Philco 71B Code 125 speaker thumping

Philco 71B Code 125 speaker thumping - Printable Version

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Philco 71B Code 125 speaker thumping - dmblackburn - 02-10-2026

Bought this set on eBay. I replaced the electrolytics and safety capacitors and the set plays but has a rhythmic "heartbeat" sound thumping from the speaker.
I am getting stations but is interrupted by the regular thumping sounds. Sounds to be around 60 per minute. It does not look like anyone has reworked the Bakelites so before I do that I wanted to see if anyone else has seen this before.

RE: Philco 71B Code 125 speaker thumping - morzh - 02-10-2026

I wonder if you have an electronic clock with a step motor nearby.
Doesn't look like anything inside would make it.

RE: Philco 71B Code 125 speaker thumping - dmblackburn - 02-10-2026

I do have an electronic clock and speaker connected to a nearby PC. I disconnected from the wall outlet and the thump continues.
I have attached a movie capture for review.
Thank you for your response

RE: Philco 71B Code 125 speaker thumping - morzh - 02-10-2026

You cannot attach movie here. It's not attached.
Put it on some videohosting and give the link.

PS. Actually, a good idea to check that whatever you attached is actually attached.

RE: Philco 71B Code 125 speaker thumping - MrFixr55 - 02-11-2026

HI DM Blackburn,

This sounds like a a capacitor problem. First off, it is important to note that the 2 main filter caps do not ground to the chassis, they connect to the center tap of the HV secondary. Make sure that the The "can" of the capacitors must be insulated from the chassis. The second possibility is dress of the grid cap for the First Audio stage (labeled Detector - Audio on the schematic. Make sure the lead is dressed correctly. If there is supposed to be a shield on this tube, ensure that it is in place. touch the wire. Does the "beat" change?

Next, "divide and conquer"

Does the "beat" noise occur with the volume control all the way down? If yes, the problem is in the audio stage or power suppl. If no, the next step is to power down and pull the detector tube. Power back up and raise the volume control. You may hear a little hum, but you should not hear the beat.

If no hum, power down, reinstall the detector tube and pull the IF tube. If no hum, reinstall the IF but leave the grid cap off. Repeat the test. If no hum, repeat the same procedure with the First detector. If no hum, repeat with the 1st RF Amp tube. This should help you isolate the stage that is causing the issue. The issue may be a bad capacitor, bad resistor, gassy tube, etc.

If the Bakelite condenser blocks have not been serviced, do so. Remember, you can't just "bridge" the caps with new ones, the old ones must be take out of the circuit. Remember, some of these blocks have 2 caps or a cap and esistor inside. Several of these condensers are "B+ Bypass" condensers. Failure of these condensers can cause this problem. Service the "Filter Condenser Block" by replacing their components also. Check the continuity of the voltage divider resistors

Mike (Morzh) has written a great article on servicing theses Bakelite blocks without having to detach / reattach the lead wires. See the attached link:
https://philcoradio.com/library/index.php/shop-talk/techniques/bakelite-capacitor-rebuild-without-desoldering/

Hope this helps

RE: Philco 71B Code 125 speaker thumping - RodB - 02-11-2026

Is it a putt-putt sound like an old motor boat or an intermittent buzz pulse like an electric fence? Try to see if you can control it with volume or antenna signal strength. We need to narrow it down to feedback or anything picked up on the antenna.

RE: Philco 71B Code 125 speaker thumping - morzh - 02-11-2026

...and if we could listen to the sound (video or just audio file), it would help.

RE: Philco 71B Code 125 speaker thumping - dmblackburn - 02-11-2026

Can you tell me which video hosting app you use to save the video and create the link ?

RE: Philco 71B Code 125 speaker thumping - dmblackburn - 02-11-2026

Try this link to view a video of the thumping noise. I'm new at this so I hope this link works

https://studio.youtube.com/channel/UCZR7FiMRB8QTOsIV_3UqQjQ/videos/short?filter=%5B%5D&sort=%7B%22columnType%22%3A%22date%22%2C%22sortOrder%22%3A%22DESCENDING%22%7D

RE: Philco 71B Code 125 speaker thumping - morzh - 02-11-2026

Youtube is good.

And if you make the video public, we won't have to sign in to view it.

PS. And after I jumped through some hoops to sign in from work, it said i have no permission to view it.

Just go to the studio and make the video public.

RE: Philco 71B Code 125 speaker thumping - dmblackburn - 02-12-2026

I checked YouTube "Your videos" and the short is designated as Public with no restrictions

RE: Philco 71B Code 125 speaker thumping - morzh - 02-12-2026

Then you should give us the link to the public version. You probably gave us the link you view yourself when you are in your account.
What is the name of it (exact)? We then could find it by name.
Or log out from the account, find it and give us the link to it then.

RE: Philco 71B Code 125 speaker thumping - dmblackburn - 02-12-2026

I signed out of my YouTube account and did a search for "Philco 71B Code 125 speaker thumping" and could play the video short.
My YouTube account is listed as Daryl Blackburn @darylblackburn52
Hopefully, this will work for you. Again, sorry, I'm new at this. Thanks for staying with me on this

RE: Philco 71B Code 125 speaker thumping - morzh - 02-12-2026

Yep. It worked.

I think, yes, your radio is doing this.
Something drives the output to saturation maybe. It is a pretty sound hard click.
Does not look like motorboating.