Rerurn to Romy the Cat's Site

Paul S wrote:

After a few minutes, I checked the amps with a (Fluke 189) DMM, just for drill. Voltage was set down to 175, but current was about 450 mA.  Dialing down the pots, I could not get  the current below 390 mA, even though the pots still turn freely.

Actually when you hit the end it will not turn freely. It will still tune but you will feel that it is wand and that something is flipping inside. With a new 6C33C it is normal to have excessive current what the tube is too fresh. Burn is a bit longer a d the initial rise of current will be stop. I would lower the plate voltage to 130-150V and let the tube to burn at lover currant, let say 300ma that would make 45W plate dissipation. After 10-12 hours your tube in this mode will not push more then let say 230mA. Then set the cruse plate voltage and play only with current. Again, it is normal behavior for this tube. One of the reasons why Lamm I presume charges $1.000.000 per tube that he sells is because he pre-burns his 6C33C – a slightly aged 6C33C has no effect of current rise during start up. BTW, I have written about it before.

What is interesting to note that observed this behavior only with 6C33C in ML2.  Milq with it’s fixed bias has no such an effect. I did not look I not ML2 and I do not know what kind out stage biasing Lamm uses. The plate is regulated for sure but with biasing it is not clear. Since that 6C33C behaves in my amp and in ML2 differently I might presume that ML2 does not use a straight fix biasing. 

Rerurn to Romy the Cat's Site