tweed tremolux sounds bad with depth control over 1/2

[mort]

Hey guys, this is happening on an amp I built and shipped to a friend so I do not have access to the amp (it's in West Virginia). Guy messaged me up today and sent me this video of its behavior. I told him to try swapping out the tremolo tube and also the PI tube but haven't heard back from him yet. Any thoughts on what to look for? He says once the depth control is at half or less it sounds fine. He's had it about a year or less. It already had to get sent back once for a shorted B+ winding in the PT. Never found a cause for the failure and I just replaced the PT and added a B+ fuse. (he may have inserted a recto tube incorrectly with a busted guide pin but that is unconfirmed). I don't get the idea that the two issues are related but I thought it worth mentioning. He also said the power light is flickering a little.


It's this schematic but with a 5u4gb recto: http://www.thevintagesound.com/ffg/s...e9-a_schem.gif

And the video of the amp behavior:

[mort]

Never mind. It was a tube. It's all better now

[mort]

Holy crap check this out. So after putting in a fresh tube and everything going back to normal he sends me another message saying that he figured out why the power light was blinking, that the outlet is loose and he wiggled the plug and now it's not blinking anymore. He had also reported the power light as blinking just before the PT blew. I said DUDE, that's the whole problem right there! That's more than likely what took out your PT and damaged that tremolo tube!

It never did add up before about the PT blowing. I didn't find a single issue with the amp or tubes and Mercury had done a tear down of the PT and said the problem did not generate from inside the part (but they graciously honored the warranty anyway as a 1 time courtesy). A stinkin' OUTLET. That's a lesson learned and an important thing to consider when troubleshooting.

[Enzo]

I used to train techs in a different industry (coin arcade equipment), and a typical day would be morning classwork, my lecture/demonstration, going over schematics, analyzing the mechanical stuff, discussing troubleshooting procedures. I then sent them to lunch and set up machines with problems for them to solve when they came back. Pinball machine, for example. I might disable one flipper, or make a row of lights not work. Maybe some of the score displays were missing digits. But one thing I ALWAYS did was make the machine dead at the start. Zero sign of life. I might put a blown fuse in the main holder, or a wire off a power switch, a transformer Molex unplugged. But dead as a doornail to start.

In the shop we used drop boxes for power - a square outlet strip sort of thing. A pair of your basic duplex outlets like on your wall, in a square conduit box, and a power cord trailing off to some wall outlet or overhead outlet. Each work station had a drop box on the floor with the game plugged into one outlet, leaving three outlets for a work light, maybe soldering iron, whatever.

Now I am a sneaky bastard. Each team of two guys would return to find a station with an open pinball machine, I had the glass off and the playfield raised like a car hood, and a clamp type work light illuminating the innards. I watched to see who applied the troubleshooting methods, and who just guessed. A dead machine, some guys went right to the drawer for a new fuse, others started checking powr switches, wires, etc. I'd have a guy tell me he knew the outlet was powered because the work light was lit, and it was plugged in next to the pinball's plug. perhaps you see this one coming. I had disassembled the drop box, and disconnected one of the short jumper wires between the two duplex outlets. So the left pair were hot, but the right pair were not. Plugged the work light into a left one and the pinball into the right. Very few guys actually tested the outlet for power until they had gone through the machine looking for voltage. One guy even said he was sure the machine must have a bad power cord, because he "knew" the outlet was hot, but no voltage arrived in the machine.

I was not unfair, I had encountered exactly that problem in a field repair call. But it was my favorite "problem".

The point of that little first step in the lesson was that the problem with a unit isn;t always the unit itself. A lesson now also learned in the Mountain State.

[Tom Phillips]

...he figured out why the power light was blinking, that the outlet is loose and he wiggled the plug and now it's not blinking anymore. He had also reported the power light as blinking just before the PT blew. I said DUDE, that's the whole problem right there! That's more than likely what took out your PT and damaged that tremolo tube!...

What is your line of thinking regarding how an intermittent line voltage feed would damage a PT or a tremolo tube?

[Chuck H]

Agree! I don't claim to know all the mechanisms that MAY cause a failure in any given component. Perhaps repeated spontaneous HV with only partial filament voltage!?! Seems unlikely to me based on my own clumsy shenanigans. But it is the only anomalous circumstance identified by mort.

[mort]

What is your line of thinking regarding how an intermittent line voltage feed would damage a PT or a tremolo tube?

If it's enough to make the bulb cut in and out then you're gonna get a) repeated inrush current b)low voltage/high amp draw, both of which can cause current higher than spec through the PT, and the B+ windings being of the lowest current rating would be the first to be affected in this scenario. Of course it's a guess since I can't have been there to witness or prove it.

It would be not unlike a control wire barely making contact with ground (high resistive short). This can cause a higher current draw through a transfomer but not necessarily enough to pop a fuse. Let's say a control circuit has a 3a fuse and a fault occurs that causes 5a of current to pull through. That fuse isn't gonna blow right away. It could stay closed long enough to eventually short the transformer. A quickly intermittent power supply or loose connection could cause similar conditions, no?

