Philips Model 922 Tube Radio Video #2 - Grid Voltage Anomaly

I've decided to check the key tube voltages and I find something interesting that I cannot explain - yet.

[@randomsteve4288]

28:40 If the grid coupling cap can be ruled out and the grid bleeder resistor is not open, such a slowly creeping up positive going grid voltage is mostly a sign of either a gassy tube or grid emission. The latter often due to evaporated cathode material depositing on the grid, which in turn is often a result of an overheating of the cathode. In any case changing the tube is the way to prove it, because in rare cases dirt or degradation of the tube socket may cause external leakage paths from a screen or plate pin to the grid. That tube socket degradation and the resulting development of leakage paths, sometimes leading up to even carbon tracking, has (at least in europe) been seen frequently on sockets made from resin bonded paper (Pertinax) from the 50s. And in most cases it involved the miniturized 9 pin tube sockets in combination with the extremely hot running audio output tube EL95 (6DL5), which to make matters worse has the ground referenced heater and plate on adjacent pins.

[@crr8297]

Being able to understand schematics is important, if pin 2 is internally connected to pin 5 on the 50C5 that means the "missing" resistor can be on either pin 2 or 5, it's on pin 5 in this case BTW, Jim doesn't read comments so this info is for anyone else who does.

[@hestheMaster]

Those old carbon composition resistors as they age are troublesome. Applying a voltage to them "heats" them up and change value, sometimes dramatically.

[@thethirdrail8397]

you might need to replace your mouse, when you start having the mouse do things you are not wanting. I may suggest a new KB too. that way, you do not have to go buy another Part for your PC! esp. if the store(s) in your area run short on Items. our stores here in the US sometimes have trouble keeping stock .

[@edmondedwards6729]

didn't that grid resistor read 525K?....It is supposed to be a 474K resistor, so isn't it part of the problem, being about 50K too high? Perhaps a new resistor should be installed, and if the volts are still too high, replace the tube with a known good one.

[@randomsteve4288]

30:00 You have seen 8V on the 150 Ohm cathode resistor... The schematic calls for 6,5V only. The 8V you see correspond to a cathode current of 53 mA. The intended current per schematic is only 43mA. 53mA instead of 43mA, thats like 25% over So you will load down the rectified b+, thereby increasing the hum and stress on the rectifier tube. And you will also be putting more power dissipation into the primary of the audio output transformer. But since this is a "guarantee void if radio leaves workbench" fix, go ahead and redesign the radio. Philips didnt know what they were doing. You know better...

[@bellytripper-nh8ox]

JIM: HOOK ONE END OF AN RCA CABLE TO YOUR BELLY BUTTON AND THE OTHER END OF SAID CABLE TO THE GRID TUBE SOCKET OF YOUR RADIO AND THE ANOMOLY SHOULD GO AWAY OH, ONE MORE THING, SIR: **YOU NEED TO HAVE ADS EVERY 5 SECONDS IN YOUR FUTURE VIDEOS: **NEW KZbin RULE!!**