Too close?

I have the "upgrade" bug and am wondering if the Russian PIO's are a little too big in diameter for the ST-35. I have the K40Y-9 0.1uf 400V which are 14mm dia. The Illinois 0.1 uF 630V that come with a Dynakit are 10.5mm dia. Not a heck of a lot of difference except that the Russian's will get you about 2mm closer to the output tubes. I can mount the caps (which are closer to the output transformers), under the hood, but the outer ones will have to be mounted on top. From the pictures you can see how close these caps will be - if I want them snug to the PCB. I suppose I could move them more towards the edge of the chassis to get them away from the tubes a little more, but would rather not for appearance sake.

As you know, there are very few caps that will fit these amps, especially if you opt for the 630V models. I would really like to try these Ruskies if possible . I'm sure others have and I'm sure others have used even larger caps. Will the oil in the cap hold up from the heat of the tubes? These caps seem very robust, but maybe sensitive to heat. Has anyone tried these?

Wonder if you could get away with mounting them vertically between the tubes and just stretch the leads if they're not long enough? Heatshrink the leads and keep the caps forward of the tubes to give maximum distance. Grounding to the case is an issue with the metal shells, and I expect you also wouldn't want to be touching them without keeping a hand in your pocket ...

I insulated mine using ground burial heat shrink. Got it from the local hardware, and just printed up some paper labels to pretty them up.



PS ... if you're gonna stretch the leads anyway, maybe there's some spare room under the chassis for those too. Not sure what impact longer leads would have on performance though ... maybe one of the gurus can check in on that.

"I insulated mine using ground burial heat shrink. Got it from the local hardware, and just printed up some paper labels to pretty them up."

Very clever and neat solution for that issue!

" Will the oil in the cap hold up from the heat of the tubes?"

These military grade caps can handle anything including a nuclear blast.  Bob took a Russian PIO apart and the oil is really a jelly at room temps.  Plus heat rises and if you use white colored heat shrink as shown above you will probably get years of service from these caps.  Black shrink will get warmer.

Thanx ... lot purtier than the bare metal can too. Only worry I had was if the caps themselves were to heat, the cover might cook em a bit, but they stay cool to the touch under operation.

Here's the stencil I used if anyone's interested.



I had some fun with photoshop, printed them up on some old Avery floppy label stock, then clear coated them with package tape. No signs of peeling so far ...

PS ... the ground burial heat shrink is some pretty heavy stuff, so you really need a heat gun to do it right ...

[quote="sKiZo"]Wonder if you could get away with mounting them vertically between the tubes and just stretch the leads if they're not long enough? Heatshrink the leads and keep the caps forward of the tubes to give maximum distance. Grounding to the case is an issue with the metal shells, and I expect you also wouldn't want to be touching them without keeping a hand in your pocket ...

Skiz, there's no room between tubes. The cap is wider than the gap, and placed vertically would be worse since there would be more heat. Some people ground the case of these tubes, so resting on the chassis shouldn't be an issue. I like the idea of shrink wrap though. I may try that.

sKiZo wrote:Here's the stencil I used if anyone's interested.

sKiZo - I am not 100% sure how to interpret your markings but is that 0.15 uF +/-10% @ 630 volts?

And is ground burial heat shrink different from the typical 2:1 heat shrink tubing they sell at your local electrical store?

Thanks

Haven't a clue what some of that stuff is, and I took a couple years of Russian in high school. I just copied what was printed on the cans that Bob provided with the kit upgrade.

The ground burial head shrink is a LOT thicker than the standard stuff. Not sure what the shrink ratio is, but it tightened up right nice on the PIOs. I left it about a quarter inch long on each end and that allowed it to shrink around the corners too. With standard heat shrink on the leads, only exposed part isn't all that exposed either.

I made a stencil for .22uF too - Somebody else had that value in their amp and wanted it ... had a new drawing tablet, so that one's actually cleaner ...

I am not 100% sure how to interpret your markings but is that 0.15 uF +/-10% @ 630 volts?

That is correct!  My ex- is Russian so a little rubbed off.  The Greek looking "phi" after 0'15Mk stands for farad.  And the large B after 630 has a "V" sound so is shorthand for volt (волт).

Thanks sKiZo for the tip on the heat shrink.

Thanks arledgsc for the Russian lesson. See now I can tell my girlfriend that I learn more then electronics on these forum sites