3 Bias Circuits Explained For RF Amplifiers Using 2sc2879 Transistors
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- Опубліковано 4 вер 2024
- 3 Bias Circuits that work with 2sc2879 transistors are listed here in this video that are and have been used in wide Banded amplifiers using BJT Devices in the last 30 Years plus.
I was asked by a buddy of mine to help him with this first time attempting to bias an amplifier that was current at a Class C operation. I thought that this would be a great way to help him out and now maybe it can help out others.
This is an extension of the series Gatekeeper In Amp Building Concepts.
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I am grateful for these how to videos.
I am glad vmvud I will be doing more
Thank you so much gatekeeper,I'm just in the learning process,and I want to put SSB I'm my boxes,this is priceless info.
Im glad i could help ya brother 🙏 if you need any transistors at good prices shoot me a text 678 557 4846
Thank you so much for sharing this!
No problem buddy...want to pay me back...share this on your FB or anywhere you can.
Thank you for sharing
No problem buddy thanks for stopping by.
Thanks so much for explaining this to us
No problem bud!
Great info here, the entire video brother.☑️ 73
Thank you brother!
GK........... good info as always. Keep em coming brother
I will bud gonna be releasing some repair videos soon
Do you enjoy videos like these? If so leave a comment and let me know what you want to see. Give me some ideas 💡
Hey 1883 could you send me a list of all of the capacitors, resistor’s, and all the other things that I need to build a amplifier? I just need to know what to order lol. If you could I’d appreciate it very much. 73s buddy.
@@rodneymclemore8587 send me and email lets talk threemanpro at gmail dot com
Or text me 678 557 4846 well go from there
Gate,you should make some vids on what you covered in all these videos,but on DVD format.I would love to be able to watch these anytime l wanted on my TV w/o using my phone data.Nobody on youtube ,that l have seen,cares to share the knowledge you have with us.Thanks so much man,your videos have helped me understand these amps alot more.👍
I would like to see some vids on troubleshooting common problems with old solid state amplifiers.I have a TX-150 l am struggling with at the moment.l may end up rebuilding the whole dang thing like you did on your 150,😜.Thanks,Grunt.
1883 excuses to many
@@gruntohseven5803ooooooooh good idea man really good idea!!!! That is am amazing idea
Imma do it
Excellent video, thank you very much, ...
Your very welcome 🙏
Very good video. I have test and learn and burn transistors, I have learn from you and other.
Thank you for sharing. Something that I was analyzing is that a 61 ferrite core will not give us 10uH at only does 2uH I think that’s the reason I was burning the resistors 1.6ohm with the bias. RF feedback to the relay over saturation! (I think) I will test again next week…
Thanks for your videos and sharing your knowledge.
Exactly right....the rf will do that...that is why you need to choke it off with 10uf to 22uf. Ill do more at times to make sure no rf goes back lol. Or atleast keep it low
But you want to use a high permeability ferrite... I use 43.
Thanks for stopping by and leaving a comment brother.
Always love the learn brother.B-bias isnt as big of a secrete it was years ago lol.Keep up the good work down there and always remember Jesus Rules!
I actually made this video 3 and 1/2 years ago to help our mutual buddy while he was beginning to learn to bias. I am not sure if he has picked up on it yet that this is the video that I made for him yet....Imma wait and see if he comments lol.
nice ! 3 simple bias that works. now you can use different diodes to change voltage a bit. shocky diode can make around .5V or so. I make circuit with out RF amp just to test diodes and resistors. The 2 caps across diode is filtering. 104 is RF and the 10Uf or so is audio . helps with harmonics . you can get fancy but not needed. I used 317T voltage reg tip 120 etc. does no better then basic circuit . looking at spectrum analyzer was no difference. coming down to dirty radio more dirt out . and tunning the amp. I found the xforce bias circuit can change the tunning a bit. I usually use a 2 pole relay for bias and key the big transmit relay. taking to load off keying transistor. some times I use a tip 120 for keying transistor. can handle big relay. and need less Rf to key relay. 3 and 4 pole transmit/ receive relay can be used as well. RFC can be used in place of type 43 bead. I found HG like lower bias. I put my diode right on top of pill or on heatsink . 1N4997 diode works well for this. had a amp repair that had 4997 press into heatsink. buy small hole drilled . I found but testing that thermal compound on diode to top of pill or heatsink does the same drop as it heats up. helping with thermal runaway. now LD-MOS and MOS-FET has way different bias voltage. My at less DCA pro does tell me gate voltage that gets in the range of what needed. . remember BLF 188XR and MRFX 80H are 2 FET's in 1 pill . The little battery in tester gives appx gain and is great for matching . I got 3 meters from the,. LCR and ESR I have as well. 73's
Dood you are one smart joker man....I am very forchinate to have you on my comments lol...id love to chat with you one day on the phone I think we would enjoy our nerd talks lol. You have a lot of knowledge and im pretty sure you have been In this longer then I have. I am just guesing..would you be up for a chat sometime..if so email me your number and my procrastinating ass needs to reply yo your last ones dammit 😒
Dude you’re the man!! Thanks for sharing all this information. I’m going to be attempting to build my first 2 pill sometime soon and these videos have been super helpful. -294 in eastern TN
I would love to see it when you do bud.!!
