How to fix Realistic DX-150 Ham Radio Receiver Power supply Hum Buzz

[@randyab9go188]

Just got done recapping my DX - 150B. Looking at some of the comments about C76 I decided to leave it out. I have absolutely zero hum on the output even with the RF gain turned all the way down and the audio gain turn all the way up. If you didn't know better you would swear it was turned off. No background noise or hum of any kind. What I did notice on mine was C76 was an afterthought. There is no silk screening on the PC board and there are no traces going to C76. Just two holes drilled in the board and C76 leads folded over to cross to R50. Maybe they were trying to give it the sound of an old tube radio 😁. My radio is dated June 1972. I had a chance to either buy a Hallicrafters S - 108 or the DX-150b. After looking around on the web I decided to get the DX-150b. I was going to use this as a bedside radio and I will fall asleep with the radio on. So a solid state radio would seem to me to be much safer! I saved $70 over buying the Hallicrafters and it would have to be recaped too as it was all original. A complete electrolytic cap replacement (all Nichicon) cost me less than $10 at my local parts supplier. Couldn't have done the Hallicrafters for that! I'm thankful there is still a local parts supplier around!

[@randallhulette4973]

Just completed a recap and added this mod. Definitely did the trick in removing the 60 cycle hum. Easy and quick for a big audio gain.

[@CraneofBoulogne]

When I was young I used to bail hay and cut firewood and all sorts of farm chores, save my money to go to Radio Shack and get a piece of gear so that I could do more and learn more. I hated it when Radio Shack became centered on sell phones and lap tops. I hate it even more now that they are gone. I too own a DX-160 and it is my go to radio. It sits by my favorite chair where an old guy can sit and listen most any time of the day or night; there is always something on a DX-160. Now I want to try and do this mod to my radio. Thanks D-Lab for this video, it is great for those of us that own one of these great receivers.

[@mikesradiorepair]

Power supply circuits always seem to be the first place bean counters hit to reduce production cost. See a lot of consumer level receivers and transceivers that suffer from this same problem. Simple solution to a pesky noise problem. And that is a pristine condition receiver you got there. I'm sure you will get hours of listening pleasure from it.

[@gngng5626]

Wow. That brings back hours spent with my old Panasonic listening to overseas broadcasts. Nice to know it is still a vital resource.

[@fredfeldmeier8228]

Beautifully brought up from the 60's generation.. God bless ur soul.. thank u

[@old64goat]

Great MOD, sounds GREAT!

[@bucyruserie1211]

Hi Terry, I went to my towns recycling as I do every week to well, recycle, and I usually get some of my best items there. 2 days ago someone put a 1953 Zenith Oceanic radio down right in front of me (not my kind of thing), but it works, as I was putting it in my car, another person brought one of these DX-150B's. I did't know what it was, but it's as clean as your's.. It needed a fuse, and yes the lights threw me off, no speaker but I have tons of little speakers. Thanks for uploading, Tom

[@gngng5626]

Radioshack is a sorely missed resource. I have an battery powered lcd display alarm clock I bought 27 years ago that runs many years on one AAA. Radioshack was a mecca for us gearheads.

[@richardbrobeck2384]

nice unit Ii had a Dx-150 or 160 but decided to keep my Heathkit Mohican GC-1A Shortwave Communications Receiver that need to restore

[@saulomoura9402]

Realistic is a fantastic equipment. I enjoy it. Good work. Good sound !!!

[@RobertKohut]

Sometimes people do weird things to make things better but this was a Realistic upgrade!!

[@d-labelectronics]

Yep, sometimes the hum just made me feel like CHOKING it.

[@cardboardboxification]

D-lab Electronics lol

[@valakatz3967]

i have one exactly like it, I will try to do this modification.

[@TheRadioShop]

These were really great receivers. I regret ever letting mine go. Thanks for sharing the mod Terry. Really made a big difference.

