Can anyone comment on the differences in build quality & performance for the "New" re-intorduced Connex 4600 Turbo vs the older, original model? Do they tune up as well as the original unit? Thanks for the input.
Difference in build quality & performance for the "New" Connex 4600 Turbo vs Older
Discussion in 'CB Radio Forum' started by Holy Moses, Sep 22, 2014.
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The capacitance and threshold voltage being the two parameters of greatest importance when trying to get power to balance between several Mosfets in parallel (the design method used to replace those 2SC2290's). The threshold voltage Vt is merely the gate voltage at which the volume density of electrons in the inversion layer is the same as the volume density of holes in the body. The capacitance of the depletion layer is the second parameter one must match. I buy IRF520's (the device used for your 'new' 4600 from driver to final to all devices in the amplifier) hundreds at a time so grabbing a few will give a fair estimate of how well they match on average. Taking 5 new IRF520's at random out of several hundred I measured C and Vt. I measured them at random and listed the five in order of increasing depletion layer capacitance. I did not bother comparing Rds(on) (Drain-Source resistance), or Oxide layer capacitance. Frustrating, the board keeps aligning data to the left so I use - dashes to separate (not to be seen as negative signs).
------1------2-------3-------4------5
C = 838 pF, 842 pF, 922 pF, 940 pF, 1,100 pF
Vt = 3.0 V,--2.9 V,--3.9 V,---3.8 V,--3.9 V
I could have tested 500 of them and the results would be the same, parameters varying quite wildly and I buy only prime devices. I did this with a half dozen ERF2030's and found higher capacitance and deviations of both C, Vt, from similar to worse than the IRF520's. The simple fact is minute variations in doping, purity, deposition thickness to name a few create great deviations in parameters, and C, Vt, are not the only parameters to consider. What this means is no matter how many radios you choose to investigate you will never find one with matched devices. This can cause catastrophic failures in the amplifier (holes in Mosfet body, flame out, etc.) to occur quickly even with an antenna system with only moderate SWR, one where bipolar devices could tolerate without harm over long periods. All dependent upon your operating habits of course. This applies to all models and manufacturers on the market now, not just the Connex 4600 Turbo.
In my opinion nothing beats the Toshiba bipolar devices in these export class radios. I do not really care for the Mosfets at all but they are so cheap get used to them the manufacturers are not going to commission a factory to start building lead containing bipolar RF power devices. As many have discovered the lead free copies built in China are not worth a nickel. I would rather find a used older version 4600 but one also must consider what it has been through and whether or not they are ending up with a can of worms (bad controls, switches, leaky finals, etc.).Last edited: Sep 22, 2014
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Thanks for the unabashed input Outlaw CB. Anybody else care to chime in?
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