Thank you for sharing!!!!
No problem bud...make sure to share with your social and friends that may be interested.
Think you
No problem bud.
Good day mate. Thanks for the sharing. How we do bias on a SSB? I'm still new on this hobby.
Their are circuits right there buddy. Just take your pick and make the circuits by them selves and test away from amp.
Non biased class C works fine with AM or FM, SSB need 0.7 volt bias to sound not distorted.
Well done again professor of the backyard University. Quite thankful for all that you are doing if you don’t mind would you tell me what size diode that goes on the relay thanks. Schoolboy in Ala.
On your actual relays coil(snubber diode) just a 1A Diode like a 1n4001 will suffice. If you really want to feel safe just get some 1n4007 and be done with it. :)
I love watching repairs but now I need to know why. Like being a mechanic anyone can be a parts replacer but those who understand why and how are much better are diagnostics
You couldn't have said that any better...EXACTLY RIGHT!
So the divider is supose to equal the voltage which the diode is holding at the anode for the class b?
Pretty much the divider in the class b are the two 10 ohms on the base in parellel.
if i use ab bias the amp can then be used on ssb correct
Correct! You use a class c on ssb as well but of course bias will allow yout actual audio to be the same as the actual audio coming from your radio
Just ❤ this 🎉🎉🎉🎉🎉
I have a 2 pill That's I am trying to fix ....every time I key the mic in the my relay pulls in and jumps back out while holding the microphone keyed only one time if manually Or applying ground the relay stays pulled in Why is this?
There is a preamp received on this Amp It's a golden Eagle 150
Also I have a 1 driving 3 tubes amplifier rebuild the keying circuit and have no output can't figure out.... new to RF
Sounds like a keying transistor or cap on keyinging circuit some times it is best to replace everything in the circuit and be done lol. The tube amp is beyond my knowledge I don't understand tube amps but really want to learn.
@@1883GotDown thanks you 73's
Hey gatekeeper . Silly question but have you ever experimented with 3pdt relays for bias ? There very interesting as I've been playing with some myself 🤣. I never understood why they were not used more with amp builders is it because of cost ? Take care my friend. And thanks for uploading this amp series videos. 73s bro. 👍. Take care. Keep safe
Very very good question. Yes I have used these before and it does save time & wire using these so you can use one Pole for the bias.
It is honestly a good question. Maybe some people would rather keep there AC and DC separate. It could be that they buy the DPDT relays in bulk and use one of their smaller relays for the bias relays. There has been times I honestly didn't think about it lol & I could have used a 3PDT instead. I have maybe 4 or 5 of these left and I need to use them.
Really good question bud.
Thanks bro. I just thought it fascinating that no one uses them .it just made sense to me to use a 3 pole instead of adding another relay as you use the 3rd for supply volts. I have a few 3pole relays here and I got then for the same price as the dpdt ones. Maybe because there not as popular ? I don't know. Thanks for answering Gatekeeper. Take care my friend. Best 73s.... Your UK bud until the end .👍
@@worldradio456uk5 Glad to have you in the UK 🇬🇧 viewing my channel. I'd love to have a lot more viewers from the UK. Bring me some more UK viewers lol. Ive often wondered how the 11m scene is In your area. Does people mostly use FM or do they operate AM on the regular 1-40 channel? Or do they mostly work freehand USB?
Hi Gatekeeper. In England we can use all modes now as am and ssb had finally been legalized a few years back. I've had a few good contacts on AM myself but am a big ssb lover. As you know because we spoke a few times in the last solar cycle 🤣. Localy we chat either FM but usually ssb . We are all waiting like everyone else is for the big cycle to really start up again and really do hope we can all talk to each other across the pond again . Take care bro. 73s. Wr456. UK
so I can add this circuit to any class c 1, 2, 3, or 4 pill amp correct ?
