Zenith H500

I wanted to send the tube pin voltage chart from my H500 Service and Restoration Manual as an attachment, but there seems to be no way to do it. Contact me directly at gc@sdlcforms.com if you want it and I will e-mail it to you.

Gary Clark

I have not heard of that issue before, but one of two things seem appertaining to that. Either the 1L6 tube is getting weak, or a resistor in the grid circuit has changed values, and that is because of age. The 1R5 doesn't have the needed bandwidth for higher frequency stations but works fine on the lower bands.

So if you have a tube tester please check the original 1L6 first, if it checks Ok then you need to check the resistors and capacitors in the Detector/ Oscillator section. Using the other tube will cut off at high frequencies because the tube elements are not as close togather, causing lower performance at high frequencies. 
 You may also check the bias voltage on the grid, but I don't remember what the value of it is,if you do want to measure it be sure to use a digital or VTVM. so as not to load down the bias voltage while measuring.

Hope this helps.
Here is a military manual that is very similar if not exact. See my link below.

http://www.nj7p.org/Manuals/PDFs/Military/R-520%2026-Jan-53%20KG7BZ.pdf

Has anyone run into this problem?  I have been repairing these radios for many years and this is a strange one.  With the 1L6 installed the audio is a distorted under water sound, however with a 1R5 sub it plays crystal clear.  Any tips would be greatly appreciated.

Tubenut