Sunn Grid Noise

[plexi50]

I have excessive grid hiss noise on one of (1) of (2) 6550 tubes. C308 270pf 1000 volt ceramic cap is my suspect. I swapped tubes and no change. All bias,plate,board resistor's and coupling cap's are new. As well as the 270pf cap. I am ready to un-solder C308 and replace again with the same cap and voltage values. BUT: Before i do i would like some input. Attached is a pic of the tube's/grid area.
I am using Doug's listening device.

[plexi50]

Can i just snip it out all together? I don't see why not. NOT!

[plexi50]

I don't get this. Remove C308 which is nothing more than a snubbing capacitor to me and i have no sound. The plate resistors are going to there respective coupling caps regardless of C308.

[sluckey]

I don't get this. Remove C308 which is nothing more than a snubbing capacitor to me and i have no sound. The plate resistors are going to there respective coupling caps regardless of C308.

You obviously did more than just snip that cap. It's called collateral damage.

[plexi50]

The circuit board and all components are where they should be. Working again with new 270pf 1KV cap. Crazy. Don't understand. Never seen this before. Don't make sense. Uploading a Video on my facebook page Triodeamplification.

[plexi50]

Oh my god! I found the problem. I have a 820 ohm plate resistor instead of an 82K plate resistor. Man i really screwed the pooch. Back in a while with results. CRAZY DAYS ARE HERE AGAIN!

[plexi50]

820R

[sluckey]

You need to rewind a week when you said the amp sounded glorious. Quit fixin' if it ain't broke.

[plexi50]

You need to rewind a week when you said the amp sounded glorious. Quit fixin' if it ain't broke.

Yeah i need to slow down a bit. It was in the 82K bag i have. I don't know why i didn't see the orange marker. And yes it sounds even better. No more loud grid hiss through listening device.

[thetragichero]

https://www.ampbooks.com/mobile/amplifier-calculators/long-tailed-pair/calculator/
8k2 or 820r makes for a VERY unbalanced phase inverter

[plexi50]

https://www.ampbooks.com/mobile/amplifier-calculators/long-tailed-pair/calculator/
8k2 or 820r makes for a VERY unbalanced phase inverter

Yes it did. The reason i took the chassis out of the cab again was because i could hear abnormal hiss with the master at full CWR. And silent at CCW. Volume control were off. I used the listening device and when i probed each grid of the 6550 tube's, one of them was hissing away loudly. So i started looking at the PI and finally found my error. 820r in place of an 82K. The rest of the bag is full of 82K resistors. Still don't know how i missed it when i installed it. It is what it is. Cured now. And again,does sound very good.