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  #17  
Old 02-03-2009, 07:58 AM
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Quote:
Originally Posted by linearone View Post

do you own a 16 pill freecell? Have you ever ran one with a current shunt inline?
I would ask that we should examine this statement again.

I apologize for sounding rude and I am whole heartedly impressed with ALL of your posts regarding technical know how etc but the fact is a 16 transistor amplifier even biased will never draw 320 amps, not even for a millisecond. I find that most people when running them as measured by a inline shunt will use about 150-160 amps upon keyup and when modulated they will usually be around 190 ish, MAYBE 200, depending on how the person runs it. I have sold two fatboy 250 amp power supplies and they run 16 pills flawlessly, for 2 years in one case. the Fatboy 250 amp supply is great bang for the buck, and will run a 16 pill with ease. I have personally load tested them to over 300 amps and they might hum a little there but they are still over 13v.

Long and the short of it Frecell I apologize for making this into a little war but I have a tough time with the specs, especially regarding current needs for amplifiers. EVERYONE will buy an amp from ANYBODY and when queried as to the currrent needs they will open the Xforce website and read from it verbatim. Xforce makes a good product, I understand why they rate things the way they do, they want the average cb'er to have 320 amps on tap to make sure it will never exceed the supply, and to ensure good performance. I get this concept but the reality is 99% of these class C 2879 boxes is that they will draw, MAX 10-12 amps per transistor.... Until you own one, build one, run one, buy a 500 amp meter and shunt, any opinion on its needs will be just that. an OPINION. You can read my signature line about opinions, BOB85 said it best. I can back it up with real world experience, real measurements and real time.

Sorry if this offends all the data sheet readers.

Sorry if I was abusive FreeCell.
I hope our friendship wont suffer.
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Last edited by linearone; 02-03-2009 at 08:10 AM.

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  #18  
Old 02-03-2009, 08:25 AM
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"but the fact is a 16 transistor amplifier even biased will never draw 320 amps, not even for a millisecond."

they will at 12.5V. the higher the voltage the less current that is drawn.

maximum collector power dissipation for a 2SC2879 is 250W, period
12.5VDC X 20.0A = 250W
13.8VDC X 18.1A = 250W
17.0VDC X 14.7A = 250W
20.0VDC X 12.5A = 250W

10-12A of average or rms current is equal to 14-17A of peak current.

they're current devices, quit volting them and let them draw current.
X-Force builds crap and i'm not stupid enough to use class c amplifiers
on am and ssb. current shunts don't turn average current measurements
into peak current measurements.

a 2SC2879 produces 100W of output at 27Mhz. with 5W input with a third order IMD mil spec. of approximately -24db.. @ 100W out that represents 400mW. of third order harmonic energy. @ 160W out that increases to 2W. as the amount of 3rd, 5th and 7th order products increase your wattmeter oversamples these products and lies to you about the amount of power being measured @ 27Mhz. and because amp builders are unaware as to what's going on they simply parrot the measurements without understanding what they're looking at. install a well designed low pass filter and all the out of band power products disappear.

(EVERY WATTMETER ON THE MARKET WILL SHOW THAT FIGURE MULITPLIED SEVERAL TIMES OVER AND EVEN MORESO AS 5TH AND 7TH ORDER ENERGY DEVELOPS, LEADING TO ABSOLUTELY ERRONEOUS AND INACCURATE (HIGH) MEASUREMENTS. this oversampling effect is so pronounced that at the fifth order harmonic (135Mhz) that 1W of power at this frequency is measured as 10 - 20 watts on the typical hobbyists wattmeter. (that includes Bird))

this feature will never appear in the junk manufactured by builders like AmPower, Davemade, Destroyer, Fatboy, Gator & XForce because once they implemented such a feature all the mythical power would disappear. you can't sell crap amplifiers if you can't create the illusion of a single 2879 producing 200, 250 and 300W of output. these levels of power ARE NOT OCCURRING as a result of additional energy @ 27Mhz.. when there is just as much importance attached to the IMD spec. as there is to all of the rest of the specifications then some will have a clue. you may now return to the matrix.

all of the above is the result of readily observable scientific fact, not of any opinion/s.

Last edited by freecell; 02-03-2009 at 11:01 AM.

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  #19  
Old 02-03-2009, 09:20 PM
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WOW!!! I should've gotten some popcorn before reading this thread!!

Actually, it's been quite informative (& FUN!!) to listen to two guys w/ their quite different beliefs, opinions, views,.... whatever you want to call it.

I currently run a TS-667V into what I'm guessing is a class C 8-pill. I only say "guessing" because I don't know enough about how transistor amps work to know by just looking "at a glance", which class it is. I know the TS-667V is class A/B, because of what their (Texas Star) website says or claims it is.

When I bought the 8-pill, I was using a Ranger AR-3500 (150 watt output), & was told I didn't need more because of the charging system in my new Dodge (& computer) wouldn't take it. I've learned through lots of "Trial & error", what works & what doesn't as far as a "pill box" is concerned.

I understand "HOW" a tube works as I own SEVERAL tube amps (30+), & the difference between a "PNP" & "NPN", & listening to knowlegable people here on this website sure helps.

I can see what Freecell is saying, & I also understand what Linearone is saying, but I wonder how many shootouts Freecell has been to where a "whatever pill"- volted box that shouldn't work (according to what Freecell is saying) is spanking every single amp that some "techie" ham has brought?

