why will the 1969 final do more power in a 29LTD than in a 148GTL?

[loosecannon]

hi all,

i know this has been discussed before, and i do not want to get into a debate about whether or not its possible, and blah, blah, blah...

i would like to hear from the people who know the why's and how's of this; what are the differences in the circuitry of the 29LTD and the 148GTL type chassis that make the 1969 final deliver more power in the 29LTD type chassis?

please be as specific as possible in your responses, and sounding "techy" is not only allowed; it is encouraged.

thanks,
LC

 

[Shockwave]

Since you are comparing the 148GTL against the 29LTD I will assume we are talking about AM power output. In this case the answer is really quite simple. The 148GTL only applies modulated 6 volts to the collector of the final and driver since it uses a series pass modulator on AM. The 29LTD applies 12 volts to the final and modulates this voltage through a transformer.

There are ways to get around the 6 volt issue in the 148GTL. You can disconnect the wire that feeds voltage into the final. Use a choke in series to feed 12 volts to the final (not the driver). Connect a capacitor to the final side of the choke to feed audio to the final directly off the audio chip. The choke must be a value that is high impedance to the AF so that the audio chip is not loaded down by the 12 volt line and can be decoupled.

This use to work great in old school 148GTL radios. I have been able to spot distortion on some of the later units when this mod is done. Not sure what the difference is but I've seen it enough times to know there is some variation between the old radios and the newer ones.

 

[loosecannon]

shockwave, thank you so much for your response.
yes, i am referring to AM mode, and you have hit upon the exact reason i asked this question.

so, by doing the mod you posted, where the 13.8 volts is applied to the final instead of the driver; will the 148GTL chassis exhibit the same wattage output as the 29LTD will? (assuming of course that the 29LTD chassis had been "hot rodded" with the 1969 final along with the other mods involved)

one thing im looking to find out is what difference, if any the transformer is making in the whole equation.

i have heard people in the past say "the voltage gets stepped up by the transformer". but looking at the schematic, the voltage is fed through the primary of the transformer. so how is the voltage stepped up?

what am i missing in my assessment of this? (there's always something LOL)

thanks again, looking forward to learning more about this,
LC

 

[Moleculo]

but looking at the schematic, the voltage is fed through the primary of the transformer. so how is the voltage stepped up?

Look at the specs on the transformer used. If there are more turns on the secondary, then it's a step-up transformer.

 

[loosecannon]

so how much voltage actually gets applied to the final in the 29LTD chassis?

seems to me that the voltage feed to the final is not changed in the "50 watt mod", so if the radio is in complete stock form, is the stock final also receiving this "stepped up" voltage?

i am trying to get the straight facts on this so that when i am asked about the merits of this mod; i will have some solid info to offer.

thanks for all the input so far,
LC

 

[Moleculo]

In the 1969 mod the voltage isn't changing. If you look at the components that are replaced, they're all about delivering more modulation / drive to a final that also has more gain (I'm assuming the 1969 has more gain than the stock final). At least that's my take on it.

 

[loosecannon]

thank you moleculo, thats exactly what im trying to figure out.

so, the final gets 13.8 volts in the 29LTD whether the "50 watt mod" is done to it or not. right?

if thats the case, why wont the 148GTL chassis do 40-50 watts when 13.8 volts is applied to the final?

surely the 148GTL chassis, if modded, can apply an ample amount of modulation to push the peak watts up.

i hope there is an answer at the end of this road, LOL,
LC

 

[Switch Kit]

In the 1969 mod the voltage isn't changing. If you look at the components that are replaced, they're all about delivering more modulation / drive to a final that also has more gain (I'm assuming the 1969 has more gain than the stock final). At least that's my take on it.

This sounds pretty logical. A 50 watt 148 with what final and driver it already has ? Well "My guess" would be , why it wouldn't work would have something to do with it being AM and SSB type radio.

Modulated/drive to final , even the 1969 mod is not a perfect science. The 148 has a 2166 driving a 1969 (or did) I believe the 2166 is a 15 watt transistor and the 1969 is a 25 watts. I see what your saying LC , but I would certainly think it had to do with the 148 being a SSB radio ?

I have seen them put 1 2290 in 148s and get them to do over 50 watts. But that's another story.When you talk about 148s/2000s over the years it's pretty much been the same old story. Always has been a radio that never needed much more then a light tune up or tune down , because to much was always to much on those to begin with. Don't volt me dude !