Part 1 : 關於 TT21 與 KT88/6550 聲音表現上的問題:

Typical question:

Any idea if it(GEC TT21) really sounds better than the famous Genalex KT88?

Answer 1:

I use this tubes in my Quicksilver KT88 Monos for almost 4 week and
my amps never sound better!! I have try every KT/6550 family exept
Gold Lion.Where You find and how much You pay for this tubes.
I'm looking for place to order more! Is the same tube like KT88
only have top cap.

PS. Many people say it is the better tube !

Answer 2:

Sylvania 6550 is inexpensive and beat all Sovtek and Svetlana
6550/KT88 in my amps of course GEC TT21 is the best of the best.

Answer 3:

	4 years ago, I bought 4 GEC TT21 to replace my old Genalex/Gold Lion KT88 ,

which I have used for almost 10 years. The GEC TT21 and the Gold Lion KT88 have similar

sound quality, I even think that TT21 has  deeper base and the soundstage is deeper ,too.

The GEC TT21 and GEC/Genalex KT88 are absolutely the best among any types of KT88/6550. 

I really love the sound and after 4 years ,the 4 TT21 still look very new ,

I think I can use them for another 4 years or more ,since I was told

that the TT21 is the military version of KT88 and should have longer life than KT88.

However , they are both very rare and vary hard to find and getting more expensive now.

I am still looking for more GEC TT21...

Part 2 : 關於 TT21 與 KT88 的規格上的問題:

Typical  question:

    Ive had these 20+ yrs. and never found a book that covered them. 

They(TT21) look like KT-88 with the plate ran out the top instead.  Are they

equivalent?  Ratings?

Answer 1:

I can tell you that the GEC/Genelex TT21 is exactly the same as the

KT88. In fact it is a KT88 with the Plate connection brought out at the

top. They where used by the UK military in Modulator or Final amplifier

satges of Transmitters. Because the Plate connection is brought out to

the Top Cap they can withstand up to 1.2kv on the Plate. If you have

Answer 2:

The TT21 is a GEC transmitting BEAM TETRODE that looks just like a KT88 with a top cap connection. The specs are the SAME as a KT88, except the TT21 has a HIGHER PLATE VOLTAGE maximum rating. The top cap anode connector gives better isolation between anode and grid. Superior sonics to KT88 Genalex / GEC.

Part 3 : 關於TT21可承受的屏壓更高,壽命更長的回答:

Answer 1:

       Killerfantastic...These guys would take the peak voltages of AB2

operation really well.  Kind of a waste now to use them as an RF output

tube.  When that supply of KT-88's starts to dry down for real, the TT-21's

should keep the music playing for a while longer.

 Answer 2:

       The TT21 is the RF equivalent of a KT-88 It is exactly the same tube

but has the anode connector on top of the bottle to prevent arcing 

when operating in HV-RF resonant  circuits.

Answer 3:

One difference from a KT-88: a TT21 can handle up to 1KV on the plates!