ayan wrote: ↑Tue Aug 27, 2019 4:23 pmI'm curious to know if you have tried different types of resistors and not heard any difference?
Yes, and I have noticed that some are noisier than others.
ayan wrote: ↑Tue Aug 27, 2019 4:23 pmII replaced the four V1 and V2 plate loads and the amp's OD character was decidedly different.
This is exactly the test I have been wanting to do for some months, except I want to switch the resistors A-B fashion so I can compare them with no delay in-between, and back and forth. The problem is I don't have matching old and new parts of the same value. As noted above and previously, the 97.5k Tony sent is not available in new Dales. If I'm going to be listening for the difference between resistors of the same type and style made by the same manufacturer, I do not want a difference in resistance contaminating the result. Even if it is only 2.5%.
Replacing 30 carbon resistors might add up to something noticeable.
ayan wrote: ↑Tue Aug 27, 2019 4:23 pmII replaced the four V1 and V2 plate loads and the amp's OD character was decidedly different.
This is exactly the test I have been wanting to do for some months, except I want to switch the resistors A-B fashion so I can compare them with no delay in-between, and back and forth. The problem is I don't have matching old and new parts of the same value. As noted above and previously, the 97.5k Tony sent is not available in new Dales. If I'm going to be listening for the difference between resistors of the same type and style made by the same manufacturer, I do not want a difference in resistance contaminating the result. Even if it is only 2.5%.
You could always try to compare three resistors: (a) The "newer" 100K; (b) A vintage 97.5K; and, (c) A vintage 107K. There are many possible outcomes. If the 100K sounded best, it probably would set your mind at ease. Of course, you wouldn't know whether to attribute it to the fact that it is a newer Dale or that it is exactly 100K, or both. Still, you'd probably be happy knowing it sounds "best" -- I know I would be. Or, all three could sound identical, in which case everyone would eat some crow and we could all save a lot of time in the future. On the other hand, if the 100K turned out to be the worst sounding one you'd have other things to chew on.
About the 2.5% difference in value from one resistor to the next, I think it is small number if one considers that tubes are hand made and that everything having to do with a tube is subject to a much greater deviation that that. Imagine if we came up with a perfect amp design, only to have to change it every time we needed a tube replaced!
ayan wrote: ↑Tue Aug 27, 2019 9:56 pmAbout the 2.5% difference in value from one resistor to the next, I think it is small number if one considers that tubes are hand made and that everything having to do with a tube is subject to a much greater deviation that that. Imagine if we came up with a perfect amp design, only to have to change it every time we needed a tube replaced!
There is variation in many of the components, but this is not relevant to the question I'm trying to answer: If nothing else changes, is there any tonal impact using old Dale metal film resistors vs. new Vishay-Dale metal film resistors of the same type and value for the plate loads. Mixing different resistances into the experiment will only confuse things.
I wonder why did Dumble use so many different plate loads?
100K-120K-180K-150K-220K-
So here is a question for all you repair guys...let's say you ran across an old Showman and found the plate resistors had drifted badly over 10% but the amp sounded spectacular!.. Would you change the plate loads or leave the amp be?
Dumble really only used 4 types of plate resistors throughout the life of the ODS. 30 years.Coincidence??
IRCs
1975 RN65 Dales
Roederstiens' MK3
NTE's very few!
There were a few one off's here and there along with oil fills like in #70 ODSR but that's it really
Tony
Last edited by talbany on Wed Aug 28, 2019 4:33 am, edited 2 times in total.
" The psychics on my bench is the same as Dumble'"
talbany wrote: ↑Wed Aug 28, 2019 1:16 am
I wonder why did Dumble use so many different plate loads?
100K-120K-180K-150K-220K-
Harmonic complexity, I think. Each of those plate loads, with its unique cathode resistor value, produces different distortion content HD2, HD3, HD4, etc.
talbany wrote: ↑Wed Aug 28, 2019 1:16 am
I wonder why did Dumble use so many different plate loads?
100K-120K-180K-150K-220K-
Harmonic complexity, I think. Each of those plate loads, with its unique cathode resistor value, produces different distortion content HD2, HD3, HD4, etc.
I know what each plate loads do!
My point is! Dumble used many different plate loads,why?,He liked the sound?..So who is to say you or someone else wouldn't like the "distortion content" of a 97K or 107K resistor instead of a 100k or 120k?
it's virtually impossible to find an old amp loaded with carbon comp plate and cathode resistors that measure exactly 100k and 1k5 and still sound great. (Perhaps this is where Dumble got the idea to use different plate loads?). If Fender or any other amp manufacturer in the 60's and 70's really cared they wouldn't have loaded CC on RP/RK knowing how badly they drift. All that matters is does it sound good to you, given most preamp tubes have mismatched triodes and no 2 draw the same amount of current! therefore generate a different harmonic structure anyway.
G.D Thermonuclear devices
Looking forward to your test!
