09-07-2022, 02:30 PM
For some reason it wouldnt let me attach this last pic in the last post?
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Grid coupler change?
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09-07-2022, 05:09 PM
Check value of grid resistor.
Try 470K if the official value is 1M Sometimes the UL84s are leaky. I've one very leaky.
09-07-2022, 05:27 PM
The grid leak resistor Mike is a replacement 470k, I have tried other ul84 including some nos ones I have here.
09-07-2022, 08:01 PM
(This post was last modified: 09-07-2022, 08:02 PM by Mike Watterson.)
Try 220K?
Is the base of the UL84 clean on the inside of the valve between the pins? No strange deposit? Does the service info specify cathode volts?
09-07-2022, 09:12 PM
(09-07-2022, 08:01 PM)Mike Watterson Wrote: Try 220K? See my post number 14. The advice has already been given!!
10-07-2022, 09:47 AM
(29-06-2022, 07:16 AM)Murphyv310 Wrote: A work around would be to lower the grid resistor or just add a 220k between G1 and ground, audio level may drop slightly as might bass response but changing the grid coupling cap to a 0.02uf would restore the bass.Yes, I forgot. Likely any change in bass or audio level might not be noticed.
10-07-2022, 05:23 PM
(This post was last modified: 10-07-2022, 05:24 PM by Murphyv310.)
Hi.
Over the years I've discovered that when offering sound advice it's not taken up, it could be a post is missed or its dismissed as wrong. The issue with this radio is common with PCB’s of the age. They are paper based effectively and damp storage or carbonising can cause leakage. Ideally lifting components will be a cure but it's not always possible. Some plastic bases are known to leak as well, I've had to replace many in my work and hobby. There are workarounds, for example decrease the grid leak resistor value or/and increase the value of the cathode resistor either will remove the positive potential on the control grid WRT cathode and reduce cathode current and obviously anode current with the benefit of protecting the output valve and transformer. |
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