Tuesday, December 9, 2014

Operation Rock Garden Phase One: Supplies!




I've decided to call my One Tube MOPA project "Operation Rock Garden." Because it is another project that involves a crystal controlled oscillator, I figured, why the heck not?

Phase one deals with power supplies. Not supply in this case, but supplies. There are three distinct voltages for this project, 2 different DC B+ voltages, and an AC filament voltage. Each one needs to be able to handle a certain amount of current as well. bBcause of this, I'll probably need a few solid state parts, like diodes and voltage regulators, for creating a rectifier circuit, or voltage doubler.

Step 1 of this phase is to light the filaments. To do this I need a circuit that can supply 9.7V at 600 milliamps. The easiest way to get there is to take the massive milsurp filament supply voltage I have, and series up the proper combination of taps to get as close to 9.7 as possible.


It came from a homebrew power supply for a Heathkit SB-102, and other than that, I don't know much about it, but I figure if I connect tap 8 to tap 9, and take my voltage from tap 7 and tap 11, I should have somewhere in the neighborhood of 9.45 Vrms, maybe a little more, because this primary is listed at 117 Vrms, and I'm around 120 consistently here.

Backside, showing taps.

I don't see this as an optimal solution, but it can handle the current, and the voltage should stay reasonably under the max. The supply has this lug sticking out of it.




The lug is behind taps 5 and 3. I think it's there so the core can be grounded, but I'm not sure the core needs to be grounded in the application I'm using it.

I will take advise in this matter.

Here's the plan for tonight when I get home from work:
1. Hook up the Transformer, ground (or not) the lug.
2. Construct tube base breadboard.
3. Go to bed. Light the sucker when I'm sure I have at least 9.4 Vrms, and after I've rested.

I'll be listening to 3579 KC while building, and the NoGA Twin Tube 80 will be standing by...


***EDIT***
General concensus is that the lug can be grounded with no ill effects, and the filaments should be ok at that voltage.
We'll see if I can get 'er done tonight!
******

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