Tony
" The psychics on my bench is the same as Dumble'"
talbany wrote: ↑Wed Aug 28, 2019 1:16 am
I wonder why did Dumble use so many different plate loads?
100K-120K-180K-150K-220K-
Harmonic complexity, I think. Each of those plate loads, with its unique cathode resistor value, produces different distortion content HD2, HD3, HD4, etc.
...
Looking forward to your test!
Tony
Hmm... Not sure I would bet any money on Martin doing the test with the 97K resistors, at least at this time.
martin manning wrote: ↑Wed Aug 28, 2019 4:29 am
Harmonic complexity, I think. Each of those plate loads, with its unique cathode resistor value, produces different distortion content HD2, HD3, HD4, etc.
...
Looking forward to your test!
Tony
Hmm... Not sure I would bet any money on Martin doing the test with the 97K resistors, at least at this time.
Your probably right!. It does't really matter anyway!.Next
Tony
" The psychics on my bench is the same as Dumble'"
talbany wrote: ↑Wed Aug 28, 2019 5:20 amMy point is! Dumble used many different plate loads,why?,He liked the sound?..So who is to say you or someone else wouldn't like the "distortion content" of a 97K or 107K resistor instead of a 100k or 120k?
100k, 120k, 150k, 180k, 220k are all standard values, and they will produce a range of distortion content. 220k has roughly 2x the HD2 of 100k, but over 3x the HD3. My guess is that HAD was using different values to build more complexity into the sound.
Why did he use precision metal film resistors for plate loads and cathodes? I think the answer is most likely because they are accurate, stable and quiet.
Why did he use those particular manufacturers? Who knows. Maybe that was what he could get locally, or from his usual catalog house. The world before the www was a very different place.
Here's a trace of old (dashed) and new (solid) Dales from 0-350V run on a tube curve tracer. Old and new parts both display linear characteristics (no surprise), and again there is nothing to suggest that there is anything special about the NOS parts. Unfortunately I don't have any CC to compare; it would be nice to see if there is any noticeable nonlinearity with voltage.
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talbany wrote: ↑Wed Aug 28, 2019 1:16 am
I wonder why did Dumble use so many different plate loads?
100K-120K-180K-150K-220K-
Harmonic complexity, I think. Each of those plate loads, with its unique cathode resistor value, produces different distortion content HD2, HD3, HD4, etc.
martin manning wrote: ↑Thu Aug 29, 2019 2:58 am
100k, 120k, 150k, 180k, 220k are all standard values, and they will produce a range of distortion content. 220k has roughly 2x the HD2 of 100k, but over 3x the HD3. My guess is that HAD was using different values to build more complexity into the sound.
Hi Martin,
I don’t understand the statement above that 220k has twice the HD2 of 100k. The 220k load line is not as steep as the 100k one. That means it’ll afford a greater output voltage swing before clipping — in other words, more gain for the stage — which at the same time means less harmonic distortion. While the 220k continues to make the output larger, the 100k arrangement is squashing the top of the output more.
Merlin’s second edition book states, on Page 22, that the 100k will result in 4.3% HD2 and the 220k in 3.3%. Voltage gains are 60 and 68 dB respectively.
Gil
Last edited by ayan on Thu Aug 29, 2019 4:08 pm, edited 1 time in total.
I’ll look at that later. The distortion figures I quoted were my calc using the method described in RDH4, assuming max unclipped amplitude. The assumed load is involved in that too, as I am on the AC load line. On the gain, are you sure it’s dB you are quoting from Merlins book? I think that is voltage gain, and 68 vs. 60 is 1.1 dB.
martin manning wrote: ↑Thu Aug 29, 2019 2:37 pm
I’ll look at that later. The distortion figures I quoted were my calc using the method described in RDH4, assuming max unclipped amplitude. The assumed load is involved in that too, as I am on the AC load line. On the gain, are you sure it’s dB you are quoting from Merlins book? I think that is voltage gain, and 68 vs. 60 is 1.1 dB.
Martin et al,
1. Oops, gain expressed as linear voltage ratio, not dB.
2. "using the method described inRDH4" Would that be Radio Designer Handbook?
3. The info I referenced can also be found here, Table 1.1, Page 22:
"In general, a larger load resistance will increase gain and available output swing, but reduce harmonic distortion. ... with a larger load resistance the anode voltage is pulled down lower as the 0V grid curve is approached, and therefore grid current will be greater when it does eventually start flowing.... Increased grid current will result in slightly harder grid-current clipping, which likewise will lead to a slightly harder or crisper overdrive sound"
I recommend anyone interested consider buying Merlin's book, BTW.
RDH4 describes a shift in the harmonic content when changing plate resistor from 2x internal plate resistance from mostly 2nd harmonics to 3rd and 5th harmonics mostly when going to a plate resistor equal of 4-5x internal plate resistance of a tube. So the harmonic content shifts when doing that, and the result is very audible in these overdrive amps.
PS: yes that is the Radiotron Designers Handbook, 4th ed.
