Galaxy saturn

[BAGEBOY]

Can. Someone shed some light on modding the galaxy Saturn to mosfets. U can state the pros and cons.my Saturn when from 15rms to about 7rms I have have finals capacitor diodes Etc been at it for 2yrs. If I change to mosfet may it change the out put?also typical output of a dual final. Galaxy Saturn

 

[nomadradio]

You'll need a power supply with nearly twice the current rating. Fortunately a chinesium 10-Amp switchmode power supply will fit nicely where the original transformer, rectifier bridge and filter cap are now. The modulator transistor TR51 (Q51?) will overheat from the additional current demand of the MOSFETs. There are two easy options here, either upgrade to a Palomar MaxMod transistor, or do the "RWOB", (red wire on bottom) mod. This consists of powering the two finals' collector circuits directly from the power supply, rather than from the modulator transistor. This will just slightly increase peak RF output since the finals are now getting a Volt or so more juice by bypassing the voltage drop inside TR51. Mostly it takes the load off of a factory-stock TR51 such there is no risk that it will overheat now unless a boo-boo with bias settings or high SWR or such cause an overload.

Of course the input side circuits for the new MOSFETS are totally different. The bias diode, bias trimpot and fixed resistors associated with them have to go. They'll get replaced with a small zener diode, new trimpot and fixed resistors attached to it. They will have much higher resistance values than stock.

That's the simplified version. I would spend whatever this costs toward either a spare set of the original finals, or into a piggy bank for a linear.

If the objective is more power, you're spending dollars per Watt. An amplifier can be had at Watts per dollar.

Kinda like comparing "gallons per mile" with "miles per gallon".


73

 

[BAGEBOY]

You'll need a power supply with nearly twice the current rating. Fortunately a chinesium 10-Amp switchmode power supply will fit nicely where the original transformer, rectifier bridge and filter cap are now. The modulator transistor TR51 (Q51?) will overheat from the additional current demand of the MOSFETs. There are two easy options here, either upgrade to a Palomar MaxMod transistor, or do the "RWOB", (red wire on bottom) mod. This consists of powering the two finals' collector circuits directly from the power supply, rather than from the modulator transistor. This will just slightly increase peak RF output since the finals are now getting a Volt or so more juice by bypassing the voltage drop inside TR51. Mostly it takes the load off of a factory-stock TR51 such there is no risk that it will overheat now unless a boo-boo with bias settings or high SWR or such cause an overload.

Of course the input side circuits for the new MOSFETS are totally different. The bias diode, bias trimpot and fixed resistors associated with them have to go. They'll get replaced with a small zener diode, new trimpot and fixed resistors attached to it. They will have much higher resistance values than stock.

That's the simplified version. I would spend whatever this costs toward either a spare set of the original finals, or into a piggy bank for a linear.

If the objective is more power, you're spending dollars per Watt. An amplifier can be had at Watts per dollar.

Kinda like comparing "gallons per mile" with "miles per gallon".


73

How do you do the RWOB Mod? Thanks. For the info what is strange I have change almost all parts in the Rf section. Finals. Caps resistors even new trim pods. And still power. Is about 25/30pep it use to be 40watts plus on Ssb and Am

 

[nomadradio]

I have change almost all parts in the Rf section.

Um, "changed" as in replaced with original types?

Or "changed" as in modified for MOSFETs?

The RWOB mod removes the "mirror" board that serves as a jumper wire feeding modulated power from the modulator transistor to the driver transistor and to the two final transistors. A wire goes from the innermost 'fork' contact to the outermost contact. This restores the modulator transistor's connection to the driver transistor. Never hurts to check bias current first before soldering this connection in place.

A longer wire goes from the main power-supply filter cap's hot side to the center of the three fork contacts. Likewise, connecting a current meter between the wire and that contact will allow setting bias current before it gets soldered in place.

Not rocket surgery, just a "power jump" as folks like to call it.

Have you checked the power supply voltage? Has a big effect on peak output power.

73

 

[BAGEBOY]

Um, "changed" as in replaced with original types?

Or "changed" as in modified for MOSFETs?

The RWOB mod removes the "mirror" board that serves as a jumper wire feeding modulated power from the modulator transistor to the driver transistor and to the two final transistors. A wire goes from the innermost 'fork' contact to the outermost contact. This restores the modulator transistor's connection to the driver transistor. Never hurts to check bias current first before soldering this connection in place.

A longer wire goes from the main power-supply filter cap's hot side to the center of the three fork contacts. Likewise, connecting a current meter between the wire and that contact will allow setting bias current before it gets soldered in place.

Not rocket surgery, just a "power jump" as folks like to call it.

Have you checked the power supply voltage? Has a big effect on peak output power.

73

I have replaced with original np arts I used the dx11b.schematic from cb tricks

 

[nomadradio]

There are four slug-tuned coils in the transmit chain that bear a look. A radio called "Galaxy Saturn" was produced for decades. Production differences showed up every few years.

Just the same, pretty sure all of them use the same callout numbers for the four tuned circuits in the transmit chain that can cause trouble. L40, L42, L43 and L44 each have a tuning slug that should show a proper peak with the top of the slug BELOW the rim of the hole in the top of the can. Best way to see a sharp peak is to transmit on sideband with a steady tone into the mike, and the mike gain set for around 2 Watts.

If any of those four appears to peak with the slug DEAD EVEN with the rim of the opening, that can has a failed capacitor inside.

And if all four of them pass that test, the fault lies elsewhere.

73