How many Ohm for triode strapping?

[Salas]

I have seen triode strap of 100 Ohm to 1K Ohm range on EL34 or 6L6, 6550, KT88, KT90, from screen electrode to anode. Is there an optimum sounding value? What is the difference of 100 vs 1K say on an EL34?

 

[Klimon]

Related; imo beats any value of resistor: http://www.t-linespeakers.org/tubes/triode-trick.html (contains a few errors)

Simon

 

[sajti]

My experience is to use as small as possible to avoid the oscillation. I used 22ohms for PL509 triode connection, and 47ohms for 6550s.

Sajti

 

[Eli Duttman]

Salas,

An important consideration in sizing the resistor is staying within g2 dissipation limits.

The screen grid in an EL34 is tough. If the anode voltage is low enough, a piece of wire is OK. 100 Ohms should be plenty even at anode voltages that approach the tube's limit.

 

[Tubelab_com]

There are people that recommend a 1K resistor with an EL34. Mullards own data sheet mentions this value. It was said that 1K minimizes distortion. It was in a push pull design.

I have tried everything from 0 ohms to 1K ohms in my SE designs. I prefer 100 ohms. Higher values lower the output power somewhat and don't lower the distortion. I tried JJ, Svetlana, Electro Harmonix, Winged C, and Valve Art EL34 tubes. All give similar results. Oscillation was observed near the peak of the sine wave with 0 ohms on some tubes. 5 of these amplifiers have been built, although not all of them currently use EL34's they all use 100 ohm resistors. It is a good compromise with all the tubes used (EL34, KT88, 6550, 6L6GC). All 5 amps were tested with all tube types. I use 100 ohms in triode mode and in UL mode (2 of the amps are switchable).

I was using 1/2 watt metal film resistors, but I had 2 of them die, so I have switched to 2 watt carbon film resistors. I have had no issues at B+ voltages as high as 500 volts, and I have even flipped the mode switch (triode - UL) at full power (not recommended) several times.

 

[Salas]

Thank you, I currently have 1k on EL34s PP, can It be serving 6L6GCs without being too detrimental for them? Or is it better to go 100 Ohm for across the board best sound?

 

[Tubelab_com]

Or is it better to go 100 Ohm for across the board best sound?

Everyone has their own definition of "best sound." My experiments prove that it won't hurt to try it.

 

[Wavebourn]

Hi Tubelab.com, nice to see you again!

I wander, if you've tortured 6p14p, 6p15p, 6p18p tubes. However, manufacturers don't rate them for triode connections, but rate for intended applications. 6p15p, for example, is rated for less 2'nd grid voltage than 6p14p. However, specifying that they guarrantee less distortions than 6p14p in pentode connection. The question is, are they different in triode connections? Does it mean less 2'nd grid power means weaker grid design, or specs only?