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#41
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Hey Pat, I just tried a 6SN7 as an input stage to my previous 12AT7 concertina: looks so good at 100KHz I can spot the small notch in the peaks that my signal generator has. The total gain when using 480V B+ is exactly 15, in other words 3V in to get 45 V peak to peak output. I'll try a higher gain triode next and see how things shape up. Just to confirm things, if my datasheet for the 4X150 wants 48V peak grid drive, then that is equal to having two 48V outputs from the phase splitter?. Regards Mark Harriss |
#42
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Ross Matheson wrote:
Mark Harriss questioned: : I mean if I don't need the extra power they provide : what would make them advantageous?. Loosely bouncing off this to where the RSGB 3rd ed. is talking about SSB linear amplifiers, and Choice of Class of Operation, p.322, an approach I like "Before proceeding to a practical design, the question of whether the amplifier is to be operated in class AB1 or AB2 must be resolved. An advantage usually claimed for class AB1 is that, as grid current does not flow at any time, it is possible to drive the stage with a voltage amplifier incapable of delivering power, and that a regulated bias supply is un-necessary. There is little or nothing in the first point; any driver, no matter how heavily swamped by a resistive load, ought to be able to deliver the fraction of a watt required to drive the amplifier to full input in class AB2. The second point is valid, but potentially dangerous. In most cases it is virtually impossible to guarantee that the grid will not be driven positive from time to time, and when this does happen the distortion will be excessive. Even if the intention is to operate an amplifier exclusively in class AB1 it is desirable to design the driver, input, and bias circuitry as if operation in the grid-current region were intended. The extra complication in construction will be a small price to pay for effective insurance against high distortion if the stage is slightly overdriven." Radio Society of Great Britain "The Radio Amateur Handbook" 3rd Ed. '61-'62. __ OK, they are talking about an RF Single SideBand linear amp here - but I thought it was worth sharing, in the context of designing amps with RF valves, and possibly worthy of a considered transposition to audio amp driver design. Perhaps someone else may have already commented but I think the distortion one worrys about in the case of an SSB Linear Amp is the frequency sidebands developed out of channel as the concern here. That is a serious problem for the RF guys so that it is a primary consideration for them. Cheers, JLS |
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