KT120 transformer failures

I wondered the same thing, but went with a standard factory matched quad without "cryo" treatment just to be cheaper...and now I'll never know! Supposedly the fact that you bias each tube individually makes it less important to have them so carefully matched (according to the manual), but I'm no expert. I did read more about the "cryo" treatment later though and it seems interesting. My amp is still sounding fine, and better actually...KT120 tube break in? Maybe get a custom matched set of KT120s and send 'em out for cryo treatment someplace...your local college science lab might do it for free!

What's with all the posts about TCtubes all of a sudden everywhere on every thread that has to do with tubes?

A rhetorical question I deem unanswerable. I am the "deemer".

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.