Correct! Just make sure to remove the choke that goes to ground
When checking with RF with a choke on my meter. What should the biss drop to? Mine goes negative
That almost sounds like RF is getting in your meter...that is why I like to use a Fluke Meter they do well with RF in thr last I had go wrap my leads well... but when you key with RF you should get around the same with out RF but it can change once things heat up.
@@1883GotDown I use a fluke 117 and have a choke on my leads
@@1883GotDown when the bias is off the only reference to ground for the input transformer is through the 5ohm resistor and the diode right. Cause when wired directly to ground it's class c. What I've noticed is that when bias is off and it runs through the resistors it actually makes less power than actually being soldered to the board in direct class c. Have u ever noticed the biased boxes make less power than the class c boxes even when the bias is off?
When the bias is off and I check voltage at the 5 ohm resistor it's actually -0.45ish volts depending on drive. I just want to know if I'm doing something wrong or if this is Normal. From what u said sound like it's not normal so now I need to figure out why my measurements that seam rock solid aren't correct or there is something else going on. I appreciate all the help. All the knowledge your willing to show in your videos will keep this hobby alive.
@@1883GotDown ua-cam.com/video/71N6f_BCVeQ/v-deo.htmlsi=bmPJfVGZI8Lsl7yt
@@electromechanicalstuff2602 well a biased amp will do more power with less drive meaning it will do a bit more power let's say with 10w drive while a class c needs to be drove a bit harder till it gets to the same output. Now IDK what 5 ohm resistor your referring to...im not sure which bias circuit you are using your self.
Like I mentioned RF will get in your meter when trying go test with RF present also...before I got a good meter I had go gorilla force wrap my leads like crazy to keep rf out of my meter. You should be able to dry key and get your 0.38 to 0.42 if b bias or 0.62 to 0.68v and should get the same exact reading if you do a carrier and check it.
With you getting a neg(as if your have your leads backwards on a dc signal) its seems as if your meter is seeing the AC signal from your RF.
Just check from the back of your transformer to ground.
But when it comes to sources to ground....it has the diode and the 10 ohm resistors on each base. They are part of the bias circuit as well.
Now if you try to use the amp in bias mode with it off the amplifier isn't going to work as well cause it is in class mode then with no direct couple to ground all it has is the 10 ohm resistors.
Class will do the most power with less current with out linearity and a biased amp will give o soem of its top end power for linearity but will pull much more current but like I said a biased amp will get up and go with less drive since base is open more already then if it was class c which uses the rf to open the transistor.
Hope this helps man im not a genius eith this stuff by no means.
I'm wondering why your curious what it is doing while your talking I guess your just wanting to make sure that its working correctly..as long as your wire is thick enough and have a good B+ going to the bias circuit then ur good.
It can be real real tuff to see the DC voltage with rf mixed in
Hello gatekeeper' 'the other day i was telling u about my magun 2000 amp'' i told u that it had (2) Motorola 9706 rf transistors'''''im sorry i was wrong'''' they are strapped so i could not read them right''''''''ok'''' i read them right today' 'they are (2) Motorola- MRF-455''''IT DOES 250 with 27 what swing on SSB'''''what do you think about the MRF-455''''''thank you sir''' James ''Oklahoma.
Is the .65 volts measured with the choke connected or disconnected ? Measured with the bias out of circuit?
Reading in DC it doesn't matter....It can be read anywhere after your bias circuit. Meaning at the base of the pill, back of transformer etc..... If your keying up with RF present then its a good idea to check after the choke..that is why that choke is there to minimize the rf going that direction.
If you cannot tell if hes lying or not. Sometimes he comes through. On big project Good Luck he will tell you its in the mail over n over again 1 million great excuses
I've already explained the full situation to you and you won't be a man and speak with me on the phone so I can show you your case and all your parts is outside waiting for after this 2x8 base ive worked on for 3 days now... you took me you were ok waiting till your actual turn instead of me doing it ahead of others last time we spoke. All I ask is for you to chill let me get this 2x8 done and if you see that I'm not deliver you can have your way with me...heck ill design you a bot where you can comment bomb me 24/7....all I'm simply asking is to chill for a bit longer and let me get this guy out of the way please brother please 🙏