Bias resistors

[Guitarist]

Daz, you are hilarious! If only there was a perfect amp you could just buy! I can attest to not having monster PI caps and discovered that here is not the best place to over-engineer. This herniated the output grids and sounded like it, but I looked elsewhere erstwhile prior to discovering the farlt was here. Sometimes .01 are just fine anywhere in an amp, but my main, Partridge equipped, amp currently has .047uf at the PI.

My theory is that big cap values can often worked better with strats (vs. Les Pauls). Greenbacks also tightened up old bassy Marshalls by raising the low end slope-off; a high pass sandwhich

[anson]

I found two data sheets indicating that the max grid to ground resistance for an EL34:

http://www.drtube.com/datasheets/el3...funken1955.pdf

http://www.pentalaboratories.com/pdfs/EL34S.pdf

...Generally they say the the grid 1 circuit resistance for an EL34 is 500k Ohms for calss A or A/B, and 700 k ohms for class B.

I'm actually finfing it difficult to find data sheets that say an e;-34 has a max grid resistor value of 100k. That's more like a 6550 value, as far as I remember.

I've got 470k resistors in my EL34 amp, to try to encourage more power tube break up before PI breakup. Haven't have any problems yet with that set up and LTP PI.


Anson

[daz]

I read your post and tried 470k just to see what THAT did. It became considerably harsher. You may wanna try 220k even if you once had that value in there. Mine was quite a bit smoother and les harsh when i stuch the 220ks back in. Now i'm thinking maybe i should try 100k again, thho unlike the difference between 220 and 470, i didn't seem to notice any between 220 and 100.

[anson]

I personally wouldn't use 'harsh" to describe the effect of 470k grid resistors on my amp. It seemed a bit louder and brighter though after swapping out 150k resistors I previousely had in there with the 470k resistors. I tried 220k too. I never remember experimenting with grid resistors as low as 100k. Maby I should try it sometime. I haven't had any stability problems with the 470k resistors on my 4x el34 setup, except when I tried using a paraphase PI. Then there was a very low freqency oscilation that caused the plates to glow red at about 2 hz. BUt with a LTP it's fine. Don't know why.