470k for R9, 15, 16, 23, 24 all reading high

[pjb]

Trem circuit... I bought a bunch of these NOS 470k half watt resistors for R9, 15, 16, 23, and 24. I'm having a hard time finding resistors within 10k of the required 470k. How critical are these values for the specified positions. They are all Bradley's carbon comp. I've found these to be a tight tolerance in the past. They have an additional yellow band after the gold, but the five-band-online-calculator doesn't recognize the last yellow band. They all measure around 490k with one or two being 510k. ideas?

-Paul

[PeddlerPete]

Trem circuit... I bought a bunch of these NOS 470k half watt resistors for R9, 15, 16, 23, and 24.
I just pulled a batch of 6, many a few read >500k.
I'm having a hard time finding resistors within 10k of the required 470k.
Who says 470's required?
Using 'the' 10% tolerance rule as a guideline, you'd need +/_ 47k to exceed +/-10% of 470k.
How critical are these values for the specified positions.
Might be interesting to take a lighter to one of the high ones, and a new resistor of ~same value to see which ones drifts more and by how much.
Two are for the unbalanced PI, the scale of the value doesn't critical at all, neither is the actual comparitive value of the two grid resistors, match or mismatch if you must, probably start noticing the gain setting changes very slightly around <400k and >860k or 680k, anywhere around the ballpark of big resistor will work, some prefer >330k.
same thing basically on the output tube grids, you want big, about the same value resistors there...or not...too small and the signal all shunts to ground, too big and the grid won't bias etc., 470k is a good place to start.
Every once in a while a resistor sets a parameter [like maybe in tremolo], so having it 'scaled' more exactly might be desirable.
See posts of dropping grid resistor values.
They are all Bradley's carbon comp. I've found these to be a tight tolerance in the past.
how do they look?
They have an additional yellow band after the gold, but the five-band-online-calculator doesn't recognize the last yellow band. They all measure around 490k with one or two being 510k. ideas?
The thing I might choose to not worry about, other than a really mismatched PI, is that when the amp warms up, all the resistances 'warm up too, and the amp starts playing louder or plates start glowing, if the resistors drift much with heat, having more stable resistors will make it easier to keep the bias under better control. Some amps take 15 minutes to really warm up.

[57chevy]

10k:470k would be a 2% tolerance. Those are 5% tolerance so the value can be as high as 493,500 ohms and still meet mfg tolerance. The yellow band is a reliability indicator. It's a mil spec thing.

The first and second bands are numeric. The third band is multiplier. Fourth band is tolerance. Fifth band is reliability.

[pjb]

10k:470k would be a 2% tolerance. Those are 5% tolerance so the value can be as high as 493,500 ohms and still meet mfg tolerance. The yellow band is a reliability indicator. It's a mil spec thing.

The first and second bands are numeric. The third band is multiplier. Fourth band is tolerance. Fifth band is reliability.

Thanks for the info... I appreciate it...
-Paul

[pjb]

Trem circuit... I bought a bunch of these NOS 470k half watt resistors for R9, 15, 16, 23, and 24.
I just pulled a batch of 6, many a few read >500k.
I'm having a hard time finding resistors within 10k of the required 470k.
Who says 470's required?
Using 'the' 10% tolerance rule as a guideline, you'd need +/_ 47k to exceed +/-10% of 470k.
How critical are these values for the specified positions.
Might be interesting to take a lighter to one of the high ones, and a new resistor of ~same value to see which ones drifts more and by how much.
Two are for the unbalanced PI, the scale of the value doesn't critical at all, neither is the actual comparitive value of the two grid resistors, match or mismatch if you must, probably start noticing the gain setting changes very slightly around <400k and >860k or 680k, anywhere around the ballpark of big resistor will work, some prefer >330k.
same thing basically on the output tube grids, you want big, about the same value resistors there...or not...too small and the signal all shunts to ground, too big and the grid won't bias etc., 470k is a good place to start.
Every once in a while a resistor sets a parameter [like maybe in tremolo], so having it 'scaled' more exactly might be desirable.
See posts of dropping grid resistor values.
They are all Bradley's carbon comp. I've found these to be a tight tolerance in the past.
how do they look?
They have an additional yellow band after the gold, but the five-band-online-calculator doesn't recognize the last yellow band. They all measure around 490k with one or two being 510k. ideas?
The thing I might choose to not worry about, other than a really mismatched PI, is that when the amp warms up, all the resistances 'warm up too, and the amp starts playing louder or plates start glowing, if the resistors drift much with heat, having more stable resistors will make it easier to keep the bias under better control. Some amps take 15 minutes to really warm up.

And Thank you also for the info... here I am thinking it was a science...!!!

-Paul

[PeddlerPete]

The point being you can work with them.
If you are right next to a parameter 'threshold', little value changes like that can add up. You might like a little more grid swing on the PI or the Otubes, if you have extra ~500k's try paralleling two pairs for 250k grid bias resistors on the PI, the idea is they're supposed to be balanced, however not in this amp.
Some discussion about PI balance and this amp...the point I question [lol the 'PIQ'], is if the input is leaning 'left', then the output put grid on the 'left' is leaning low, the left side, if the right side happened to get the resistors which drifted high, would put the PI far out of balance, cool, assymetric distortion !
Yea, thing is with all of them ~high sprinkled among gain stage grids, you might not or even want it tamed a bit.

[pjb]

So what we have is a starting point, right? A center point? What baffles me is how someone can listen to the amp and decide "mmm... yes that PI is way too out of whack" How do we tell what causes different types of distortion characteristics etc? Is it really all as loose as it is appearing to be?


-Paul

[PeddlerPete]

There's an old thread in DIY stompbox forum about "When does 'it matter?".
Long thread, many pages, good stuff.
Mostly it's a matter of understanding why it might matter, then deciding if that works for you, I often have to try it the 'other way' to tell if it really matters.