Best locations for metal film resistors?

I know metal film resistors are alot quieter than carbon comp but where do you install them? I have a 5E3 that is a bit noisy and plan to build a 5F4 so I'm getting ready to order parts. I've also read that higher wattage resistors are also quieter. Here's a schematic if it helps. Any suggestions/ideas?

12954

Other than wattage, resistor placement is usually not too important.

For less noise, place them in your preamp plate resistor slots. For more grit (and noise) place lower rated carbon comp in the same locations.

The 12AX7 and 12AY7 spots - the 2 100k on preamp #1 and the 100k on preamp #2.

The critical locations are the preamp plate load resistors (100K). I Use Ohmite 1/2 watt carbon comps and don't have any noise issues. Using MF's in the power supply might help a little.
http://i70.photobucket.com/albums/i115/teleamp/100_1237.jpg


A good grounding scheme is more important for noise reduction IMHO.

If turning the volume controls down eliminates the noise, you need only put the MF's on the plates of the 1st tube.

I'm getting a hum which increases or decreases as I adjust either the volume or tone control. I also read where it's recommended to use cc only on the tone section of the amp for best results. Where is that on the schematic?

Noise is never only about resistors. Some old antique Fenders have less noise than modern amps... old worn out carbon comps and all.

Check your lead dress, grounding scheme, heater setup (twists, center tap, routing, etc).

Sometimes, depending on the chassis real-estate, you have to honestly try a lot of things. I often use shielded wiring on preamp sections and use low watt Carbon Comp for plates for more dirt/warmth (honestly, not much if any difference in sound often)... sometimes I have to use Metal Oxide, shielded wire, and a sheet of copper backplate shielding for high gain builds.

I'm getting a hum which increases or decreases as I adjust either the volume or tone control. I also read where it's recommended to use cc only on the tone section of the amp for best results. Where is that on the schematic?

Is this with nothing plugged in? If so, you could have the input jacks improperly wired or there could be an issue with them not shorting to ground properly. If you have some test leads with aligator clips ground the input jack side of the 4 - 68K input resistors and see if you still have the noise. Some slight hiss is normal with no input and the volume cranked if you are using CC's, but if its loud with no input, I'd check tis possibility before replacing resistors.


The 100K ohm resistors that go via wire lead to pins 1 & 6 of the preamp tubes, any faulty connections, cold solders in those eyelets and wiring to the sockets can be an issue as well as lead dress. As well as the grounding and connections/solder of the filter cap powering those resistors. Also if you are using CC in the power section.

I tried what you suggested with the alligator clips and there's definetely something up with the bright channel. When I grounded the input side of the resistors there's a pop and the hum gets louder. When I touch the chassis the hum lessens and when I wave my hand over the bright input the hum gets louder :confused: . I dont know if you can gather anything from the pic.

12958

I can't see the input wiring very well, nor the grounding.

Check your grounding - it needs to be rock solid. Also, make sure the shorting jacks' tabs can contact the dimpled short tab. Look for cold solders on your jacks as well as on your grid resistors (the 68k the jacks go to), as well as to the tube socket's grid.

It may also be a lead dress issue since moving you hand over the input seems to make a difference... 8 out of 10 this has been my problem with these similar symptoms (but not always).

CAREFULLY use something non-conductive (most folks recommend wooden chopsticks) to lightly tap and/or move the input/grid wires with the amp on. See if this makes much difference. If/when you find the noisey wire, you can then double check it's solder/connection, or relocate the wire away from other wires.

Also check the V1 tube. Swap it for a few other tubes and see if this helps. My 5E3 actually had a bad/noisey (even borderline microphonic) triode in V1. A new tube fixed it right away.

Be careful... if you do not know what you are doing, do not do it. Inform yourself first, or take it to a repair shop.
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Be careful... if you do not know what you are doing, do not do it. Inform yourself first, or take it to a repair shop.

Funny thing is, this is my first build and when I finished it I turned away and closed my eyes and it fired right up no problem. http://www.clicksmilies.com/s1106/aetsch/cheeky-smiley-024.gif
The hum started about a month later so maybe something worked itself loose. Thanks for the advice but I tend to fly by the seat of my pants and learn as I go, so if I dont post back within 24hrs or if tomorrows headlines read "Major blackout on the west coast" ........
Johnny remind me to put you in my will. :wink: Thanks again everyone.

Those jacks look awful close to the board, and some eyelets.

Rotate them a little bit to get the jack tips a little more away from the eyelets.

Funny thing is, this is my first build and when I finished it I turned away and closed my eyes and it fired right up no problem. http://www.clicksmilies.com/s1106/aetsch/cheeky-smiley-024.gif
The hum started about a month later so maybe something worked itself loose. Thanks for the advice but I tend to fly by the seat of my pants and learn as I go, so if I dont post back within 24hrs or if tomorrows headlines read "Major blackout on the west coast" ........
Johnny remind me to put you in my will. :wink: Thanks again everyone.


Then this is less likely to be a real estate issue. Lead dress only if something moved. I would first try swapping pre tubes. Then start prodding with a chopstick. Something is picking up AC that shouldn't be, either conductively or inductively.