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why the hell do i keep blowing my speakers

#61
Here's a question I don't think anyone has asked yet: When you play with your band, is your cabinet on the floor behind you blasting the backs of your legs? If so, you might actually be much louder than you think, because you're the only person in the room who can't hear you. If so, you need to either get the cab up on top of something (like a stand) closer to ear level, or put it farther away and angled so it's pointing at your head.
 
#62
Thanks everyone. This SVT is like a precision sports car. I need to maintain it like one. I'm already pretty close to the price of a new one. But I've learned a lot. #1 Get the Guitar Center warranty. #2 Read the manual before you touch it. #3 Don't trust any tech. #4 Talkbass is an awesome community and I really appreciate everyone's time here. And not one person belittled me. :)
 
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#64
RavenTenderfoot said:
Thanks everyone. This SVT is like a precision sports car. I need to maintain it like one. I'm already pretty close to the price of a new one. But I've learned a lot. #1 Get the Guitar Center warranty. #2 Read the manual before you touch it. #3 Don't trust any tech. #4 Talkbass is an awesome community and I really appreciate everyone's time here. And not one person belittled me. :)
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Except that with a little bit of care and common sense, they tend to be quite reliable. Your experience is IMO the exception to the rule.
 
#66
RavenTenderfoot said:
I did buy it used at Guitar Center, and it did hum. Who knows how abused it might have been. Apparently, they are easy to abuse. Just by hooking it up to the wrong cab is all it takes.
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Not in my experience. It (generally) takes some pretty stupid decisions to damage a transformer. Not saying it's not possible, but don't believe much of what you read on the internet... those "experts" usually don't have much credibility to back up their statements.
 
#67
i never buy used gear at a store. go to craigslist, or talkbass, or whatever classifieds, and buy from an individual, but go in prepared and don't be afraid to walk. my SVTs ( magnavox, ) were all from CL in sf bay area, loved but never babied, performed like tanks with just the occasional pro tune up. if they weren't so frickin' big and heavy i might have kept one. they are rugged and durable with just a little care.
 
#68
RavenTenderfoot said:
Is there any audible way to tell if the output transformer is bad?
I see they run about $300 bucks for the Heyboer and $307 for an Ampeg. The Heyboer is USA made. No idea about the Ampeg.
If the output transformer is bad and a new one takes a few weeks to arrive, will recording with the amp destroy more than just the already bad output transformer? I'm expecting a "hell ya!" Can I get a "hell ya?"
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Yes a few simple tests will tell if a output transformer is bad.

But it's is most likely not a transformer problem. And is the most unlikely issue.
Pretty much never ever see bad output transformers. It happens...but highly unlikely

The amp has gone into protection mode from excessive current draw. And you have bias lights not working properly.

This is a bias issue.

The amp had a hum issue as well.
And as a shotgun repair attempt all the tubes have now been replaced.

So we have the previous problem...hum
Which wasn't fixed. And a new problem.
A new tube set. Which most likely wasn't measured and balanced properly for bias current.

You don't bias 6 output tubes " by ear"
It's a current sharing nightmare with 6 tubes. They all get measured for current draw. And then you balance each side by mathematically calculating which tubes will closely average the same current draw. Then you bias the amp to the proper bias current with the bias detection circuit in the amp. According to the manufacturer. Not by "ear" how do you " hear" current draw. Answer is you don't.


When bias lights don't work proper with new tubes. It's because you can't just buy tubes and plop them in there.
Most likely what happened. Tech just plopped them in there. Has no idea what current draw is of each tube. And never balanced the set. And then overbiased the living hell out of it " by ear"

Likewise no bias lights situation. Most likely is the usual problems with this circuit. Cathode resistors have been cooked and drifted in resistance. Circuit won't properly work with incorrect value resistors.

Or one or 2 screen resistors haven't popped yet. But likewise have been cooked and drifted. And pretty close to popping.

Pretty normal for a amp that hasnt been biased correctly. And had tubes just tossed in their. And one or 2 sockets/resistors gets cooked from whatever tube draws the most current.

Of course it could be many other things and a tech needs to check and measure all cathode and screen resistors for drift.

The original hum situation could just been a typical 12au7 or 12ax7 on the power amp board is on its way out. That's a easy change. But If you replace those tubes the amp also needs rebalancing or the DC offset checked. Pretty straight forward SVT phase inverter checks.