[@stephenquail3168]

Love it .That hum is outta there.

[@deanhutsell3144]

My first radio was a DX-150. In tech college I build the digital frequency counter highlighted in Radio Electronics....worked really well. I wish I had it back. Saw a DX-160 at a hamfest for $75 last spring but didn't have the cash with me.

[@tubeDude48]

Choke Part Number: Mouser #: 553-C40X

[@charlesw318]

great work as usual D-lab.

[@Gordonseries385]

Nice job, yes the same here. I just did not have enough money as a kid to get one. 2 years ago I finally got one, this is the first generation germanium transistor positive ground and neg ground audio amp unit (1967 year low serial number). Right now its playing, and no hum. mine was a bigger problem with the hum problem but it was worth fixing it, this is my baby to. Fix the drift problem and I have to say I have it very close to the 150b its hard to tell the difference. My question to you I can not find a schematic for it. I have the schematic for the 150a, 150b, and 160. First generation 150 is different but still the basic circuit layout for the most part. Thank You and enjoyed your video 73`s

[@demodoc]

I did this mod to my DX 150 A and it definitely helped. Will it work on a DX 200 as well? I just replaced all electrolytics, even increased the filter cap from 2200 mfd to 4700mfd with no reduction in hum at all.

[@nickking1510]

Thanks I have dx160 in mint condition which I got for 20$ Canadian . I have the hum and will do the mod I may make a choke

[@NSNorfolk]

Nicely done!

[@rohnkd4hct260]

did not know it was such a good receiver

[@d-labelectronics]

Yes, I am a big fan of the B model. Seem's to be the best built of the series. I plan to run it with a CW QRP TX + post a vid soon.

[@DavidFederLimitlessGuitar]

Thanks for this! Do you have a suggestion for how to convert this to a three prong AC plug. I don't like the Hot Chassis issue...

[@SilverBeardGuerilla]

Hey D-Labs , I recently inherited a handful of old audio stuff from my father which included a 1956 Bogen CHB 50 and 2 old radios ,a RCA and a Philco both with RCA 16K FC speakers that he had replaced .The Bogen has outs for a variety of speakers including a 3 pin 70v and was wondering if the 16K's would work .Would love to drop both into the Philco cab as the woodwork is still in great shape and plenty of room for both .

[@medhawk4885]

Great video and thanks for the tip on the fuse. Makes me want to go out and find one now :-) ~N4TYX~

[@rciancia]

Great Fix Terry... Makes you wonder if RS engineers just didn't know how to make it quiet, or chose not to , to keep the cost down.

[@d-labelectronics]

Hi Ron, I would say, just to keep the price down. If you run the radio on external 12vdc, there is no hum at all in the stock configuration. I plan to run this jewel on CW mode over Holiday break. I have a cool QRP tube TX to team up with it.

[@rciancia]

cool

[@alphabeets]

So what is the difference between a choke and, say, one of the windings on a transformer?

[@Chattanoogachoochoo_0105a]

I didn't realize this video is 6 yrs old and hope to get a response. I couldnt really see where you connected that cap to. I saw the schematic but still couldnt see the connecting points.

[@killz66]

Could this issue also be resolved by using a a decent filtered external 12v dc supply?

[@johnbellas490]

Terry Just a short word here, Just want to say Have a Merry Christmas and a Happy New Year !!!!!! from John A Bellas KC2UVN 73's Terry.

[@tedcross7634]

Hello,im recapping a dx160,there appears to be a typo in the service manual parts list,c72 is listed as a 47uf,the original was a 470uf,c33 is listed as a 470uf,the original is a 47uf,has anyone noticed this? the originals have the glue glob so it doesnt look like a mistake on a previous recap attempt,thanks

[@Kennynva]

I did just what you said...bought a DX-160 for $15, the fuse was blown..Now can you tell me what the transformer T5 is for..I know it has something to do with the BFO...but on mine it does zero, nada, nothing..when turned all the way down, and all the way back up..

