2502 bias and tube types

[metalms]

I have just ordered the 2502s power amp and was wondering if the instructions for biasing new tubes is the same as the 2902s ?

Two 90 two bias

When you open the top and look at the main board, the bias pots, which are located on the rear left area of the main board are easy to spot because they are the only variable pots on the board, and they are each marked the this text: BIAS. We normally start a new unit in QC with the pots set in the halfway position, but that’s unnecessary when replacing tubes. You can simply start with the existing position and tweak accordingly, or go back to the mid-point and adjust from there. We set the bi…

I have those instructions from when I had my 2902. Can those be used for 2502 as well?

Also, can I use 6ca7 power tubes in the 2502 given it has el34?

I have two quad sets of electro harmonix new as well as some tung sol el34b quad set.

Any issues or different biasing with these tubes ?

Can’t wait to try the synergy preamps with this power amp.

Thank you for your time.

[metalms]

@DavidPhelge Could you please answer my questions in this post at your convenience? Thank you for your time.

[DavidPhelge]

The 2502 bias procedure is a little different than the 2902. I’ll have to send you that document later. I don’t have access to it at the moment.

We use and recommend Mullard EL34 for best overall performance and reliability. These have been our standard for production since they were released in 2001.

Tung-Sol and EH are good too.

Current production 6CA7s are OK, but they’re not the most transparent or musical.

Recommended bias is 35mA.

Dave

[DavidPhelge]

Here’s the 2502 bias procedure.

With minimal test gear, such as a DVM for example, you can accomplish item # 2 and be very well in the ballpark.

Dave

2502Bias.pdf (48.7 KB)