Hello. I purchased a new LA-610 last month. Over the last week I began to experience extreme distortion with the unit. I always let it warm up. With my bass guitar through the HI-Z input, the signal would sound normal for a few seconds and then it jumped radically in level and distortion. Additionally the High and Low EQ selector switches had no effect on tone. I suspected a bad tube so I began swapping tubes one by one. The problems seemed to stop when the V4 12AT7 was swapped. When swapping tubes, I actually started with the EL84, played for about 20 seconds, determined the EL84 was not the problem, and returned the stock EL84 to its position. QUESTION: Does the unit need to be re-biased if the EL84 was swapped for about 20 seconds? Thanks.
LA-610 Mk II Tube Question
- Thread starter Eric H
- Start date
Geir
Shareholder
Hi,
No you don't need to re-biased the tube the bias is set for. But given the issues you are having I would check factory set bias just to see if they had a bad day at work.
You should return the unit and ask for a new one if you only have had it for a month, new from the shop. Or at least get it serviced to rule out that there is nothing else wrong than a bad tube.
If you have the skill set for repairs you should start with the power supply and check that all circuits are working as designed from power to output using multimeter and scope. It might be more than a bad tube or wrong bias, resulting in tubes burning up. Preamp tubes should last for years if everything is in order. But if the current feeding the bias adjustment is faulty, it will kill tubes. Might look fine when you check it for a few seconds, but during some hours there might be burst or dips from a faulty component you didn't catch while adjusting bias.