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Not a good sound... - Printable Version

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Pages: 1 2

Not a good sound... - OldRestorer - 09-08-2014

Ok so I was testing the 37-620 cathedral after a full recap and I am getting a real loud base squealing. If i turn the tone control it get higher pitched and then starts sputtering intermittently.

It was not making any sound at first so I checked all the tubes and cleaned the controls but now this is happening..

What the heck did I do?

Kirk

RE: Not a good sound... - Mondial - 09-08-2014

Do you have the tube shield on the 75 tube and the grid cap wire inside the shield?

The 75 is right next to the 42 output and it picks up feedback from the output tube unless the shield is installed.

RE: Not a good sound... - morzh - 09-08-2014

I was about to ask same: do you have any tube that should have grid cap wire inside the ahield and has it outside?

And for this matter, are the shields installed?

RE: Not a good sound... - exray - 09-08-2014

Shields first. And watch the proximity of that 75 grid cap lead to the 42.

RE: Not a good sound... - OldRestorer - 09-09-2014

What 75 tube and what 42 tube?

Here is the schematic

http://www.nostalgiaair.org/PagesByModel/212/M0013212.pdf

Kirk

RE: Not a good sound... - Eliot Ness - 09-09-2014

Quote:What 75 tube and what 42 tube?
He was looking at a schematic for a model 620. Your first post didn't specify that it was a 37-620 Icon_crazy

RE: Not a good sound... - OldRestorer - 09-09-2014

oopsie!

Update, I re-cleaned all the contacts on the tubes and turned it on. I jiggled the 6Q7G tube and the noise stopped. jiggled more and back came the sound and the vibration. I of course don't have another 6Q7G but it tests good on all settings. The base is loose, as is the top contact so I dont know...

Kirk

RE: Not a good sound... - morzh - 09-09-2014

Maybe you need to clean contacts and not change the tube.

RE: Not a good sound... - OldRestorer - 09-09-2014

I cleaned them already. I will do it again but even when the sound stopped there was no reception...

Kirk

RE: Not a good sound... - codefox1 - 09-09-2014

Replace the socket if you can't clean and re-tension. You can also get a 6Q7 (metal version,) and make sure pin 1 is not used as a tie point for anything other than ground (re route if needed,) and then ground pin1.

RE: Not a good sound... - OldRestorer - 09-09-2014

Tension is good on the socket and I dont think I even have a 6Q7 metal but I will look.

Thanks
Kirk

RE: Not a good sound... - Eliot Ness - 09-09-2014

Quote:The base is loose, as is the top contact so I dont know...
You can re-glue the base as well as the top cap with a drop or two of glue. Then you can heat up each tube pin and flow in some fresh solder. That would eliminate a flaky connection at one of the tube pins. Also try lightly tapping the tube when testing, especially when testing for shorts.

RE: Not a good sound... - Phlogiston - 09-10-2014

What did you use to clean the volume control?

RE: Not a good sound... - morzh - 09-10-2014

Knowing Kirk....coarse grit sandpaper Icon_mrgreen

RE: Not a good sound... - OldRestorer - 09-10-2014

Contact cleaner spray was used.

Sandpaper.... har har har Icon_lolno

Kirk