| Author |
Message |
    
Seymourduncan
| | Posted on Thursday, August 21, 2003 - 11:18 pm: | 
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hey,anybody see anything wroung with turning
L-14 out a couple of turns and vr-4 all the way
and back a hair .....cobra 29 ltd ,,,this sounds real beefy .think it will hurt the radio ,,,just experimental for a friend
seymour duncan |
Tech808
| | Posted on Thursday, August 21, 2003 - 11:37 pm: |
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Well,
You need to Adjust: L12, L13, L14 for AM Power.
You can Adjust VR4 or cut D11 for Modulation.
Lon
Tech808 |
Seymourduncan
| | Posted on Friday, August 22, 2003 - 7:17 am: |
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will This hurt the radio , 808? |
Tech808
| | Posted on Friday, August 22, 2003 - 9:11 am: |
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No it will not hurt the radio.
Adjust: L12, L13, L14 for Maximum forward swing on power and back down a little.
Adjust VR4 all the way Open and then back down a little.
I personally do not like Clipping or running a Radio all the way open on Power or over 100% Modulation.
If you want a more power without spending a lot of money, I would suggest a KL40 Amp. $29.99 and it will give you 28 - 30 watts of good clean power out.
Check out the Review on the KL-40 in the Subscriber (Preview Section} of the Forum under Product Reviews KL-40 Modile Amp.
http://www.copperelectronics.com/cgi-bin/checkitout/checkitout.cgi?catalogSTORE:CKIE:prodW90-KL40+
Lon
Tech808 |
Taz
| | Posted on Friday, August 22, 2003 - 12:30 pm: |
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808,
In a mobile clipping the resistor isnt too bad, but on a base neighbor problems can start. |
Seymourduncan
| | Posted on Friday, August 22, 2003 - 6:07 pm: |
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thanks 808 and taz ,,,,how do you adjust L-13 its just a spring and L-12 dont effect the power any
just trying a few things dont like cutting something that aint broke thanks
seymourduncan
Seymorduncan,
You Spread the Spring open Very carefully!
Watch your Watt meter & you will know when to Stop.
Lon
Tech808
Lon
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Seymourduncan
| | Posted on Saturday, August 23, 2003 - 2:17 pm: |
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thanks again,808, im learning slowly,but surely.
these little tricks really make a diffrents in
the radio thanks
seymour duncan |
228
| | Posted on Wednesday, September 03, 2003 - 10:25 am: |
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forget the KL-40 and leave C-73/D-11/TR-18 alone. the 29 will do 25 - 30 watts with the stock final. with the 2SC1969 the 29 will do 35 - 40 watts. i just finished a 29 that does 40 watts from 6 watts of carrier with the amc backed down 1/3 from the fully open setting.
228 |
Tech808
| | Posted on Wednesday, September 03, 2003 - 4:52 pm: |
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228,
Sorry, but NO!
A 2SC1969 18 Watt Final is NOT! going to throw anywhere near 40 watts.
No, Stock Cobra 29 is going to throw anywhere near 25 let alone 30 watts.
Somewhere you have received a Whole Lot of Mis-information on the Cobra 29's
I would suggest you invest in a NEW WATT METER.
Lon
Tech808 |
Bigbob
| | Posted on Wednesday, September 03, 2003 - 6:47 pm: |
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Regardless of what you do with a stock 1969,21 watts is pretty much it ,I believe adshare said something in another post about reengineering the bias system to achieve greater power,but I go for simplicity and low cost, Lon has a good point. |
Adshar64
| | Posted on Wednesday, September 03, 2003 - 11:21 pm: |
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Well a bad meter is probaly to blame for most of that. However the 18w rating is conservative collector dissipation heat level. The final (if in good condition) will go to 30w without too much work. You just need to know the right values of capacitance and inductance to use in there. Also drive and voltage(15v on the money)needs to be beefed up. Replace the plastic insulator with a mica with good heat paste. Without voltage/pi network changes 22 is probaly around where you will get on a accurate pep meter. Also a lot of guys overheat finals on tune up leading to a weakened unit with internal leakage - take it easy and tune at a lower mike gain or around 10w pep peak there and check results ltr at normal drive. See if it drops power after a while of QSO useage. Otherwise a good final and they do vary in performance. The pre-driver 12v mod is a key here. I have spent a lot a time checking its capabilities and if you get 26 ~ 28 w be very happy  . I just do this stuff because Im a pcb explorer lookin for new frontiers lol. Keep it nice and reliable. |
Taz
| | Posted on Thursday, September 04, 2003 - 12:58 am: |
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A basic tune got me 4w carrier 19w swing.
