The Amp Garage

There is a problem lurking there for guitar amps. Screen grid resistors live a fairly easy and easy-to-calculate life until the tubes are pushed hard. Then screen grid current skyrockets, as the screen grid starts acting like a second plate - the real plate is driven very low in voltage, so more ele...

are you anticipating that folks will pull the old parts and then stuff the new boards..., or are you thinking that folks will buy new parts and stuff the new boards with new parts? A combination of both new and old parts perhaps? Thanks. I was not thinking that pulling the old parts would be a usef...

Let's try more simply. Each tube has a range of the highest voltage it can withstand without failing in some way, and the highest current it can allow through without damaging the tube and dramatically shortening its life. Get outside those and the tube has a vastly shortened life, perhaps only seco...

Looks like a variant of "Lynn's Jig".

That's the first place I saw a threaded rod used for indexing boards to cut finger joints in all-in-one.

This one has had some cleanup and refinement from the original Lynn's version.

1/4" vinyl tubing; Home Depot sells you 20 feet for $3.

Just slice off what you need.

Back when I was a wet-behind-the-ears engineerling, I went to work for a computer company we'll call Three Intitial Corporation (TIC). This was in the 1970s when if it was an electronic part, it came from the USA or from the highest tech of Europe. There wasn't anything else. TIC had a whole divisio...

Why marry it to a speaker cab? Why not just a module that has a speaker out and can be used with any speaker available? Good question. My reasoning is that a module that's attached to the speaker cab makes setup/tear-down and moving easier, with less thought needed. The physical design of the amp m...

There are powered monitors and PA speakers available already, so what would be different here? Among other things, DIY-ability :D Also, designed for guitarists, not monitor/PA, which is somewhat different. Then there is, as you note: - higher than line level input? (maybe switchable?) Yes, that's a...

I'm turning over in my head the possibility of designing a power amp module designed to: - bolt into a 1x12 cabinet - get its AC power from its own power cord - receive preamp-size signal on an input jack - drive the speaker - re-drive the signal out to another such unit (or two) - accept a pull-to-...

Thanks, Steve. Yes, I'd like to see the info. I've tracked down what I *think* is the right way to design that transformer and output stage, but it took me nearly 20 years of occasional when-I-thought-about-it looking. And I'm sure that by no means do I have the full story. I have a recipe for a Vox...

Is there a mandatory size / other (?) relationship of the output to power transformer, or can the two be similar size? There is no direct correlation between the sizes of the PT and OT. This is an outgrowth of the physics of transformers (which I'll try not to drag you through very much :D ) and th...

Here's some thoughts on this from about 14 years ago. http://www.geofex.com/article_folders/pt-to-pt/pt-to-pt.htm A couple of salient points: - PCBs have tiny parasitic capacitances. So do point to point layouts and tagboard layouts, and every other circuit technique. The devil is in the details of ...

Its the model 1081 R G! Change the 3.3 ohm bias resistors to 12 or 13 ohms nominal. This gets you to about the same "on-ness" that Thomas used for the outputs of the Berkeley 3 or Guardsman silicon outputs. Those are the closest standard values to the value I calculated, 12. 7 ohms. There is a trad...

Sometimes the entire house ground gets high impedance. A loose wire in the main breaker box can do this, as a single point of failure. It's rare, but happens. An even more dangerous situation can happen - a high impedance neutral wire back to the power-pole transformer. When this happens, the two ha...

Thanks for the info R G! Hey, I have a 66 reverb twin and I want to change the outputs to silicon types, are there any value bias resistors you recommend starting off with? What model number? Edit - I should have also noted: There is a fair amount of info on repair/refit/refurbing Thomas Vox at my ...