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Why such low power with DIY tubeamp kits?

Hi all,

This is not meant as a criticism, just a question so I will understand better.

For some background, I hand-built a guitar amp kit from Allen Amps. David Allen is really respected in that biz, and he supplies either pre-built or kit Fender Blackface clones. I built his variation on a Super Reverb head. Depending on tubes, it puts out either 40w or 25w and also has a switchable tap for 4 or 8 ohms. It’s really sweet... all hand-wired (by me) on a board with just holes for the resistors and caps and diodes. Not a PCB in other words.  I hand-soldered every single connection on that amp.   It was a really fun project.

So lately I was looking at DIY stereo tube amp and pre-amp kits and all of them (that I found, anyway) were 8w / channel max.

I know my guitar amp is not stereo, and that we expect and even desire distortion in a guitar amp, so I can understand that a really clean and distortion / noise-free hifi tube amp will require more and better components (or maybe "different") as well as being more expensive generally.

But given all that, why is the lion’s share of DIY hifi tube-amp kits so low-powered?

Are there any higher-powered kits? Ones that do not use a PCB? I can follow a wiring diagram but not a schematic.

Thanks in advance,

Eric Zwicky
Richmond VA
ezwicky

Showing 1 response by herman

herman
2,212 posts
 
Your amp is class AB, push-pull, with each output tube only working half the time. They are biased so the tubes are just barely conducting with no signal. Most of the kits I've  seen are class A single ended triode  which means the tube is on about 50% all the time. It has to be biased so it is about 50% of the supply voltage so it can swing up and down. With class AB all other things being equal you can get a much larger voltage swing than class A since one tube can swing all the  way while the other rests'

There are some tubes that can be biased class A and get much higher power but they are not common and would be expensive. The power supply would have to considerably more robust to handle the extra power also increasing the cost,

The DIY market caters to the lower power SET crowd so that's what you see offered. Years ago there were some push-pull kits by Heathkit and Dynaco. That said, I found  a link to a company that makes an updated Dynaco ST70 kit that will get probably 35 watts a channel

http://www.triodeelectronics.com/hifikits.html
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