Give me Some General Tips on Caps and Resistors

[The New Steve H]

I'm working on the BOM for the amp my buddy wants me to build. Couple of questions.

Randall Aiken says wirewound and metal film resistors are good for reducing hiss, and he says bigger resistors are quieter. I'm thinking I should go ahead and get wirewound and metal film resistors and get them in 1 watt or larger. Is this a good idea, or totally pointless? Seems like it can't hurt, and it's a cheap choice.

Is there any point in getting expensive electrolytics? As far as I know, all electrolytics are fairly crappy. I notice Spragues cost a great deal more than other brands.

Finally, Randall Aiken says plastic conductor pots reduce hiss. Any point in using them? Seems like they're hard to find.

The amp will be based on the Trainwreck Express, but these questions are so general, they didn't seem to fit in the Trainwreck area.

http://www.aikenamps.com/ResistorNoise.htm

[The New Steve H]

By "bigger resistors", I mean resistors that are rated for more power, not higher resistance.

[Phil_S]

If I were concerned about hiss, I'd use 1W metal film plate load resistors. If I were concerned about great tone, I'd try to get by with 1/2W carbon comp. Not everyone will hear the difference. The TW is a high gain amp, and I'd lean towards the 1W MF. Others will probably flame me for saying this and they are probably right to do so. WW high wattage resistors, except for power supply dropping and power tube cathode bias are too expensive and too clunky to consider. FWIW, that's my $0.02.

[diagrammatiks]

There's no really no downside to going for the highest wattage resistor you can afford and that's reasonable for that position.

an rn60 will do for the most part. rn65 gives you some breathing room. rn70 is probably the most you'll need.

for power resistors 3-5 watt wirewounds are pretty cheap. a vishay rs2b is plenty although you could go up to an rs5/rw5.

for electrolytics f and t's are good enough.

bourns makes conductive polymer pots in log and linear tapers.

[paulster]

WestLabs has Clarostat conductive plastic pots.

I like 2W resistors generally, either KOA Speer carbon film (also sold as Kiwame) or Beyschlag metal film. The 1W PRP GP1 resistors are really nice and very quiet too, although they are quite large (long) for their rating, so can be bit of a squeeze in a tightly-packed board.

[dju]

There's no really no downside to going for the highest wattage resistor you can afford and that's reasonable for that position.

an rn60 will do for the most part. rn65 gives you some breathing room. rn70 is probably the most you'll need.

for power resistors 3-5 watt wirewounds are pretty cheap. a vishay rs2b is plenty although you could go up to an rs5/rw5.

for electrolytics f and t's are good enough.

bourns makes conductive polymer pots in log and linear tapers.

please excuse my ignorance, could you explain what rn60/65/70 and rs2b, rs5/rw5 are? this might be one of those "DOH" moments when you say what they are and hopefully I'll be able to say I knew that. but at the moment I have no clue what they are.

thanks for the education,
dj

[ToneMerc]

please excuse my ignorance, could you explain what rn60/65/70 and rs2b, rs5/rw5 are? this might be one of those "DOH" moments when you say what they are and hopefully I'll be able to say I knew that. but at the moment I have no clue what they are.

thanks for the education,
dj

"RN" is series of mil specs and RS & RW are just Dale/Vishay series codes for a types of wirewound resistor they offer.

All about "RN"

http://www.dscc.dla.mil/Downloads/MilSp ... l10509.pdf

TM

[The New Steve H]

So it sounds like these ideas won't hurt anything, and I'll feel like I made an effort to contribute something to the design.

I had to look up F&T.

I have one or two Clarostat pots I bought for my 5f6a. Didn't know they made plastic ones. I found a plastic pot that doesn't cost a ton, but I don't know if it's any good.

http://www.bitechnologies.com/pdfs/p231.pdf

I figured I'd just use whatever Vishay metal film resistors popped up on Mouser.

The local electronics store has NHE resistors, but the packaging doesn't say what's in them. Crazy. All I know is, they're blue.

[diagrammatiks]

There's no really no downside to going for the highest wattage resistor you can afford and that's reasonable for that position.

an rn60 will do for the most part. rn65 gives you some breathing room. rn70 is probably the most you'll need.

for power resistors 3-5 watt wirewounds are pretty cheap. a vishay rs2b is plenty although you could go up to an rs5/rw5.

for electrolytics f and t's are good enough.

bourns makes conductive polymer pots in log and linear tapers.

please excuse my ignorance, could you explain what rn60/65/70 and rs2b, rs5/rw5 are? this might be one of those "DOH" moments when you say what they are and hopefully I'll be able to say I knew that. but at the moment I have no clue what they are.

thanks for the education,
dj

as tonemerc said they are just standardized designations for resistor types. It's not actually confined to a particular brand. Firms that apply for mil-spec rating just have to build a resistor that meets that particular rating. Usually the same resistor is also sold under a commercial designation.

