The Amp Garage

Can you lift one end of the 0.1u coupling cap (I can't see what number it is)? It sounds like you may be getting heater buzz, coupling onto the high-impedance grid of the cathodyne. Does the humdinger have any effect?

Short out R5 (the feedback shunt resistor). Yes the hum may increase but it is much easier to trace the hum when the amp is open loop.
Also short R2 (input grid leak).
Now connect a big cap (1uF or more) from the input triode place to ground. What happens to the hum?

Re: the clean headroom, you can change the rectifier to a 1/2-wave voltage doubler, and you should be able to get between 450-500V out of it, which is enough to ensure you can raise the B+ throughout and get more clean headroom. YMMV. Caution: This implies that the transformers can handle four time...

Obvious option: Turn your guitar volume down.

Alternative option which you may or may not like: Remove the cathode bypass cap on the power tube.

The Ballzz wrote: I couldn't open any file on the linked page,

I'll put it here temporarily:
https://dl.dropboxusercontent.com/u/578 ... enfold.pdf

As a novice, I'm curious as to whether or not an oscilloscope can be set up to... view the response curve ANother option is to make your own sweep generator gadget which allows you to 'draw' the frequency response on a scope: http://freestompboxes.org/viewtopic.php?f=70&t=24864&p=241412&hilit=penfo...

It is nothing more than an attempt to "harvest" royalties from future users and a method to scratch an itchy ego. I'm not sure it's as sinister as a money-grabbing opportunity. I suspect that J. Scott knows perfectly well that it is not an original idea, and I also imagine he has neither the money ...

So Merlin's scale control combined with a standard master volume is patentable? I think he would be unable to defend it. Please elaborate... It's not my scale control, I just called it a 'pseudo scale control' in my book (I'm talking about the variable bias resistor for the LTP). The principle has ...

OK, in order to stop everyone stealing my original ideas I will be patenting this. Let this put an end to all future guitar amp patents.
[img:800:480]http://i81.photobucket.com/albums/j207/ ... f6xa1j.jpg[/img]

Gaz wrote:This really irritates me:

https://www.google.com/patents/US20130028447

Very funny! Thanks for posting!

Well, I can't see any rectifier in there, and it looks just like any moving-coil meter, so I would guess it is actually a DC meter and needs an external bridge rectifier to be used with AC: [img:478:385]http://sub.allaboutcircuits.com/images/02225.png[/img] So you can test it the same way as any DC ...

Most DC analog meters are moving-coil meters, and work in exactly the same way. You put some current through it, and the needle moves. It is a simple matter of figuring out how much current is needed to push the needle all the way to the end, which is called the full-scale-deflection (FSD) current. ...

Is there actually a way to measure this with a multimeter? Feed in a sine wave of 50 or 60Hz and make sure the amp is not clipping, and you should be able to measure the signal voltages on the AC range of a multimeter. (Provided you measure it at points where there is no DC on the signal, of course...

Hi Martin, the u-Tracer still isn't quite up to the task of doing R&D in the real world - although bumping the HT supply up from 300V to 400V is a good start. It would be nice to see it be able to go up to 600V plate and screen, or, better yet, 800V plate and 600V screen, What on earth do you think...

Cliff Schecht wrote: I guess for most any tube we deal with in guitar amps, yes this isn't true. It's really an issue with directly heated cathodes in higher power tubes.

Ah yes, DHTs (directly heated triodes). That makes more sense.