I have an Allied 333 tube receiver (which is a Pioneer SX-34 clone) that I got off the bay a few months ago. It has hum/buzz that increases with volume, but at max volume, it disappears somewhat and there is just a low level hiss. I have replaced all caps in the input and amp sections (did not mess with the radio as I do not use it). I also replaced the two 12ax7 input as well as the four 6bm8 tubes and sockets. After all this, I still have an audible hum on both channels. I have resoldererd most of the joints and replaced the rectifier diodes.....still hums!!! The only thing that takes away the hum is by grounding the grids to the chassis ground. After grounding the grids the hum is gone from the speakers and I can hear a buzz coming from the power transformer. I have also replaced most of the resistors on preamp and amp sections as well as the mono/stereo and tape record slide switches. Adjusting the two hum pots does make a small difference, but it is a very small difference. I am at my wits end with this! Any input would be much appreciated.
No, the amp still has the original two prong cord. I have read mixed reviews about swapping it out with the three prong some say it can make hum worse so I left it as is.
Try reversing the plug in the AC socket. If that makes a difference, you'll need to try reversing each AC plug of your system for lowest noise.
Do this with no other connections to each component than the power cords, and an AC DVM connected from each chassis to the power line ground.
Select the position with minimum noise for each component. Then connect everything back together.
Try to change Your power cord to 3 wires cord. Two active wires conect to the same points, like old cord, and 3d wire /maybe yellow-green/ connect to main ground near to PS or metal ground screw /that is connected to ground of PS/ and another end connect to ground point of Your plug. /Don't mistake....You can burn amp....First connect side of cord to amp, and than to new plug.
I tried turning the socket over, but no change. I also have tried it on multiple outlets and no change. I have it on my bench currently hooked to test speakers and nothing else. The receiver also hums with or without an input connected. I am using an iPod connected to the aux hi input.
Ok, then it's likely an internal problem, such as bad electrolytic capacitors, bad solder joints, etc.
Try substituting a different volume control, or wiring a pair of resistors in place of each section.
Is the unit very corroded looking?
Last edited:
When you say wire a pair of resistors in place of each section, do you mean in place of the hum pots?
I notice when I ground the tape/record switch to chassis ground there is much improvement.
Last edited:
In an older unit, the problem can be almost anything corroded.
Try to use the process of elimination.
You could try replacing the volume pot with a pair of resistors per channel if you suspect that.
No, the volume control.
If there are hum pots, try adjusting them. You should be able to change the hum at least a little.
If you are grounding the signal terminal to chassis and cutting the hum, that means the problem is before that point.
I may try that, but I will lose the loudness tap and also the balance is built into the pot as well. I is a very weird pot that I cannot find anywhere else.
Yes, the problem is then before that point. Be careful not to ground a circuit point with high voltage.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.