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4 pill hg 2879c output capacitor value

3-500zg

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Dec 14, 2018
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I have a 4 pill hg2879c amplifier and I think the output capacitor is the wrong value. It has a 150pf capacitor in it. Can’t really find much info on it . Any help would be appreciated.
 

4 HG 2879C, so many building with, using different turns on combiner or different sized ferrite and material. Different wraps on transformers or different size transformers. Multiple answers to that. What Shockwave suggests is easiest. Takes out the guessing. But I will say this. Using comp 61 transformers, 3 turns, 2 turns plus ends on 61 1/2”x1/2” ferrite combiner using 18awg Teflon wire. It takes about 130pf. Any variation from what I said will change value needed.
 
Good luck trying to get a datasheet for the C version. I went to their website and couldn’t find one. As to the regular HG 2879, they basically copied the Toshiba specs. Yet it is a different animal.
 
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Thanks for all the input. I will use the arco trimmer to get in the ballpark. Measure the value and put a fixed cap in.
 
Consider the resistance of a capacitor is a big deal for a part used in this spot. Physically-large capacitors are better. More metal in the bigger cap means lower resistance, means less likely to burn up from high RF current.

If the circuit calls for 150 pf (for example) using three 50pf caps in parallel will split the current three ways, and reduce the heating of each cap.

Let your finger be your guide, if you don't have a fancy IR thermometer. A cap that gets too hot to touch will have a short service life.

73
 
Consider the resistance of a capacitor is a big deal for a part used in this spot. Physically-large capacitors are better. More metal in the bigger cap means lower resistance, means less likely to burn up from high RF current.

If the circuit calls for 150 pf (for example) using three 50pf caps in parallel will split the current three ways, and reduce the heating of each cap.

Let your finger be your guide, if you don't have a fancy IR thermometer. A cap that gets too hot to touch will have a short service life.

73
Amen!
 
I have not tried them and do not think I even own one. If I do own one it would be a gift from Gatekeeper. I am not one to chase after max power out of a signal device. So the idea of the 2879C from HG has zero appeal to me since I own 16 or so of the their regular 2879 marked product.

I am the type of guy that would build a 4 transistor device and proceed to run it at 2 transistor output levels on a heat sink large enough for an 8 transistor setup.

Build an 8 transistor amp and run it at 4 transistor output levels again with 2x the heat sink others would use.

Once in a great while tickle the electro-pixies just to have a some fun responsibly. So pushing harder on a part from a company with questionable quality control for more watts when I could just add more transistors makes no sense to me at all. Either way the volts and amps needed is so close tot he same for the added power compared to tossing another pair in inline it is false economy. HG's do not like running more than 15V reliably with out random popping it is not like the glory day of Toshiba 2879's that you could easily push to 21-24 volts and expect them to hold! Even the TRW and MOT transistors could largely be volted and expected to survive longer than they should have. If you can not push the volts up than the current requirement will be much higher and higher current means a lot more heat!!

The only people I know that really like the 2879C's tend to be people that run amps like idiots so keydown, drunk agitators and bowl type people not running tubes or LDMOS etc....They do not seem to offer much to the average user that uses an amp for actual rag chewing two way intelligent communication with other human beings. The builders that push them tend to cater to that sort of customer base and the meter-baters(sp) did I spell that right? Heard it said on youtube but never seen it in print!
 
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Any math to use to figure input and output capacitances when rebuilding/repairing?
There is but it never matches real world especialy with chinessium parts with fake data sheets and specification printed on parts that never match what you actual get. Arco's are your friend!
 
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