I thought it was acceptable. |
Seymourduncan
| | Posted on Thursday, September 04, 2003 - 9:17 am: |
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dead key 9 watts swing 18 to 20 watts depends what freq. they say it sounds like a trucker radio
thanks dudes,,,,,,,,,,SeymourDuncan |
228
| | Posted on Thursday, September 04, 2003 - 9:53 am: |
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the 2SC1969 is rated at 18 - 22 watts output with one watt of drive @ 12 volts, which also means that they produce higher output levels with more drive and higher Vcc, either or both. yes they will do 30 watts out without too much work, and more. no one thinks anything about pushing a tube for example to several times its rated plate dissipation and yet they deliver a few years of service. in common use most tubes are operated at 2 - 2.5 times (and higher) their rated plate dissipation in am and ssb service. since the duty cycle during the brief periods of TIME that the modulation peaks occur is a fraction of the non-peak periods the tubes can handle the higher than normal excursions from the plate ratings without too much problem. the same goes for solid state devices. i will admit that 40 watts is "pushing it" for a 1969 but it will do it, without deviating from oem biasing and without excessive levels of heat buildup.
as for the wattmeter used for the tests, i will just add this. the meter is a wawasee blackcat standalone with the LARGE meter movement. it is also one of the few analog meters using a jewelled D' Arsonval meter movement to allow faster response times to aid in peak measurements. it is calibrated once a year in one of the standards labs here in the state.
i'll just leave you all with one more thing. how many of you would buy a Galaxy 33/44/66 if it only produced 19 watts of transmitter output? yet magically the same 2SC1969 in these radios will produce 30 - 35 watts, without gutting the amc.
what's wrong with the idea that the same device in the 40 channel radios should be able to perform as well?
think about it.
228 |
228
| | Posted on Thursday, September 04, 2003 - 10:54 am: |
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Seymourduncan,
if your radio is tuned properly it should do EXACTLY THE SAME POWER on ALL channels when measured into a resistive, 50 ohm dummy load.
i would double check the alignment of both sides (cans) at L-21 and re-align to balance the power across the 40 channels.
in addition, the higher the carrier level the lower the modultion levels will be. rule of thumb (established by yaesu in the 60's) is that the peak power output should be at least 4 TIMES the carrier for optimum modulation levels.
for example, 4 watts carrier/16 watts peak, etc..
228 |
Bigbob
| | Posted on Friday, September 05, 2003 - 7:10 am: |
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There is a caviot "if" you only run am/fm you could rebias for class c like the old 23 channel am only rigs of yesteryear,copy some of their tank circuit designs,and reengineer,with proper heat sinking you could theoretically increase your output 3-times,kewl. |
Crafter
| | Posted on Friday, September 05, 2003 - 7:09 pm: |
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I have never got over 18 watts out of a 29ltd, there good radios dont get me wrong but a if your getting that much someone is volting the final and it wont last long. Must be like them 50 watt 148's everyone brings me that turn out to be 15- 24 watts on ssb clipped and strapped with a holley 850 and a tunnel ram. |
Bigbob
| | Posted on Friday, September 05, 2003 - 7:27 pm: |
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As I said class c biasing,is more efficient,runs cooler,higher output,also a more powerful modulator will fully modulate the carrier,the greater the carrier the more powerful the modulator must be,or just stick with the stock 29 and get a kl40 ala Tech 808. |
RCI 2990
| | Posted on Saturday, September 06, 2003 - 1:12 am: |
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Jack 228..
I have a Cobra 29 LTD classic that has the 1969 final and it will do exactly what you claim.
Welcome aboard.
