Mixing Resistor types?

[Bloodcore]

Hello, I'm currently trying to decide between using Metal-film or Carbon-comp resistors in my new XiangSheng 708B.

I've read on various forums that Carbon-comp would give me a "warmer" result and metal-film would be a bit sharper and edgy.

And since I would like a more balanced result.. Would it be a good idea to use both resistor types in this amp?
Or is mixing resistor types a very bad idea?

Thank you for reading.
🙂

 

[aardvarkash10]

lol.

There are good technical reasons for using the different types in different positions. The technical reasons do not include warming the tone of the amp.

That way madness lies.

 

[Eli Duttman]

Metal film resistors are excellent in grid to ground positions, as they are low noise. Carbon composition parts make superior grid stoppers, as they are both non-metallic and non-inductive. Carbon film parts, along with wirewound parts, work well elsewhere. Unfortunately, the inductance of most wirewound resistors can be troublesome. Non-inductive wirewound resistors are available, but they are costly.

 

[Bloodcore]

Thank you for the fast replies.
I guess I'll order a few Metal-Film resistors for grid-ground and use some of my MilitaryGrade philips resistors I've got lying around as grid-stoppers instead of buying new ones.

Thank you for the help. 🙂

 

[DF96]

Carbon composition parts make superior grid stoppers, as they are both non-metallic and non-inductive.

Unless you have UHF parasitics, carbon film should be good enough. They are substantially resistive up to VHF frequencies. Their inductance (due to the spiral cut) will not be a problem because they will be very lossy inductors. The inductance could even help by moving parasitic frequencies lower down.

I think I saw this in RSGB RadCom a few years ago. People were saying that carbon comp should be used for RF attenuators and low power dummy loads, but measurements showed that carbon film was fine for HF and low VHF. For parasitic suppression even more inductance can be tolerated.