I guess what I'm trying to say, it's just like when you go drag racing & see some poor guy dumping a 10LB bottle of NO2 (Nitrous Oxide) into a stock engine. Sooner than later he winds up w/ a blown motor.

Nobody @ a CB shootout is looking @ an O-scope or worrying about "3rd order IMD" while listening to the Watergate playing back "Relay, Relay, Relay!!!"

BTW - I run the 667V on low, w/ the vari. output set to 50 watts deadkey-swinging 250 when I have the 8-pill on. 50 watts deadkey into 8 pills = 6.25 watts for each transistor. Anymore than that & my "signal" would swing backwards.

Just my 2 cents worth....

Last edited by Suicide Ride; 02-03-2009 at 11:45 PM. Reason: Spelling

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  #20  
Old 02-04-2009, 04:14 AM
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Im not even talking about being volted in competition, I am just talking about running a 16 pill on the base, he needs a 250 amp power supply.
thats all
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  #21  
Old 02-04-2009, 07:26 PM
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First off, I want to apologize to Freecell for my last post as I MEANT NO DISRESPECT towards him. His immense wealth of knowledge is what is needed on a site like this so folks (like me) can hopefully learn before burning up very expensive & sometimes RARE equipment!!

I'm curious Linearone, I thought the question was about any issues running a 16-pill Joker (a comp. box built for volting?) for a base amp.

When the Firebird tube amp deadkeys 112 watts or more (It's bound to happen: "forgot this was on, or that was off", etc.), & the 16-pill is hooked up to ANY SIZE power supply "running 16-17 volts", how many amps WILL the transistor amp draw (MAX)? Wouldn't it be better to have more amps available than needed?

I know when a transistor amp in a vehicle isn't being fed enough current, the audio out and/or signal suffers, so if the P/S running the 16-pill isn't big enough, wouldn't the same be true for the base?

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  #22  
Old 02-04-2009, 10:45 PM
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"....50 watts deadkey into 8 pills = 6.25 watts for each transistor. Anymore than that & my "signal" would swing backwards."

50W is too much carrier for 8X2SC2879's. that transistor complement runs out at 200W carrier & 800WPEP at -24db. for third order (81Mhz.) IMD products, with less than 50WPEP, not carrier. if the peak-to-carrier isn't just at or under 4:1 then you don't have a modulation index of 1, or 100%. another way to state the exact same thing is that a modulated signal with an index of 1, (100%) occurs when the PEP exceeds the carrier by exactly 6db., as in the example of 200W carrier & 800WPEP. the modulation amplitude is directly dependent upon the peak-to-carrier relationship of the transmitted envelope. this peak-to-carrier ratio is next to impossible to obtain when using class c amplifiers because of the amount of base input signal required to overcome the reverse bias condition of the power transistors. class ab amplifiers operating in the middle of their power range will mirror exactly the peak-to-carrier relationship generated by the transmitter

even at -24db. the amount of amplifier power @ 81Mhz. is approximately 3.2W or *8X2SC2879's @ 400mW apiece. to make things worse that amount of power @ 81Mhz. is greatly amplified when measured with the common wattmeter due to oversampling in the line section pickup and saturaton of the detector diodes in the bridge circuit.

to suppress the third order power to the point where it is reduced to less than 100mW would require an IMD spec. of -40db.. that can be accomplished by the addition of a low pass filter at the collector combiner output.

now you might think that 400mW - 3.2W* isn't anythng to worry about and neither did i until i found a receiver that would allow me to copy am signals from 80.895 - 82.215, the entire third order range of the citizens band, just below the bottom edge of the fm broadcast band. some of you might be surprised just how far low power harmonic energy is capable of travelling at those frequencies. it's not often you hear "break 19" at 81.555 Mhz..

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  #23  
Old 02-04-2009, 11:29 PM
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@ 250W you are already exceeding the maximum drive input for the type and number of devices used in the 16-transistor amplifier by 90W.
Wow, I asked Peakaboo the builder of this amp and he said I could swing 500 watts into the box and be OK. 160 watts pep is all it takes to drive a 16 pill? So then at 100 watts per pill 1600 bird watts is what the 16 will do with 160 watts of drive. That’s 10 watts pep drive per pill. Amp builders I have seen recommend a 1x4 driver for their 16-pill box. What about the 1600 watts dead key and 3200 watts pep rating for a 16 pill? If 160 watts were all that was needed to run a 16 pill then a 2 pill variable box would be enough. I suppose if I look at the situation from a scientific point of view then what FreeCell says is true. But if you look at what everyone has been doing, even what I have been doing for over 5 years running my 16 pill the way I was told then I have just been flirting with disaster and sooner or later something will blow. I am interested in running a clean station and I suppose that even I can learn something. Is 160 watts the proper drive parameter for an AB 16 pill? Well I don’t know what to think anymore. There is obviously some conflicting information here. The spec sheet was done at 12.5 volts. My batteries and system run at 13.8 volts. I am confused about what to use as a driver now. So out of knowledge comes confusion. I had plans of sending my 16 pill in to get band switching and filtering installed. Peakaboo used to offer these services when he was building. I definitely have plans on buying a low pass filter and I like the idea of using a power supply.
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Last edited by AE5RD; 02-04-2009 at 11:51 PM.

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  #24  
Old 02-04-2009, 11:55 PM
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LMAO @ a 16 pill drawing less than 250A.

It must be 90% efficient.

What did you use to run it in the mobile, Tejano?

AB is a current hog.

I do wish you luck.
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