Sharing Another Neat Circuit! The Super Simple RF Preamplifier That Works Great.
Added 2019-02-10 03:10:52 +0000 UTCHere is a very basic RF preamp that can be used in many applications. You can build this on a "terminal tie strip," or even "Dead Bug" style. See in this video how it brings old receivers to life! Use it for your frequency counter, for a buffer amplifier..... So many applications can benefit from this "super simple" circuit.
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Comments
Is there a better transistor to use, or it doesn't matter? Will RG-174 work, OK?
Ted Mieske
2025-03-05 01:02:21 +0000 UTCHi Paul, I scrolled thru the comments for a bit to find answer (to the question I am asking here) but could not find it. My question is, will this pre-amp work with modern amateur radio rigs like IC-7300, FT-857D or a communication receiver like Icom R75? Or these radios already have a front end amplification with which this pre-amp will not produce result like we see on Echophone radio in your video?
Praveen
2023-05-29 20:11:24 +0000 UTCThank you For Another Great video
LoSaYa
2022-10-17 19:52:32 +0000 UTCI live in a part of South Dakota that has very poor signal reception on both AM and FM radio receivers. I was considering building one of these to try and fix this problem. Years ago when we lived nearby on a farm in North Dakota we listened to AM radio but father had put up a long wire antenna from the house to the outhouse ( we had no plumbing or electrical service so it was batteries all the way as well as kerosene for lighting and white gas for the holiday and company lighting from the Alladin Company.) With the long wire and a ground rod that was 4 feet into the earth we could get pretty good reception on the radio when it was time for "the shows" (this back in the 1950's) Recently we got our first FM station in town which is just a retransmission of the same programing on the AM that was installed in 1965 here in town. FM is a weak signal so a good set is required and a good antenna helps. In my easy chair where I spend most of my waking hours, there is NO FM signal available or if any then a very fuzzy reception. Could this improve the FM? Wondering since mom who is now in the nursing home loves the radio. With all the electronic in the home AM is very bad and FM is weak. My daughter found a nice FM only set with built in auto clock and auto scan on the radio. Problem is, only mom knows what buttons to press and if she leaves the room others screw with the radio and somehow lock it up. Unplugging it is the only reset available and mom can't reach the plugs from her wheel chair (at 96 she is still sharp mentally but her body is getting old and weak. I installed a press button that interupts the power from the wall wart that powers the unit so she now just has to press that and it resets the set and it is back in business.. Just curious if this circuit could work on the set. There is room in the case for the strip version and since the wart gives a good 9V DC I think the power would not be a problem. The set uses the power cord for an antenna so again, I could break that side of the cord on it's way out of the case and hook it up that way.
Jerry Ericsson
2022-01-23 20:23:48 +0000 UTCI have to agree with you on that mike alot the people who build things could do better specially when they are messing with rf and electronic test gear
Andrew Murphy
2022-01-06 18:57:23 +0000 UTCi was wondering if you use a power transformer if you can build it in case make portable and it would work for power it
Andrew Murphy
2022-01-06 18:56:32 +0000 UTCPaul, could you please show us a good bias-t circuit to power this fantastic pre-amp? I can find plenty of bias-T circuits, but they don't explain them like you do. I'd like to use it for a small magnetic loop receive antenna I'm putting together.
Mike Donnell
2021-09-30 14:08:30 +0000 UTCHi Paul.I am writing from Bulgaria.My name is Barosov.I need a working schematic of RF amplifier that can amplifying-150mv at 40MHz to 3..4 volts at 40 MHz.Can you recomend my some schematic?I done about 10 diferent schematic but none met the recurements.
Barosov
2020-07-12 13:05:44 +0000 UTCDo you have the schematic for the preamp using the 6688 tube? I thought this would be the preamp you used in the video with the nixie counter buffer circuit.
Chris Kucera
2020-06-18 19:24:46 +0000 UTCFocusing is a problem
Eric Kyle Tallman
2020-06-11 22:06:00 +0000 UTCThis is really Great!!!! How much signal in terms of mV should one use to figure out how much amplification is needed? In other words, how weak is the signal coming from the antenna?
Bill Hall
2020-05-01 16:20:41 +0000 UTCThanks Keith!
