Considering upgrading both electrolytic and film caps

[arsun]

Paul, thank you very much for your informative reply. I guess I am all set. Numerical values also helped with it. Is there any resistors, which might benefit from an upgrade? Maybe 1.27K Ohm ones? Are the value and the type of those important? They are referred to as metal film in the parts list in the manual, but carbon composite in the instructions. That made me curious...

I am only upgrading 120 Ohm ones in the headphone section and the grid stoppers along with current set resistor in C4S board as of now.

Thanks.

[arsun]

I wish you everyone here a happy new year and thank you for your help so far.

Apart from the question regarding the 1.27K Ohm resistors (if it is worth to upgrade and/or is there a range for that value), I have another question about the 22uF 450V electrolytic capacitor: Can I replace it with a higher capacitance value like 30uF while ordering (like the recommended 70uF value from Obbligato instead of 47uF 450V)?

Thanks again.

[Grainger49]

Arsum,

Happy New Year!

The resistor you asked about is on the cathode of the driver stage.  I have upgraded a couple of plate resistors but never a cathode resistor.  I haven't upgraded a plate resistor for quite a few years.  There are more places to affect the sound that give greater bang for the buck than the plate or cathode resistors.  Stick with Doc's value on the cathode resistor.

After a quick look at the schematic I think you know all the components that give you improvements in the sound. 

Increasing the 22uF to 30uF shouldn't cause any trouble.  The amp will turn on a tiny bit slower as larger capacitors are charging, but you may not even notice that.

If you want to spend some cash that will make a big step in sound quality upgrade to the MQ Iron.

[arsun]

Thank you Grainger for your reply. I decided on the following then:

Resistor upgrades: 120 Ohm ones in the headphone jack and current set 499 Ohm ones in C4S boards, also 220 Ohm grid stoppers.
Electrolytics: 1000uF, 22uF and 47uF ones. 1000uF will be replaced with Elna Silmic IIs having 50V rating. 22uF will be replaced with 30uF Mundorf M-Tube Caps, 47uF will be replaced with again 47uF M-Tube caps. (The reason I switched from Obbligato caps is their huge size- I saw a picture of 22uF cap and it is really big, I think I will have difficulties with installing that considering I want to replace both 22uF and 47uF ones- and I want to order only from one place).
Interstage coupling caps: Vcap teflon 0.1uF
Parafeed caps: 2uF OIMP
I already have MQ irons.

That covers it, but I am open to further suggestions. I want to cover all the important sections in the amp. I am really looking forward to this. I think I have been bitten by the DIY bug .

The part cost is really huge, but I am buying each month something, so this is a long time project

For the caps that don't have wire leads (M-Tube caps), which wire/cable do you recommend to make the connection to the capacitor lugs? Will the teflon cable work that I am using in the amp?

[tsingle999]

Sounds like some fun upgrading there! It would be great if you would do 1 upgrade at a time (i personally have a hard time doing this as once i get under the hood i wanna do everything at once!) and let everyone know which ones were the most worthwhile to you.
As far as wire to connect the mcaps i would be tempted to use something stiff to help you hold the caps in place better (so they don't flop around as much)

[arsun]

Thank you for the comment. I thought also that it would be nice to hear one change at a time, but then I decided against it because of the burn-in times of the caps especially.

If the teflon wire is ok, then I will probably use it, cause I have some spare now. I am thinking of using some blu-tack to hold the caps in place.

[ssssly]

you can build a simple rig to burn in caps. That way you can burn in a bunch at once and then install them at your leisure. I forget where the link is but it is someplace in the community section. Came across it looking at Foreplay II stuff linked there.

I normally use velcro to hold large caps to the sides of the case until I decide if I like them or not then I if I am going to keep them in I'll make a simple bracket out of an old cotton T-Shirt. Kind of like a little cap sock and screw it to the inner wall of the case. Blue tack is great for vibration dampening but if you have a decent size cap it will only keep it in place for so long (in my experience). But I also shoehorn some huge PIOs into my gear. My Foreplay has about 2lbs of caps in it.

