I have a Conn Elkhart 72H bass trombone for sale. Its 9.5 inch bell .562 bore Single Plug Slide has been overhauled and is in silver plate. Bell is as originally intended. Blows nicely and is substantially lighter than a double plug, blowing a little freer. Its a bargain at £850. Send me a PM if you would like some photos emailed or have any questions. Cheers.