How much hum is too much? - Videokarma.org TV - Video

ldatlof · #1 08-18-2005, 01:28 PM

I just recapped a Westinghouse H-204 AC/DC radio. It plays really well now, except I noticed that if you are standing right next to it you can hear some hum. The hum is there always there and doesn't increase with volume and can't be heard when music is playing or if you are not right next to it. The hum is most easily heard when the volume is at zero. So I was wondering if there was an acceptable level of hum for these old radios or whether there should be no hum at all?

I have not replaced the line cord yet. I also replaced a can capacitor that was 50/50/20 with one that was 50/50/50 and with a higher voltage.

Chad Hauris · #2 08-18-2005, 03:26 PM

You should not be able to hear any hum except maybe a small amount if the ear is held right to the speaker...if you can hear it humming at a usual distance then it's too much...there may be heater to cathode leakage in the audio output tube introducing hum from the AC filament circuit in the audio circuit. Would recommend trying a known good output tube.

vintagecollect · #3 08-19-2005, 03:30 AM

If all tubes are good, try larger cap values for power supply. Later ac/dc sets have slight disadvantage of no choke in power supply or field magnet /choke found in older speakers to further smooth out ac ripple in power supply. This should have some effect, especially if hum is annoying while trying to listen to set at lower volumes. Some reference books say some hum is acceptable, but by todays standards, probaly not for most people.
As a further note: A half wave rectifier will have more AC ripple voltage than Full wave rectifier output voltage using same filter caps. Give it a shot and let us know!!!!

ldatlof · #4 08-19-2005, 04:07 PM

Thanks for the quick responses.

I have ordered a new output tube which should arrive early next week. Hopefully, the new tube will solve the problem as it is the easy fix.

Quote:

Originally Posted by vintagecollect

As a further note: A half wave rectifier will have more AC ripple voltage than Full wave rectifier output voltage using same filter caps. Give it a shot and let us know!!!!

Vintagecollect - If the new tube doesn't eliminate the hum, did the above quote mean I should change out the half wave (1N4004) with a full wave rectifier? The ones I have seen have 4 leads instead of two. I am not exactly sure how to hook it up.

BTW, I bypassed the 1N4004 with a .01mF 500V ceramic cap. Didn't seem to make much of a difference though.

vintagecollect · #5 08-21-2005, 09:11 AM

Actually, I meant larger main filter caps for your power spply section in your radio. This would be easiest to do. You said put in 50/50/50 in set. If new tube doesn't solve problem, try a 80/80/80 cap. The cap you have in their now is close to original value, that's probaly why there's not much difference. Working on more sets, you'll find out larger caps were used mainly for hi/fi & TV due to part costs.--- Larger value caps are now mass produced and cheaper. Do this intead of attempting to install full wave rectifier as set is not designed for this and more involved. I only mentioned difference between half & full wave recifiers as a discussion------- & no suggestion as replacement unless you can do all needed modifications to make upgrade work properly. I'm just saying ------ half wave rectifiers REALLY do need larger cap values for main filter caps. GOOD luck. This will be nice upgrade to your set.

I have a 1950 zenith am/fm set that recapped. The tone control didn't make much difference in tone so I had to upgrade to larger value--- tone control cap. The original speaker was disconnected and a newer panasonic hi-fi speaker with sub woofer connected by speaker wire, original zenith speaker still in cabinet. Used new speaker to take advantage of full sound quality of fm!!! Quality of sound/tone is excelent rivalling newer stereos. Unorthodox upgrade but fantastic results!!! I was stupid once and wanted to sell set, my wife enjoys listening to it too, so wont sell set. She insists we keep it to listen when on patio..

ldatlof · #6 08-26-2005, 04:33 PM

Put in a supposedly NOS Sylvania 50B5 (it actally tests lower on my Lafayette tester than the used Admiral tube it replaced). Initially it had more hum than the original tube. Then I noticed that the 12BE6 tube was not properly seated in its socket. Pushed it back in and most of the hum is gone. Now you have to put your next ear next to the speaker to hear the hum. Looks like I got an extra output now.