For example, Vishay/Dale has the ccf series which is their bulk industrial resistor with 5 band id marking.

Then the cmf is the same as the rn/rl which is the first level of mil-spec followed by erc/rnc and then erl/rlr.

[tubeswell]

Hiss comes from a number of sources, e.g.: from increasing gain, and also from increasing resistance, and also from increasing heat. In addition, certain types of resistors (MF) are quieter than others (CF) which are in-turn quieter than others (CC) all other things (power handling etc) being equal.

So to minimise hum, keep resistors as-small-in-resistance value as you reasonably can (whilst not loosing too much signal), and/or use chunkier resistors, and/orl use MF instead of CF or CC, or use CF instead of CC. Its possible to have quiet CC if they are chunky enough.

[overtone]

Is there any point in getting expensive electrolytics? As far as I know, all electrolytics are fairly crappy.

One reason to invest a little more in an electrolytic could be the lifetime rating. Digging into the datasheets and comparing the life ratings against price and performance can really illuminate your choice.

Two long lifers which may not be on your radar:
- radial Panasonic EE series
- axial Rifa PEG124 series

have fun,
best, tony

[The New Steve H]

I ordered 10 3w metal film resistors from China, via Ebay. Just arrived. Got them cheap and fast.

I miss the glory days of American manufacturing, but thank God someone else is taking up where we left off.

These are 4.7K resistors. They go after the 3rd filter cap on my 5f6a. Since current is actually from negative to positive, this means the juice that flows through this resistor goes through two 470 ohm wirewound resistors and then to the screen grids on my output tubes. On the other side, the resistors go to the plates on the phase inverter, past two resistors and a cap.

Can I assume, then, that changing the 4.7K to a big metal film might reduce hiss? I would think it would have an effect on the output plates.

[Structo]

About the only down side in using over spec power ratings is the physical size of the component.

Many times the leads are larger on bigger resistors and caps so you might have trouble fitting several into an eyelet if you use them.

For power supply dropping resistors I like to use 3 watt.
These can be metal oxide flame proof or wire wound.

For plate load and other resistors in the preamp I like to use 1 watt metal film.
The Vishay CCF60 series is what I used mostly in my last 100w ODS build.
Although they are listed as 1/2 watt they are more like a 3/4 watt in performance and size.
http://www.vishay.com/docs/31068/ccf60.pdf

http://www.mouser.com/Vishay/Passive-Co ... 8wZ1z0iwnz

I think for everyday high quality resistors you can't beat most of what Vishay/ Dale offers.

The Dumble guys like the RN65D resistors for plate loads.

[paulster]

Can I assume, then, that changing the 4.7K to a big metal film might reduce hiss? I would think it would have an effect on the output plates.

You'll get very little hiss from your power amp, so it'll probably have no audible difference at all.

Hiss is mostly caused by the first gain stage and the fact that this is then amplified significantly through the preamp. Each gain stage will add its own amount of hiss, but the more significant source is the amplification of the hiss (along with the signal) from the preceding stage(s).

For example, take most amps that have three preamp tubes and pull the PI tube. It'll be just about silent. That's just the power tubes left running. Put the PI back, pull the middle preamp tube and dime the controls (in case there's a post-PI master volume). It'll be a tiny bit louder now that the PI is in there but still ostensibly quiet.

Now put V2 back and pull V1. Louder, since you've put another one or two gain stages in, but the biggest difference will come when you put V1 back, which is the first gain stage (or two) of the preamp.

[tubeswell]

Can I assume, then, that changing the 4.7K to a big metal film might reduce hiss? I would think it would have an effect on the output plates.

The benefits of certain types of resistors in the resistor/hiss equation manifests itself more greatly where resistors have a direct effect on the AC in the signal path, i.e.: plate resistors, cathode resistors, grid leak resistors. Changing to different type of resistors in the power supply may alleviate a teency weency portion of hiss, but in the overall scheme of things won't reduce hiss that much, because the supply resistors are decoupled from the signal path by the filter caps.

But having said that, there are extraneous noises/signals in the power supply (that one tries to eliminate with RC* decoupling, and electrolytic filter caps are far from perfect at decoupling AC), which can benefit from HF decoupling with smaller high voltage film caps (e.g. 10-100nF) in parallel with the filter caps. Usually one (high voltage) 10nF or 100nF film cap in parallel with the reservoir cap is sufficient to get rid of these more unstable high frequency elements in a B+ supply.

* the particular combination of the values of 'R' and 'C' produce different points of dB reduction at particular frequencies, hence when you decrease a supply resistor, you really (technically speaking) should increase the filter cap at that node by a corresponding inverse ratio, in order to keep the freq roll-off of extraneous noises in the power supply at the same point.