• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

One channel has less glow

yan6

Member
2008-11-23 2:27 am
Hi there, I have a yaqin MC-10l. I just changed tubes to some used ones a friend gave me. After re-setting the bias on both channels the same; I noticed one side has much less glow on the two tubes. I'm not sure yet if the audio is stronger in the one channel, if it is its not that noticeable. Any thoughts, is this common?
 
Hi there, I have a yaqin MC-10l. I just changed tubes to some used ones a friend gave me. After re-setting the bias on both channels the same; I noticed one side has much less glow on the two tubes. I'm not sure yet if the audio is stronger in the one channel, if it is its not that noticeable. Any thoughts, is this common?

I assume you mean heater glow? This is common. I have a couple of projects that use multiple 807s, 6AQ5s, 6BQ7s, 6BQ6s. Some of these have heaters that are a definite red, yet others a brighter, almost red-orange glow. So long as the heater voltage and current are within spec, and they bias up properly, then the only difference is aesthetic.
 
Snap! Same Amp, Same problem. I think it is due to heater drop as all my latest 6CL6 were uniformly bright but after a time some glowed less than others. I noticed that the heater had physically dropped down inside the cathode on the dimmer ones, the cathode providing more shielding from the heaters glow. I checked the heater volts on all four and all are correct.
Les
 
You will need a multimeter, preferably a digital one, set to measure AC Volts.
Connect it as per the attached photo, you can do it on any tube holder though I have a special extender box so I can measure the heater voltage with the tube plugged in. BE CAREFUL ! ! You will see that 450Volts lurk on other pins!
Avoid :eek:
Les
 

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