Mr Carlson's Lab
2019-12-24 22:47:04 +0000 UTCI would love to see you use all that great test equipment- in your TE lab and use an RF Sweep gen and spectrum analyzer to show the gain versus frequency of the preamp. As usual from MCL has superb material from the Master Himself. Bravo ! Always brings a smile of appreciation to our faces.
KEITH MILLER
2019-12-24 00:53:48 +0000 UTCHi Don. You are at a level that has direct access to my email, If you have questions, that email gets my attention right away. I have a few more pre-amp designs to share too, its all about time to make boards for them as well. I will do this soon.
Mr Carlson's Lab
2019-07-13 13:08:29 +0000 UTCHi Paul, This RF preamp looks pretty good. I have just finished up re-capping a BC-348-Q receiver and it has no antenna tune in the front end. I am going to build up the preamp circuit and give it a try. Also were you planning to make a silk screen to make a printed circuit board and how far down the road this will be. Please give me some advice on any components in the preamp that would work well with the BC-348. Thank you for any advice. Don Otrin KC1IEA
Donald J. Otrin
2019-06-21 19:53:17 +0000 UTCPaul, thanks for the project ... I built this this weekend for use with my Echophone EC1. It was a simple enough build for a Sunday morning and it works great! Originally I wanted to build it into the Echophone as you described but I was unable to figure out the VDC as you described. I understood your directions to tap the filament string with a diode and capacitor to ground to get the 6VDC+ but I was reading 30ish VAC on the 2&7 tube pins. Am I missing something obvious? Instead I mounted the pre amp in an altoids tin w. A 9V battery, adding a switch and LED on indicator lamp to preserve the battery. Anyway thanks again for your excellent work...I continue to learn much and am having fun. De AB1DQ/James
AB1DQ
2019-06-18 00:34:20 +0000 UTCHi Tim. The resistor to the base is to bias the transistor. This configuration is also known as collector feedback or (shunt feedback.) Any increase in collector current (transistor draws current) will cause a drop across the 330 Ohm resistor "reducing" the base current.
Mr Carlson's Lab
2019-06-13 08:04:16 +0000 UTCPaul, is the DC (negative) feedback from the collector to the base providing the biasing for the transistor? That is a neat trick because as the signal gets stronger, the biasing increases and as the signal is weaker the biasing is lower. Running in class A this saves a lot of power. Or am I totally confused?
Tim Taylor
2019-06-13 05:29:47 +0000 UTCHi Dion. It (the radio) very well may already have a strong receive section, and this little circuit is just overloading it. Can you make a small "Unlisted" video and send me the link in a PM? I will have a listen.
Mr Carlson's Lab
2019-04-17 07:53:27 +0000 UTCThat is, 3x the IF frequency.
Dion Morehouse
2019-04-16 20:06:07 +0000 UTCI forgot to mention that the offending local station is at 1360 KHz. It's probably significant that that's pretty close to 1/3 the IF frequency of the radio.
Dion Morehouse
2019-04-16 20:05:38 +0000 UTCHi Paul. First, I'd like to just say how much I enjoy and am learning from your videos. Thank you for creating them! I decided to make a bit of a project out of this simple amp, as a simple learning vehicle for creating my own PCB layout (I decided on DesignSpark PCB for my software). I first breadboarded the circuit, then moved it to PCB, and I have the same issue with both --which I believe is due to the broadband nature of the circuit, possibly exacerbated by the radio I am using (a 1937 Zenith 12-S-265). In a nutshell: When I turn on the amp, weak stations (and even stronger ones) are completely buried in other RF signals (does not sound like static, more like the sound of amplified distant signals). There's also an intolerable imaging of a strong, local AM station that appears in over 100 spots across the shortwave bands. It sure doesn't give me the result that you demonstrated on your Ecophone. What do you think? It the selectivity on my Zenith just to poor? Maybe the IF bandwidth is too wide? -Dion
Dion Morehouse
2019-04-15 18:32:17 +0000 UTCLooks like a good preamp for a few of my transceivers. With using a relay to switch it put during transmit I imagine it would need to be grounded out to prevent swamping the front end?
Michael Rousseau
2019-03-28 18:40:21 +0000 UTCOne of my project list items is to come up with a low noise vhf preamp that would be tuneable in the 110-174Mhz band. I’d love to see how you would design that. Maybe a tuneable preselector with a JEFET ?
Bill Moran
2019-02-28 16:42:54 +0000 UTCVery nice little circuit. It might be useful too to use as audio for an active probe? Thank you!