You know who i am BTW....... :-) |
Adshar64
| | Posted on Saturday, September 06, 2003 - 1:15 am: |
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I run a 2SC1969 at 28w and its been going strong for over a year with weekly usage. Happy to send anyone photographic evidence as I dont BS.Volting the final is just a term for replacing high level am modulation with a constant 14v collector voltage, making it a linear stage follower to the driver . With a reduced carrier and npc mod it works good on am with less heat.
There is no volted final mod for ssb as thats how it ALREADY is. The means to achieve the higher levels of output in a efficient manner are perhaps beyond what you haven't delved into yet. if you understand the principles of input and output impedance and internal p-n junction capacitance on a final then you can learn how to unlesh its potential. Just because you cant tune a radio past 18w doesnt mean thats the end all and be all of it. Re-educate yourself in electronic principles to become a real tech and not just an adjuster. I wont put up with people who dont know what they are talking about. The class C deal is a efficiency thing but doesnt mean you are able to get three times nominal output, really just that it uses less power. You are not getting 100% modulation with class C. That is class A where forward bias current flows through 360 degree's of the input sine wave giving 100% linear replication. Class C relies on some reproduction of the original sine wave from external inductance in the output filling the gaps. there is a involved procedure for beefing up the 29. Anyone who would like it let me know. |
ChillyDog
| | Posted on Saturday, September 06, 2003 - 11:55 am: |
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I find it interesting that so many "golden screwdriver" experts have the "secret" to squeezing a few more watts out of a particular semiconductor device or a certain brand of radio. Volt this, bias that, tweek here, replace there. In my opinion, it's so much c**p!
The fact is, for the most part, it is possible to get more overall power out of any device when exceeding design specs. So what?
If you understand radio propagation and circuit design and have practical experience, you'll know these stupid games don't buy you any ability to communicate better.
It is no challenge to overdrive and/or overmodulate and/or poorly bias a unit to show more BS power on a typical CB meter. Does it help communication? NO!!
For the most part, an AM radio modulated at a 1:4 ratio of carrier to PEP is optimally tuned. It is possible to utilize some compression and/or expansion techniques to increase the overall average transmitted power, but there are tradeoffs in terms of audio quality and intelligibility.
If someone is bragging about a 1 watt "dead key" and a 20 watt "swing" they demonstrate complete ignorance of real radio physics. Does anyone who advocates this b**l really listen to their output? I'm not talking about "talk back;" do they ever use another radio to monitor what they put out? Further, do they ever tune off channel to listen to the splatter they generate? Of course not!
Here's the bottom line. For the most part, any modulation past the afformentioned 1:4 carrier to PEP ratio is overmodulation. Overmodulation results in out of channel along with out of band interference. Not only that, it sounds bad on channel! Overdriving an amplifier also results in out of channel along with out of band interference. It too sounds bad.
Legality ignored, if you want to have a more powerful radio here's the intelligent thing to do. Tune the radio to manufacture's specs. Use a voice processor to optimize your modulation characteristics without generating overmod. Properly use an amplifier (a good, well engineered one) to get more power, again without generating overmod distortion products. Transmit into a good quality transmission line/antenna system.
Forget about forcing a few more trashy watts out of a radio. For one thing, it's ineffective for communication. For another, do you really think you know more than the design engineers, who are working with proper training and equipment? Can you really do better with your little meter and magic screwdriver?
