6L6 vs KT66

[jelle]

The higher primary impedance of the OT make a big difference.

Simply put: The 3400 ohms primary (50w) yields a more 70's tone compared to the higher 6600 ohms OTs (also 50w) that were used in 60's marshalls.

I have not tried the KT66 though, but I'm getting curious! I have only tested this with ef2 EL34 tubes and the difference was very clear.

Jelle

[mhuss]

Has anyone here tried the new JJ KT66s yet?

--mark

[David Root]

No, I haven't, not yet, but I surely will, assuming they are in fact REAL KT66s and not 6L6GCs in a big bottle. I'll consult my tube supplier, Lord Valve. He's always up-to-the-minute on new tubes.

The best JTM45 OT, the Radiospares De Luxe, had both 8k pentode and 6k6 UL secondaries (also 9K pentode for EL84s). Most folks seem to use the 8k pentode for the JTM 45, but 6k6 is the logical step between 8k and 3k4.

Is your EICO OT a standard pentode winding or a UL winding? Sounds like a good bet to me either way, especially as it's "large"!

[Phazor]

I've been on vacation last week so I didn't see your post. The Eico has UL taps but I didn't check the voltage ratio on them when I calc the Primary at 6.6K. I'll check the turns ratio on them but It would be a lower Impedance than the plates. The Eico is a potted tranny and quite large. I orignally thought about a Wreck tranny with EL 34's but will pickup some KT66's from Lord Valve next time I'm at his shop.

[leadfootdriver]

Would I use the same Screen and Input Grid Resistors from the 6L6 when switching to KT66?

The amp I have uses 470R for the Screens and 2.2K at G1..

[Roe]

Would I use the same Screen and Input Grid Resistors from the 6L6 when switching to KT66?

The amp I have uses 470R for the Screens and 2.2K at G1..

hardly, since a real kt66 draws more screen current than a 6L6. What is the voltages and the Z?

[leadfootdriver]

Dunno.. I don't have it all together yet. But I'm flip flopping on Power Tubes.
I'll start another Topic..

[Stevem]

Do you know what the KT stands for?

[mhuss]

Do you know what the KT stands for?

Mentioned up the thread, KT stands for "Kinkless Tetrode." Normal tetrodes have a kink in their characteristic curves. Beam-forming plates in KTs (and 6L6) largely remove this kink and provide a smoother pentode-like response.

[ViperDoc]

See here:

http://www.r-type.org/static/grid14.htm

[pdf64]

Would I use the same Screen and Input Grid Resistors from the 6L6 when switching to KT66?

The amp I have uses 470R for the Screens and 2.2K at G1..

hardly, since a real kt66 draws more screen current than a 6L6 …

I never even seen a real MOV KT66, nevermind tested an amp with them to see how they perform. But comparing the 250V pentode conditions for 6L6 and KT66 indicates the g2 currents seem pretty similar.
Whereas suppressor grid type pentodes such as EL34 will have somewhat higher g2 current.

https://frank.pocnet.net/sheets/126/k/KT66.pdf

https://frank.pocnet.net/sheets/127/6/6L6GB.pdf

https://frank.pocnet.net/sheets/010/e/EL34.pdf

[Roe]

Would I use the same Screen and Input Grid Resistors from the 6L6 when switching to KT66?

The amp I have uses 470R for the Screens and 2.2K at G1..

hardly, since a real kt66 draws more screen current than a 6L6 …

I never even seen a real MOV KT66, nevermind tested an amp with them to see how they perform. But comparing the 250V pentode conditions for 6L6 and KT66 indicates the g2 currents seem pretty similar.
Whereas suppressor grid type pentodes such as EL34 will have somewhat higher g2 current.

https://frank.pocnet.net/sheets/126/k/KT66.pdf

https://frank.pocnet.net/sheets/127/6/6L6GB.pdf

https://frank.pocnet.net/sheets/010/e/EL34.pdf

some of the newer kt66s perform more like 6L6s, particularly the tung-sol and to a somewhat lesser extent the chinese shuguang ones. Basically, these draw less screen current than the old UK kt66s (the gold lion RI draws more than the chinese ones typically)