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PF50T problem

Funkabilly

Funkabilly

Aug 11, 2015
363
408
60
Richmond Ky
#1
Just got my PF50T in this past weekend. When I plugged it in, everything seemed to work fine. I played an hour or so on my SVT212AV (4 ohms), then plugged into my SVT210 (8 ohms). After about an hour of playing on it, the amp started blinking purple and red, and stopped making any sound. I looked at the back, for the first time, and no bias lights were on. I turned off the amp, and when I turned it back on, everything worked, but the red light on the bias indicator stayed on all the way from the range of adjustment. The green light came on and off in the normal range of adjustment. I turned everything off and made sure the tubes were seated good, which I really didn't feel like any were loose, and turned it back on. Everything worked great, and I was able to adjust the bias. I left the amp on for several hours, and everything was fine. Is is possible I have a weak tube? Should I just be glad it works now, or should I have it looked at?
 
#2
Did you make sure to set the impedance switch properly by the speaker out on the amp? An impedance mismatch could have potentially caused issues. It's also important to remember that you cannot run a tube amp without a speaker load attached, or damage could occur. This means that every time you want to change the impedance on the amp, or unplug the speaker for any reason, the amp should be powered off.
 
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#4
akrachanko said:
Did you make sure to set the impedance switch properly by the speaker out on the amp? An impedance mismatch could have potentially caused issues. It's also important to remember that you cannot run a tube amp without a speaker load attached, or damage could occur. This means that every time you want to change the impedance on the amp, or unplug the speaker for any reason, the amp should be powered off.
Click to expand...
the pf50t has a dummy load and can be run safely without a load.
 
#6
Funkabilly said:
Just got my PF50T in this past weekend. When I plugged it in, everything seemed to work fine. I played an hour or so on my SVT212AV (4 ohms), then plugged into my SVT210 (8 ohms). After about an hour of playing on it, the amp started blinking purple and red, and stopped making any sound. I looked at the back, for the first time, and no bias lights were on. I turned off the amp, and when I turned it back on, everything worked, but the red light on the bias indicator stayed on all the way from the range of adjustment. The green light came on and off in the normal range of adjustment. I turned everything off and made sure the tubes were seated good, which I really didn't feel like any were loose, and turned it back on. Everything worked great, and I was able to adjust the bias. I left the amp on for several hours, and everything was fine. Is is possible I have a weak tube? Should I just be glad it works now, or should I have it looked at?
Click to expand...

Is this a new amp? If yes and it continues to have problems, take advantage of the warranty.

Yes your problem could be tube related. New tubes have a high infant mortality rate. Also new tubes may be a bit gassy. Tubes have a component called a getter that is designed to remove gases, but it only works when the tube is hot. As the getter does it's work, the operating point of the tube may shift a bit, so you have have to adjust the bias to compensate. If the vacuum of the tube's glass envelope is good, the getter will eventually clear the remaining gases and the tube will stabilize.
 
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#7
Hence the " burn in" myth
Run vacuum tubes for awhile and getter over time removes contaminates.

I've rarly seen purple glow
And from what I remember is from poorly sealed tubes and is a vacuum leak.

Red plating is from too much grid current.
Or indication of over bias or a bias circuit issue.

Since you had bias issues with the bias lights after the fault. Couldn't possibly say for sure the amp has a bias issue.

But if it did, it's Intermittent. Means sometimes it happens. Sometimes it doesn't.
Meaning possible connections issues effected by thermal cycles. Getting warm cold etc. Solder joints.

Never seen PF50 schematic. Will only guess it's similar op amp comparator like other Ampeg bias circuits. Sensing voltage/ current on the cathode resistors.

If there is a problem I'd assume usual problem with solder joints on tube sockets or cathode resistors. Or some random voltage peak causing latch up on the opamps. More common with fet input opamps
 
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#9
Yes definitely

Something as simple as well seated tube
Can be life saver.

