The Amp Garage

Screenshot 2026-07-12 011653.png First pic is with the OT primary connected "correctly". Screenshot 2026-07-12 011842.png Second pic has an asymmetric connection to the OT primary via a 40% UL tap on one side. Other half of primary connected normally and B+ connected to center tap as usual. Lots of...

It looks like a strong second harmonic might actually be pretty easy to reproduce. All it takes is connecting the plates on one side to the UL tap instead of the correct connection at the end of the winding. A couple people (both here and in the youtube comments) suggested a mis-matched primary wind...

If you re-watch the video, at the 27 minute mark he shows the anode voltages at both ends of the OT primary and explains that "if we go to the other side, the other pair of 6V6s, you can see that kink is there but it is obviously inverted." That's just how a transformer works. No matter on which si...

In this case, I suspect that the real cause has been mentioned - the changeover from one to two pairs of outputs at a certain signal level. Not the cause but I think that’s when it happens. The kink only shows up in the positive swing of the output signal (25:10), so it’s only happening on one side...

Also its not present unless the volume is turned up, maybe to where it transitions from A to AB1? Sequence starts at 25:00. Could a problem with one of the cathode bias resistors or capacitors cause that kind of issue? Half of the "push" side and half of the "pull" side operating at a different bia...

I would consider a VVR feeding the screens, with its input voltage coming from the screen node (just after the choke). I convinced TAG member bcmatt to try it with a pair of KT88 and it worked fine. It will track the voltage sag and keep the screens at a more or less fixed fraction of the plate vol...

I've heard of better way to turn a push pull amp into a quasi single ended is with a pot or mute switch that turns off the control grid signal to one of the power tubes. That leaves the idle current flowing through both halves of the OT (and both tubes' current through the single cathode resistor in...

I suppose my issue with the supplied answer is why isn’t current from the 6V battery flowing through the 3 ohm resistor and the 2 ohm resistor. It seems this path has been ignored. My memories of how to apply Kirchoff's voltage law are pretty distant too, maybe someone else can help with getting th...

The first tone control section looks at least a little bit interesting. The parallel fixed mid boost and scoop sections with a blend pot isn't something I remember seeing anywhere before. Most of the design is pretty plain though. There's no negative feedback in the power section, which isn't unique...

There are so many things I like about this build that I feel bad that my comment about it is a suggestion for an improvement in the layout. One of the specific things I like (and I'm planning to do the same thing): the divider between the transformer and the audio signal path. One detail that has ro...

I've been comparing inverter stage spice simulations the last couple days (definitely going to go look for #124 next), so I spiced this choke tail pair last night, but now that there's obviously some interest I should probably jump on the bandwagon and post about it too. The last time (and first tim...

Amazing thank you, is the capacitor necessary? I see so many amps without it but have one I can put in if needs be. Any Tonal affect I would hear whilst playing if it’s not there versus is there? The cap provides frequency compensation, which like you've already noticed isn't used or talked about m...

A good place to start is the datasheet for the resistor you plan to use. The model in Aiken's schematic is pretty easy to find. https://www.vishay.com/docs/30201/rhnh.pdf Page 3 has a lot of relevant info: Vishay RH resistor wattage ratings are based on mounting to the following heat sink: RH050: 12...

I found this paper helpful https://www.valvewizard.co.uk/Grounding.pdf Merlin recommends using a ground reference at a point in the circuit that minimizes the power supply current flowing past/through the ground connection point. Specifically: connect the ground reference at the cathode of the inpu...

I just found a really thorough introduction to Thermal Resistance and Heat Dissipation, and I wish I had found this a few years ago. basics_of_thermal_resistance_and_heat_dissipation_an-e.pdf If the Texas Instruments pdf above was too specific for your tastes, this Rohm Semiconductor lesson covers a...