Escabusa Roy
2019-02-25 06:56:40 +0000 UTCIt would be great if this type of project could be expandend for higher frequencies. I listen to DAB radio in my work van everyday and in certain areas I get drop outs or even lose service. My favorite station operates on block 11D which is 222.064MHz. I was thinking of making a RF pre amp tuned to that frequency that I could switch in to give a bit more front end gain, sort of a VHF pre selector pre amp if you will. Any suggestions would be greatly appreciated.
Zed
2019-02-23 18:28:25 +0000 UTCHi Paul, would this circuit work with a single wire antenna input instead of a coax line? (sorry for the previous post)
Ronald Drew
2019-02-23 00:35:23 +0000 UTCHi Paul
Ronald Drew
2019-02-23 00:32:18 +0000 UTCusing a 2n5088 and 9v, I had to adjust resistor values significantly to get it to work, and not sure why? using some pots, I landed on: 100k from +9v->Collector 500k from Collector->Base gives huge boost.. my 2n5088 doesn't seem to function at all with less than 56k from 9v->Collector
Ben K
2019-02-22 16:41:39 +0000 UTCHi Roman. I use lacquer thinner. Always do this in a well ventilated area, following the precautions on the can. Use gloves and eye protection too!
Mr Carlson's Lab
2019-02-21 00:41:01 +0000 UTCHello Mr Carlson! Please tell us how you clean flux residue from your circuit boards. I have made a couple PCB's recently and cleaning them has been a long ordeal. I have used MG's flux cleaner, IPA, Methyl Hydrate, and water with dish soap. The boards look good, but not perfect. Umpteen applications of these chemicals and scrubbing with a toothbrush, also a short bristle brush. PLEASE HELP!!
Roman Charak
2019-02-20 15:39:24 +0000 UTCIt would have been interesting to see this circuit swept on a spectrum analyzer, as part of the video, to show the frequency response.
Dave Gale
2019-02-19 03:32:37 +0000 UTCChuck: Interesting possibilities with this, how about adding it to an antenna input of an amature transceiver using the relay switching capability to bypass it as you hit the transmite switch and then return to the receive position to help pick up those distant weak stations, similar switching when you are using a Linear amp with the transceiver.
Charles Outhouse
2019-02-18 01:00:21 +0000 UTCGator, take a look at the following link, which gives some guidance on capacitor sizing for power supplies: <a href="https://www.allaboutcircuits.com/technical-articles/why-the-capacitor-in-your-power-supply-filter-is-too-big/" rel="nofollow noopener" target="_blank">https://www.allaboutcircuits.com/technical-articles/why-the-capacitor-in-your-power-supply-filter-is-too-big/</a>See also: <a href="http://www.skillbank.co.uk/psu/smoothing.htm" rel="nofollow noopener" target="_blank">http://www.skillbank.co.uk/psu/smoothing.htm</a> Have fun!
Garth Wood
2019-02-18 00:26:09 +0000 UTCthe amp is a soundtech pl-1402 there are pdfs on line of the schematic...the problem i have is that 8200uf 100v caps are hard to find here in Brazil... the 10000uf 100v are more common.... the caps are used in the power supply section...
Gator
2019-02-17 01:07:50 +0000 UTCThere is a good chance you can, but without seeing the schematic and knowing some other details, I can't tell you for sure.
Mr Carlson's Lab
2019-02-15 16:15:12 +0000 UTCgreat video... i have a question...i have an amp that need to be recapped.. it has 4 8200uf 100wv caps.. can i replace them with 10000uf 100v caps?
Gator
2019-02-14 15:48:50 +0000 UTCThis is similar to the preamp section of my MFJ-959-C receiver tuner preamp.
Albert G.
2019-02-14 13:22:37 +0000 UTCPaul, I still do AM DXing. What would be needed to terminate this into a small loop that would couple to the ferrite bar antenna in a portable AM radio? Thanks
Greg Newberry
2019-02-13 13:38:08 +0000 UTCIf you make your circuits much simpler, the crystal receiver bunch will start browsing your posts! LOL
Bruce Havourd
2019-02-12 18:55:49 +0000 UTCDid it with some vintage can-packaged transistors, worked at first try :D
Michał Nowicki
2019-02-12 18:21:28 +0000 UTCThanks, Paul. Very interesting. Since I'm not a radio guy (Audio amps only, at this point) It seems like this could be dropped into a circuit as a valve amp boost where needed. Yes? Dave
David L Cunniff
2019-02-12 16:45:37 +0000 UTCGreat video! The 100k resistor biases the 3904 with 60uA to 120 uA depending on the supplied voltage. Seems like you rely on a hFE aruond 100 which probably is ok for frequencies below 30 MHz.
