Finals 2166 / 1969

[Shockwave]

The reason that transistor shows higher peak power in a Cobra 29 has to do with the modulator circuit. The Saturn never puts more than 12.5 or 13 Volts onto the final transistors' collector circuits. The 29 puts audio peaks of 24 Volts or more onto a 2166. This is why a typical Cobra 29 will swing roughly twice the peak power that a Saturn with two 2166 finals should get.

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Give any series pass modulated radio the same advantage as the 29LDT with modulated 12 volts feeding the finals, and it makes the 29 look far less impressive. That modification worked so well that it's a shame it's been butchered by those who insist on only suppling 12 volts with zero modulation.

In most cases you have the same 5 watt audio chip as the 29LDT but, it does nothing on TX in these radios other than drive the Darlington modulator, with about zero power required to do it. Use that wasted audio chip power to modulate the final, through an AF choke (alternator whine filter). Forty watts or more PEP was not uncommon but, it sure did require a final upgrade.

To get the right final for this mod, go on eBay and buy and old Motorola 25 watt low band Moxy radio and rape the final out of the back heatsink. That transistor is high gain and rated at 25 watts continuous carrier. It has ample headroom to be biased into class AB and support 40 watts PEP with a 10 watt carrier. None I installed, ever came back for a final.

 

[BAGEBOY]

I have received my finals I got (2) original 2312 and I bought (6) Hg 1969..
I check 2 hg in my 2950 and the output was(29watts) 2-4 watts more on the Mitsubishi
I placed them in the Galaxy.Saturn I see only 2 watts using (2)2 2166 the finals get barely warm..to confirm. I remove and place back in the 2950 and the power was what I saw when I first checked. So it .means I have a problem with the saturn which causes me to see only 2 watts. I tried the 2312 in the 2950 saw 34 watts in the saturn almost 4 watts Any ideas

 

[nomadradio]

Might have a look at C166. If it's a ceramic disc, it could have overheated and failed. In the mid-1990s the factory part got changed to a silver mica cap. So did C165. We got in the habit of installing a silver mica in any radio we serviced that had the older ceramic disc in those two spots.

Of course, making sure the full drive signal is reaching the driver transistor matters. Pretty sure we already covered the importance of the physical position of the tuning slug in L43, L42 and L40, to make sure the slug shows a peak at least one whole turn below the rim of the hole at the top of the housing on each one. When any of them shows a peak dead even with the rim, that indicates a failed capacitor inside that can.

If used right, a 'scope can reveal where a signal is not being amplified properly. But with no way to measure this directly, this becomes a trial-and-error guessing game.

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