BIAS AMP 2 WONT STARTUP ADMIN HOW TO
I know its got something to do with that you have two cathodes in parallel at ground potential in the 5G9, and that each grid needs to be at a negative voltage with respect to each cathode.Īlso I understand from plodding through Jack Darr's book, that the gain from the previous stages results in the signal voltage going into the Output tube grid, and that this signal voltage needs to be of a given quantum that is somehow related to the plate and screen voltages to make the tube work optimally, but I'm not sure how to calculate this voltage, nor what the relationship of current and resistance is in this? What I want to understand is how this differs from a PP amp with fixed bias? The plate is seeing about 40mA) I understand I could bring that down to a more desirable 12.6W if I changed (lowered? or raised?) the cathode resistor, or dropped the B+ about 30V. (On that amp there is 19V on the cathode and 344V between the cathode and the plate and with a 470R cathode resistor giving 13.76W. It runs a little hot but it seems to work fine. I have learned from when I built my 5F2A that I have to bias the output tube correctly to get the appropriate dissipation - But that amp is cathode biased.
BIAS AMP 2 WONT STARTUP ADMIN PDF
pdf version of the schematic I got from the Fender Amp Field Guide site is a little fuzzy.įurthermore, can somebody explain to me the relationship between current, and voltage swing and resistance for signal at the output tube grid? and kindly edjamacate me about how I calculate the appropriate signal strength to drive the 6V6 s properly with this amp, and what setting the grid bias has got to do with this? At least I think it says -27.5V?) The lettering on this. There doesn't appear to be a "bias range resistor' in the 5G9, (or is the 82k the equivalent of this?) Hoffman's bias circuit only has one bias capacitor, the 5G9 has two - one on either side of the 82K - is that because it needs to be decoupled from the 250k Depth control? (I gather if I use 10uF 450V caps in here instead of 8uF 150V caps, it won't matter?)Īlso if I read it right, I'm trying to get -27.5V at each 6V6 Grid (and not -22.5V?. I've seen different explanations of an adjustable bias circuit on the Hoffman site here:īut those circuits ain't quite the same as the 5G9 circuit. A (rather lengthy) design question before I start my build - If I want to make the bias adjustable, (because I've had to get a custom-made PT and I won't know, until I hook everything up and get it going, exactly what I'm going to end up with in terms of B+, despite having asked for it to be wound to put out 300-0-300), then can somebody please confirm for me whether it is the 82k resistor I replace with a (100kN?) pot (with only wiper and input wired) in order to adjust the bias on a 5G9?
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