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Fixing my Ampeg SVT - CL Crackling Test Suggestions

#64
check voltage test points, bad tube or component going out/ desoldering bad solder connections from heat. heater connections, heater voltage screen resistors..etc etc you can poke around with chopstick. or maybe a obvious voltage drop will pop up. if you had pair of tubes you could swap 2 at time to see if it is just bad tube. its kinda expensive though to shot gun it and replace all the tubes just find out the problem still exist. maybe its a screen resistor about to pop. and again screen resistor could be getting stressed from a tube going bad as well. so if you were swapping 2 tubes at a time you could do voltage test with old and new tube. if you do isolate a bad tube, its good idea to check the screen resistor on the socket bad tube came from. so if the resistor is about to go it wont go with the new expensive tube in there.
 
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#66
beans-on-toast said:
Go to a hardware store and buy a ¼" hardwood dowel. You can cut it to desired lengths, put one end in a pencil sharpener and use that to poke and tap inside the chassis. You can buy different diameter dowels, I have one turned into a mini baseball bat. Good for tapping on anything microphonic. A wooden drumstick works as well for tapping.


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I like to go to a Chinese restaurant, eat a nice meal with a fork and bring the chop sticks home for tapping my tubes.
 
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#67
Update:

I gave myself another couple weeks to try and figure it out and eventually gave up and took it to a tech. I just got it back last night and he said that there was cracking/bad solder throughout. Not sure how this would have occurred and I thought the QC on the USA models was better - guess I got a bad amp.
 
#68
jmone said:
Update:

I gave myself another couple weeks to try and figure it out and eventually gave up and took it to a tech. I just got it back last night and he said that there was cracking/bad solder throughout. Not sure how this would have occurred and I thought the QC on the USA models was better - guess I got a bad amp.
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Bouncing the amp around during transport can cause that. It takes a toll.

There was a customer service bulletin issued for some SLM revisions that called for re-soldering the power tube sockets. The tube sockets were not mounted with standoffs against the PCB like the later revisions were. This resulted in cracks in the solder joints on those sockets due to mechanical stress.
 
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#69
beans-on-toast said:
Bouncing the amp around during transport can cause that. It takes a toll.

There was a customer service bulletin issued for some SLM revisions that called for re-soldering the power tube sockets. The tube sockets were not mounted with standoffs against the PCB like the later revisions were. This resulted in cracks in the solder joints on those sockets due to mechanical stress.
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I did drive the amp ~8 hours so maybe it was that.

That sounds like that might have been what happened to mine since I was confident it was a power amp issue.
 
#70
jmone said:
I did drive the amp ~8 hours so maybe it was that.

That sounds like that might have been what happened to mine since I was confident it was a power amp issue.
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Normally a long drive would not damage an SVT but possibly if it was bounced around a lot, you never know. One good bump on a hard surface is all it could take. The tech bulletin is attached. But it isn't unusual for any vintage amp to need some maintenance, including reflowing solder joints. You should be fine now.
 

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#71
beans-on-toast said:
Normally a long drive would not damage an SVT but possibly if it was bounced around a lot, you never know. One good bump on a hard surface is all it could take. The tech bulletin is attached. But it isn't unusual for any vintage amp to need some maintenance, including reflowing solder joints. You should be fine now.
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Well mine was made in 2004 so this tech bulletin wouldn't apply - nonetheless maybe it was one "good" bump. I do lug it on a trolley in my parking garage, maybe I nudged something - whelp I'm not sure.

Thanks for the info
 
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#72
jmone said:
Update:

I gave myself another couple weeks to try and figure it out and eventually gave up and took it to a tech. I just got it back last night and he said that there was cracking/bad solder throughout. Not sure how this would have occurred and I thought the QC on the USA models was better - guess I got a bad amp.
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Your amp is a 2004 and it just started crackling a few weeks ago, and that's bad QC? Nah, probably not. They did have some problems dealing with lead free solder when the EU mandate to eliminate lead in solder started in the 90's, but by 2004 those problems were pretty much ancient history.
 
#73
yeah like i said, BAD SOLDER or component going out. some amps fizzle n crackle after being warm for awhile cause you can literally hear the things desolder themselves. likewise do exactly the opposite and crakle cold and stop after warmup, random and annoying. sounds like a basic bad preamp tube crackle but its not and drives you nuts finding it. likewise big old ceramic voltage dropping resistors to power all the opamps mounted flush to the boards. will cook anything near them and desolder anything near them. dont know dont care if peg uses them, but seen plenty of others use it. and they seem to love mounting channel and effect switching diodes right next to them. not only crakle dickly dackle. but switching operations can start randomly or intermittently going hair pulling bad being cooked. yeah no compliant solder aint no myth and extra steps can be taken to assure it dont effect your designs

it can be fixed just takes a patient good tech to go over things

not really though 62 years or so of 6550 applications and ampeg still cant figure out minimal and maximum tube spacing, you dont put fans in tube amps unless you cant figure it out.

