squeal and moan presence control

[andrew]

Hello,I changed the OT on my D'Lite copy from a small 18watt with 6v6s to a Hammond 1650 25watt (7.6k) with 6l6s. The presence control worked fine with the 18watt OT but with the Hammond I touch the 8ohm or 4ohm tap with the NFB lead and it makes a very loud squeal and rumble. I am going into a 8ohm speaker. Thanks for any help.

[tubedogsmith]

Try swapping the plate leads on your power tubes, one to the other and vice versa. that'll take care of it.

[andrew]

I don't know how important it is but I have the NFB resistor lead attached to the 8ohm tap at the speaker jack( 8 ohm speaker).It works now. Thanks! However, if I attach the lead to the 4ohm tap like in the schematic it rumbles. Are Hammonds wired differently? Thanks again.

[andrew]

Sorry, I had the 4ohm tap wired incorrectly. Now all is well. Thanks again!

[heisthl]

Try swapping the plate leads on your power tubes, one to the other and vice versa. that'll take care of it.

For the newbies - when you read "Swap the plate leads on your power tubes" and you're saddend by the fact that one of them has been cut too short to swap, just swap the 2 leads from the PI to the output tube grid resistors. It does the same thing.