SVT CL cuts out. Speaker Cab or Amp??

[dusty]

Need some help in diagnosing a problem.

Been playing through an SVT CL at my drummers practice space. Lately it's developed a few problems. After about an hour or so, it quits (no sound, amp stays on). The time before it quits is pretty random.

The other day, I got a mean squeal from it. Figured it was the pre-amp, so replaced all the tubes ( 2x 12AU7 and 12AX7). Mistakenly (or hopefully!) thought this was where my problem was. Well, it played fine for about 1.5 hours and quit again. This time I turned it off and hooked it up to another cab (proper impedance and everything) and it worked fine. Is it the cab (410HLF)? Or could the cool down period from powering down and switching cabs have played a part? Could the crossover in the cab have blown a component? How should I go about testing it?

My next step is to bring my V4B and cab to test both SVT CL head and 410HLF cab.................but the V4B and cab are such a bear to tranport!!!

Thanks!

[Amp Kat]

A crossover is basically a variable transformer so theres really not any components to make it go bad but the switch contacts or pot depending on it's design could be bad. Could also have a bad speaker cable causing intermittent connections. How about the power tubes ? Did you have the (6) 6550's tested ? Weak tubes will do it in a second. The preamp tubes you changed are actually the PI post section tubes. There are three more inside the front of the amp by the controls which are 12AX7's and are the preamp tubes. Check the bias lights on the back and see if they cut out when it cuts out.

[dusty]

I swapped out all the cables to rule those out. I didn't test the power tubes. That's also on the list.

You are 100% correct on those PI tubes. My bad. I didn't even see those little buggers (2 x 12AX7s) back there. I'll have to swap those with some known goods.

I'll also check the bias lights. I'm guessing the lights going out indicate a power amp problem??

When I have had power tubes fail on various amps over the years, they have slowly got crappy sounding + decreased volume over time. Do power amp tubes also just cold cut out. I haven't noticed any changes in sound quality since the partial retube.

Thanks for the info!

[Rick Erickson]

[A crossover is basically a variable transformer so theres really not any components to make it go bad]

A crossover is a combination of individual coils and capacitors, any of which can and do fail, solder contacts can come loose, jacks lose contact etc.. My guess is that your SVT CL amp needs to be thoroughly gone through, cleaned, secured and soldered. There are a number of common problems with these amps. Randomly throwing tubes at it is not a likely or advisable solution.

RE

[Amp Kat]

[A crossover is basically a variable transformer so theres really not any components to make it go bad]

A crossover is a combination of individual coils and capacitors, any of which can and do fail, solder contacts can come loose, jacks lose contact etc.. My guess is that your SVT CL amp needs to be thoroughly gone through, cleaned, secured and soldered. There are a number of common problems with these amps. Randomly throwing tubes at it is not a likely or advisable solution.

RE

Actually it's a combination of coils ,capacitors and resistors and yes they can fail and you should check it or bypass it with another cab and see if it stops cutting out. I do agree that these amps get quite dirty and can vibrate parts loose.. Swapping tubes is a hit or miss and ok for 12AX7's but 6550's are expensive and should be tested. When they short is when you run into problems so getting them out of there before that is a good thing. I've fixed several of these with power tube problems and other problems deeper as well and having the amp gone over is a good idea

[Rick Erickson]

and resistors...

Yeah - those too!

RE