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(First of all, I'm no electronic technician. In fact, I'm no kind of technician, although I can change the oil in my car and change the tubes in my preamp.)
Things got weird today when I changed out all the tubes in my preamp. After the tube swap, I fired up my system up and everything seemed copasetic. I left my system on, planning to come back in 20 mins to listen to after it warmed up,
I returned about 30 minutes later and I heard a 'putt-putt' coming from the speakers. I decided to check that the tubes were seated properly, As I started to do so, moving from tube to tube, the noise got either loud or soft. Putting my hand over the regulator or one of the 12AX7s caused the noise to get louder and moving it to another spot caused the noise to stop.
I'm assuming one of the tubes is bad, since this seems logical.
What's up with this and what's the cure?
Thx
GP
Follow Ups:
Hi, Last year I suddenly started hearing a "putt putt" sound out of my speakers. I tried all sorts of things trying to get it to stop, replaced tubes moved wires etc, then one day I was describing the sound to a co-worker (non audiophile) and he suggested I move my router around to see if that could be it. Well it worked!! The putt putt sound went away!!
A few months later it started again so I moved the router around (just angled it around in the same spot) and it stopped again.
Tish
Yup. One of those things you'd never suspect. The darn cable box.
When I got AT&T U-Verse I had the putt-putt in the JBL computer speakers.
When I set the thing up I thought I disabled the wireless feature in favor of direct wire but the service guy that came said the wireless feature is always active unless you go to a website to turn it off or on.
Sure enough, when I turn the wireless back on, the computer speakers putt-putt.
Garibaldi,
I responded to your thread on Agon.
The pinout on the 5751 and 5755 are not the same. Check my responses to your Agon posted thread.
No joy. I can't get the motorboating to stop. Is it possible (if it's not a coincidence) that I trashed something when I installed the new tubes?
I seriously doubt you trashed anything as a direct result of your actions. Motorboating is indicative of some component failure that was just waiting to happen and it just happened to picked now. Was the last time you shut off your car the reason it won't start now? So, maybe it would not have happened if you'd not swapped tubes, but it was gonna happen sooner or later. Again, sorry for your trouble, but it may be time to seek competent repair services. If you'll let folks here know where you are they might be able to point you to a good tech.
I live in Western Massachusetts, near Springfield.
Thanks for this suggestion.
GP
GP
The noise you heard when touching the tube can be the capacitance of your body which is normal depending on where the tube is.
Try putting the original tubes back in and see what happens.Is this an Audio Research preamp by chance? I have seen circuits thru the years that were tube brand dependent..It wasn't often but on the 3.58mc color oscillator on the Zenith 21 color inch set you had to use the Zenith 6Gh8A or the Sylvania or color oscillator would not lock on.This is a rare occasion but it does happen and depending on what you have a for preamp you may have an issue where the regulator is responding to even a filament change or a change in B+ and it's going into motorboating.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Edits: 02/06/15
Could be a bad tube. Swap the old ones back in, one at a time to find out which one.
Having said that, it is also a pretty good bet that you have one or more tubes sockets that need cleaning or where one doesn't grip the tube pins tightly. This sort of problem tends to pop up at a tube change because the mating surfaces have been disturbed.
Could be the tube, or it could be the socket. Put the old tube back in and see of the problem goes away.
The problem can be how the tube pins seat in the socket, the socket could be dirty or loose and not gripping the pin. The other thing could be the solder joints on the bottom of the socket, one could have broken when you pulled the tube out.
I reinstalled the original tubes one at a time and checked to see if the noise went away. Nope. I cleaned the pins and the sockets, made sure they were seated well.
A couple of pieces of info: The noise is in both channels equally. It gets louder with the volume control. The putt-putt is a constant and a regular beat. Nothing else has changed in the unit that I know of.
Thx,
GP
GP
what kind of preamp is this? You are going into motorboating because the regulator is responding to a voltage change and it's keeping the preamp in a semi-shutdown mode.
"If it measures good and sounds bad, it is bad; if it measures bad and sounds good, you have measured the wrong thing."
- Daniel R. von Recklinghausen
Michael,
The preamp is an Aikido-based unit that was built for me about eight years ago. I returned the original tubes to their initial positions and the motorboating continued.
Most likely your problem is coincidental to your tube change. What you have is something in your power supply, most likely your B+ supply, is on the fritz. Could be a bad connection, a bad resistor, a bad cap, a bad transformer.
I'm no kind of technician either, but this putt-putt you're describing sounds like what a tech might refer to as motorboating. If so, could be a blown resistor or maybe a bad cap? Maybe some of the smart people here like Mr. Samra can chime in with some help. Sorry for your trouble. I know how bummed I feel when one my amps gives me issues.
Edits: 02/06/15
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