Seen some loosey goosey hanger wangers that made things look bad.
But just loose lol

Resisting my urge to talk about cheap poop sockets. But technically did it anyways lol
 
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#10
BogeyBass said:
Hence the " burn in" myth
Run vacuum tubes for awhile and getter over time removes contaminates.

I've rarly seen purple glow
And from what I remember is from poorly sealed tubes and is a vacuum leak.

Red plating is from too much grid current.
Or indication of over bias or a bias circuit issue.

Since you had bias issues with the bias lights after the fault. Couldn't possibly say for sure the amp has a bias issue.

But if it did, it's Intermittent. Means sometimes it happens. Sometimes it doesn't.
Meaning possible connections issues effected by thermal cycles. Getting warm cold etc. Solder joints.

Never seen PF50 schematic. Will only guess it's similar op amp comparator like other Ampeg bias circuits. Sensing voltage/ current on the cathode resistors.

If there is a problem I'd assume usual problem with solder joints on tube sockets or cathode resistors. Or some random voltage peak causing latch up on the opamps. More common with fet input opamps
Click to expand...
I don't know man, seems like an awful lot of issues with tube based amps that simply don't exist with SMPS and class D amps...

I could use all the same silly words you use to describe SMPS here... except that SMPS/class D don't glow and sputter or red plate or need bias, etc.
 
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#11
agedhorse said:
I don't know man, seems like an awful lot of issues with tube based amps that simply don't exist with SMPS and class D amps...

I could use all the same silly words you use to describe SMPS here... except that SMPS/class D don't glow and sputter or red plate or need bias, etc.
Click to expand...


Opamps and Blinky winky lights don't belong in tube amps.

Besides it's a Ampeg. So be happy it works

Smps and class d definitely don't belong in a bass amp. Either
Most designs include add copy or tube pres to emulate these blue glow wonders.
And still try to convince people they sound tubey.

Tube amps are still a mythical magical standard that all others are based on.

Would I personally wave solder or use cheap sockets in a tube amp. No
I'd just base the design on well established components, from well established suppliers. Some have been successful making these parts since the 1940s. And likewise there is well over 100 plus years of very successful tube amplifier designs.

Rack mounts , biamps, 50 billion worthless bands of EQs. And numerous other wonderful bass amp fads have thankfully died.

But tube amps. Will never die.
And still be the standard and fantasy that live on in musicians.

If you do make it into the Rock n Roll hall of fame before your liver explodes lol.
I'm pretty sure good 70 to 80% of the current members have been onstage or made their fame with a Ampeg tube amp.
90 percent got there with a tube amp
 
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#13
Not really dude. You still think class d and regulated supplies have any value in a bass amp.

And pretty aware of how much musicians love tube amps.

Likewise never wasted any time trying make tube amps with mini power tubes for TV sets lol

Likewise owned KT88 amplifiers that successful operate these " new" " bad tubes" without failure

Ampeg sold, Mesa Boogie bass amps discontinued. Guess the Japanese will show you how it's done.

All you need is 2x or 4x 6L6 , 6550 or KT88
Just operate at the data sheet recommendation. Which includes understanding what topology does and doesn't support max screen values
 
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#16
InhumanResource said:
I gotta admire the purism... but the last thing I want to do after loading up a bunch of PA gear (That's what I get for buying a truck) is head back to the garage and shlep a hundred pound tube head every time I get a job.
Click to expand...

Me too. To me, tube amps are great....in the studio. But give me a well designed and reliable class d amp any day for live work.
Most people in an audience wouldn't know the difference anyway.
 
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#20
Funkabilly said:
After about an hour of playing on it, the amp started blinking purple and red, and stopped making any sound.
Click to expand...

The OP is referring to the status light at the front of the amp: Red = Standby, Purple = On. It doesn't sound like those colors were emanating from the tubes. Also, These amps do not need a dummy load, a selling point for some folks. Glad to hear it's worked itself out.
 

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