chart of output transformer pri impedance vs output tube

[mikepukmel]

Hi All,
Looking for a chart with output tube type vs output transformer target primary impedance. (2 or 4 tubes). Must be out there someplace. I tried looking through data sheets, didn't know which numbers to use. This number depends no plate voltage, so is there a formula for this based on other tube characteristics?
Thanks
MP

[pdf64]

There are too many variables for such a chart to be feasible.
Have a play on nickb's page Interactive Valve Data Sheets
Select the tube type and operating arrangement.
Click and drag the sliders for electrode voltage, load impedance etc.
Take care to note on the results when the operating class moves from AB1 to AB2, as that's only feasible in practice when the driver is suitable, eg interstage transformer.

[mozz]

There is a somewhat correct chart out there, i may have a copy, will look after work.

[soundmasterg]

There is a range with all tube types for optimum primary impedance for power output that depends on plate voltage, bias method (cathode bias vs fixed bias vs grid bias). As you go one way or another from that optimum point (which is more like an optimum range) then you get lower power and increased distortion. The problem is that the range is quite wide and the circuit will work fine throughout the range. For instance, a pair of fixed bias 6L6GC's at 450V B+ will work fine at 4k, but it will also work fine at 8k with slightly reduced power and a little more distortion. If you change the B+ to 360V, then much the same is true...it will still work fine at both extremes with a different set of performance variables than the one at 450V. There is math to figure it out in advance to a reasonable degree, but the Radiotron Designers's Handbook is notoriously hard and technical to read.

Greg

[mikepukmel]

Thanks everyone.
Cool web site, nice calculator.
Tubeampbooks has the radiotron designers handbook! Wahoo!.

[J M Fahey]

The proper answer here is to learn to do the graphic calculation and design yourself.

Itīs not hard at all, of course like anything else you start slow and then pick up speed, and luckily all the needed data is there, on the datasheets.

You choose all the operating points: plate and screen voltage, idle current, biasing, and impedance is the *result* of all these.

[mikepukmel]

Thanks Juan. I have a few good books, went through the graphical methods, but the info is not quite at the tip of my fingers yet, as they say. I will go through again. Also, great site NickB has with the calculator.

[SoulFetish]

The proper answer here is to learn to do the graphic calculation and design yourself.

Itīs not hard at all, of course like anything else you start slow and then pick up speed, and luckily all the needed data is there, on the datasheets.

You choose all the operating points: plate and screen voltage, idle current, biasing, and impedance is the *result* of all these.

Fahey took the words right out of my mouth. Learning how to draw load lines was one of the most useful skills I've learned. It's one of the quickest ways to get a pretty accurate big picture (Pun intended, I suppose) analysis of the operating conditions and circuit behavior. You're going find commonly used primary impedance loads for popular tubers, but as previously mentioned, you can often find a wide range of load impedances for a given tube provided in the data sheet. The operating class, bias, and terminal voltages are the determining factors.
I was going to screen shot a page in a 6L6 data sheet to show you that you'll find optimum Loads from 2.5k-9k for a pair of 6L6s, but I see that soundmasterg was a step ahead of me on that one
Don't cheat yourself out of the process of learning to do this. Nicks interactive datasheets ia a great tool and I use it often. It's like the automatic transmition of load lines plotting.
It's great to kick back and drive an automatic, but real men still know how to drive a standard.

[J M Fahey]

I am *certain* about having posted a couple practical examples here, somebody else also did, maybe searching back with the proper keywords can succeed.
"loadline"? "graphic calculation"? ....