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Help needed understanding component values.

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Good evening,

Since my design skills are limited, I was wondering if someone could help explain what effects changing values of several components in my amp would do.

-1k gridstoppers - Why 1k, what happens if the value is changed lower or higher?

-100k input resistor - what are the effects of raising and lowering the value?

-.1uf coupling cap - From what I have read, the higher the value, the lower -3db is at the bottom end. Also the value is tied to the input resistor. Since the original input resistor was 470k, the coupling cap should be around .1uf. Since the input resistor was changed to 100k, the value of the caps should now be around .40-.50uf. This is based on several calculators that I have found. Is this correct?

-1k resistor and 16v 100uf cap on the 6SL7. What is their function and what effect does changing the values have?

- 250R 5W and 50v 47uF capacitor between the output tubes - What is this section/combo called? What happens when you change the value up or down.

I am trying to get an understanding what the various sections of the amp do and how tweeking them affects the sound. This will help me see why certian values are chosen and help me understand the overall design.

It is amazing how much info can be learned in a small amount of time....

Thanks
Brian
 

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Good evening,

Since my design skills are limited, I was wondering if someone could help explain what effects changing values of several components in my amp would do.

-1k gridstoppers - Why 1k, what happens if the value is changed lower or higher?

as long as you don't move far (say, 560 to 1.5k), not a lot. Make sure they are carbon though. Cheap as you can get...

-100k input resistor - what are the effects of raising and lowering the value?

changes the loading on your preceding stage - in this case probably your source - CD or tuner or whatever. Modern devices will be happy down to as low as 50k, but 100k is a happy medium

-.1uf coupling cap - From what I have read, the higher the value, the lower -3db is at the bottom end. Also the value is tied to the input resistor. Since the original input resistor was 470k, the coupling cap should be around .1uf. Since the input resistor was changed to 100k, the value of the caps should now be around .40-.50uf. This is based on several calculators that I have found. Is this correct?

Largely. Don't forget the parallel and series values and the capacitance of the grid circuit.

-1k resistor and 16v 100uf cap on the 6SL7. What is their function and what effect does changing the values have?

the resistor sets the DC bias voltage for the SL7. The cap bypasses the resistor for AC purposes.

- 250R 5W and 50v 47uF capacitor between the output tubes - What is this section/combo called? What happens when you change the value up or down.

As above. Strongly advise you to read through this to get the idea!

I am trying to get an understanding what the various sections of the amp do and how tweeking them affects the sound. This will help me see why certian values are chosen and help me understand the overall design.

It is amazing how much info can be learned in a small amount of time....

Thanks
Brian[/QUOTE]
 
as long as you don't move far (say, 560 to 1.5k), not a lot. Make sure they are carbon though. Cheap as you can get...

Just curious, why carbon and cheap as I can get for the grid stoppers?

I am using Kiwame now, but when I finish the new pc boards, I was going to install Takman resistors.

Are cheaper better for this, or do the more expensive resistors just not function any better for this application.

Thanks
 
The IHF "standard" calls for "line" level units to drive a 10 KOhm load. Commercial CDPs do that easily enough. IMO, any DIY design offered to other folks should comply too.

Fair enough too Eli - but often we are unsure what is going to be in front of a device. I tend to err on the side of caution (100k) but don't go stratospheric (250-500k).

Carbon because of the purpose of a grid stopper - to stop oscillations. Cheap is just a reasonably sure way of ensuring you are getting a carbon resistor. Also, since the tolerance is irrelevant in this location, no point paying for 1% pieces.

Others will argue the relative sonic merits of their favourite brands. Meh. Whatever.
 
Get a good book on the math behind all of the electronic components. Go to borders or order online.The basic components are resistors , capacitors and inductors. This is all you can do in a circuit by the way! It is just as simple as math! "You can only add to a number and subtract from a number and nothing else". Electronics are simple to a point, and then it becomes art when you start using components made from different materials and configuring them in unique ways. The sound quality can change just by changing the material the wires are made of, copper, silver, aluminum, gold. Good luck bro!
 
Just curious, why carbon and cheap as I can get for the grid stoppers?

Because carbon ones are non-inductive. More expensive high precision types are usually metal foil.

Expensive resistors are right up there with transformers with solid silver wire and few other audiophool gimmicks: something for gullible suckers to waste their money on, rather than investing it in better parts build-quality or design wise. Opting for transformer of same design but with more iron in the core and consequently larger primary inductance and lower bass response, or using only film capacitors in place of electrolytics for durability reasons etc. would make more sense as an investment than "brand name" $10 a pop resistors do.
 
