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Author Topic: timtron mod dx-100/apache question  (Read 2365 times)
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NR5P
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« on: June 28, 2010, 01:34:59 PM »

The timtron turbo mod that provides a better match for the audio tubes to look into located here http://www.amwindow.org/tech/htm/dx100.htm I want to perform but I'm having a hard time understanding exactly how this transformer works.  I know it is configured as an auto transformer and I know what an autotransformer is but I'm confused for some reason when I look at the schematic and I don't want to make a mistake and just move around wires without knowing what Im doing.  Seems simple take 500 ohm tap and move to one of the plates of the el34s and disconnect the bottom of the transformer at the transformer.  The highvoltage will still need to run through this bottom line to get to the primary. 

I just get a little confused as I try to understand this reconfigured circuit and how it is working after the mod is done.
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WD5JKO
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WD5JKO


« Reply #1 on: June 29, 2010, 07:23:12 AM »



OK, lets look at this in steps. You can take the primary of a push pull transformer and hook up two P-P driven audio tubes to it, B+ goes to the center tap. Then take either plate and tap into the wire and make this modulated B+ to plate modulate a class C RF amplifier. This is called push pull Heising modulation. If the mod transformer has a secondary winding, it is not used.

The beauty with this concept is that a zorched mod transformer can be replaced with a P-P hi fi output tranny (or maybe a HV power tranny) so long as the primary current imbalance does not saturate the core. If it does, then the E&I laminations might need to be re-arranged to add an air gap.

So with modified Heising as described we have a limited peak swing available (70-80% of B+) due to the modulator tube saturation characteristic at maximum signal level (plate V min cannot get to zero volts). This limits the maximum modulation percentage to ~ 70-80%.

So what Tim did with the article mentioned was to take the 500 ohm winding and properly phased and put in series with the mod B+, it increases the peak AC level to overcome the limitation of Heising modulation such that a higher modulation percentage can be obtained. Those trying this with a power transformer, can similarly use the 115v winding like Tim did with the 500 ohm winding.

To know further how Tim's mod changes the modulator P-P load impedance to get more audio power requires knowing the turns ratio of the transformer between all the windings. Does anyone know the published impedances, or turns ratios?

The mod transformer secondary now does nothing since one end is disconnected.

I hope my explanation is clearer than mud.. Roll Eyes

Jim
WD5JKO
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