Tube Preamp: How many tubes does it take to .................


My McIntosh Tube Tuner/Preamp has 17 tubes (some for tuner of course).

https://www.ebay.com/itm/275808078607?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5338381866&toolid=10001&customid=2bcceb8a-2310-11ee-a804-333735616563

...........................................................................

 

This EAR 802 Tube Preamp has 14 tubes (and either MM or MC phono)

https://www.ebay.com/itm/275949778364?mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5338381866&toolid=10001&customid=a2033c2a-230e-11ee-a2d3-636437633039

.....................................................

Some have as few as 2 and no mention of Hybrid

Some call themselves Hybrid

What _____________________________?

 

elliottbnewcombjr

There are many ways to design pre-amps.  And many different designs can sound good based on execution and taste.

The basic functions of a line stage pre-amp: 
 - Select from multiple sources
 - Support maximum source input voltage (no overload)
 - Control attenuation (most common) and amplification as needed
 - Provide a high enough input impedance to the source to not affect the frequency response or dynamics
 - Deliver enough gain to drive the amplifier to full output
 - Provide a low enough output impedance for the connecting cable and amplifier to not affect the frequency response or dynamics
 - Add minimum noise
 - Add minimum harmonics (a.k.a. "distortion")
 - Minimize phase and timing errors
 - Do not restrict bandwidth

If you prefer a KISS approach, a single ended pre-amp can get by with one triode gain stage per channel.  This could be one dual triode tube, or two single triode tubes.  Tubes by nature have a high input impedance.  If chosen carefully, a simple single triode stage can meet most of the above criteria usually for a short cable and highish impedance (often tube) amplifier.

There are many other approaches.  A design like the classic Dynaco PAS uses feedback as so requires two high gain tubes stages (one tube) per channel.  Some designs use a cathode follower which requires another one or two tubes.  Other designs (like some Conrad Johnson) use many paralleled triodes per channel.  If a pre-amp is fully balanced, then everything is doubled.

As mentioned previously, some pre-amps use tube rectifiers (one shared or one for each channel) and some designs also use tube voltage regulators.

As you add functions and features you can add even more triodes/tubes.  A phono stage adds a minimum two triodes (one tube) per channel but can be more.  Other features requiring more tubes can be a tape loop and phase inverter.

So, depending on performance, features, and convenience requirements/preferences, old and current pre-amps can use few or many tubes.  This variety makes our hobby fun, IMO.

pdspiegel provided great insight. My Conrad Johnson ET3se has a single 6922 tube.

I have had many tube preamplifiers over the years. Ranging from only two tubes to many! The best that I have heard in my home, across multiple systems is the entry level Backert labs Rhumba 1.3. It uses only two tubes. It excels at detail, soundstage, clarity and more. I like the tonality. It is vivid and dynamic!. 

The Audio Research LS2B had a single tube. It was part of a system that was flat out phenomenal. I remember the session after 25 years.

1965 MX-110Z is hardly a maintenance nightmare……. an excellent engineer w ears…. paid heed to SOE ( safe operating envelope ) of ALL the components in circuits, including line voltage variability = legendary tube life and reliability…. so Gow and company understand this w the RCA tube design manuals as stone tablettes  ( yes that was intentional )… Of course further genius like Roger Modjeski….. used the envelope advantageously …..10 k hour tube life….in a power amp…