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How to Trace Out Tube Amp Schematics

Posted on February 11, 2017 at 05:28:16
Randal P

Posts: 31
Location: NYC Area
Joined: August 19, 2004
I have a few tube amps that works perfectly and sound great but are not well-documented. I would like to be able to trace out the circuits and create schematics for them. I can recognize components and trace out wiring, but am pretty inexperienced at this level of detail. Does anyone have suggestions or other helpful hints?



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RE: How to Trace Out Tube Amp Schematics, posted on February 11, 2017 at 05:58:50
Uncle Mike

Posts: 2222
Location: Eastern Pa.
Joined: June 20, 2003
I have been using LT Power CAD for some time now. It's free (as well as LT SPICE)but can have a steep learning curve if you have limited electrical/electronics experience. There are others that you could download and try.
You can start with pencil and paper to break it into parts of loops (power, line input, phono input, I.E.) then begin building it in a CAD program. It does help to start small.


How to Trace Out Tube Amp Schematics, posted on February 11, 2017 at 07:35:03
Interstage Tranny

Posts: 2986
Location: Eastern
Joined: October 4, 2006
Do you have any university libraries near you ? Even any public library has some electrical or electronic texts which will help. Sure, online research is helpful, and your search engines will be beneficial. However, topic specific sites can be elusive.

Whenever younger sound devotees ask theory questions, I have always directed them to find the earliest magazines and publications concerning our field of interest. As it turns out, the earlier and sometimes earliest texts about radio engineering tend to be the most enlightening. Why, you ask ? Because, the authors knew their audience.

Imagine if a middle school or high school teacher used lighting as their examples instead of "how fast did one train travel until it caught up with another train" questions. We might have all learned electronics at a much younger age...The early radio engineers and PA soundmen knew the folks desiring info probably did not have formal electronic training, so they wrote and "spoke to us" as if we needed all the info in a slower fashion. Later radio and audio engineers seemed to presume the average reader already studied the science, so they dived right into confusing formulae without explaining.

Nevertheless, the early 1930s and 1940s amateur radio "annuals" are extremely helpful to us. They show the schematics and the actual, beautiful underside wiring on close pages. Look for "Radio" annuals from the early 1940s and the like.

Here is a modern online link which is becoming reference grade. Patience while downloading/streaming and going back to the home page often will definitely enlighten you today ! Remember to start with the early publications first...


RE:I would start with putting it on a ruled notebook, posted on February 11, 2017 at 09:03:38

Posts: 1757
Location: PACIFIC
Joined: August 8, 2010
December 0, 0000
I used to save my schematics on computer but after that computer died i switched to copying them on 2 notebooks that i put all my audio info into. This makes it a hardcopy with nothing but a pen needed. Also the act of drawing it out should make your understanding of the circuit better as well.
Copying schematics may seem hard to do with hand drawings but after doing a few you can get fairly good at it. Working with ruled or graph paper makes keeping things in good alignment. Of course the accuracy of your copy is dependent on your accuracy so one needs to triple and quadruple check the copy for errors. When you breakdown an amp into a schematic it actually is simpler than the real thing. If you are into building amps it makes keeping track of changes and the results of the changes much easier than going with a subjective impression. cheers.


RE: How to Trace Out Tube Amp Schematics, posted on February 12, 2017 at 10:23:19

Posts: 1853
Location: Cape Cod
Joined: September 12, 2008
It might be helpful to remember that there is a good chance that whatever circuit you are trying to figure out is a common archetype used over and over. Examples are the Williamson, Mullard 5-20, or Dynaco ST70. There are variations of these, but what is common to each of these archetypes is that they are composed of predictable stages or blocks of components that relate to each other to provide a function.

These stages can be very generic and easy to figure out and easy to draw because you can follow a schematic of the archetype. Here's an example. The Williamson amplifier is certainly one of the most popular audio circuits ever developed so it is extremely common in commercial and hobby builds.

You see below the Williamson amp is composed of five discrete blocks of components that each serve a specific purpose. Each of these five blocks of components is common to many different amplifiers, so it makes sense to learn to draw these typical blocks and expect to see them in the amp you are attempting to draw.

So, starting with the yellow we have the power supply block. Every amplifier is going to have a variation of this one here: draw it in. Pink is the output stage. Every push pull amp is going to have a variation of this. Dog puke green is generally called a "long tailed pair" or differential amplifier; it's a common gain stage in amps. Blue is the phase inverter; this one's a split load inverter. The first stage is the most common triode gain stage there is.

Draw out these stages as practice and then look at the amp for which you need the schematic and look for the power supply components: fill them in to your drawing. Check out the output stage: is it similar to the Williamson? Discover each of the discrete blocks of your amplifier and put them together. Now that you know what you are looking for and how to draw them, the job should be easier.


RE: How to Trace Out Tube Amp Schematics, posted on February 12, 2017 at 17:17:06

Posts: 785
Location: Arcansaw
Joined: February 10, 2004
Absolutely spot on. Some of the most enlightening articles for me are from the 30's and 40's. Great stuff especially the early radio mags.

High sensitivity, wide dynamic range, low distortion, and smooth frequency response. Pwk


RE: How to Trace Out Tube Amp Schematics, posted on February 14, 2017 at 05:48:02

Posts: 1516
Location: Pacific Northwest
Joined: August 22, 2003
January 6, 2017
Another intermediate step I've found very helpful is to do the 'decoder ring' between an amp (or other piece of gear) and its schematic. What I mean is, to find a place on the schematic, say, the connection between the output tubes and the output transformer, and find it physically on the amp. Keep relating the devices and junctions on the schematic to the physical landmarks in the system, and it will help you gain familiarity with the translation process, typical appearance and arrangement of components, and so on. Though schematics may proceed in a nice left to right, input to output fashion, the physical implementations in the hardware aren't always laid out in as obvious or orderly a manner.


Sharpen your pencil first , posted on February 17, 2017 at 09:30:19

Posts: 520
Location: Alberta, Canada
Joined: August 4, 2004
I do this I first draw a sketch of the schematic, then make that into a neat drawing
Finally, add the component values. Some people are more comfortable using computers to draft things, I prefer a pencil and paper. Then scan it so you have a back up copy.

If you want to get fancy make sure and add tube PIN numbers and transformer wire colours.

Then make a copy of your drawing and double check it against the amplifier, crossing off components a small you locate them.


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