|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
222.166.2.239
I was reading below about the difficulties of getting non-inductance cathode resistor. I have a related but different problem.
I recently purchased a Sonic Frontier Power 3 amplifier (each with 4 pairs of 6550). The amp use fixed biased circuitry.
Few nights ago, Two of the cathode resistor for the 6550 output tubes (4.7 Ohm in value) suddenly burnt off. Parts Connexion advised to use 1w 'fusible' resistor or 0.5W normal resistor.
I thought the power handling of these resistors are too low.
But on the other hand, I think these resistors are designed to be burnt off so that other components such as the output transformer, power transformer are protected from burning off, should the output tube draws too much current.
So which side of the argument is correct ?
Alan
Follow Ups:
I would NOT substitute those resistors. You didn't say what their power rating is, but even a 1/2W 4.7 Ohm resistor should be able to handle several hundred mA. Do you have a schematic for the amps? You need to determine WHY the resistors burned before you do anything else. Generally speaking, the first thing to do is remove the output tubes and determine whether that amp has normal bias voltages. Next, the tubes need to be individually tested under load. An alternative to that might be to install them in the amp and operate it at reduced line voltage using a Variac. However, that might also reduce bias voltage, so an external bias supply might be required for this test. If you're not a tech and/or don't have access to test equipment, it's time to have a professional evaluate the amp.
--------------------------
Buy Chinese. Bury freedom.
As long as the cathode-tied resistor is of relatively low resistance (~10 ohms or less), you do not need much more than 1/2-watt rated resistors.
The question is, why did the cathode-tied resistors blow in the first place? What is the condition of the screen resistors? And grid stoppers?
That is also my concern.
It almost had to be a tube shorting. Sometimes, a tube shorts intermittently, and clears the internal short in the process. Replace the resistor, and it may work. It may happen again, though. Good idea to mark the suspect tube and watch it for shorting.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: