05-07-2014, 04:16 PM
I thought I was done with the restoration of my Model 19, but now that I've been listening to it for a couple of days, I have a minor problem
The problem is a combination of tone and volume dependent. The tone switch has four positions. When the tone control is turned to the far right (with the most bass), it takes almost no volume to hear a kind of a "rattle" or a feedback in the audio. With the tone turned one setting to the left of that, the sound is much better,. You can listen to the set at almost normal volume, but if there is much bass in the sound you start getting the same effect. The two leftmost tone positions with the most treble seem to not induce (or mask) this issue.
Other findings:
1) There is a small tear in the speaker that I never noticed when I had everything out of the cabinet. The tear is kind of "V" shaped, less than .5 inches on a side. I'm not sure if I tore it when I was putting it back, but I don't think so. I will repair the speaker in any case.
2) If I place my finger on the top grid cap of the 36 oscillator tube (with the tone control rotated all the way to the right), the sound cleans up considerably. This tube is missing it's shield. I am in the process of trying to locate one for this tube, but no luck so far, maybe I'll hit paydirt in Kutztown on Friday
.
3) I tried the chassis/speaker out before I put it all back in the cabinet. I didn't notice this, but it is quite possible that I simply missed it if I had the tone control set to one of the two leftmost positions.
Is this microphonics?
Could the speaker tear cause this? I kind of don't think so because the rattle goes away with less bass, and also goes away when I touch the osc grid.
Would a shield on the 36 tube help this?
Any suggestions on what to look for?
Thanks!
Jon
The problem is a combination of tone and volume dependent. The tone switch has four positions. When the tone control is turned to the far right (with the most bass), it takes almost no volume to hear a kind of a "rattle" or a feedback in the audio. With the tone turned one setting to the left of that, the sound is much better,. You can listen to the set at almost normal volume, but if there is much bass in the sound you start getting the same effect. The two leftmost tone positions with the most treble seem to not induce (or mask) this issue.
Other findings:
1) There is a small tear in the speaker that I never noticed when I had everything out of the cabinet. The tear is kind of "V" shaped, less than .5 inches on a side. I'm not sure if I tore it when I was putting it back, but I don't think so. I will repair the speaker in any case.
2) If I place my finger on the top grid cap of the 36 oscillator tube (with the tone control rotated all the way to the right), the sound cleans up considerably. This tube is missing it's shield. I am in the process of trying to locate one for this tube, but no luck so far, maybe I'll hit paydirt in Kutztown on Friday
.3) I tried the chassis/speaker out before I put it all back in the cabinet. I didn't notice this, but it is quite possible that I simply missed it if I had the tone control set to one of the two leftmost positions.
Is this microphonics?
Could the speaker tear cause this? I kind of don't think so because the rattle goes away with less bass, and also goes away when I touch the osc grid.
Would a shield on the 36 tube help this?
Any suggestions on what to look for?
Thanks!
Jon