[@Kennynva]

To anyone aligning this radio, dont do what I did and not turn the band-spread dial all the way clockwise....it will not align right if you dont..I found out the hard way..and its not in the manual.

[@martyyoung598]

Mine has the D-Lab calibrator, I didn’t see it in yours, Terry. The cobbler’s children have no shoes?

[@Skynd303]

If I may ask where are about are you located D Labs? In in Colorado.

[@Kennynva]

I just installed a 1000 mfd electrolytic cap between the positive side of the fuse to ground..and it go rid of about 80% of the noise.. Mine wasn't humming at all but thought I would try it.

[@Boffin55]

Wouldn't it have made more sense to just replace R49 with the choke, and drop a cap on the backside of it ?

[@TrevorsBench]

I just did a restoration on the DX-150B. I found the hum was from capacitor C76. Once you remove and toss the capacitor the hum goes away fully without adding capacitors and chokes to the raw DC supply. Somebody goofed by adding this cap. It actually couples the ripple hum to the base of the transistor which causes the regulator to pass the hum along to the regulated DC line to the receiver, C76 has no useful function in this regulated power supply and should be eliminated

[@brucefriend3760]

Watched this and put my DX-160 on the table and tuned in a local AM station. Listening to Christmas music right now. It is noisy and I'm sure it needs recapped, cleaned and aligned. Guess it just got moved up the list. I'm interested in whether changing C76 cleans up the AC. It would be cheaper and easier than installing the choke.

[@d-labelectronics]

Yes Sir, I will check into that. Hopefully C76 is the true culprit. Either way adding the choke is always an improvement. Thanks for sticking with D-lab.

[@yoadrian24]

Can you show us your antenna set up or is that in a different video? I have several Shortwave radios and none pick up as many statoions as yours does. Nice job!! I enjoyed the video, and a simple modification took care of that noise.

[@d-labelectronics]

Thanks, glad you liked. My antenna is a 80 meter inverted V up 45 feet at the apex.

[@HappyHellscapes]

Have you ever thought of doing a video on how to build an am transmitter? I’ve been thinking about building one myself as there’s not much in the way of am stations out here, and that kinda stinks because I collect am radios.

[@Kennynva]

They have that choke at "element" now for like $3.38, would a larger one...or one with different measurements help more..or is this the most or best one to get..?????

[@d-labelectronics]

That's a very good deal. I picked that one since I had a few on hand. You can use other values, just watch the resistance, current is low, about .5 amps to run the radio.

[@whynotme5926]

I have a request if you have not already done it. Talk about grounding issues. This is one of my problems with building an amp.,even though I used to wire houses. Chasis ground verses earth ground in the amp and which components are hooked to which and if they tie together at some point or are totally separate and not to make a loop. Thanks for any help. Or maybe you can recommend a good video on this subject.

[@chuckheff]

You use an Electrolytic 470 uf cap with - side to ground and + side to fuse. right?

[@d-labelectronics]

Yes, + with the new series choke

[@waynehall1]

Referring to the Stock PS Circuit, the 3 components C71, R49, C72 for an elcheapo "pi" filter. Resistors are sometimes used to avoid the necessity/expense of buying a choke & ostensibly work nearly as well as a choke for low current loads, but perhaps what we saw here is just how "well" this one worked - fairly well but could be better. It might be a better fix to replace R49 with the choke, but it would be less convenient than jumpering one across the fuse holder - but you would still have a fuse that worked! I am curious that the regulator Q11 didn't wipe out any residual DC ripple... And the presence of C69 & C70 across the rectifier diodes seems like a guarantee there will be AC on the rectified output. Except for strings of HV diodes, with equalizing caps & resistors, I can't recall ever seeing a rectifier diode shunted by a capacitor like this. Wonder how neatly a replacement of Q11 & associated bits with an LM7810 regulator chip would perform???