Robert Eliassen
2019-02-12 15:35:59 +0000 UTCI have seen very similar circuits using opamps in place of the npn. Is there any advantage to using a discrete transistor? Is there any advantage to using an opamp - assuming a single supply, rail-to-rail type?
Chris Sutton
2019-02-12 12:47:04 +0000 UTCVery simple I love it! I will build this in the next couple of days I do not have any 2N3904's but I do have a few 2N5109's.
Michael Lamb
2019-02-11 20:08:09 +0000 UTCI studied with a very talented jazz guitarist who would give me "screenshots" of his mental process. It was a wonderful window deep into the magic. I get the same feeling with your presentations. Many thanks. Jon
Jon Powell
2019-02-11 16:15:27 +0000 UTCHi Allenc, all of that. Its was also more stable as well, (less prone to oscillation)
Mr Carlson's Lab
2019-02-11 12:11:45 +0000 UTCQuestion: you mentioned that the 2n3904 was 'much nicer' than the 2n5089. Why did you like the 2n3904 more? Less noise or distortion? More gain? Or something else?
allenc
2019-02-11 06:16:31 +0000 UTCThat diode tuned preamp sounds interesting i really like this one as well quite a useful thing. Would like to see the other one just to get my head around how they work. As always very educational thanks for all the good knowledge am always intrigued by all that i see here and have learned alot.
Jason Martin
2019-02-11 03:20:19 +0000 UTCYou should see the cage dipole!
Mr Carlson's Lab
2019-02-11 02:37:36 +0000 UTCThanks for your kind words Ralf!
Mr Carlson's Lab
2019-02-11 02:36:55 +0000 UTCThanks again Mr. Carlson. This is neat simple stuff.
Donald (Don) Stewart
2019-02-10 23:57:18 +0000 UTCCould this circuit be used to boost the signal from a OTA TV antenna?
RBE
2019-02-10 23:56:29 +0000 UTCI would love to see a tunable circuit for use in higher frequency applications.
Ellen Hardin
2019-02-10 23:37:03 +0000 UTCThis shows the beauty of your course Paul! Pros can immediately benefit from your circuits which makes their work much easier and at the same time this is a great learning experience for people like me! Not an easy task :) Thanks for all you do!
Reb Elba
2019-02-10 22:57:58 +0000 UTCCircuits like this that are easy to build and are known to work are a fantastic resource when home brewing or restoring. A tunable versions is intriguing. Thank you and keep 'em coming Paul.
Jim Edmondson
2019-02-10 22:18:43 +0000 UTCLooks great,going to add this to my DX160,thanks!
Ted Cross
2019-02-10 19:08:27 +0000 UTCPaul, I'm thinking this may be used in a small bench built transmitter for the home. Thanks as always my friend.
Carl Loar
2019-02-10 18:58:51 +0000 UTC6 Meters is definitely the magic band !
Bob Sheldon Sr - KC9ITB
2019-02-10 18:46:23 +0000 UTCRG-393 all the way to the center of the dipole? #6 stranded silver wire for an 80m antenna?! You must throw one heck of an antenna party.
Chuck Lemken
2019-02-10 18:01:07 +0000 UTCi know, but it is basic and some people probably over-think. i like it as reminder. very useful
SD
2019-02-10 17:46:32 +0000 UTCah, thanks. not your average common emitter type amp. well thought out, simple. thanks
SD
2019-02-10 17:43:06 +0000 UTC...and the reason this schematic, which could be found in any transistor RF application note, is "NOT PUBLIC DOMAIN"? o.0
Peter Sage
2019-02-10 17:40:43 +0000 UTCYeah, a tunable variant will also be great...
Victor Bigea
2019-02-10 17:04:28 +0000 UTCThank you very much. Great simple circuit. Just built mine on a breadboard to see it in action. I cannot wait for the varactor and relay version of it. Also cannot wait to see the built for the automatic transistor tester/box to use in conjunction with Curve Tracer. Speaking of curve tracers I'm currently working on a curve tracer that will be placed inside a small TRIO CO-1303A oscilloscope I've just purchased recently on eBay.
