How to Determine Push Pull Plate Resistance
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How to Determine Push Pull Plate Resistance
Hi everyone, I am still planning out my first tube amp venture. I will be using submini's, namely 5902's for the output tubes. I want to run them in a push pull configuration, but I don't know how to take what I find in data sheets and apply it to this situation. The data sheet lists a plate resistance of 3k (I am assuming this is the resistance the plate wants to see, such as for transformer specifications). I am guessing that that is for a single tube and I was wondering if that value changes any if I put the tubes in pp. I assume that it does, my main question is how so, so that I can calculate out what kind of ratio I need in an OT. Thanks.
Exact science is not an exact science
Re: How to Determine Push Pull Plate Resistance
Not 100% sure but I think it would be 1.5K for a pair.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: How to Determine Push Pull Plate Resistance
It's not plate resistance you're looking for -- it's load resistance. For most (or many) tubes I'm familiar with, the nominal load resistance in push-pull AB1 is about one-third higher than the single tube Class A load resistance. There must be some data sheets out there with detailed specs for various voltages.
Re: How to Determine Push Pull Plate Resistance
Yes, you are looking for effective plate to plate load or Rpp.
For pentode and beam tubes this is chosen with regard to distortion, plate dissipation and power requirements. I suggest you read information on loadlines here http://greygum.net/sbench/sbench101/
Valvewizard.co.uk also provides a quick way to determine it [edit: for PP class AB or class B] without need to draw the composite characteristics. Essentially you draw a load line on the plate characteristics from Ebb to the knee of the Vg=0 curve. The slope will be -4/Rpp. Experiment with various lines and if interested work out the distortion characteristics from method in S Bench's website.
Edit: close enough is usually good enough
as unless you want to get an output tranny wound to spec you will have to use off the shelf units. The valve wizard site also gives excellent and clear insight into the conduction and loadline of each tube in the push pull config. In it you can see how changing the bias while maintaining Ebb and Rpp affects the load line for each tube. It gives a good uncluttered insight to bias and plate dissipation and that 70% rule.
For pentode and beam tubes this is chosen with regard to distortion, plate dissipation and power requirements. I suggest you read information on loadlines here http://greygum.net/sbench/sbench101/
Valvewizard.co.uk also provides a quick way to determine it [edit: for PP class AB or class B] without need to draw the composite characteristics. Essentially you draw a load line on the plate characteristics from Ebb to the knee of the Vg=0 curve. The slope will be -4/Rpp. Experiment with various lines and if interested work out the distortion characteristics from method in S Bench's website.
Edit: close enough is usually good enough
as unless you want to get an output tranny wound to spec you will have to use off the shelf units. The valve wizard site also gives excellent and clear insight into the conduction and loadline of each tube in the push pull config. In it you can see how changing the bias while maintaining Ebb and Rpp affects the load line for each tube. It gives a good uncluttered insight to bias and plate dissipation and that 70% rule.
Last edited by Ears on Fri Feb 20, 2009 2:16 am, edited 1 time in total.
Re: How to Determine Push Pull Plate Resistance
oops, an edit turned into a quote