Can someone recommend replacement tubes for my MFA MAGUS A2 Preamplifier please?

I just purchased a MFA MAGUS A2 preamplifier and I am getting a loud roar noise after playing thru my MIETNER MTR101 monoblocks after about a half an hour.  My speakers are BOZAK URBANS. I also want to change the fuse in the e tee also power supply and need suggestions for that as well. Thank you. Bill A  
I suggest calling Andy at Vintage Tube Services for NOS tubes.

Plenty of current production tube sellers including:

Below is some information that might help other who want to offer their advice. There is also a FAQ on tubes at

 Classic MFA Magus A2 preamp designed by Bruce Moore. Has outboard power supply, 2 12ax7s for phono and a 12au7 and 6DJ8.
Thank you JPerry. I did reach out to the Tube Depot who were very patient and helpful. I ordered 2 of the Tungsol 12AX7 as a start and I’ll see how they help. 
I've been there with other equipment.

problem must be isolated before jumping to new tubes.

problem in both channels?

what channel?  first move tubes 1 at a time l to r, see if problem moves to other side. If not, switch another one.

cables? anything new?

rare, but something in speaker crossover could be amiss, do you have small speakers to hook up just to prove the problem persists with any speaker?

Here's a suggestion: call Scott Frankland (the F in MFA) and ask him directly. I spoke with him yesterday about my Magus preamp and he is very helpful. His number is (408) 926-6731. 
TonyKay and Elliot, 

I replaced the tube that in my MAGUS is the one that after reading the manual and receiving advice from the very gracious Scott Frankland the problem persists. To ship the unit to Scott and have him repair it would cost as much as $800. total and that creates the question of wether it is worth the cost to repair? I just do not have the requisite expertise to answer that question and hence I am hesitant on spending what will be over 50% more of my original budget for a tube preamp, the MFA MAGUS, the MIETNER monoblocks and the BOZAK URBAN speakers all for $1,450.. should I buy another used tube preamp or a new one such as the Schiit Preya+ or do the repair? 
As an impulse, I just bought an Audible Illusions L-1 preamp here on Audiogon. It’s like new and I paid around $800. I paid $750 for my MFA Magus a few years ago. I would try to find a competent local tech to repair your MFA. $800 is just a lot to pay to repair a $750 preamp. I now have both the MFA and the AI. My plan was to have the AI while the MFA was in the shop. I’m not sure where you live but my advice would be to ask your local high-end dealer who they use for repairs. That's how I found my tech.
I actually found a highly recommended local tech through a local audio shop that I happened to see the owners being interviewed on YouTube. Thank you for your comment.