[@d-labelectronics]

Seems like R49 (.47 ohm) is more like a fuse-able resistor for the collector of Q11. Very low value to have any PI filter effect. I"m not sure what they were thinking back in the day of this PS design

[@W3KW]

Well, the access to the wires at the fuse are convenient. Why not just use a terminal strip to add the new components in circuit and keep the fuse intact? Plenty of space there. I think I’ll try this mod on my DX-160 and report back. This mod clearly removes the ripple and hum.

[@paull5609]

Can you recommend a source for the choke?

[@emylrmm]

By the way, it's 120Hz buzz, not 60Hz and you can see that it's a full-wave rectified raw d.c. with a center--tapped transformer with D12&D13. You were looking at the raw d.c. ahead of that linear regulator circuit (Q11 & D15), but you didn't check the d.c. on that 9.4Vdc regulated voltage rail which is the ONLY d.c. supply for receiver. If that regulated voltage rail is not close to 9.4V (say if it's 13Vdc) you've got a shorted Q11(or opened D15 Zener), and all the ripple on the raw d.c. gets into the audio circuitry. (VE7DQS)

[@valakatz3967]

Please can you tell me where the fuse go?

[@z95m]

Nice job, Terry. I've got a DX-150A which I bought new in the late 1960's. I replaced all the electrolytic caps recently, and would like to try your mod. Where would I be able to buy the choke? Thanks.

[@d-labelectronics]

Hello Mouser part number: 553-C40X

[@z95m]

Thanks!

[@z95m]

Mouser Electronics = www.mouser.com

[@kornami8678]

I still say there is something wrong with the Q11 regulator circuit. There should not be any ripple on the 9.4V output from the regulator. If there is ripple, then something is wrong with the regulator. Get rid of the C76 cap. It is forming an AC voltage divider with C72 to the Q11 base and I suspect doing nasty things. Here is the way it is supposed to work: R50 and C72 form a low pass filter at 7Hz. Any 120Hz ripple will be highly attenuated at the base of Q11, so all that results is 10V of DC with very, very low AC ripple component. Therefore, there should be no ripple at the Q11 emitter, which I suspect there is (before the addition of the choke). However, C76 defeats this R50/C72 low pass filter and puts ripple back on the Q11 base. Remove C76 (and remove the choke). The choke fixes the symptom and not the cause.

[@randyab9go188]

I'm sitting here right now redoing a DX-150b. The interesting thing on mine is c76 was a fix from the factory. there was just two holes drilled and no traces running to them. C76 leads were just folded over and tacked across R50. the designation also was not silk-screened on the PCB. For some reason in production and unknown engineer decided this cap was necessary. Since right now I'm doing a full recap I think I will check the output and see if it makes any difference if I add it in or leave it out.

[@randyab9go188]

Just wanted to do an update. I left c76 out of the circuit and I have absolutely no hum. Even with the volume control turn all the way up and the RF gain all the way down it is dead silent. If you didn't know better you would swear it was turned off.

[@emylrmm]

I concur. It appears that the regulator was overlooked

[@emylrmm]

Agreed. I would say that C76 is a design flaw. It should be removed

[@frederickmooney2305]

My DX-150A has no C76. It does have some 120Hz sawtooth hum on the DC outputs, although about half the amount shown in the video.

[@squarewave2]

Hi D-lab, I want to modify my DX-150 as you show. Am I reading your mod diagram correctly? It looks like you have completely eliminated the fuse. I am a beginner and would appreciate your help.Great videos, by the way!!

[@d-labelectronics]

Hello, Initially, I did jump the fuse, now its back in line. Just re position your choke. The mod is well worth doing. Thanks for the comment, stick around

[@chuckheff]

What do you mean reposition choke? on circuit drawing it looks like choke is still across fuse or there is no fuse. Are you saying hook one side of choke to R49 and other side to + side of 470uf cap and - of cap to ground?

