The Amp Garage

Rob, You are fundamentally misunderstanding the notion of a cutoff frequency here. It is "wrong" in this context to define Vi as the AC signal on the plate of V2a, and then try to calculate the frequency for which Vo/Vi = .707. Why? Because the 40k output impedance of the 2nd stage effectively shift...

With no bypass cap, there is degenerative feedback through the cathode resistor, which increases bandwidth at the cost of gain. Think of it this way: if the gain bandwidth product is constant and adding a bypass cap increases gain, then bandwidth goes down! You are thinking about bandwidth the wrong...

Did you forget a factor of 2 when converting from rad/s to hertz? The -3dB freq. should be around ~400 Hz. That said, emphasizing the midrange and treble is how the late 60's superleads got their "crunch". Designs with "better" low end response (like Blackface Fenders) don't do the crunch thing as w...

M Fowler wrote:I didn't find that PFD to accurately follow the K19 circuit?

I don't think the schematic that guy posted is correct either. But there is a gut shot of a K19 on page 2.

I put the socket for V1 right next to the input jack. Helps immensely.

think about it, even if you had all 60 volts on the 10k pot, then it would be dissipating 60*60/10000=0.36 watts. I personally wouldn't use anything less than half a watt. I am not sure what the wattage of the regulas bias pots are. Try tubesandmore.com, they have what you're looking for. In genera...

Yeah, the DC coupled cathode follower changes the way that the stage before it clips! In practice, there is really only an attenuation difference of about 2 dB between a plate driven FMV tonestack and a CF driven tonestack. The magic of the CF is how it pulls its grid current from the plate of the p...

Just an observation, if you want to preserve the clean to mean characteristics of the K50, it would be better to use a fixed bias output section.

There is no degenerative feedback through the tail resistor since the grid reference is between the cathode and tail resistors. The tail resistor is there simply to raise the PI's local "ground" to a DC voltage.

I doubt you will hear a difference with or without the cap there.

I agree, "signal path" doesn't really mean anything. Analog circuits are like trampolines...

Yes, you will move the -3dB point of the first stage down by a factor of 2, giving you more bass. This may or may not be a problem, and you may like the sound better with the extra bass (I actually like using a 1MA volume pot and a .001 or .002uF coupling cap for even more bass). If you want to main...

Without the tonestack loss, I think there would be a LOT of gain...probably way too much. You could try building a 6G3 deluxe (ditch the trem and 2nd input) and taking the input to the PI below the 100k plate on the 2nd stage, rather than the junction between the 100k and 15k. I think that would hav...

jestaudio wrote: i,ve had a look at building one from scratch but concluded that it may be a little ambitious just at the moment

It would almost certainly be easier than converting a studio .22, and plus you get 2 nice clean amps rather than one hackjob

Frequency doubling distortion

With the extra resistor, the sound is smoother and less "grubby". If you don't like it, it's just as easy to remove as it is to install.

I strongly recommend soldering the 470k directly onto the tube socket pin.