Testing a KT66 tube

[Leland47]

Hi. My Weston tube tester roll does not have KT66 listed. (At least not that I can find)

Can I test em as a 6L6 or maybe as an EL37?

Any ideas? I don't have an amp to try them out.

 

[Leland47]

Thanks!

 

[primosounds]

My Sencore uses the same settings for all 3. You might see slightly different emmissions levels if you compared them but it should work.

Right the kt66, el37, 6l6, also 5881, 7581, and GB and GC all are compatible except the heater current for the first 2 are higher.

 

[Dave451]

My B&K707 shows the same settings for 6L6, EL37, and KT66 as well (for mutual conductance testing).
Dave

 

[Leland47]

Thanks!

Picked up a pair at an Estate Sale last weekend.
They test great!!

Date code for 1952!

One guide pin broken..

 

[Dave451]

Just be careful plugging the one with the broken pin in properly. I've used multiple octal tubes with the guide pin broken.

 

[gadget73]

Repair bases exist, and they are cheap

 

[Leland47]

Repair bases exist, and they are cheap

I've seen those...will have to look into that.

 

[Chriscolt]

I just ran into this with my Heathkit (True) Mutual Conductance Tester (restored and calibrated per factory spec) - fortunately they have updated roll chart supplements up to 1978 and a European to USA tube conversion chart - e.g. EL84 = 6BQ5, EL37 = 6L6, EL34 & KT77 = 6CA7, EL90 = 6AQ5, KT88=6550 and in this case a KT66 = 7581 (not a 6L6) - makes sense since the 7581/KT66 is a higher output (35 watt @ 500V Plate/450 Screen - connected to Ultra Linear Transformer - 6L6GC/EL37 @ same voltages & UL dissipate 30 Watts) more rugged tube - so the settings (at least) on my HK TT-1 are different (the signal level, meter and bias settings, pin settings exactly the same as 6L6) as are the minimum umhos for the KT66 vs the 6L6. For kicks I measured a so called new Tung-Sol Russian pair of KT66s that I bought about 7 years ago but never used (may have been a bad batch as Tung Sol has improved their QA dramatically over the years) . The ones I had and tested read 1800 & 1650 umhos where minimum is 4080 & new (RCA Manual) is 6000 umhos - so very bad, compared to new Russian TS 7581 same age but unused (TS revised the 7581 to 7581A which measures a lot better don't buy the 7581) they read 3400 & 2200 as a so called matched pair from Tube Depot (7 yrs ago - unused) - I tested this against a QUAD of used but still good Phillips 7581A ranged from 4000 to 4200 for the 4 tubes - so a bit better than the new stuff and pretty well matched. These tubes definitely test better at higher voltages - my tester only provides max of 250VDC on plate and Screens - this tube was designed for higher voltages - as was the 7027A (600V plate max/35 Watts - used in many Ampeg bass amps) and of course the next step up KT88/6550 which are beasts. The 35 Watt 6L6 type tubes (7581A/KT66 & 7027A) were designed also for more clean headroom at louder volumes.

 

[primosounds]

I just ran into this with my Heathkit (True) Mutual Conductance Tester (restored and calibrated per factory spec) - ............... These tubes definitely test better at higher voltages - my tester only provides max of 250VDC on plate and Screens - this tube was designed for higher voltages - .

How do you know if the tubes test "better at higher voltages" if your tester only goes to 250v? The reason the tester is set for 250 for the 6l6 is that 250 is the recommended rating for class A use for plate and G2 voltage for the 6l6 types including kt66 and 7027