[@RobertKohut]

Nice!

[@Kennynva]

HI..can you do me a favor and look at the band-switch and tell me if you see any dark or black looking contact where the wipers go...is your all brass colored, cause mine is half black...yes I think lightning hit...I am still trying to repair this radio..had it about a month..

[@randyab9go188]

A lot of time that black look is from the silver tarnishing. I am working on a 150b here that was so bad it wouldn't function. A shot of deoxid 100 fixed it right up. You can also use Tarn-X to clean the switch, but be sure to rinse the switch with alcohol when you are done.

[@andydelle4509]

Nice job on the CLC power supply. Many hobbyists think this is only tube power supply technology but as you have shown, it is quite applicable in solid state power supplies as well. But one thing concerns me here. With the 9v regulator and 300mv of ripple, there should not have been any ripple on the 9v rail. 300mv is well within the regulator drop. Are you sure the ripple wasn't 3 volts? That would make sense. I also assume you did verify the regulator is working and the pass transistor not shorted across the EC junction? EDIT: A comment below suggests the audio power amp is on the unregulated 12v rail. That too would explain your findings.

[@emylrmm]

If I recall, the audio is fed by that regulated 9V supply

[@ardenhall3833]

I have a DX-150 the board is alot different than the DX-15oa so I didnt,dare to try to get rid of the hum

[@kathyschuyler8423]

I have a dx150a and the band spread cord is broke, does anyone have the diagram on how to restoring it.

[@umajunkcollector]

Kewl Terry, who made it for RS? I'd consider installing a small SLA battery, and use its supply to recharge it. Come in handy for portable or power outage use. Another simple fix, use a one amp wall wart on the DC input. I hve a bunch of those wall warts.

[@d-labelectronics]

I know they were made in Japan. Maybe by Trio? Allied and Lafayette also sold re-branded shortwave receivers. Great days gone by. TD

[@spresc2180]

Wall warts, depending on their build quality can be very noisy DC power supplies, in case you did not know that.

[@randyab9go188]

@@d-labelectronics they were made by GRE.

[@russellhltn1396]

The choke got you the results, but the real problem is the voltage regulator. 0.3V of hum should have been easy to strip out in the regulation down to 9V. The question is why does the regulator suck? I'm wondering about C76. If they were concerned about oscillation or RF problems, then I'd expect it to be a few pF. But by being a 47uF, it forms a AC voltage divider with C72 and puts hum into the reference voltage. I'd pull C76 or replace it with something far, far smaller.

[@d-labelectronics]

Hello, Great idea. I did not look a the the caps around the regulator except for the 470uf value. I will check that component and jump the choke, see what it does. Thanks for the input.

[@russellhltn1396]

Dry caps is certainly a possibility, but I'm seeing a questionable design. It sure seems like it would couple the 300mV ripple of the raw voltage into the zener diode. Any ripple there will find its way to the regulated voltage.

[@jbrobertson2758]

8:43/OMG!

[@anthonycosta1776]

I didn’t bother. Just use my Aston 20 amp supply.

[@ronalddaub5049]

My 160 don't do it

[@kardRatzinger]

Wouldn't you get the same result by replacing the first filter cap with a $1 10.000uF cap?

[@d-labelectronics]

You have to be cautious when increasing capacitance way above the original value. It can cause damage to the power transformer/diodes/pop fuses, etc., due to the initial surge current. Yes a choke is rather expensive but does a super job killing noise in DC circuits. Lots of info on the web.

[@kardRatzinger]

That's true, however, I'm not sure how high would you need to go with the capacitance to actually damage a solid state rectifier. I used to use 10.000uF caps for heater filtering in high-gain valve amps, with no problem. I always feel chokes were a good idea back when an electrolytic capacitor of a suitable value and voltage rating would be prohibitively bulky or expensive, not so much nowadays. Anyway, thanks for the great content.