5e7 build - where to use carbon comp resistors?

ginomolinari · Post by **ginomolinari** » Mon Jul 15, 2019 9:06 pm

Hi everybody I am new to amp building and I have a conundrum I hope Incan get some help with. I have bought a 5e7 chassis from Weber and sourced all the parts myself. I wanted to go the safe route and get all modern compinents untill a friend in the audio business unloaded on me a bunch of VOS parts. Now I am considering using carbon comp resistors sparingly. I have read they should be used only where high current drups occur like plate and phase inverter. Here is my question: i have no idea where these resistors are in the lauout. Could some expert give a hand to this noob?
Any feedback would be greatly appreciated. I promise lots of pictures.
Thanks

sluckey · Post by **sluckey** » Mon Jul 15, 2019 9:17 pm

Fender used carbon comps for every resistor in that amp.

martin manning · Post by **martin manning** » Mon Jul 15, 2019 9:18 pm

http://www.geofex.com/Article_Folders/c ... oncomp.htm

ginomolinari · Post by **ginomolinari** » Mon Jul 15, 2019 9:47 pm

Yea that is the article I have read as well. Unfortunately I dont know which resistors are connected to the plate and before and after the PI. Can you point them out for me?

ginomolinari · Post by **ginomolinari** » Mon Jul 15, 2019 9:48 pm

Here is the layout

ginomolinari · Post by **ginomolinari** » Mon Jul 15, 2019 9:53 pm

Thank you Sluckey. I have seen a build from a member of this forum and he used all carbon comp as well. Not criticizing that choice. I just would love to minimize the use of carbon comp resistors to where the are actually making a difference.

martin manning · Post by **martin manning** » Mon Jul 15, 2019 10:26 pm

Looks like there is exactly one resistor that fits the criteria in RG's article, the 100k on the tube socket (second from the right in the layout sluckey posted). The other candidates are either on input stages or inside the feedback loop.

gingertube · Post by **gingertube** » Mon Jul 15, 2019 11:19 pm

Carbon Composition resistors suffer from noise problems, that noise is proportional to current, so you should NOT use them anywhere that there are highish currents, particularly not for anode load resistors.

I see some do say use them for anode load resistors, the rational for that is that their real resistance has some voltage dependency which means that their resistance "modulates" with the audio signal. That will introduce some additional 2nd harmonic distortion. The additional distortion is hardly noticeable over the natural distortion of the tube itself and is not worth the sacrifice in noise performance.
Oh - they also have good peak voltage withstand but not significantly better than a 2W metal film.

Use modern metal film resistors everywhere. Carefull of the 0.5W and 0.6W metal films - they often have voltage ratings of ONLY 350V. Use 1 or 2 Watt metal films for a 500V rating (or use 2 off 0.5W of 1/2 the required value in series so they handle 1/2 the voltage each).

The ONLY place I would comtemplate using carbon comp is for gridstop resistors where their non-inductive nature maybe of benefit.

My opinions only.

Cheers,
Ian

wpaulvogel · Post by **wpaulvogel** » Mon Jul 15, 2019 11:36 pm

The reason why one would use the carbon composition resistors is for the noise. They make the amp sound like it is supposed to sound. Therefore it would be best to use them in every position except maybe in the power supply. I’ve been told that the amp will have no color without them. Goes for 5E3’s, 5F6-A etc. I hope this helps. You can just build it without them but it won’t be the same.

ginomolinari · Post by **ginomolinari** » Tue Jul 16, 2019 11:25 am

Thank you! OMG, i just checked the ratings for the metal film resistors I have bought and the 1/2 watt are as low as 200v. That means, I have to reorder almost everything!!

Post by **xtian** » Tue Jul 16, 2019 3:54 pm

wpaulvogel wrote: ↑Mon Jul 15, 2019 11:36 pm The reason why one would use the carbon composition resistors is for the noise. They make the amp sound like it is supposed to sound. Therefore it would be best to use them in every position except maybe in the power supply. I’ve been told that the amp will have no color without them. Goes for 5E3’s, 5F6-A etc. I hope this helps. You can just build it without them but it won’t be the same.

Totally disagree. Carry on.

wpaulvogel · Post by **wpaulvogel** » Tue Jul 16, 2019 9:00 pm

Alright sorry, I've never built anything with carbon composition resistors. There was just a guy at an old electronics store in Atlanta where I would buy some parts and that is what he said. He built some tweed stuff and swore by them. I stand corrected. I don't want any extra noise myself, and I'm not happy with the white noise in certain amps but sometimes it's just part of the gain. I'll shut up.

Post by **xtian** » Tue Jul 16, 2019 9:25 pm

wpaulvogel wrote: ↑Tue Jul 16, 2019 9:00 pm Alright sorry, I've never built anything with carbon composition resistors. There was just a guy at an old electronics store in Atlanta where I would buy some parts and that is what he said. He built some tweed stuff and swore by them. I stand corrected. I don't want any extra noise myself, and I'm not happy with the white noise in certain amps but sometimes it's just part of the gain. I'll shut up.

I feel like, when I started building about 10 years ago, that there were still a few "vintage cork sniffers" in town, who held similar beliefs, like, "Leo did it that way, thus, that way is best, and all other ways sucketh." Seems like the cork sniffers are a dying breed around here...or at least, around me...and the musicians who remain much prefer tone, low noise, and reliability over snake oil.

ginomolinari · Post by **ginomolinari** » Tue Jul 16, 2019 10:42 pm

Xitian, I appreciate your input and I share with you the idea that playing music is an experience that shouldn't be influenced too much by the tools you utilize. I do find it interesting though that you use the term cork sniffer. If you appreciate wine it is quite a normal thing to do that can tell you a lot a about what you are about to drink. Same thing to me if you are doing anything you are passionate about. I am spending a pretty penny building this amp. I waited a very long time to get to this point and I want to make sure I do it right and I don’t cut corners. Plus, a little snake oil seams to work with the ladies.

billyz · Post by **billyz** » Wed Jul 17, 2019 12:12 am

I built a clone of the 5e7 bandmaster and used ALL Carbon Comp resistors just like the original 57 I cloned. There is no noise to speak of and it sounds awesome. Not bashing metal films or carbon films, just want to point out the noise is not an issue at all. Better to pay attention to lead dress and grounding for a quiet amp build. These vintage fender circuits are not high gain monsters that are extremely sensitive to any noise.
The Clone I built is so quiet you don't even know its on. By the way, I used old cloth wire pulled from an organ and NOS
film and foil caps ( tested) , a NOS domino treble cap and New Electrolytics of course.

The Amp Garage

5e7 build - where to use carbon comp resistors?

5e7 build - where to use carbon comp resistors?

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