Ovi4
2019-02-10 16:58:30 +0000 UTCThanks for the great project. Definately interested in the tunable version as well. What is the output voltage on this? S9 is about 50uv. Thanks!
Greg Newberry
2019-02-10 13:58:08 +0000 UTCThanks Paul, and hopping to see more RF stuff. The tuned pre-amp will be great follow-up. Did you ever consider sharing a simple (very simple) receiver design?
David Senabre
2019-02-10 12:55:49 +0000 UTCI designed one myself a few years ago. I gave up on the transistor version and used a MOSFET instead. I was not able to obtain a good signal to noise ratio with the BJT. The MOSFET however worked well.
Egil Hansen
2019-02-10 11:31:01 +0000 UTCCeramics work well in RF related circuits (amplifier stages) but NOT in an RF oscillator circuit, unless they are NP0 rated. They also work very well for RF bypass.
Mr Carlson's Lab
2019-02-10 09:19:46 +0000 UTCThe variable version, I would want to use it on a 6m receiver I'm building, even though I have all this HF to play with, my fascination always 6 metres, the magic band 73 Paul
Paul Collins
2019-02-10 09:15:57 +0000 UTCI have a couple of frequency counters, I just can't part with, which I think would benefit from this. thank you Mr P
Paul Collins
2019-02-10 08:46:14 +0000 UTCYes, YES! More PCB designs to make! I am just baffled about your choice of using a ceramic capacitor here.
S.M.D.
2019-02-10 08:37:52 +0000 UTCHi Adam, I would need to see a schematic.
Mr Carlson's Lab
2019-02-10 08:01:25 +0000 UTCThanks Paul, I have just the radio to put this in. A cheap unknown Japanese transistor all-band receiver from the 1970s called a Rajisan MK-59 that I picked up in a 2nd hand store so I could use it to test RF circuits without my having to use my Kenwood TS-830S which is awaiting a recap. With no online schematic and (apparently) little or no pre-amplification in the front end this little circuit could be just the thing I need to make it work! Also looking forward to the varactor tuned version on HF bands.
kmpres
2019-02-10 07:13:41 +0000 UTCWould there be any problems with piggybacking Filament power in DC 6.3v to this preamp to the receiver?
Adam
2019-02-10 05:59:55 +0000 UTCBless Your Bunions!...Mr Carlson.
David O. Hamilton
2019-02-10 05:39:02 +0000 UTCAnother great little circuit. I can't wait to build it!
Mitchell Smith
2019-02-10 05:13:02 +0000 UTCMore RF stuff! You mentioned a varactor oscillator design in the previous video. Consider that such a design could be tied in with a varactor tuned preamp you mentioned in this video. Thanks for the RF related content.
allenc
2019-02-10 05:03:29 +0000 UTCLove all your "stuff".
Howard Higgins
2019-02-10 04:40:41 +0000 UTCHi Rob. Just an every day universal power supply. If you like, you can power it from a battery. 9 Volts would work well.
Mr Carlson's Lab
2019-02-10 04:37:38 +0000 UTCThank you Paul! This little RF amp will work great in my Hallicrafters S-38 and the Hamarlund HQ-200; that's the plan for the coming snowy days here in the Pacific NW...
Victor Bigea
2019-02-10 04:28:55 +0000 UTCPaul, what are you using for a power supply in the video?
Upton O'Goode
2019-02-10 04:22:16 +0000 UTCThanks Paul! Time for me to get some soldering done.
Robert Calk Jr.
2019-02-10 04:07:41 +0000 UTCWhat a great little circuit! Thank you! I'll certainly be using this for a few different applications. I like all of your variations.
Adam
2019-02-10 04:01:50 +0000 UTCThanks Paul! This was a VERY nice surprise to see a new video before the middle of the month!! Very handy circuit as well!!
Michael, KE4EST
2019-02-10 03:58:17 +0000 UTCThanks for more!
Aaron Brinkman
2019-02-10 03:53:46 +0000 UTCLOL, Surprise!
Mr Carlson's Lab
2019-02-10 03:39:45 +0000 UTCLOL... Stop breaking what I know!! :-) I know that you can never work with RF if the traces are not made by lots of planning and I certainly do know that you can never work with RF on a breadboard!! :-)
Fried Mule
2019-02-10 03:29:18 +0000 UTC
