Rating for EL-34 grid stoppers?

I'm wiring a bare ST-70 chassis, and need to know the power rating of the 1K0 grid stopper resistors on pin 5 of the output tube sockets. 1/4 watt or 1/2 watt?  The current in the control grid circuit should be minimal to non-existent, right?  If I'm using carbon composition grid stoppers, should I go up one value (from 1/4 to 1/2 watt) to reduce the noise inherent in carbon comp types?

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If you want less noise I would use Metal film 1% 1/2 watt or at least carbon film 5% 1/2 watt. You can pull a schematic for the original ST 70 in the manual section above.

Actually above,
Sticky: Free Dynaco tube schematics

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I prefer to use carbon composition (CC) resistors as grid stoppers, as they have essentially zero inductance (just a tiny bit of lead and stray inductance). The drawbacks to carbon comps really don't cause trouble when they are used as grid stoppers. The noise is not an issue since the current in a grid circuit is vanishingly small which means the "microarcing" noise CC resistors generate is pretty much nonexistent. Also, the drift issue is not a concern, as grid stoppers exact value is not critical - anywhere close works fine.

That all said, metal and carbon film resistors can work fine in that spot in nearly every case. The spiraling does cause them to have more inductance than a CC resistor, but the low resistance values used mean not too many spirals are cut so the added inductance is quite low.

At least we agree on the 1/2 watt.LOL   I guess I am biased against carbon because I have been replacing noisy carbon resistors with film for the last 40 years. It started when I modified my first Dynaco PAS 2 in 1976. They may have a better tone when installed but let's compare them at 5 or ten years from now. But at the end of the day  to each there own . The most important thing is to enjoy the music.
Oh and to answer the original question. You want to go up in Watt rating for the same kind of resistor to lower the noise because the PPM rating is based on temp. and a larger resistor can dissipate the heat better and run cooler therefor quieter. However the original was 1/2 watt and that is what I would use. As you said there isn't much load on that resistor to begin with so there is really little heat to dissipate.
PS Just read Jim's post and I think he nailed it. Great post Jim.

Thanks for the replies. Jumping the gun a little, I ordered a small handful of 1/4W and 1/2W Ohmite 'Little Demon' carbon comp types.

I'll try one or the other, and attach the body as close as possible to the lug on pin 5 without actually making contact. I understand that such close placement (i.e., short lead length) helps in the parasitic oscillation minimization department.

Onward and upward.

P.S. Hi, Jim. Long time, no correspond.    Thanks for your input, and be well.

Mike Pinsky

Downhome Upstate wrote:Thanks for the replies. Jumping the gun a little, I ordered a small handful of 1/4W and 1/2W Ohmite 'Little Demon' carbon comp types.

I'll try one or the other, and attach the body as close as possible to the lug on pin 5 without actually making contact. I understand that such close placement (i.e., short lead length) helps in the parasitic oscillation minimization department.

Onward and upward.

P.S. Hi, Jim. Long time, no correspond.    Thanks for your input, and be well.

Mike Pinsky

Hi Mike!! Great to hear from you.

Solder those .5 watters in there just the way you described and they'll do a fine job for you! Best of luck with your project!!

Can Anyone say why theres no grid stoppers on the 6AN8.... stock MK3 board....?
Was as Most say .....Cash?
thanks








thanks for the site Bob........

Look at the tube sockets, between pin 6 and 5.

Any help.......
Mcintosh not so much...never like the VTL amps.................12at7....not for me...better than a 12aX
on the grid stopper on the 6AN8. input tube in the MK3s.......yes, No, maybe................dose the 6AN8 need a.............grid stopper??
why not.....?





thanks for thje site Bob...........................have fun with tubes................

I assume you are talking about the 6AN8 input side and not the output. If this is the case it is because it is a pentode first tube and in most cases it is not necessary to use one on a pentode. However your triode tubes in many cases do need a grid resistor.

Thanks for the info.....i have put a 250ohm 1/4 watt... it sounds better i think...