Preamp Deal of the Century

abe:

the yamamoto is a 45 tube amp and it is tube rectified. i have a few 80 tubes that i can roll to see if that reduces the hum. i emailed kevin covi and he seems to believe the hum is caused by the 101D tube as when i switch the amp to mute, the hum disappears.

Kgturner,

Let us know what is kevin Covi's recommendation.

here is what kevin covi had to say:

"The hum is coming from the 101D's, and unfortunately hum (and microphonics) are all-too-common attributes of directly-heated triodes."

i sent him a picture of my setup to which he stated:

"I can see right away that the Cab power supply is too close to the preamp, as are the components sitting on top. The DHT's are quite sensitive to external fields so it is essential to keep them far away from any equipment that contains a power supply. The output transformers are also susceptible in this way. The extremely high sensitivity of your speakers just compounds the problem. You also might try building electrostatic shields around the 101D's. As an experiment try placing an empty tin can over each tube to see if the hum goes away. Or maybe aluminum foil. Either way make sure the shields touch the chassis to shunt the noise to ground."

abe:

the yamamoto is a 45 tube amp and it is tube rectified. i have a few 80 tubes that i can roll to see if that reduces the hum. i emailed kevin covi and he seems to believe the hum is caused by the 101D tube as when i switch the amp to mute, the hum disappears.

I see! If that is the case, ask Kevin if the 101D's filament supply is AC or dc. If ac, maybe he can say if its possible to convert it to DC (by means of adding an SS rectifier inside the chassis). If that is the real source of the hum, using dc filament supply will knock down the hum at least 90 to 95%. IME!

regards,

Abe

Anyone have any experience with changing the 6j6 tubes in the Chenin? I read the entire 'tube swapping' Supratek thread and no mention there.

Currently, I'm using Phillips M8081 (unknown age, got em used). I swapped in the original Sovtek 6j6 tubes and it sounded awfully shrill with glare.

Other tubes I'm using and very pleased with are Bendix 6106 regulator, Ken Rad 6sn7, Sovtek KT66. Thanks to the many who suggested these.