Are carbon ones non-inductive? Carbon composition, maybe, but they are difficult to find nowadays. Carbon film uses a spiral cut to adjust the value so is slightly inductive, although the inductance can be ignored up to VHF frequencies. I'm not convinced that they are much better than metal film as grid stoppers, although they are cheaper. A bit of inductance doesn't matter as long as the resistance dominates at the potential parasitic frequency. In many cases the lead inductance is greater than the resistor body inductance anyway.
 
Now that you mentioned it, it is sometimes very ironic to see long lengths of wires running throughout the chassis to keep with the "old" look, with all the parasitic inductance that brings, only to have to damp it later with a suitable stopper. I rarely do old-style (rat's nest) wiring, mostly PCB, but I use stoppers anyway jkuist to be on the safe side. They don't hurt anything (when reasonably sized) and there is absolutely no need to squander money on luxury brands - that money will be better spent on larger capacitors, a filtering choke, better OPT, more robust switches etc. This is just like LEDs for voltage reference - one can buy incorrectly when going solely by the price (high brightness types have higher Vf than the old, cheapest run of the mill kind of same color, green for example).

Since grid stoppers are meant to dampen VHF/UHF nasties that's precisely where I'd be concerned about potentially inductive nature of said resistors. They should have zero effect in the audio band (I size mine so that Fc is 1/2 to 1 decade above the higherst frequency of interest - this way they cut below MW radio yet well above audio).
 
A bit of inductance doesn't matter. By "ignored" I meant that the resistor still looks essentially like a resistor. You can use a resistor as a dummy load up to low VHF without any problems. Even after it gets quite inductive it is still a lossy inductance as skin effect ensures that, so it still damps down any VHF/UHF resonance.

I would keep stoppers below about 10K, as otherwise they can start to look like capacitors at VHF. Above 100K they start to affect the audio passband, which seems to be a trick used in some guitar amps.
 
Good evening,

Since my design skills are limited, I was wondering if someone could help explain what effects changing values of several components in my amp would do.

Another question you might ask id "Why are the two 100K plate load resistors set to the same value and why 100K? Your other questions are kind of chipping at the details.

Typically you get better balance if the two load resistors, are slightly different. Only measuring a after you've built the stage or modeling in Spice will tell. But the answer will be (I bet) they want to be about 5% tio 120% different to minimize un-balance and 2nd harmonic.

Same with cathode bias resisors on the power tubes. Are they the exact best values? You can't know because it depends on the tube not all 6v6 are the same. You will need to measure after the amp is built

Does any of this really matter? Yes and no. The amp will make a bunch of sound even if every component is "off" by 20% to 50%. You can improve the sound by carful measurments and some analisys


Some things matter a lot (choise of load resisters and bias points) and some things don't (like a few uH of inductace in the grid resisters) It is very instructive to get a copy of some circuit moding software and just look at what happens. try putting a small mico-henry choke in series with a resisters and see it effects distortion components. Of course you could just built the amp and try these things but you like lack the test equipment to take the meeasurements and with modeling you don't need that equipment.

But don't go nuts looking at the third decimal point in the model result. Even if the math in the simulator is perfect we don't know the component characteristics well enough to trust the result to 1%. But 10% yes and that is good enough that you can sort out the good advice for the **. And on an internet forum you get both kinds.

The software is free and it might take 5 to 10 hours of study before you can use it. But it is worth it to have the ability to validate ideas and check component value changes before building. More info and links here.
The Spice Home Page
While you can get it for free, there are many outfits who will offer to sell you enhanced (or not) versions of it too.
 
PS=Phase Splitter (PSU=Power Supply Unit)

The phase splitter (half the 6SL7) gets an input of about 1/3rd of the sum of the 6V6 grid drives. A 6SL7 triode has a voltage gain of about 50-60 (from memory), so the PS gain is about 15-20. This means it needs an input of about 5-7% of the 6V6 grid drive. In turn this suggests that the imbalance will be 10-14% (twice my rough estimate above). This is not as bad as it sounds, as the output stage could easily have a 10-20% imbalance itself.

The solution is either to change one of the 100K anode resistors, or to modify the PS input - add a 10K resistor to the bottom 220K.
 
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