Almost done

jnew · Post by **jnew** » Fri Nov 28, 2014 10:32 am

Hey guys, finally got everything I need to finish my 68, Iskra/Mustard 100 watt plexi. The last four resistors are enroute and I just received ******'s 1.8" PT. Some final questions:

1) I've seen some amps with four, 5.6K resistors on the power tubes (one on each tube). And some I've seen only have two. One between V's 4&5, and one between V's 6&7. And I've also seen the same arrangement with one 1.5K for V's 4&5, and one 1.5K for V's 6&7. What's is the significance with these arrangements and values?

2) This is a repeat. This PT isn't a dual B+ option but I still have a standby switch that has the two on positions. Can I use this for one option to be used with the polarity cap while the other would just be normal/without a polarity cap? It would be nice to A/B the differences. Also, what value is that polarity cap for the 100 watt plexi's? I only know it was 1000V's. And where can I find a little tag board to use for this polarity thingamajig?

Thanks gents.

Jeremy1283 · Post by **Jeremy1283** » Sun Nov 30, 2014 12:22 am

I cant wait to see it man..

stef · Post by **stef** » Sun Nov 30, 2014 8:59 pm

jnew · Post by **jnew** » Sun Nov 30, 2014 10:21 pm

I know. I keep saying it and it's true. I'm pretty much done but this polarity thing has me all twisted up. I can't find info on it. I've got it all wired to be able to toggle it in and out but something just doesn't seem right to have AC to this cap to the chassis and I need to learn more before I give it a go. Still waiting on the last four Iskra's too. They had to go all the way back to Slovenia and be resent because of some retard in our postal service. Soon my friends. Very soon.

Strat78 · Post by **Strat78** » Sun Nov 30, 2014 10:42 pm

Correct me if I'm wrong, the polarity switch simply reverses the old two prong plug wires. The cap was there just to prevent a loud popping sound when the switch was used? Still, when I flip the polarity switch on Star Guitars 68, it POPS really loud! The way I set up a mock polarity switch is to run the black wire from the power plug through two switches with one buss wire. One switch is the on/off switch and it works normally whether the "polarity" switch is off or on. The polarity switch has the .05uf cap that simply goes to ground. When the switch is off the cap has no current. I think Ralle just runs the cap directly from the on/off switch to ground without the extra switch. This way the cap is always seeing a current when the amp is on. This is silly stuff, but I admit that I do this to most of my personal builds just for the heck of it.

Probably reversing which way the current runs through the PT would change the tone in a more noticeable way?
https://flic.kr/p/qfBfDp

emmjaydubya · Post by **emmjaydubya** » Sun Nov 30, 2014 10:58 pm

jnew wrote:I'm pretty much done but this polarity thing has me all twisted up. I can't find info on it. I've got it all wired to be able to toggle it in and out but something just doesn't seem right to have AC to this cap to the chassis and I need to learn more before I give it a go.

Some here refer to it as the 'death cap'. If the cap fails it goes open circuit and...?

I'm not surprised that Strat78 does it on every build, he's known to have way more balls than most around here.

Strat78 · Post by **Strat78** » Sun Nov 30, 2014 11:19 pm

Actually, I ain't got a lick of sense. So, just for the record I'm saying DONT DO IT!!!!

jnew · Post by **jnew** » Mon Dec 01, 2014 11:17 am

Yep, I'm a bit in the reckless camp myself. So what, It's fun.

Good points on the subject there Strat78. There's the actual operation of changing the direction current flows through the PT. It seems plausible that this could in fact affect the tone. It would be in incredibly interesting to read an article from an artist from back in the day, talking about his amp's polarity experiences. Sort of like "You know, one night my amp would sound fantastic but everything on stage shocked the piss out of me. Couple nights later, the stage was safe but the amp sounded like shit".

Damnit! I'm gonna have to go down this rabbit hole. I just know it.

The other point, which is where I'm at right now, is the cap. I've got the power wired to an ON/OFF/ON switch . So ON in one mode with that cap in the circuit and the other ON mode, without it. I think you're right about Ralle just having it straight to ground, ON all the time. It's hard to tell by his video clip but that's how it looked.

I have to admit, I really dig the little vintage nuance it adds to the appearance of having the little tag board in there.

jnew · Post by **jnew** » Mon Dec 01, 2014 11:19 am

What's up with the photo attachment? Trying to post a pic.

jnew · Post by **jnew** » Mon Dec 01, 2014 11:42 am

BTW emmjaydubya, your build looks so killer. I've kept that photo and refer to it often. Clean work my friend. I can't make out the values of those pin resistors on the power tubes. Did you go with the 1.5K or 5.6K?

demonufo · Post by **demonufo** » Mon Dec 01, 2014 1:36 pm

emmjaydubya wrote:
jnew wrote:I'm pretty much done but this polarity thing has me all twisted up. I can't find info on it. I've got it all wired to be able to toggle it in and out but something just doesn't seem right to have AC to this cap to the chassis and I need to learn more before I give it a go.
Some here refer to it as the 'death cap'. If the cap fails it goes open circuit and...? I'm not surprised that Strat78 does it on every build, he's known to have way more balls than most around here.