oh yes i know people get there little feelings hurt but seriously its not very hard to make a wave soldered amp not cook itself. and no im not trolling the ampeg thread there is plenty of self cooking fenders too. but they fixed those problems and learned lessons with their combos years ago. ampeg still uses same tube spacing and fans. oh well dont get mad at me i didnt design them.

even a classic model T has bad tube spacing, buttt the chassis and big resistors are all vented and no board mounted sockets, and vented sockets, no problem, yes i know board mounted can work even be superior, but there is few basic things to make it work. especially with 80 to 90 watts of heaters just idling. then more heat from operation. its harder to vent sockets with board mounted sockets but possible. dont know what peg uses dont care. see tightly grouped tubes and a fan...nope were done no buy.

hey dont get me wrong ill rock a rented SVT any day, otherwise i wouldnt wanna own one. its been around for awhile, i woulnt mine having one butttt.... no thanks

definatly not trolling the op, ive been through this krap and its frustrating and costly, just saying you didnt do anything wrong, and dont put the amp in a trailer if hauling equipment, and aside from foam or shock mount road cases. yes ive always stuck foam under tube amps for long drives after learning hard way. any amp can have bad solder joints its not just a wave solder thing. but alot of designs just arent up to heavy use/travel with board mounted junk. no its not a generalized bullcrap, they can work. some just dont get it. and blinking lights dont fix stuff.

sure your tech is competent ill say it again, its ok to " shot gun" 20 cent resistors i dont take chances any socket had bad tube change the screen resistors. ampeg seems to think resistors are fuses and they are designed to pop and those 1/4 watt screen resistors pop. specially after new tubes go in lol.
 
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#74
BogeyBass said:
not really though 62 years or so of 6550 applications and ampeg still cant figure out minimal and maximum tube spacing, you dont put fans in tube amps unless you cant figure it out.
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#75
what? lol sorry goshhh just saying...not my fault
this is how you do it...you increase spacing and vent the chassis .... 47 years later still cant figure it out
hiwatt400.png
 
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#76
BogeyBass said:
what? lol sorry goshhh just saying...not my fault
this is how you do it...you increase spacing and vent the chassis .... 47 years later still cant figure it out
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That's a pretty judgmental comment against a product that has stood the test of time don't you think. Your way is not the only successful way no matter what you might believe.
 
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#77
beans-on-toast said:
With no cable inserted, the signal flows through a shunt in the jack. The shunt is a switch, the contacts become oxidized with time. This impedes signal flow. When the instrument cable is connected, the shunt is opened, signal now flows out the preamp out jack, through the cable, into the power amp in. This bypassed the shunt connection. If it corrects the issue, the shunt needs to be cleaned. The solution is to partially insert a plug which will open the shunt and apply deoxit to clean the oxidization. This is a maintenance task that most amps require fom time to time.

I presented this test because it is a possibility and easy to test. You have to sweat the details and check out the possibilities. But because the issue goes away after the amp is on for a while, it appears to be a heat related issue. A bad contact is getting better when metal is heated and expands. An easy thing to check is a bad tube or a loose tube socket contact. There are other possibilities that a tech could check out.
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Sorry to necro this old thread, but I wanted to thank you for fixing my SVT-CL. I've been trying to figure out why I got sound straight into the power amp input, but not from the front 1/4" jacks. With a patch between them, everything is perfect and it sounds like heaven.

I've tried cleaning with Deoxit to no avail so far (with a cable inserted), and I've used a cotton swab to clean it out too. As far as I can tell it looks clean and like-new. Is it possible for the switch to fail entirely, or do I need to take it apart and clean the jack from the inside? Could there be anything else responsible for this kind of behavior?

If I can't get this working, is it safe to just leave an instrument patch between the preamp out/power amp in forever, or until I get it figured out?

Does anyone have the part number for that dual jack if I end up having to replace it entirely?
 
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#78
Vermouth said:
Sorry to necro this old thread, but I wanted to thank you for fixing my SVT-CL. I've been trying to figure out why I got sound straight into the power amp input, but not from the front 1/4" jacks. With a patch between them, everything is perfect and it sounds like heaven.

I've tried cleaning with Deoxit to no avail so far (with a cable inserted), and I've used a cotton swab to clean it out too. As far as I can tell it looks clean and like-new. Is it possible for the switch to fail entirely, or do I need to take it apart and clean the jack from the inside? Could there be anything else responsible for this kind of behavior?

If I can't get this working, is it safe to just leave an instrument patch between the preamp out/power amp in forever, or until I get it figured out?

Does anyone have the part number for that dual jack if I end up having to replace it entirely?
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If it works with a shielded cable inserted, the problem is oxidation on the jack. It might look clean to the eye but the shunt contact is so tiny and it isn’t easy to get the cleaner in there.

If all else fails, it won’t hurt the amp to leave a patch cable in there.
 
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