Cherry 180 / Black beauty 305

Pardon my tube amp ignorance but I want to know what is the purpose of the small tubes and what type are they...as in 12AX7 etc etc.

Someone else will have to answer more specifically.

But the typical tube amp (if there is such a thing) wil have an input tube that acts as a voltage gain stage first.

Then if it's a push-pull design, there will be a phase splitter stage. This splits the signal into the positive going signal on one side and the negative side of the waveform routed to the other side. There are several styles of phase splitter stages, it could be one tube or two.

Typical tubes used, like all the Dynaco and follow ups to them, often use tubes like the AX in the voltage gain and the AU in the phase splitter.

One additional small tube that Bob uses in many of these is a small signal rectifier tube. It's in the output tube stage and is used in the bias circuit. If I remember right, it might be a 6AL5.

Maybe somebody else can be more specific about the models your asking about, Eric. I think they may have been some version of a schematic around here somewhere.

Mark

MRHP, I'd recommend that you pick up this book (from Amazon or eBay..): "Elements of Radio" by A. Marcus and W. Marcus. It's old, but unique in that the 1st half of the book goes into the "evolution" of tube amplification and how all these "little tubes" came into play into the circuit of an audio frequency amp (and "radio detector", RF amps, etc.). Probably not all of Bob's "tricks" are covered, but the basic reasons for the "little tubes" pretty much is... Has an entire chapter on all the different types of tubes and their function. NOT a bunch of data and statistics on each; just the how and why of the different types. Also covers power tubes in // and push-pull. The 2nd half of the book delves into the math and science part of circuit elements, magnetism, electricity, etc., but they try and keep the 1st half more "words" and common sense oriented....

The three small tubes are:

12AX7
12AT7
6AL5

The 12AX7 and the 12AT7 are input driver tubes
The 6AL5 is for BIAS

This is taken from the owners manual:

The input stage of these amplifiers consists of a 12AX7 current sourced, long-tailed balanced pair direct coupled to a second long-tailed balanced pair comprised of a 12AT7. The 12AT7 drives the grids of the output tubes through a pair of coupling capacitors that provide low frequency loop-gain stability. A 6AL5 DC restorer ensures that the bias voltage remains correct over the entire audio signal cycle.

Thanks to everybody.