here's a picture to illustrate my frustration:



(no I'm not really doing that )

[nad]

Replaced the solid state rectifier with a GZ34, replaced the 12AX7, and replaced the 6AN8A. Nothing. Nada. Zilch. My "everything works" amp isn't living up to it's description. Anything else I can do? Otherwise it's off to a tech and I doubt I'll buy anything this old on Ebay again.

Not happy.

[i_got_a_mohawk]

Like i said, take it to a tech, you are probably replacing parts you dont need to, there are alot of parts to a tube amp that arent tubes