I have two whistle tenders, 2671W and 6466W that I am cleaning up. The 6466W works great, but the 2671W whistles okay until I power up to maybe 75 - 80% throttle. From there to full throttle it stops whistling because the whistle relay drops out. If I release the whistle control, the relay will pull in but will immediately drop out. No problems at lower throttle. Again, no problems with the 6466W across the entire throttle range. I am using a KW transformer with nothing else running.
Make sure the whistle relays are clean and the bottom contacts are free to move. Clean both contacts on the relays with a fine emery board to remove any dirt or corrosion. Confirm the contacts are touching each other squarely and firmly when the relay pulls in.
If the problem persists after cleaning, swap out the relays and see if the problem follows the relay. If it does, the relay is faulty and needs replacing.
Larry
Thanks for the suggestion Larry. I have a lot of other cleaning and maintenance to do on my collection, so it will be a while before I try swapping the relays, if it comes to that.