The Jolida 502 and 504 are the same amp except for 4 resistors that make the amp use either EL34’s or 6550/ KT88’s. The rated output for the use of EL34’ is 50 WPC and 60 WPC with the KT88 or 6550 tubes. This amp has been completely upgraded! This is one of the first series of this amp and does not come with a remote. This amp has been modified so it uses EL34’s. It has been completely recapped, all of the power caps are bypassed with small film caps. The old inexpensive film output caps were replaced with WIMA MKP10’s that were bypassed with small copper film in oil caps. The litz wire for the inputs was replaced with cryo treated solid core Kimber Cable wire. The RCA input connectors are silver plated, and the binding posts have also been upgraded… all of the connectors were cryo treated. The chassis has been damped. The three front control knobs are solid brass that has been painted to match the chassis. The paint on the transformers has been redone in black and the screws and nuts that hold them together have been painted with gold high temp spray paint. The feet are Vibrapods to absorb vibration. The amp comes with a complete set of tubes. Four new issue Tung-Sol EL-34’s, two Philips Miniwatt 12at7’s and two Phillips Miniwatt 12ax7’s- all cryo treated. As a bonus you get a pair of old school Mullard 12ax7’s that the paint has come off of- they were branded “The Fischer”. You will also be getting a complete set of silicone tube rings, one each for the small tubes and two each for the large tubes as in the photo- these help if micro phonics ever develop. Each tube has its own box.I had a custom cover made for it from nylon/canvas as tube amps are hard to clean. (there is a tuner under it in the photo so it droops- see photo) HOW DOES IT SOUND? The upgrades made a dramatic improvement in the sound quality, the warm tube sound is still there but there is much more detail and it is markedly more dynamic. The best stereo I have owned was a fully upgraded Alta Vista tube amp with a Herron preamp. This is just a step below that! To make sure you have everything you need to take care of your new amp you get a multi-meter to adjust the bias as well as a small screwdriver and two long probes that will stick up above the output tubes so you don’t burn your fingers. You also get a 14 AWG “Bob Crump” style power cable with solid copper connectors- everything is cryo treated. The amp also comes with 4 extra fuses and the original plastic knobs. The four resistors to run the unit with KT88’s or 6550’s are included as well.LET ME KNOW IF YOU WOULD LIKE TO BUY IT FOR LESS WITHOUT THE TUBES. This amp is for sale on an audio site for less and via money order so it may not last. The package is triple boxed and the amp is heavy so shipping is a flat $80 CONUS insured. I have several photos of the packing if you would like to see them just ask. PS. I used to own Cryo-Parts so I know that all parts were treated.