Transformer Testing

[skyboltone]

Ben:
Just give me the DC resistance of the HT winding, red to red and I'll run the virtual test. 5K is just about right. I'll try 4007s and a 5AR4 just for grins.

Dan

[benoit]

83.5 Ohms, red to red. I appreciate your help immensely. Would you mind explaining both how you implement this setup in the software (i played with it some but didn't fully figure it out) and what it all means?

Thanks much,
Ben

[skyboltone]

83.5 Ohms, red to red. I appreciate your help immensely. Would you mind explaining both how you implement this setup in the software (i played with it some but didn't fully figure it out) and what it all means?

Thanks much,
Ben

Well, I'll tell you right off the bat that you have a fairly robust transformer. The lower the number the better regulation (i.e. capacity) you have.

Open PSU Designer II and you'll see a transformer with a bridge rectifier, a 220uf filter cap and a 5K load.
Hover over the the words "Bridge SS" and right click. Click change. You'll be given a few options, tube, full wave, half wave, bridge, SS etc. Choose SS and Full wave.

Hover over the transformer description and right click. You'll see edit. Click on that. Change the voltage to the center tapped value. In other words, the half coil voltage. 295 and the DC resistance of the whole coil. (I think it wants the whole coil resistance. Somebody correct me if this is wrong)

In the lower left panel you see listed a bunch of values of I,V, and later as you start to add loads at each stage L sub I and sub V.

But as it stands now, you see a 5K load, your transformer and a 220uf filter. Hover over the filter cap and right click. Edit to the value you want.

Then, down the left panel of values, click the ones you want to look at graphically. For now, try V R1. You'll see about 383.5VDC with about 3 volts of ripple. That's about 1.29 for a cap entrance filter. Ideally we like to see 1.35 to 1.4 if the transformer is rated for a 5K load at voltage. Phil_S gave you some other tube resistance ratings to try. I'm quite sure that your tranny would be good for a couple of 6V6s or EL-84s and may even handle a pair of EL-34s. But it's probably not ideal for (say) 4/6550s for instance. If the graph scale makes the whole screen turn one color, there are some magnifying glass gizmos in the right corner that help you to put it in scale.

If you hover over the 5K load and right click you'll see the option "insert". This allows you to put in constant R or constant I loads, and LC or RC filters. There is an example PS given with the program with I think 5 nodes. You can just edit that and "save as" so that you always have the original to fall back on.
From there Ben, just play with it. It's intuitive compared to most any electronics program. The hard part is to decide what the I is for any given stage. The program gives no help in that department. The tube manual will give you idle plate and screen loads. These are the largest. PI loads can vary from a couple of MA to about 7 or 8. Each stage of a 12AX7 can vary from .5MA to 2MA. I've figured no sure way to tell. Design for 1ma per preamp stage 5ma for the PI and the book values for screen and plate loads. You'll be close enough. Then tweak the dropping string as needed when the amp is running.

One more item. You'll see the button for simulate followed by two windows for varying time values. To start leave the delay at 0 and the duration at (say) 10 seconds. This allows the graphic display to show you how the PS ramps up to it's final values.

[M Fowler]

Old thread but Ben dropped these transformers off along with a bunch of other chassis and chokes, transformers etc.

A Magnatone with 6v6 is the plan.