Iskra vs piher

[RockinRocket]

I doubt any one could notice a difference between 47p and 60p let alone 100p in that spot. The bigger the value the more super high frequncys get eliminated. The cathode caps would make a more noticeable effect if a +/- 10% .68uf measured .62uf vs .74uf. The gain boost in those frequency would start to add more low mids the bigger the cap.

Heres a fun little calculator. Adjusting the .820 cathode resistor to the later 2k7 resistor will result in a brighter combination with the .68 uf cap.
https://www.ampbooks.com/mobile/amplifi ... capacitor/

[whopperplate]

Ok, that's what I already understood to be true concerning higher values here. I have definitely noticed a preferable difference between 47p and higher values. Thanks for the calculator.

I will post progress on the build in the appropriate forum when time comes. Thank you all.

Charlie

[whopperplate]

Old thread with pertinent info:

viewtopic.php?f=5&t=33920

[Doug H]

I did a bunch of AB'ing on teh plate of V1 using a piher, a stock cheap carbon film and a couple fancy modern brands. I did feel I could hear a difference, ironically the standard CF sounded the most like the piher to me. Both the fancy brands were cleaner, had less attitude, and one of them seemed to add some compression.

I can't say for sure what I heard was there, but I think every time I forgot which resistor I had switched in I ended up guessing right.

I think on the plates is going to be most revealing, and I have no doubt a guitar with all CC plates will sound different than one with all CF plates, even if they were all matched to within 1 ohm. But between different brands of CF? well I'm a believer, but I could have been hearing things.

[whopperplate]

When I swapped in the piher on v1 plates in my 12series amp it became a tad more stiff and lacked the low mids and cutting high end in comparison to the stock metro kit CF 1 watt resistors, probably has something to do with the piher being 1/2 watt I assume. Was unfavorable in this amp so I went back.

AB carbon comp vs piher CF on v1 grid was an obvious difference imo. Piher was cleaner, tighter, and harmonically richer and clearer. AB is mushy and dull in comparison, fat and chewy, but not as percussive. I kept the piher there. Still need to a/b the AB on the plates with other makes.

Charlie

[RockinRocket]

One difference between modern resitors and Iskras and pihers is the old ones had tined copper leads and probably were leaded. Modern Xicon have no copper and are ROHS compliant. Copper is a better conductor..

But still for me I could turn the amp off wait an hour and it again sounds different with out modding

[jnew]

FWIW, take the PI fizzy cap and alligator clip in a 150pF. Play it for a few moments and then alligator in a 25pF. You will hear what happens but even with that big of a swing, it's not a drastic measure but it does make a difference.

And I will add this as well. When I built a 68 plexi, I spent lots of time and $ to find all Iskra's and all Mustards. I can honestly tell you that as accurate as this is, it is sooooo not necessary. My 50 watt with mixed CC's and cheap Carbon Film resistors with cheap Mallory 150 caps, is every bit the amp the 100 watt is. No exceptions.

Lastly, caps in the Cathode Follower positions are of key importance IMO. You can really hear changes from one material to another in these positions. Probably more so than any resistor material changes anywhere else in the circuit.

[RockinRocket]

Lastly, caps in the Cathode Follower positions are of key importance IMO. You can really hear changes from one material to another in these positions. Probably more so than any resistor material changes anywhere else in the circuit.

Do you have a technical reason for this? I can understand CC resistors having a greater effect there because of the 150+ voltage they see on the follower. But why is there more of a change here for capacitors than for the plates where the caps block much more voltage?

[jnew]

Not sure I understand the question but I say this because I've changed my .68's between Mustards, two different Philips chicklet types, Mallories and WIMA's. These all reveal more noticeable changes than CC resistors and Carbon Film comparisons.

[RockinRocket]

Hmm I think I lost you.

You said cap material was more important in the Follower position. Next sentence you talked about resistor composition. Two different things here. I though you were talking about resistors and caps in the cathode follower spot. The tone stack circuit in these amps.

Now your talking about the gain stages cathode bypass cap. Cathode follower capacitor and cathode bypass capacitor are two different things.

Bypass caps have the least tonal change.. if any from my experience and from a technical point.

[whopperplate]

Ahh behold the wonderfully diverse interpretations of the English language.

Correct me if I am wrong, but I believe all jnew is saying is that the sonic characteristic differences yielded from different capacitor construction materials, when referencing specifically usage in the cathode follower position alone, are far more severe compared to the differences yielded between different resistor construction materials.

Interesting info about modern copper free leads and vintage tinned copper leads. A whole amp with one or another I am sure would produce differences, just arguably discernible as always.

Charlie

[jnew]

Ahh behold the wonderfully diverse interpretations of the English language.

Correct me if I am wrong, but I believe all jnew is saying is that the sonic characteristic differences yielded from different capacitor construction materials, when referencing specifically usage in the cathode follower position alone, are far more severe compared to the differences yielded between different resistor construction materials.

Simple as that.

[emmjaydubya]

I can honestly tell you that as accurate as this is, it is sooooo not necessary. My 50 watt with mixed CC's and cheap Carbon Film resistors with cheap Mallory 150 caps, is every bit the amp the 100 watt is. No exceptions.

Aww jnew yer no fun.

[jnew]

I know. But believe me, I have no regrets about making that journey. In fact I'm doing another one now but not with Iskra's. All Riken RMG resistors and Mustards.

[neikeel]

jnew

Please clarify exactly what position of caps you mean and the values and materials

You mix cathode bypass caps and cathode follower caps in different emails