#46
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You might have to drill different holes to match the footprint of the replacement transformer. The original transformer is mounted a little different, with long through bolts, so it sits above the chassis.
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#47
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Unfortunately that persistant and untraceable hum is still there and I still cannot figure out where its coming from. |
#48
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Well for sure something's not right with this radio because the back of the radio says it's rated for 65 watts at 120 and the radio as it sits with its incessant 60 Hz hum is only 43 Watts so something's not right, either one of my filter caps failed or there's a bad tube or something else odd is going on with this radio.
I've tested all of the tubes in this radio and the 6K7 tube and the 6F6 tube both tested as having a H-K Short in it so I subbed them out with known good tubes and the hum is still there and the radio pulled the same amount of wattage, So I'm not sure what's going on with this mystery of a radio. I'm about tempted to just salvage the bulb and tubes and capacitors out of the radio and scrap it out. |
#49
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Remove all the tubes but the 6F6 and the rectifier and see if it still hums, proving it's a power supply issue. If so, bridge the electrolytics and see if it clears the hum. The power supply is a rather simple supply using a grounded B minus. |
#50
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I didn't try bridging the electrolytics yet, but I'm not sure what you mean by that, do you want me to bridge all of the ground connections from the electrolytics? If so I'm not sure how I would go about doing that seeing as all of them are grounded to the chassis in some way, shape, or form so they should technically already be bridged, seeing as the chassis is the common ground in this case. |
Audiokarma |
#51
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Bridging simply means "connect in parallel with", using a pair of clip leads. So bridge (jumper) each individual electrolytic (one at a time) with a single unit of equivalent or higher ratings. Note correct polarity.
The caps in question would be C19 and C20 (main power supply filters). You could jumper each with something like a 20mf 450V unit and see if it affects the hum. EDIT. Those two caps should be replaced as a matter of course anyway. If they're the original cans they could be left in place for aesthetics, but out of circuit. There's also C26, a low voltage electrolytic across the cathode resistor of the 6F6. It won't cause a hum problem, but will cause reduced volume if it's gone open. It should be replaced anyway. Last edited by old_coot88; 08-28-2021 at 09:52 AM. |
#52
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I checked the capacitors that I installed in the radio and they still test good yet on my ESR Meter, (they mesured about 4-6 ohms ESR and they both are 2 4.7 MFD 450V axial lead electrolytics paralleled together to make 10 MFD at 450V). And then the low voltage electrolytic is a 10/10 @ 160V Firecracker type electrolytic cap like the original was, and that one tests fine as well. So unless one of these caps failed in a manner I'm not aware of, or that the ESR meter wasn't able to detect (dead shorted) then I don't think the electrolytics are to blame here. |
#53
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I would leave the 5Y3 in there! I don't trust the old-time metal rectifiers! |
#54
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__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#55
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With an ohmmeter set to RX1, be sure the negative ends of C19 and C20 are securely grounded (zero ohms) to chassis. Any resistance here would definitely produce ripple in the B+.
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Audiokarma |
#56
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OK, so a little update with this radio:
I changed out the 5Z4 for a 5Y3G tube and installed a 6V6G tube into the radio and the hum has gone away, but a new issue as arisen, whenever I touch the chassis anywhere including the knobs or ground my signal generator to the chassis, the radio goes completely silent. But then when I remove my hand or the signal generator ground clip from the chassis or from any of the knobs, the radio comes to life. Is it because with this radio being made to utilize the metal tubes they had one of the heater pins grounded to the shield pin of those tubes and thus to the chassis? If so should I go and unground those heater pins to make this radio work with more modern glass tubes? |
#57
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Well I got it working, unfortunately it has to be turned up full blast in order to hear anything on it, which is what you guys warned me about with this unit because of its lack of AVC circuitry, the hum is still there but its not nearly as bad as it was, in fact when I turn the volume up all the way the hum goes away.
Unfortunately I couldn't tell how good the reception was on it because my housemate (who caught covid from his dad) had his desktop computer running (which is a high end gaming desktop) which has a super noisy power supply which basically renders AM Radio useless in my house, it just sounds like a a bunch of hash noise, across the whole dial with one local station that manages to break through the noise, the weird thing is that the noise seems to be not only on the AC line but also radiated through the air because even my battery radios are affected by the noise... Last edited by vortalexfan; 08-31-2021 at 01:52 PM. |
#58
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PCs with plexiglass view windows tend to radiate RF noise as as do many cheap power supplies. When I built my PC I went with a full metal case and a Bequiet brand power supply which doesn't seem to emit any noise to hamper radio or TV reception in the slightest.
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#59
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#60
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__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
Audiokarma |
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