Plexi cap snake oil

[pjd3]

Hi there. I think I have some idea of what to expect from this question but, here we go.

So, you're building a Plexi (6V6). You have a few of .022uF Mallory 150's (white) and a few Sozo Yellow .022uF NewGens coming in the mail.

You aren't going to have enough of each to do the whole amp with one kind or the other so you have to make a hard choice of where to divide the Mallories and the Sozo's. Theres 4 coupling and 2 in the EQ of the .022uF.

Where are going to put them?

Oh, and Electric Ladyland and Axis Bold as Love consist of your favorite guitar tones, ever.

Shoot. But please not me.

Thanks,
Phil D.

[sluckey]

I'd put them on the board.

[frankdrebin]

Sozo on tonestack and after PI

[pjd3]

Ha Alright Sluckey, perhaps that suggests that you don't think there would be a difference and very well there isn't. I just get a kick out of the wide spectrum of opinions on what kind/value/brand ought to go where.

I was going to put my Sozo's on the pre and post PI coupling caps just because so many talk about coupling caps being the most "tone critical" caps and, the Sozo's cost the most! Thats where I'm at in life.

Not that its an indication of anything, I brought a few Mallories that I pulled out from my deceased Bogner Alchemist and brought them into work to test on the dedicated and expensive LRC meter at my job. First time using it but the .1uF Mallory's measured 103.55nF and 103.12nF. (with Rp's of 303k and 321k respectively). Only a two sample group but, pretty tight tolerance if found to be typical. Just for my own curiosity I'll be bringing new caps into work to measure, just to see what kind of consistency/tolerance these companies bring to their caps. A good morning break task. Coffee and cap spec measurements.

Phil D

[Roe]

I normally prefer the sozos but not on the normal channel (v1a). also, the .1uf presence cap doesn't matter much

[pdf64]

What does ‘Rp of 303k’ mean?
I suspect that key differences between film cap types may be due to their parasitic characteristics, eg series resistance and inductance, rather than their intended ones.

[sluckey]

Ha Alright Sluckey, perhaps that suggests that you don't think there would be a difference

I'm sure there is a difference but it would be wasted on my ears. I used all yellow M-150s in my Plexi6V6. My reasoning was simply to try to empty my parts bins and I came pretty close. Still got a bunch of the white M-150s though. But my goto caps are the Xicon chicklets for several reasons, none of which involve how they sound. They are cheap and small. They fit my board layouts well. And like teflon coated wire, they don't melt from a careless soldering iron!

[pjd3]

I looked it up afterward and found out that Rp is the "insulation resistance" of the cap, some call it the Parallel resistance which is the resistance across the dialectric from one plate to another. The ESR I believe is the total series resistance of the cap that includes the Rp or insulation resistance. The Rp usually takes up the very most of the ESR. And I think those values are at full DC charge up, steady state. The test I did appeared to be at 1Khz which I would assume is an applied sine wave, and I heard the tester is at a very low voltage with the AC tests. So, I have more to learn. Is Rp different at DC or AC? I'll need to find out more about the testing parameters. Its just a small side interest to me. I don't expect it to have much bearing on tube amp perfomance, at least audibly. When the new Sozo yellows come in this week I'll take them into work and give them a whirl, see how they compare to the Mallory 150's on the tester.

The reason I ask about things like this is that since I'm just starting on tube amp builds, I have to conclude that pretty much anyone doing this has greatly more things to comment on than I do! Its just a place to start and things to pay attention too.

Thanks !

Phil D.

[pjd3]

And yeah Sluckey, I wouldn't be surprised at all that how great an amp sounds is not contingent on how much money somebody spends on capacitors of any solid state component.

My "rules" for your plexi project were to use just about all Sozo nextgen yellows for coupling and maybe some EQ, F & T and Sprague for electrolytics,
Metal Film resistors for input (V1 grid), 1 Watt Carbon Film resistors for just about everything except a few of the highest voltage spots for which would be carbon comp. The other rule is to use as many "good" components ripped from the donor Bogner Alchemist as I could. I even combined a .47uF Vishay/Sprague V-730P hi-fi corksniffer type cap in parallel with a Mallory 150 .22uF to make the .68uF cathode cap for the bright channel triode.
I did spend the 7 or 8 bucks to have a Sozo yellow .68uF cap shipped with the order thats coming. Ha. That hurt. But, thats what it shall be good bad or indifferent.

This shit is fun!

My "dream" is to have a Fender head (which I just built, sounds great) and a Plexi head that both go into a 2 x 12" cab, each with there own speaker. I think Mesa Boogie even makes a 2 x 12" with one speaker closed, and one open. That would do it. An American speaker for the Fender, a British speaker for the Plexi, open and closed back, respectively. Being a 62 year old classic rock weekend warrior, that would serve well. Some day man. Now deliver my fricken snake oil ! Now !!

Thanks guys,
Phil D.