As a slight aside this post inspired me to get some resistors to test out in my gear. I let you know the results I get. Got a combination of Takman metal films and Shinkoh Tantalums for the signal paths and C4S in my paramours.

Be well.

[ssssly]

Found the link for that cap burn in rig, click on "jsn's foreplay page" on the community page.

[Grainger49]

 .  .  .   I thought also that it would be nice to hear one change at a time, but then I decided against it because of the burn-in times of the caps especially.   .  .  .  

You can burn in a pair of caps for a week then start on the next pair.  That way you listen to each improvement for a week while preparing the next tweak.  

I have used this successfully many times.  My fast burn in method doesn't do a whole string of caps at a time but it puts a higher voltage across them while burning in.  In addition to the higher voltage amplifier output, the more caps you parallel the lower the current becomes through each one.  That is why I do a pair at a time.

Click Here For My Post On A Fast Break In Method

I'm not saying JSN's method is bad.  I haven't tried it, I don't know.  

[arsun]

I know it's a bit late, but thank you very much for the information about burning in. I appreciate it...

Some recent news, due to budget constraints, I still did not order anything, but will do so in 2 weeks. I made up my mind about pretty much everything, however the size of TubeCaps are making me consider about them. I can shave a bit size and some money, if I switch from TubeCap to the MKP line of capacitors again from Mundorf. I can also pickup the correct value of 22uF with MKP. The problem is that they are rated 400V, not 450V as the manual recommends. How tight is the recommendation for these electrolytic capacitors? Also, does anyone here have any experience with that MKP line?

Before I forget, I got the top metal plate and the top part of power transformer powder coated by some local company to a very nice green. If you are in Chicago area, I recommend uvmetalarts for that. No affiliation, just a very satisfied customer. Their prices are also very fair. I will post some pictures in the gallery section as soon as I finish it. I also have a different headphone jack (which makes me think how to install the 120R resistors, but still and teflon tube sockets. I polished the top sections of MQ irons, they are nice and shiny. It is looking really good. I am looking forward to finishing this project... 

[Paul Joppa]

I recommend that you NOT use 400v rated capacitors in the SEX amp; stick with at least 450v rating for the electrolytic capacitors.

There are two ratings, the working voltage and the surge voltage. The surge rating is the maximum short term voltage, valid for only a few seconds. This should be compared to the peak voltage in the power supply, which occurs shortly after the amp is turned on, before the tubes start to conduct. In the SEX amp, with the design value of 120v from the line power, that is 470v. Allowing for up to 10% extra (132v line) which is within some specifications for power lines, the peak can be 515 volts. Surge voltage ratings for 400v capacitors are 450v; for 450v caps they are 500v.

In normal use the power supply produces a nominal 380v, which becomes 420v at +10% line voltage. However, capacitor lifetime depends on temperature, with the best lifetime occurring when operated at 50% to 80% of the rated voltage. So ideally I'd like to use 500v or 550v  capacitors - unfortunately those ratings are very rare.

Polypropylene capacitors have an expected lifetime that is dependent on temperature and voltage. At 85C and rated voltage, they are expected to last only 5000 hours, but at 90% of rated voltage they are expected to last a 80,000 hours. (This comes from some CDE data sheets; there's a wealth of information available there for those who are interested.)

I can't find the data right now, but mylar is more sensitive and I would not operate a mylar capacitor at more than 70% of its rated voltage.

[arsun]

Thank you for the information you provided. Seems like Tubecaps are the best option then, they are rated 600V anyway... Here is another question then, do you see any benefit of upgrading 220uF capacitors? The tubecaps only go to 200uF at 550V and MKP goes to 220uF at 250V. If there is a benefit of upgrading these, then I might add them to the order too, in that case, which option will be better specs wise? They are the same price with this value of cap... I really appreciate your valuable comments. Thanks again.