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all tube 30v amps
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Friday, 26 May 2006

Updated 11th February 2006!

Version 5

Changed R11 from 200 to 62. This increased the b+ from ~18 to ~28V. Thanks for Rich Chernock for pointing out that the b+ was lower than expected.

Version 4

Changed R8 from 22k to 10k. This ensures that the tube goes into saturation for clipping instead of cutoff. This change also made sure that the strat was able to produce a nice rock sound!

Version 3

Changed C2 from 0.0022uF to 0.0047uF to add some more bass. Changed R4 from 270k to 220k. This removes some of the flabiness while using the ES335. With this you can get some breakup with the strat but not much distortion. Still need to investigate some more.

Version 2

I did a small change in the design. Basically, I increased the second plate resistor (R4) from 100k to 270k. This should ensure that we can get nice distortions with most guitars (from tele to strats to hot pickups).

All right, after playing with 12V, I decided to play with a voltage slightly higher. Now, we can't talk about high voltage as the max voltage for these tubes is 30V. What I present here is my 30V design. This produces around 1/8 of a watt which is just perfect for me. This is as loud as I would need to play without anoying my neighbour. This is a cheap amp to build for the following reasons:

  • It uses as 24-25.2V Center tap transformer. I was able to find one at Radio Shack for 15$ Canadian (you can get them cheaper)
  • You can use a 70V line transformer as the output transformer instead of the Hammond 119DA that I use. Both will do fine. If you are using the 70V line transformer, use the 2.5W tap as a primary and the appropriate ohm for the secondary matching your speaker. 70V line transformers can be had for a few dollars.

Here is the schematic (click on schematic to enlarge it):

All resistors are 1/2 watt except R10 and R11 which are 2 watt
For heaters, for the 12U7 connect pin 4 to one of the heater label and pin 5 to the other heater label. Pin 9 is left unconnected. For the 12K5, connect pin 3 to one of the heater label and pin 4 to the other heater label.

Here are a few pictures of the amp

Sound clips

Here is a clip of the amp fully cranked. It was recorded on the Zoom PS04 with my ES335 clone. First part is with the P90 bridge pickup and the noodling is with the Neck (PAF inspired). Sorry for subjecting you to this aweful noodling. Click here to listen to the clip of the version 1 of the amp. I haven't had time to record a clip for version 5 which has more gain and therefore, more distortion available.

Successful builds

There are currently 3 successful builds:


Last Updated ( Friday, 23 February 2007 )