Then again there really is no guessing. A amp gets proper trouble shooting to find
" hum" by a few simple tests. And can save you a ton of money by not assuming it's capacitors or tubes. On a newer amp. I can almost guarantee a hum problem is usually never the caps. A 50 year old amp... probably. Newer amp. Usually not.

I wouldn't buy tubes or caps till the actual problem was found. Which saves about 200 to 400 dollars worth of shotgun fixing. That doesn't fix the problem.
 
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#69
Most likely , again a guess based on experience with CL SVTs
The bias light circuit uses a pretty basic opamp comparator circuit to detect correct bias levels. One voltage is preset for the comparator and it compares this to voltage on the cathode resistors. Over time the cathode resistors drift from heat and use. And the circuit doesn't work correctly. You usually replace the cathode resistors. And clean and touch up the garbage solder on the board mounted sockets. And the amp will properly bias again.
Most likely this was already happening when you originally bought the amp.
And a new tube set and a " by ear" overbiased tube set. Really started peaving off the bad resistors already there.
I've even seen the bias LEDs replaced cause " they where bad" but in reality they tend to be just fine.
I'm not about " shotgun" repairs. But it's such a pain in the butt to disassemble and reassemble a CL power board. I really have no problem replacing all the cathode resistors and all the screen resistors. When only one or two have actually measured drifting.
If 2 are bad. There is just 4 more waiting in line to go.
Another issue is the tube sockets solder connections are fine. But the pins are loose or spread out in the socket. And also the typical whirlwind twisting method guys use to remove tubes just bends them open more. It's incredible common to have a bad tube or tube about to go bad. And after a new set goes in. All sorts of new problems come up from the sockets getting stressed from replacement or turd solder connections finally get broken from the removal/ insertion
 
#76
It's in a reputable shop now. I assumed I could just change them myself, but after reading Transylvaniae's post, maybe it's always time for a tune up with new tubes. I recall people saying SVT needs new tubes every 2 years? Is that correct? I'm worse about changing tubes than I am with changing bass strings!
 
#77
The SVT needs new tubes when it needs new tubes, not based on some calendar time period. Could be 1 year, 2 years, 5 years... it depends.
 
#78
RavenTenderfoot said:
It's in a reputable shop now. I assumed I could just change them myself, but after reading Transylvaniae's post, maybe it's always time for a tune up with new tubes. I recall people saying SVT needs new tubes every 2 years? Is that correct? I'm worse about changing tubes than I am with changing bass strings!
Click to expand...
Tubes can last 1 to 20 or more years.
It's subjective by operation hours and operation environment.
In general most early American tubes are considered to have 3000 hours of operation life.
Then again many of them go for 10 or more years.
Problem is if a tube is subjected to high heat or high vibration. It's life can be shortened.
And likewise if operated below max specifications can have a longer life. Or it's wise to assume a tube operated at or above max specifications. Lifetime will be reduced.
Such as plate voltage and plate current.

Problem with most musical instrument amps. Many are operated at max voltage or above. And likewise for class A/B bias current can be high or drift higher.
And the tubes and plate are subjected to alot of vibration. Which can reduce tube life

For the most part. Most guys don't change tubes. Until you get crakles or dull sounds or a microphonic tube develops and is changed. Or with a SVT. Fault protection kicks in or a screen resistor blows or any various odd symptoms pop up.

For the most part common musical pre tubes or power tubes are rated for 3000 hrs
And many die way before that and many go for 6000 to 10,000 hours.

Military or communication tubes. We're often ran year round 24 hrs a day. Especially communication relay towers went 24/7 year round. So military class tubes were required to have a operation life of 1 year or basically a minimum of 8760 hrs compared to basic civilian tubes rated at 3000 hrs. Basically 8760 hours would be constant operation 24 hrs a day for 365 days
 
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#79
I have "modern" preamp tubes that I have tested that have well over 10,000 hours and still meet the design spec for the circuits they are used in.

I do not recommend changing tubes "just because"... you would be amazed at the number of issues I see from folks changing tubes and doing something kind of dumb or careless. Also, the number of defective new tubes is surprisingly high, and installing defective tubes in an amp can under some circumstances cause damage.
 
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#80
Preamp tubes can go a long, long time, depending on the quality of the tube. I've mentioned before elsewhere on this forum that I have tubes that are over 90 years old and still work fine. It's not uncommon for 6C4, 12AU7, T7, X7 and Y7 family to last easily 50 years with normal use, provided they aren't "boutique tubes" that are already on the way out when sold new.
 
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