ampeg b15 inverter

[catalin gramada]

interesting offshoot, same circuit with Bendix 6384's, four of them, only two get an input signal, the other two just drag idle current thru a cathode resistor, this was done by accident, started as a stereo amp but only one channel needed, what this does is regulate the power supply by keeping a constant load on the B+. amazing sound give it a try sometime.

You have a interesting ideea to present a smaller peaks of current variation related as percent in respect with biger iddle amount. think it worth to test it.

[catalin gramada]

Playing little bit with circuit:



got almost perfect output voltages balance but semi-alternances are a little bit asymmetrical supposed by different output impedances.... How do You think is better to compensate in actual circuit, please? Thanks

[nickb]

You could try this and see how it behaves. Change the 1M+68K to about 1.2M and add a 15K resistor in series with the 47nF cap of the second inverting stage to compensate for the low output impedance. This will make the output impedances, gains and time constants about the same. The signal on the second stage plate will be bigger and that might cause you a problem if you don't have enough headroom.

You will still have variation between the triodes and the output stage tubes unless they are perfectly matched. Another thought. If this is for guitar you might actually prefer the more gradual sound of the breakup when there is a good deal of asymmetry.

[catalin gramada]

better-



Thanks Nick

[catalin gramada]

The problem found with this inverter which use common cathode resistor is : if want to change nfb or bias voltage have to modify all the resistor values in cathodes network

we can move common OT wire from ground just over "shunt" feedback resistor to keep the same nfb ratio but more independent biasing options

or can generate the bias voltage completly over OT winding and nfb resistor

All three methods works but found the last two more versatile options. (of course in first instance we can play with OT taps to modify the global feedback but is a limited option)

[catalin gramada]

anyhow found this arangement to be an Acrosound design used by Ampeg and atach some files found if you.re interested by floating paraphase:

150_UL_6V6s.pdf

acro6y6-el84.pdf

The See-Saw circuit - A self balancing phase splitter .pdf

acrosound.pdfacrosound.pdf

Understanding Audio.pdf

floating paraphase inverter.pdf