| Author |
Message |
    
Kid_vicious
Intermediate Member
Username: Kid_vicious
Post Number: 180
Registered: 9-2004
| | Posted on Thursday, January 27, 2005 - 10:32 pm: | 
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am i to understand that the preamp in the kl-300p is always on? there is no switch for it on the amp and the ad says 25db gain. while it might be nice to have a preamp when you're out in the country with the vehicle's engine off; in the city, they're nothing but noise amplifiers, making listening quite unbearable. so what gives? am i misreading something? if its true, then is there a way to add a switch to the preamp.
i just got one of these amps and im afraid i might have to return it. please help.
matt |
Tech808
Moderator
Username: Tech808
Post Number: 4657
Registered: 8-2002
| | Posted on Thursday, January 27, 2005 - 10:43 pm: |
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Kid_vicious,
Yes the Pre Amp is always on.
This has been covered many times on the forum and in the description of the KL300 it also does not list a on/off switch for the pre amp.
Yes there is a mod to add a on/off switch.
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Inspector
Posted on Tuesday, March 05, 2002 - 12:54 am:
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If you want to use the pre-amp independently of the TX amp, in the KL300p, you can open the circuit at the junction of R2 and Tr2 and install a switch. With the circuit open, Tr2 will not conduct thus keeping the TX amp relay from engaging. The pre-amp relay will still function as it should.
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Just curious why would you have to return a amp in good working condition?
Lon
Tech808
CEF808
N9OSN |
Kid_vicious
Intermediate Member
Username: Kid_vicious
Post Number: 181
Registered: 9-2004
| | Posted on Thursday, January 27, 2005 - 11:39 pm: |
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i wasnt sure if there was a mod for it, and if i couldnt find one, the preamp on all the time was going to be a problem for me. you see, i live in las vegas, and this city has quite a large number of local drivers using the same channel that the local base stations have deemed theirs. with that many stations on the same channel, the heterodyne would be intolerable. im very happy to have an RF gain on my radio and i frequently turn it to 1/2 way. also my truck is a 1977 ford f250 4x4, i have a little motor noise from different sources in the truck, they are tolerable now, im afraid the preamp will amplify them also. anyway, i was checking my post because i was going to apologize for not searching a little more before i posted a question. i found the mod in the subscriber section. inspector is the one who posted it, but it is different from the one you referenced. the mod i am going to do is adding a switch to the base of TR3 so the TX amp will be on and the RX amp off. thanks for the help. you can trust me whan i say i DONT want to return this amp. i just need to make it suit my needs. i realize that this will void the warranty, but it works now, so i'll know i was the one who broke it if it happens. J/K! BTW, do you have to void the warrarnty to change the fuses?
the mod to class AB-1 looks neat, what are the advantages and disadvantages to running class AB-1? thanks again lon, im sure i will enjoy using this amp very much. who knows, maybe with the preamp on i can hear some of you guys this sunday!
matt |
Chad
Intermediate Member
Username: Chad
Post Number: 114
Registered: 11-2004
| | Posted on Friday, January 28, 2005 - 8:54 am: |
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I turn the rf gain WAY back on my 2547. I noted the S units of noise, or a distant station with the amp off, then turned the amp on and pulled the RF gain back to correspond, Marked that point with a wax pencil and wola, variable preamp! I was going to mod mine with a switch but it's now under the bench so that idea is scrapped, Still considering the class AB mod.
Kid keep us informed, if I get a wild hair and do it I'll let you know. Inspector is still active here and seems to really know the ins and outs of these amps. He may chime in and shed some light on new discoverys. He posted the mod around initally.
PS I voided the warranty after it was out of the box for 30 SEC. I gotta see what makes things tick  |
Tech808
Moderator
Username: Tech808
Post Number: 4661
Registered: 8-2002
| | Posted on Friday, January 28, 2005 - 10:52 am: |
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Chad,
If you have had it for 30 days your warrantry is history anyway as they only have a 30 day warranty from the Factory.
Also it is already an AB Amp so there is nothing to do. 
Lon
Tech808
CEF808
N9OSN
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Chad
Intermediate Member
Username: Chad
Post Number: 115
Registered: 11-2004
| | Posted on Friday, January 28, 2005 - 12:08 pm: |
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I was almost sure the KL300P is class C then the next step up (kl400) is when they start baising class AB. I see the base of the finals grounded through the drive transformer secondary on the KL300P and on the KL400 the tranformer secondary CT is biased with TR5 and D16/17/18. with D16/17 being the bias "string" It's hard to describe component numbers of the transformers as T1 and T2 functions are reversed in the schematics.
