The Amp Garage

As an aside - I've just realised that the OP's schematic shows both halves of V2 used, but only one half of V1 (rather than vice versa). I never noticed that before. Maybe it's significant...? My amp is based on the Weber JAVA which has the option of using the second half of V1 as a cathode followe...

Here are the plots for the same stage using a grid stopper instead of a cathode bypass cap. http://ampbooks.com/home/amplifier-calculators/grid-stopper/ With a 68kOhm grid stopper: [img:1880:813]http://farm3.staticflickr.com/2857/9410036803_090ddf2351_o.jpg[/img] With a 100Ohm grid stopper: [img:188...

Using the Amp Book Calculators, you can determine the frequency response of a gain stage with either a grid stopper or cathode bypass cap. Using a 1000pF plate bypass cap like I did has the following results: Here are the frequency response plots for the plate resistor bypass capacitor. The first on...

Since most, if not all modern tube shields are aluminum, and non-magnetic, how could they affect the sound.

I tried a search with no luck. Why do Trainwrecks not use preamp tube shields? With all the gain on tap, wouldn't the preamp tubes be prone to picking up external noise? I have a problem with noise in my amps due to the high powered wireless router in my studio. A combination of tube shields and mov...

Tillydog wrote:

bluesky636 wrote:My final schematic is posted on page three of this thread.

I know!

It doesn't show a grid stopper on V2b, and I was wondering whether you had tried one and rejected it, or not tried one at all.

No matter....

Sorry. Misunderstood the question. I didn't feel the need for one.

the amp is quieter with the cap across the plate resistor than it is without it. Hiss is significantly reduced with no real loss in highs ... Out of curiosity, did you try a grid stopper on V2b? I found a small one made a big difference on my Express - similar to what you're noted for the cap. Both...

Personally, I think this is all irrelevant. If the power supply is putting out enough noise that the location of this cap makes any difference, the power supply is either poorly designed or faulty. In any case, the power supply should be looked into and problems corrected because any noise would be ...

There is one important difference, wiring the cap across the anode load resistor will also cause any B+ power supply noise to be coupled into your signal by that cap. As I noted previously, the amp is quieter with the cap across the plate resistor than it is without it. Hiss is significantly reduce...

romberg wrote:Thanks for the update on that plate resistor bypass cap. I'll have to audition that the next time I pull my chassis out of the cabinet.

Mike

You're welcome. Thanks for suggesting it.

I decided to try the 1000pF cap in parallel with the 100K plate resistor on V2B. That was the magic fix! The overdrive highs are much thicker and smoother with no loss of highs when the guitar volume is turned down for a clean sound. Overall high frequency noise is noticeably reduced. Even better, I...

Yeah, the amp is sounding really good. I am very happy. Here is a schematic of what I ended up with: [img:1024:558]http://farm6.staticflickr.com/5325/9202507599_00b9f23d46_b.jpg[/img] This is a demo done by my guitar instructor of an earlier version of the amp: http://www.youtube.com/watch?v=PpONLjn...

Finally got a chance to crank up my amp. I have to say that changing power transformers to drop the B+ from about 475 VDC at the bias set point to 405 VDC at the final set point has really made a difference. Plus changing the 0.0022 coupling cap from a silver mica to a Mallory 150, the silver mica 5...

I installed the Mallory 0.0022 mF coupling cap and the 510 pF polystyrene treble cap. That did help. But I also decided to replace the Heybour power transformer with the Weber transformer that has the option of lower B+. This brought my bias set point down to 405 VDC plate voltage at a cathode curre...

I received my BSEE back when tubes were still part of the curriculum. As I get closer to retirement, I decided to re-learn about tubes and tube amp designs, so I started buying a variety of books. My current library: If you want some books that explain all this in simple terms, these are some good o...