Jolida 502 KT120 tube swapping

The Jolida is basically a Mullard 5-20 design with different tubes. Don't spend the money on the tubes. IMHO. Replace the 15k resistor in the 12at7 tail with a Compact Cascode current source kit from http://www.kandkaudio.com/accessories.html

Then replace the Plate resistors on the 12at7's. Match them at either 48k or 56k. Adjust for about 3mA per side or 6mA current across each resistor. Remember do this to both channels.

Look on the net for the Jolida schematic and you will see the resistors I'm talking about. You will thank me. This will make a larger improvement than the output tubes.

I think that's a done deal as all the important (seemingly) resisters in the signal path were replaced when Jolida MD did an "upgrade" mod before shipping the amp to me. The tube "rolling" is simply for my own amusement as every review I've seen of the KT120s (which are fairly inexpensive as these things go) has mentioned there is a significant audible difference between those and other types, and if your transformer can take the "heat" you can drop 'em in...I am merely fishing for owners who've tried them in a Jolida. I have no issue with the current Tung Sol 6550s as the amp sounds absolutely great with the supplied "stock" tubes (Tung Sol 12AX7s, EH 12AT7s).

The resistors I mentioned was not part of the upgrade. I'm sorry I was just trying to help you improve the amp.

I would be careful putting the KT120's in this amp. First they draw more current and this could hurt the power transformer with extended use. The current draw from a KT88 is 1.6A. According to the Tungsol data sheets they draw between 1.7A and 1.95A. It doesn't sound like much but it could be enough to fry the transformer over time.

Secondly these are not the same tubes. KT88 and KT120 have different operating conditions. Yes they both have 6.3v heaters and the tube pins are the same. But there is more to a tubes operation. If your amp is not set-up to run the KT120 it will not be running these tubes at their best operating point.

There are enough new KT88's to choose from. Also your input tubes can both be improved on. IMHO Roll a few and find out.

Don't be sorry. I appreciate the feedback and respect your technical tweak choices, although you assume I have the ability to install, match, and adjust this stuff when I rarely venture past soldering something that looks unsoldered. That said, I'll look into your suggestions and see if I trust myself to do the surgery. I have spoken to everybody but the janitor at Jolida at length about the KT120 having enough current available to not melt my amp, and they assure me it's overbuilt to easily handle the 120s. If it blows up they'll fix it (at least for the next 2 years). Along with the KT120 appealing to me as an amusing tweak, I'll certainly be trying whatever KT88s seem interesting also. I do plan to mess with the input tubes (I roll tubes in my guitar amps from time to time and do notice obvious differences)...I mean really...this is the entire point of this amp for me...I can mess with it! In any case, thanks again for the feedback...nice to know there's a braintrust out there.