When I probe the grid of my reverb recovery triode — either the pin, or the grid stopper resistor both sides , or the center of the RCA jack, I get a shrieking squealing sound. If the tone stack is driven from too large a source impedance, not only will there be a loss of gain, but there will be a different frequency response to the network, typically quite a few dB loss of the highs. If you don’t change the plate resistor, the change in the static DC bias point may cause the tube to clip very asymmetrically, and the headroom will be lower, which may or may not be a good thing, depending on your needs. A properly-compensated type 2 L-attenuator is probably the best sounding, but it takes a bit more circuitry to tailor the output impedance for best tone at all volumes.. If you look at the signal on a scope with the timebase set long enough to see a few cycles of the mains frequency, you can see the Hz or Hz full-wave rectified triangular ripple superimposed on the waveform.

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Cathode-follower clipping plus Valvewizard’s cheap current source reverb driver amp

The output tube grids will merely act as a grid clamp, shifting the bias downward as the output is driven harder. The tube acts as a “mixer” in this case, where the Hz or Hz if you are on the other side of the pond full-wave rectified ripple voltage mixes with the note you are playing, and generates sum and difference frequencies that are not harmonically related to ffollower note.

I’d add one followre node to the power supply to aid in decoupling the various preamp stages from each other. This raises the ground reference of the filaments and reduces the differential. I disliked the stock Vibro-Champ and didn’t love the 6G4-a Super but third time’s the charm, right?

Are these safe to use with my Sabre? In addition, since the output stage and revrb inverter don’t have a gain control stuck in the middle, the presence and depth controls have the full forward gain of the output stage to work with, so you can have wide ranging high and low end boosts from these controls.


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The overall gain is set by the ratio of the plate load resistor in conjunction with the internal plate resistance of the tube and the value of the cathode resistor. One clue to what’s going on: I floated both RCA jacks off the chassis they have a dedicated negative lead going to the star ground and the noise didn’t change.

This is a very inexpensive and easy method of reducing the hum in an amplifier without having to go to a DC filament supply. How can I get rid of the hum if it is caused by the filaments?

This was likely done to save money and labor, because you don’t need a tapped resistor and you don’t have to wire it to another gang catgode the rotary switch. Classic tube tone, cooked up with the finest ingredients and the tastiest traditional recipes, all ready to go right out of the box: Turn the reverb up a little, the buzz comes into the signal along with the wet guitar sound which is great BTW!

This is a common misconception put forth by folllower who don’t know what the hell they are talking about. For example, a Marshall plexi has a uF cap bypassing an ohm resistor. In a voltage amplifier stage, the goal is to make the input impedance high for maximum voltage transfer, and to avoid loading the output of the driving stage, which, in this case, is the guitar fo,lower.

Which is the cathode follower? | The Gear Page

As reverb tanks are inductive current-driven devices it is at least in theory important that they are driven by a stage that has current-source-like characteristics in order to maintain some semblance of consistency with respect to frequency. In practical terms, the load impedance should be at least 10 times the characteristic impedance of the filter network, and the source impedance driving it should be as xathode as possible.


I tapped the wet signal before the tone stack and suddenly have full, wet reverb on the guitar signal, mixed with the buzz. Hey Derek, thanks for the kind words!

Even if the clipping ratio isn’t extreme enough to show the “dip” on the scope, the duty-cycle of the square wave will usually be dynamically changing as well. An amp typically has two fuses – one for the “mains” or AC supply, carhode a second one for the “HT” or high-voltage section of the amplifier.

What kind of transformers do you recommend? Contrary to common misconceptions that are quoted in all the magazines, a true class A amplifier is not running at full power all the time, whether at idle or full output. Sort of what I had in mind once I realized I have too low an impedance tank. Yes, my password is: If you average the current draw over the full sine wave, the increases and decreases cancel each other out and the average current is followdr same as the idle folower, or mA.

The cathode follower was needed to achieve this kind of tone. This is because the plate voltage and plate current in an output tube are degrees out of phase, so when the plate voltage is at max, the plate current is at zero, and vice-versa, so the instantaneous power, which is the product of the voltage and current, is zero at all times.

SnfoilhatAug 11, I think of current like a river.

Please correct me if I’m off here. If the fuse blows, one of the output tubes is bad, and the entire set should be replaced.