KT120 transformer failures

The KT88 and 6550 draw 1.6A by their heaters (filaments)
The KT120 draws 1.9A by it's heater (filament)

As you can see the KT120 is higher and will tax the heater (filament) winding of the power transformer if it was not designed to take the extra 300mA. It very well over time cook the heater (filament) winding of the power transformer and burn it out, (fire is a possibility), which will be expensive to fix because the heater (filament) winding is a small part of the mains power transformer that supplies the HT (high tension) as well to the tubes, and usually the largest transformer on your amp.

Cheers George

Hi Johnsonwu

I shall offer my reasoning for posting multiple questions about TCtubes throughout the forum here. It is not as funny as Wolf's though. When trying to price out places that sold the Tung Sol KT-120 and found that they offered a service called: Precision Power Tube Matching

Direct from the TCTubes website:

"Our power tubes are burned in for 48 hours and tested on a laboratory grade Amplitrex AT1000 tube tester. We match tubes for both current draw (mA) and transconductance (Gm) at typical operating conditions (see #3 below) for no extra charge. We can also custom match power tubes at whatever specifications you provide (see #4 below)."

They then ask for amp maker/model, how to bias the amp and finally the plate and screen voltage for a custome match. I'm new to tubes and had never seen this before. I was trying to get information from members but since I never really know what the moderators will put through I have to post questions in different threads.

I'm new to tubes and don't know if this precision matching will really make a difference. I'm trying to gather info about it. I have no affiliation with TCTubes whatsover.

For me it is now down to a cryo treated platinum factory matched quad of KT-120s or a precion matched quad of KT-120s from TCTubes.

Jedinite24...did you stick the KT120s in yet? Mine keep getting better...not sure if they've peaked yet, but they likely have. Also, I discovered that some new tubes have a "new tube burning smell" that I thought might be the Jolida frying until I tried some new KT88s that had a "burning glass" sort of smell for a day or 2...just like the KT120s.

Hey Wolf
I got the KT-120s but my 502p is @ my local Jolida dealer getting upgraded. The guy is a tube expert so I trust him with modding the amp. In another couple of weeks I'll be able to enjoy the music as well as the buring smell you mention from the Jolida & the KT-120s. Thanks for the heads up on the buring smell. I probably would have been worrying about that. Which KT-88s did you try? I have my eye on the Penta KT-88SC tubes just in case if the KT-120s don't work out. Also when I spoke to the dealer/tech he said the Jolida 502p could handle the KT-120s w/ no problem. I can't wait to get up & running w/ everything.

My KT88s were an impulse purchase at a local "DIY" place and they're sets of "matched pair" Svetlanas...I think Svetlana has an OK reputation and in any case they weren't expensive (same Russian factory also). I think the KT120s have a little more clarity or something...bigger sound sort of, but the 88s do sound good (as do the 6550s). I guess I'm good for YEARS of power tubes now. Good luck with the mods, and it feels good that another Jolida tech thinks the 120s are OK as that was a hard issue to nail down. It's interesting how the 502 just keeps impressing me, and now I suppose I'll be looking at 12ax7/at7 rolling...it's endless and like it!