turbofeedus wrote: ↑Mon Feb 15, 2021 11:04 pm
BobL wrote: ↑Mon Feb 15, 2021 8:50 pm
The other 6V6 projects I have built, a Princeton Reverb and the 6G3 I'm tearing apart for this project don't appear to have any sort of cathode resistors... unless I'm misunderstanding something.
6V6 is a common choice for either cathode or fixed bias, depending on how much output wattage you want/need. A tube in cathode bias will deliver about half the plate dissipation in output wattage.
Keep in mind, the choice between cathode and fixed bias wasn't always a tonal decision like it is today. In the past, cathode bias was just simpler, cheaper, less parts, easier to swap tubes, etc. If you didn't need to maximize the output power, or were trying to manufacture to meet a certain price point, it was the preferred option. Now we have huge PAs and attenuators, so output power usually comes second to any sonic character choices.
Yeah, that makes sense.
Kind of leads me into my next question - my PT is putting out more power than what is in this schematic, and my impression is that this would add some gain and volume, and wondering how to best handle that.
Here is the datasheet:
http://www.classictone.net/40-18028.pdf
With a 5U4GB, I was getting ~340v off of it, though it was suggested I could use a 5Y3 to get a bigger drop. I'm wondering what else might be an option if the gain seems too high - in your article about the paraphase inverter, I saw a suggestion that removing the cathode bypass cap will reduce gain. Maybe that'd be a good place to start?
In my (limited) learning about tubes, I was learning how AC current to the grids is how your guitar signal is amplified, as the ac signal on the grid allows electrons to pass to the anode at a higher rate. I think I understand this concept, and that more electrons = more amplification, so I'm wondering if reducing voltage to the grids would reduce amplification, and thereby gain...
Having an impact on the gain seems, to me, to be one of (or a combination of) three options:
1. Reduce the level of the signal - which based on Hi/Lo input amps, would mean either adding an input with lower impedence by omitting (or reducing?) the grid leak resistor, or removing/reducing the value of that resistor on the single input.
2. Reduce the anode current... I'm not sure how this would be done. Increase the value of the load resistor, allowing less of the B+ voltage through, perhaps?
3. Reduce the available electrons at the cathode... this is what removing (reducing?) the cathode bypass cap would do.
Am I understanding those options correctly? I'm not sure if I have #2 backwards, if I have something wrong in general, and what the best option usually would be when trying to reduce overall gain in a circuit...