I really don't know how long this amp is going to be in the shop as I am considering the purchase of a KLV400 for the shack and moving the KL300P into the truck. I'm getting tired of using a deep cycle battery and the lady is going to want it back in the boat come spring
Any advice on the KLV400? I like toobz and think it would make a fine addition, the KL1000 looks a little rich for me right now and can think of other things to spend the extra money on(tower) that would get me better results. We will see when the tax return cometh!
Where is a good place to get a tower, or should I go knocking on doors in the country and get a old TV tower for my Imax2K? Not much wind load there Couple more months and the ground will be thawed. What is my max height and is that measured to the tip of the tower or the tip of the antenna? |
Kid_vicious
Intermediate Member
Username: Kid_vicious
Post Number: 182
Registered: 9-2004
| | Posted on Saturday, January 29, 2005 - 3:29 pm: |
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if the kl-300p is already a class AB-1 amp, then what is the mod inspector is talking about doing to the amp? i am hesitating on voiding the warranty until i find out what it actually keys at, as i have seen one that keys a bit low.
chad, i think the used tower route, (if you have a few friends to help), is definitely the cheaper route. as far as height goes; if your tower is not going to fall then your antenna wont fall. put it up as high as the law will allow!
matt |
Inspector
Intermediate Member
Username: Inspector
Post Number: 124
Registered: 12-2001
| | Posted on Wednesday, February 09, 2005 - 8:00 pm: |
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Like Chad posted, the 3oop is Class C, as the transistor's bases are grounded through the drive transformer secondary...Not good for SSB use. If you want to add a switch to turn the pre-amp on and off, Don't follow my old post as it will do the opposite of what you want. Instead do this: clip the base of Transistor TR3 and insert a wired switch between the two points. With the circuit open, the transistor will not conduct, keeping the pre-amp relay off. A more complicated way is to cut the trace between both relay coils (+Vcc) and add a switch, with one wire to +Vcc at the fuses, and one wire to the junction of D5 and R4...same effect...Enjoy! |
Kid_vicious
Intermediate Member
Username: Kid_vicious
Post Number: 213
Registered: 9-2004
| | Posted on Wednesday, February 09, 2005 - 10:16 pm: |
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thanks for the comeback inspector, i havent even hooked this toy up yet. been moving. im definitely going to do the preamp switch. not sure if i'll use this in the truck or in the house yet.
matt |
Mikefromms
Advanced Member
Username: Mikefromms
Post Number: 553
Registered: 6-2003
| | Posted on Wednesday, April 06, 2005 - 1:48 pm: |
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Lightning static from a distance took care of my pre-amp section this morning. I now need to clip that TR-3 so I can use the amp portion because it is not receiving signal at all with the amp on. What a bummer...I mean, the lightning and thunder were so distant--not even in the specific area. Now I know what happend to my shortwave receiver. Is this hard to repair?
mikefromms |
Kid_vicious
Intermediate Member
Username: Kid_vicious
Post Number: 362
Registered: 9-2004
| | Posted on Wednesday, April 06, 2005 - 11:18 pm: |
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im not sure, but i think there is a FET in the preamp section of the amp. if there is one, then replace it. they are very sensitive to static.
matt |
Chad
Intermediate Member
Username: Chad
Post Number: 239
Registered: 11-2004
| | Posted on Thursday, April 07, 2005 - 9:44 am: |
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I usually end up turning the receive gain on my radio down to where it would be normally, I would omit the preamp but I'm too lazy to un mount it now and with the weather getting nicer... doubt it's gonna happen soon.
Roll without the preamp and see if it does OK, you may not want to repair it!
Chad |
Qosmio
New member
Username: Qosmio
Post Number: 2
Registered: 1-2022
| | Posted on Thursday, January 06, 2022 - 3:33 pm: |
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KL300P best is to unsolder one leg of the diode D8 close to the on off on switch and preamp is disabled when amp is on and in use. |
Charliebrown
Advanced Member
Username: Charliebrown
Post Number: 787
Registered: 10-2002
| | Posted on Friday, January 07, 2022 - 3:32 pm: |
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It is a three leg switching transistor It is black and flat on one side. It has went bad on you more likely |
