Can someone tell me if it damages the Output Power Transformer to power the Amp "ON" with NO speaker plugged in to the amp? I'm wondering if that could be one reason for so many power transformer failures.
Posted 15 July 2013 - 05:38 PM
You should never ever switch on a valve amp without the speaker plugged in!!
i know that.... but WHY??? My question is.... "does it actuacally damage the Output Power Transformer if the amp is powered on with NO speaker hooked up"? Or, is that only bad for the tubes? Anyone ???
Posted 16 July 2013 - 07:28 AM
If you leave the standby switch off, then you should be fine. It would still be dangerous though, as turning the standby switch to on can be easily done by accident.
I use to do this a lot with a previous band and a SV MKii Head. We used in-ears, so I didn't need the cab at practice. I would just use the head on standby. However, I kept a small cheap 80 watt home theater speaker at the practice space that I would hook to the head, just in case i hit the standby switch.
Posted 16 July 2013 - 06:37 PM
Power transformers and output transformers are two different things. The problem many of us had were due to power transformers, which are the transformers in the main power supply that convert the 120V (or 220V) input voltage to the various supply voltages used in the amp's circuitry. These are the bigger, heavier transformers and endure the most stress.
The output transformers sit near the end of the signal path between the power amp tubes and the speaker and are used mainly to convert the output impedance of the amp circuit to match the impedance of the speaker.
I'm no amp expert, but you can think of an analogy of a sneeze. Unplugging your speaker and playing through your amp is like sneezing while plugging your nose and shutting your mouth. All that energy has to be dissipated. The sneeze must be released or your head would explode! In an amp, the amplified power must be dissipated to the speaker, where the energy is converted to physical motion, otherwise the amp's circuitry would blow at the weakest link, wherever it may be.
I doubt that just turning your amp on would cause a problem, I believe it would be a problem only while playing and cranking up the volume to get the circuitry working. In other words, when there is sufficient energy to blow the weakest link.
Again, just my thoughts as a hobbyist. Others can correct me if need be.
Posted 21 July 2013 - 08:10 PM
Thank you for a respectful and intellegent answer, RP. Exactly what I needed to know. We all have to start some where, right? Unbelievebly.... I was given a DT-50 that has an issue (hopefully only 1 or 2). I installed a new pair of EL34's and they both began to redplate (glowing plates) within about a minute after switching from Class A power to Class A/B power.
I found a blown F2 fuse and replaced it. I had and old pair of EL34's that I put in it when I got it home, and it appeared to be working good on all settings. So, I thought..... "hummmm, maybe I got lucky???". So... I ordered new tubes, installed them and they both began to redplate within a minute. So..... I shut it down and let it cool, put the old tubes back in.... and now it works again, without redplating??????????????????????
I'm hoping someone out there has some knowledge in this area and might point me in the right direction. I'm suspecting maybe a cap in the bias section (if this thing has one?). Anyway, any help would be greatly appreciated.
I feel bad Toneman. I just wondered what that button did.... now I know.
Posted 04 August 2013 - 02:43 PM
My transformer blew in early March. I took it in. Then got the tech 059 bulletin email and that was done while it was there. Got it back about 2 weeks ago. In class A pentode mode there is a rattling sound coming from the speaker when I resonate notes. Took it back. Hopefully will get it back in 3 months or so. I bought a 2nd DT50 at the time it blew.
So... I will wait and see.
Good news is the amp was 2 months out of warranty and Line6 honored all repairs.