Bob
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Codeman
| | Posted on Saturday, September 06, 2003 - 1:05 pm: |
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Bob I could not of said it better. You took the words right out of my mouth. yeh back in the day i remember all those so called screwdriver experts bragging about there tweeked radios but to tell u the truth you could deffently tell who had been gracing the inside of there rig with the golden screwdriver. They were the ones you could hear 5 channels away but for some strange reason there signal strength on freaquency was the same as be 4 they butchered there rig MMMMMMMMMM. Maybe what was not relized is that to increace your signal streanth by 1 S unit at distance you must increase your power out by a factor of 4 times. All that for 1 S unit? WOW hardly seems worth the splatterly trouble. I think a factory box stock rig is the way to go. the engineers who designed and built the rig know far more than us about that radio. |
Adshar64
| | Posted on Saturday, September 06, 2003 - 2:48 pm: |
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Good posts and yes they are built that way to be reliable and to meet a cost factor.What im getting above isnt overmodulated and is set up on a sampo 60 mhz scope with not much mike gain about 2 oclock. Driving a bv2001 tube amp ie 1 el509 driving 3 el509 tubes to 1.5 KW and can still watch the TV in my shack while puttin out a call and there's no effect on the sound or picture.There are some changes that really match the 1969 impedance to a sweet level. the driver - final capacitance coupling was changed to 670pf. The final output inductance had the coil reduced from 4.5 turns to 3,5 turns. The pre-driver collector was fitted with constant 13.5 v instead of 8. After a few overs I can feel the heat level on the 1969 is normal and good. this impedance match is letting the rf flow better without choking at the same current draw.for example if you fit a mrf477 in there you will probaly see 20w but its pulling current as though its making 40w. And it is and 20w is pure heat loss because the impedance match in there is terrible. Its like when you tune a tube amp its the same deal. |
228
| | Posted on Saturday, September 06, 2003 - 3:13 pm: |
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Yes Bob, We Can........
But let me get to Codeman here first........
you wrote:
Maybe what was not relized is that to increace your signal streanth by 1 S unit at distance you must increase your power out by a factor of 4 times.
"This statement is incorrect" to increase the signal strength at the receiver end by 1 S-Unit the transmitter power output has only to be doubled TWICE/2 TIMES to achieve this, not 4 times. the standard is 6 db. per S-Unit. forget about the fact that at readings below S-9 in the typical radio (any) this range is so compressed that in reality 1 S-Unit is representative of more on the order to 1 - 2 db. or less with the more accurate references occurring at S-9 and above.
Bob,
as long as radio manufacturers specs and fcc type acceptance yields <or= 4 watts of carrier with 5.5 - 6.0 watts pep then yes, all of us can do better, both the experimenter, hobbyist and theseasoned technician. that should already be obvious to most.
and let's look at what the design engineers ARE doing here for a moment. what is their JOB? their job is to build a radio that provides reasonable performance for the AVERAGE user/consumer while complying to FCC guidelines. (and to do it as cheaply as possible i might add) to do that they build a transmitter using a device which conservatively speaking will do many times the power output than is allowed and then "restrict" the device/devices from being able to achieve their rated output.
@ VCC = 12V, Pin = 1.0W, f = 27MHz the 2SC1969 is rated for a minimun of 18 watts, a typical figure of 22 watts and no maximum figure is listed.
the average hobbyist/experimenter can usually achieve these minimum results without too much difficulty and, the truth be known, can be achieved with absolutely NO circuit modifications!
of course, the transistor found most commonly in the popular 40 channel radios is usually the 2SC2075, 2SC2078 and the 2SC2166. and the tank circuit is intentionally overcoupled in these new radios for a reason. anyone with any experience knows that simply backing out the slug in the tank coil will bring the tx final stage into resonance. this adjustment alone will allow a higher carrier level as well as increased pep power output. the timid may want to stop here. or they may want to try just one more thing. find the adjustable amc control and adjust it for a wide open setting. peak-to-carrier ratios should be in the area of 4:1 at this point.
congratulations! you have just performed what i refer to as a "simple transmitter tune-up". it is non-invasive (not requiring any circuit modifications) and requires very little test equipment, technical prowess or investment. anyone can do this themselves with a watt meter, a regulated power supply, a 50 ohm rf (dummy) load and the ability to follow instruction.
for the sake of simplicity we'll take it for granted that the transceiver is on frequency and that the receiver front-end was/is aligned properly so as to facilitate the best sensitivity possible while providing adequate adjacent channel rejection. additional test equipment is required here.
Bob also wrote:
Properly use an amplifier (a good, well engineered one) to get more power, again without generating overmod distortion products.
"The fact of the matter is that if the amplifier is good and well engineered then it should be virtually incapable of generating anything that wasn't delivered to it by the transceiver driving it in the first place".
228 |
228
| | Posted on Saturday, September 06, 2003 - 3:26 pm: |
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RCI 2990,
hopeful that all is well. good to hear from you.
73,
228 |
Bruce
| | Posted on Sunday, September 07, 2003 - 12:58 am: |
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228 ?????
