Favorite Driver for 845

[Bryan]

Hey guys,

I've been listening to Grovers 845 design for some time now, and I like it very much. For those of you who are not familiar with the topology, it is a 6n7gt-el34-845.

I am in the process of tearing them down to facilitate a rebuild using nicer chassis, etc etc.

Of course, now that they are appart, and my back-up amp is in the system, the DIY bug has hit me again. I am thinking about trying some different driver setups, and possibly going with interstage trannies in front of the 845.

My question to you all is what are your favorite drivers for the 845, and what topologies do you prefer?

Thoughts?

Thanks,

Bryan

[astouffer]

I used a simple RC coupled driver with a 417A into a 6AH4 triode. No bypass caps on the cathodes to keep the distortion down. I tried a 5998 with good results but then the 417A needs bypassed to get max gain.

[tubelab.com]

I use a circuit that I call PowerDrive. It consists of a CCS loaded triode followed by a mosfet follower. My 845 amp uses a 5842 (417a) driving a 45 triode which drives the 845. PowerDrive is used between each stage. This amp sounds awesome, has very low measured distortion, and will put out 40 Watts RMS at clip. It runs in A2 to get this power without over stressing the tubes.

The schematic is on my web site:

http://www.tubelab.com/845SE.htm

I have used the same drive setup to get over 200 watts out of an 833A.

[Roger Hill]

Don't fix it! I've listened to Grovers amp for several years now. The two improvements I've found worthwhile are diode bias on the 6N7 and fixed bias on the EL34. Use four red led's to bias the 6n7. Fixed bias for the EL34 requires an additional 10k pot in series with the bias pot for the 845, adjust to get 30-40ma through the EL34. Other than those tweaks, it is as good as an 845 amp is going to get, which is world class.

Roger Hill

[dhaen]

I've got pretty much the same results as Tubelab, but using a 300B and massive interstage transformer to drive into A2. I'm very happy with the sound on my OnRyoku .
This is probably not a practical conversion possibility for yours, but it seconds Tubelab's contention that 845 A2 sounds good.
I've also tried a 6550 cathode follower (with a high current negative bias supply) as A2 drive with good results, but the power requirements are wasteful.
Perhaps you don't need lots of power, in fact I found that I only need about 25 watts / ch , so have wound down the supply voltage to extend 845 life. They still run into A2, and I feel that the overload characteristic is even gentler than A1.