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Hi i'm rebuilding my input jacks on my plexi to see if i can quieten it down, but does it
matter if the 1 meg ohm resistor is carbon film or metal film in terms of tone.
What are the benefits either way.
Could you also point out the cc resistors to change if i want it quieter.
Thanks.

That resistor isn't all that important composition wise. It's just there to keep the grid of the triode from swinging positive, gives it a reference. The 68K grid stoppers should be carbon film or metal film. They are in series with the signal, easy to pick up noise. Any resistor in series with the signal should be of low noise composition ideally.

Change out plate resistors for metal or carbon film to try and reduce noise. I would be checking your grounding/lead dress first before worrying about the noise the resistors add though.

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I would still always use metal film resistors for both the 1M reference resistor and the grid blocking resistor. Remember noise increases with resistor value, and also this is the single most sensitive point in the entire amp, as that's where the most gain is present. So I would only use metal film at the input of the first stage. The rest of the amp can be carbon film.

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Great tones come in small glass jars!

How about the physical size of these resistors? Some how I ended up with these teeny little 68ks. 1/8 watt? They're metal film (I think) but is their size condusive to noise?
Stew

Lower wattages tend to be noisier, plus real tiny resistors are fiddly to work with. I've also found that some new production metal film resistors are real small for their wattage rating. So a 1W is around the size you would expect a 1/2W to be. So with metal film resistors of this kind, I generally use 2W ones in the place of 1W of the regular kind, and get an even lower noise floor.

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Great tones come in small glass jars!

We use 1W carbon film for these position (68K & 1M on the input). Those tiny 68K 1/2W are on some TRWATTs are fine, but we're now using the 1W CF.

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Stephen
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