This statement is incorrect" to increase the signal strength at the receiver end by 1 S-Unit the transmitter power output has only to be doubled TWICE/2 TIMES to achieve this, not 4 times. the standard is 6 db. per S-Unit.
Maby im missing something but a 6 db change of receive voltage is 4 times are you saying doubling power produces a voltage change of 4X ??
again maby im missing something .... |
Bigbob
| | Posted on Sunday, September 07, 2003 - 8:41 am: |
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Bruce YOU are CORRECT 3db is a power doubling,6db is a power quadrupling,according to the ARRLhandbook,6db=1S-unit,3db is the standard least change in signal strength noticable to the unaided human ear,I've read this in many publications,from arrl,cbc international,from many hams on the forum,that's why to increase your signal by a few watts may make you feel good has no effect on your buddies recieved signal and may make it harder for him to copy you,thus 3db is the accepted minimum change every where to effect a usable power increase.The radio MUST have a modulator circuit capable of fully modulating the carrier.I type with one finger and I have a ton more to say on the subject but I just don't have the time right now.Bigbob |
Codeman
| | Posted on Sunday, September 07, 2003 - 10:37 am: |
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228 Your statment is also incorrect. to many self proclaimed experts mmmmmmm. |
Codeman
| | Posted on Sunday, September 07, 2003 - 12:42 pm: |
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SO I AM RIGHT. INCREASING YOUR WATTAGE BY 4 TIMES IS 1 DB. SIGNAL STREANTH OR SHOULD I SAY 1 S. UNIT? I MOST CERTAINLY WOULD NOT DOUBT THE ARRL WOULD YOU? |
Codeman
| | Posted on Sunday, September 07, 2003 - 12:46 pm: |
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By the way what is a 29? Iam not into this CB thing so I am not familiar with the various models or makes.
Codeman the 29 is a Cobra Model 29.
Lon
Tech808
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228
| | Posted on Sunday, September 07, 2003 - 3:09 pm: |
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Codeman,
in my haste i failed to observe that your statement was indeed correct, though we both stated it differently. obviously multiplying by a factor of 4 and doubling two times are both the same thing. (i'm surprised no one else caught that) thanks for bringing that to my attention. on the other hand, no where in any of my previous posts did i PROCLAIM myself to be an expert.
73
228
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codeman
| | Posted on Sunday, September 07, 2003 - 6:00 pm: |
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No 228 you did not. nor am I thats why its called amateur not profesional radio HI HI. 73 CODEMAM. |
Taz
| | Posted on Sunday, September 07, 2003 - 8:00 pm: |
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code is old sensae stuff, out with the old and in with the new. |
Bigbob
| | Posted on Sunday, September 07, 2003 - 9:03 pm: |
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Man, Taz you really hit below the belt. |
codeman
| | Posted on Sunday, September 07, 2003 - 9:19 pm: |
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Hey taz to each there own you=CB. Me=CW. |
Bruce
| | Posted on Sunday, September 07, 2003 - 10:20 pm: |
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Taz ....
There is nothing wrong with code its a fine mode very good for week signal work. But like FM its not for everyone if CBers were allowed to run it you would find it DOES get through where others fail......remember it had its roots with a spark gap transmitter and a coherer receiver ( pre crystal) but with the fast amount of ways to transmitt to day to someone your age there is not much atraction.
..........July 5 2003 RIP A1.............. |
Taz
| | Posted on Sunday, September 07, 2003 - 10:41 pm: |
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Bigbob,
Just because things are old, does not mean there is anything wrong with it. Actually on the contrary since its been around so long it proves its point that its an excellent invention.
I didn't mean for my post to be taken in that way, but thats the way code is going. Its going on its way out.
I bet alot of us wouldnt be here if it wernt for code.
Taz 73's |
RCI 2990
| | Posted on Monday, September 08, 2003 - 2:21 pm: |
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Code is the reason id never go for my ham ticket.. IMHO its archaic and out of date and with all the technology that we have i feel its time for it to go.... If the FCC would drop the code requirements for the HF freqs then maybe more people would go ham. But the way i look at it ham is dying because the old timers refuse to let go of the code requirements and the ARRL seems to mostly cater to the old duffers more than anyone else... |
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