Please help me understand the role of the "driver" tube in an amp?

[joeinid]

My Triode TRX-M845 amps use an 845 as a "driver" tube. Would it pay to put the BEST 845 that I can get my hands on for that position? These amps can use 211's or 845's as output tubes with the flick of a switch. Would there be a performance benefit if all 845's were the same brand, for example. Should all six 845 be the best possible for ultimate sound quality?

:scholar:

 

[Mike]

My Triode TRX-M845 amps use an 845 as a "driver" tube. Would it pay to put the BEST 845 that I can get my hands on for that position? These amps can use 211's or 845's as output tubes with the flick of a switch. Would there be a performance benefit if all 845's were the same brand, for example. Should all six 845 be the best possible for ultimate sound quality?

:scholar:

Joe, I tried a couple of 845's in the driver slot and did hear an improvement with the Psvane Replica 845.

 

[jdandy]

My Triode TRX-M845 amps use an 845 as a "driver" tube. Would it pay to put the BEST 845 that I can get my hands on for that position? These amps can use 211's or 845's as output tubes with the flick of a switch. Would there be a performance benefit if all 845's were the same brand, for example. Should all six 845 be the best possible for ultimate sound quality?

:scholar:

Joe.......The driver tube in a power amplifier is typically the first stage voltage amplifier in each channel. The driver tubes are often direct coupled to inverter tubes that are then coupled to the power tubes. This is the general explanation to give you an idea of the driver tubes importance in a circuit. The first stage voltage amplifier tube directly impacts the sound of the signal that ultimately is fed to the output tube(s). By swapping different manufacturer's driver tubes you can tailor the overall tonal balance of the amplifier's output. My pair of McIntosh MC2301 amplifiers use 12AT7 driver tubes. I have rolled in several different 12AT7's from JJ Tubes, Tung-Sol, Mullard, Gold Lion, and Siemens. For the past couple of years I have stayed with the Siemens ECC801S tubes. They are fabulously clean and dynamic.

Don't be afraid to roll different driver tubes in your amplifier. The same with power tubes. There are positive performance advantages to be gained when you hit on a compliment of tubes that elevate the sound quality.

 

[joeinid]

Mike,

I remember you liked the WE845 in the driver stage. I need to order something eventually.


Dan,

Thank you so much for the explanation. It really helps. I had a feeling but like to see it in print. It makes a lot of sense that a better tube providing voltage amplification will increase sound quality. I've already replaced the 6SN7 and 12AU7 with much better and noticed an increase sound quality. Now it's time to replace the stock 845 drivers.

 

[jdandy]

Joe.......Rolling tubes is similar to adding spices to a recipe. Some tubes emphasize midrange clarity, others smooth the upper frequency range, and still others deliver a more robust bottom end. The trick is to find the combination that satisfies your personal taste with your speakers. When I had a pair of McIntosh MC275 Mk V amplifiers I rolled all the tubes with many different combinations. That amplifier is a tube roller's dream. The problem is knowing when to stop. Tubes get expensive, especially when you are buying NOS tubes from Siemens, Telefunkin, and Mullard. Before long you'll have spent a chunk of change and end up with a cabinet full of different tubes, all good, just different tonal characteristics. Ultimately you can only use a few at a time while the rest of them remain stored. Ask me how I know.

 

[jerryz1963]

Strictly speaking a driver tube (or transistor) would be a device that provides no voltage gain, but is able to source a lot of current (relatively speaking). Properly implemented, drivers improve sound quality by NOT loading down the preceding stage. In a tube amp, the driver tube would be the tube DRIVING the power tube. Many amps do not have driver tubes. As the grid in an audiophile system (as opposed to a guitar amp) is not driven to a voltage that is positive, the grid does not (in theory) need a driver tube. That being said, I have noticed distinct sonic improvement by using driver tubes. Again, strictly speaking a driver does NOT provide voltage gain. It is commonly called a "buffer," because it's purpose is to not load down the preceding stage (which would cause distortion). Properly implemented, a buffer is not a critical device. as there is no voltage gain, it does not impart sonic qualities. Even a MOSFET can be used. Real world testing has shown that one can have a very long string of buffer stages and the listener cannot tell the difference. The same absolutely cannot be said for voltage gain stages. you can call a tube topology with voltage gain a driver if you want, but that's not a correct usage of the term "driver."