[mort]

Similarly, in the hvac field, if a compressor gets turned on and off several times in a row it will open a thermal switch built into the windings because of the overcurrent that is taking place. And it can overheat pretty quickly, within seconds. I've witnessed it happening due to a connection that's burning up or a contactor that's chattering in and out. Same principle but on a more delicate scale inside the amp, with the B+ windings being the most delicate link in the chain.

[mort]

I'd have a guy tell me he knew the outlet was powered because the work light was lit, and it wasugged in next to the pinball's plug. ......... Very few guys actually tested the outlet for power until they had gone through the machine looking for voltage............... One guy even said he was sure the machine must have a bad power cord, because he "knew" the outlet was hot, but no voltage arrived in the machine.

I'm sort of in a position of teaching and mentoring the hvac stuff. I preach to the younger guys all the time to not even try to guess what's wrong with a machine, but to just follow the voltage from A to B to F, G and beyond and let the machine tell YOU what's wrong with it. Now of course that takes some getting familiar with how each part works etc.

Low voltage problems seem to be the toughest for people to learn to troubleshoot. It took me a while to figure out that the best tool for locating a low voltage short is a clamp on amp meter. Techs don't usually associate an amp meter with a control circuit, they just think in terms of voltage. But think about it, if the control circuit is popping a fuse then you can put your amp meter on the 24v supply with the thermostat not calling for anything. It should only be pulling a small amount of current to power the thermostat, let's say .3a. Then you call for the blower relay only and it ticks up another .3 amps or so. Then you call for the cooling to come on and all the sudden your current jumps to 6a or higher for example. Then you know your short/problem is somewhere on the condenser circuit. PLus, the moment you see high current you can kill power to the machine and prevent the murder of fuse after fuse after fuse.

[nosaj]

I used to train techs in a different industry (coin arcade equipment), and a typical day would be morning classwork, my lecture/demonstration, going over schematics, analyzing the mechanical stuff, discussing troubleshooting procedures. I then sent them to lunch and set up machines with problems for them to solve when they came back. Pinball machine, for example. I might disable one flipper, or make a row of lights not work. Maybe some of the score displays were missing digits. But one thing I ALWAYS did was make the machine dead at the start. Zero sign of life. I might put a blown fuse in the main holder, or a wire off a power switch, a transformer Molex unplugged. But dead as a doornail to start.

In the shop we used drop boxes for power - a square outlet strip sort of thing. A pair of your basic duplex outlets like on your wall, in a square conduit box, and a power cord trailing off to some wall outlet or overhead outlet. Each work station had a drop box on the floor with the game plugged into one outlet, leaving three outlets for a work light, maybe soldering iron, whatever.

Now I am a sneaky bastard. Each team of two guys would return to find a station with an open pinball machine, I had the glass off and the playfield raised like a car hood, and a clamp type work light illuminating the innards. I watched to see who applied the troubleshooting methods, and who just guessed. A dead machine, some guys went right to the drawer for a new fuse, others started checking powr switches, wires, etc. I'd have a guy tell me he knew the outlet was powered because the work light was lit, and it was plugged in next to the pinball's plug. perhaps you see this one coming. I had disassembled the drop box, and disconnected one of the short jumper wires between the two duplex outlets. So the left pair were hot, but the right pair were not. Plugged the work light into a left one and the pinball into the right. Very few guys actually tested the outlet for power until they had gone through the machine looking for voltage. One guy even said he was sure the machine must have a bad power cord, because he "knew" the outlet was hot, but no voltage arrived in the machine.

I was not unfair, I had encountered exactly that problem in a field repair call. But it was my favorite "problem".

The point of that little first step in the lesson was that the problem with a unit isn;t always the unit itself. A lesson now also learned in the Mountain State.

For my first computer job (1996) They gave me a non working computer only ptoblem with it was the 220/120 switch on the power supply. Took me about five minutes to find it, but you can guarantee I was never tripped up with that issue again and I did see it later down the road on customer machines. It was always fun to watch other new techs go through their processes to get there.

nosaj

[Tom Phillips]

Mort,

I totally get the issues with certain motors subjected to multiple sequential starts or running on low voltage. However I believe that a PT, such as those used in guitar amps, should be able to survive the situation your customer described without damage. That is if that PT is properly designed for the application.

Respectfully,
Tom

Edit: I note that the light issue shown in the video was very minor. It was just a slight dimming of the light. Not even a real blinking and it wasn't happening frequently.
The transformer & tremolo tube issues may be just caused by "stuff happens." I have one customer who had three PTs go bad in three different amps within a relatively short span of time. All were quite different amps (A 50W Marshall, a 5E3 Deluxe clone & a Ceratone). No correlation was ever found.