The "death cap" is actually not the one connected to the polarity switch at all. However, it is still hazardous and a really bad and unnecessary idea. On a grounded amp it is redundant anyway, since it will behave slightly differently to what an ungrounded amp would. Quite honestly, using any capacitor across mains to ground, you would be stupid to use an ordinary capacitor. Only X, X2 or Y rated capacitors are safe to use in this application, as they are designed as such that when they do fail, they can only fail open, never short.

jnew · Post by **jnew** » Mon Dec 01, 2014 2:58 pm

demonufo wrote:
emmjaydubya wrote:
jnew wrote:I'm pretty much done but this polarity thing has me all twisted up. I can't find info on it. I've got it all wired to be able to toggle it in and out but something just doesn't seem right to have AC to this cap to the chassis and I need to learn more before I give it a go.
Some here refer to it as the 'death cap'. If the cap fails it goes open circuit and...? I'm not surprised that Strat78 does it on every build, he's known to have way more balls than most around here.
The "death cap" is actually not the one connected to the polarity switch at all. However, it is still hazardous and a really bad and unnecessary idea. On a grounded amp it is redundant anyway, since it will behave slightly differently to what an ungrounded amp would. Quite honestly, using any capacitor across mains to ground, you would be stupid to use an ordinary capacitor. Only X, X2 or Y rated capacitors are safe to use in this application, as they are designed as such that when they do fail, they can only fail open, never short.

This is good info bro. I'm glad you chimed in. So where we're at here, is basically this:
1) Whether or not that "Death Cap" in and out of the circuit plays a role in the tone or not. From what I gather Strat78 says probably not and that it only serves to eliminate the "Popping" sounds when operating the polarity switch. Ralle on the other hand says it does affect the tone and it looks like he has his permanently wired in his circuit.
2) The actual reversal of current flow through the PT. If the cap has no affect, does the direction of current flow make a difference in tone? Really only one way to find out I suppose.

Now that having been said, I understand the purpose of the polarity switch was to be able to eliminate the 60Hz hum if the amp was running on a circuit that had been wired opposite. So in my mind, that cap had to serve more purpose than just the "Popping" issue. In other words, if there was no cap at all, the 60Hz hum should still be there regardless of the direction of current flow.

Yeah, it might be a little dangerous but it could explain a lot about certain amps and the uniqueness to their tone. Or it could be a complete coincidence that the 3 best amp tones I've ever heard, have polarity caps. EVH, Strat78 and Ralle.

(mine would be the 4th best.

)

All kidding aside, there are truly amazing early VH clips floating about around here and we've all taken different roads to get them. But this is one area where little seems to be really known and understood. Again, the best amps, to my ears, have them. May or may not have anything to do with it, but?

emmjaydubya · Post by **emmjaydubya** » Mon Dec 01, 2014 9:40 pm

demonufo wrote:The "death cap" is actually not the one connected to the polarity switch at all. However, it is still hazardous and a really bad and unnecessary idea. On a grounded amp it is redundant anyway, since it will behave slightly differently to what an ungrounded amp would. Quite honestly, using any capacitor across mains to ground, you would be stupid to use an ordinary capacitor. Only X, X2 or Y rated capacitors are safe to use in this application, as they are designed as such that when they do fail, they can only fail open, never short.

Interesting, I thought it was. Read many times where guys would remove it for safety. So what is the 'death cap' then?

jnew wrote:BTW emmjaydubya, your build looks so killer. I've kept that photo and refer to it often. Clean work my friend. I can't make out the values of those pin resistors on the power tubes. Did you go with the 1.5K or 5.6K?

Thanks a lot, it was a fun build. They are 5.6k, one across each set. There are many pics on amp archives with this same scheme on the 100 watters from the factory.

jnew · Post by **jnew** » Mon Dec 01, 2014 10:51 pm

Yes. I have seen them. I have also seen 1.5K values there. I'm going with the 1.5K's and can swap out from there since they're easy to access.

This polarity thing is interesting? Yet so little about it is really known. As I see it, it didn't actually reverse the polarity. If you plugged in the amp and had buzzing going on, you flipped the switch and it looks like all it did, was put the cap to ground in the circuit.

jnew · Post by **jnew** » Wed Dec 03, 2014 12:25 am

Another thought.

Since the amp's these days are grounded and safe, wouldn't it be ok to actually reverse the polarity and give it a listen?

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