I'm running 6L6GC triode connected. The 6L6GC datasheet says the maximum screen grid voltage is 450V. Are those maximum ratings for DC-condition or for AC-condition? In triode connection the screen grid voltage could easily have higher peaks than this 450V.
How do you avoid arcing at the base/socket, when g2 is at the same potential as plate? The plate was brought out to a top cap, for very good reason. Compare the ratings of the TT21, with its plate cap, to those of the KT88. Internally, the 2 types are identical.
Do I understand you correctly saying the voltage limit on G2 is because of prohibiting arcing at the socket? I thought the top connection was for lowering capacitance to obtain higher operating frequencies?
The problem with G2 is the power it has to dissipate. When current increases anode voltage goes down, more current go through the screen grid. In triode mode anode voltage never goes below screen grid voltage, obviously, that's why pentode mode voltage limit on G2 does not apply.
A few things:
1. that circuit runs into class 2, where grid current takes up the slack from a low screen/plate voltage.
2. Triode mode doesn't dissipate too much screen current/power anyway, as mentioned.
3. The voltage rating isn't just because of screen dissipation, or arcing, though those are important factors. Typical screen ratings drop off hyperbolically above the nominal rating (e.g., See RC-26, curve page 98).
For pulsed and current limited operation, the ratings are usually higher: compare ratings as vertical or horizontal deflection amplifier against typical linear amplifier ratings. Of course, that doesn't mean anything if you want to use it in linear amplifier service in the first place...
Tim
1. that circuit runs into class 2, where grid current takes up the slack from a low screen/plate voltage.
2. Triode mode doesn't dissipate too much screen current/power anyway, as mentioned.
3. The voltage rating isn't just because of screen dissipation, or arcing, though those are important factors. Typical screen ratings drop off hyperbolically above the nominal rating (e.g., See RC-26, curve page 98).
For pulsed and current limited operation, the ratings are usually higher: compare ratings as vertical or horizontal deflection amplifier against typical linear amplifier ratings. Of course, that doesn't mean anything if you want to use it in linear amplifier service in the first place...
Tim
7027A (6L6 variant) is rated to 600v on G2 triode connection. (Not current production ones except for maybe Tung-sol. I can't find a data sheet for them)
www.shinjo.info/frank/sheets/049/7/7027A.pdf
Lots of NOS ones on ebay but a bit spendy.
www.shinjo.info/frank/sheets/049/7/7027A.pdf
Lots of NOS ones on ebay but a bit spendy.
There is current production from JJ:
JJ-Electronic - Vacuum tubes, Capacitors, Amplifiers - Power tubes
Yes there is but the JJ data sheet only says 450v max for G2 I think. So is it really a 7027A equivalent?
Tung-sol 7027A's definitely have a different plate structure than their 6L6 types but I can't find their data sheet anywhere.
7027 from JJ works very good, long and steadily more than ~3 years in AMPEG-V22 (plate voltage is ~550V!).
because pin 3 is so close to pin2 where the arcover happens, saw that happen first hand...
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