2a3 Capacitor question

[Paul Joppa]

Sorry that the discussion got more general without getting specific first!

I do not recommend any component rated for less than 85 degrees C, inside any of our amps (except of course the Quickie!).

That's because I am a moderately cautious engineer by trade, of course - I have not attempted to measure the temperature directly inside any of the cases, mostly because it will be so dependent on the circulation (inside and out), ambient air temperature, and power line voltage. Empirically, we have not seen failures with parts rated 85C or greater. We have seen failures of for example the original Jupiter beeswax caps in the S.E.X. amp - I can't remember but I think they may have been rated 50C? (Jupiter has since revised their construction, and we have added ventilation slots to that amp.) We've seen failures in C4S installations, so I've revised my design rules - many products now have heat sinks and/or use larger transistors.

For what it's worth, in the case of power transformers and semiconductors, I normally design for a nominal internal temperature of 100C, while the parts we use are rated for 150C. For the semiconductors I assume the under-chassis temperature is 60C - but I haven't verified that.

Also for what it's worth, the effective environmental temperature is usually around a 50/50 mix of sir temperature and radiation temperature averaged over the usual 4-pi steradians. If a part is close to a power resistor (for instance) it can see some high radiation temperatures!

 

[debk]

Thanks Paul, having been a cautious engineer at one time I understand you reasoning.

So the Mundorfs are a no go.  I may give the Clarity Cap MR a try, or take Grainger's suggestion and go with the Obligatto oil cap.  I wonder how the Obligatto would sound bypassed by the Vcap teflons I have siting around


Debra

 

[Doc B]

For what it's worth, I have never liked bypassing a larger coupling cap with a smaller one. The resulting sound often seems smeared. I might consider bypassing an inexpensive high capacitance 'lytic in a power supply, but what is the point of buying a boutique cap if you have to bypass it with a boutique cap?

 

[2wo]

Hi Debra,
Have you tried the Russia K40? Paper in oil. May not be as starkly truthful as the Teflons, but very easy on the ear.

And still cheep...John

 

[Grainger49]

Thanks Paul, having been a cautious engineer at one time I understand you reasoning.

So the Mundorfs are a no go.  I may give the Clarity Cap MR a try, or take Grainger's suggestion and go with the Obligatto oil cap.  I wonder how the Obligatto would sound bypassed by the Vcap teflons I have siting around


Debra

Debra,

Can't hurt to try.  The Ack! dAck! offers a "Teflon output option."  It is a 0.1uF bypassing the stock Auricap.  So it is done, and results vary. 

 

[InfernoSTi]

I do not recommend any component rated for less than 85 degrees C, inside any of our amps (except of course the Quickie!).

For what it's worth, in the case of power transformers and semiconductors, I normally design for a nominal internal temperature of 100C, while the parts we use are rated for 150C. For the semiconductors I assume the under-chassis temperature is 60C - but I haven't verified that.

Thanks, Paul, this is very helpful 

What I am wondering is that several of us are using "underrated" (for heat) boutique caps in our amps with great success and over a long period of time (I've been using Mundorf S/O in my Stereomour for a year, for example.  I believe others have even used Jupiter caps, perhaps).  Given your statement about design temps, I should remove my Mundorfs.  This is unlikely to occur, however, because they sound great! 

So what can we do to cool the interior?  I'm thinking a lot more airflow, perhaps even forced?  I don't want to get too complicated but surely there is a nice 12v DC fan that could be added in some reasonable manner to increase airflow.  I really want to try the Mundorfs in the Paramounts without too much worry.

Best,
John

 

[Grainger49]

I have Mundorf SIO in my Eros, it is up on spikes increasing ventilation.  I have the same caps in my FP 2 and the base doesn't even have feet on it.  I'll probably put spikes on it too after Paul's post.

I liked the recent picture of a custom Bottlehead product, can't remember which, with a grill at the back of the base and a fan that snuggles up to the grill to increase cooling.  Using a 12V fan on a 9V or 6V supply will decrease the speed, lower the CFM rating and make it very quiet.

Edit:  Found the pictures.

http://www.bottlehead.com/smf/index.php/topic,3046.0.html

 

[Paul Joppa]

I do not recommend any component rated for less than 85 degrees C, inside any of our amps (except of course the Quickie!).

For what it's worth, in the case of power transformers and semiconductors, I normally design for a nominal internal temperature of 100C, while the parts we use are rated for 150C. For the semiconductors I assume the under-chassis temperature is 60C - but I haven't verified that.

Thanks, Paul, this is very helpful 

What I am wondering is that several of us are using "underrated" (for heat) boutique caps in our amps with great success and over a long period of time (I've been using Mundorf S/O in my Stereomour for a year, for example.  I believe others have even used Jupiter caps, perhaps).   Given your statement about design temps, I should remove my Mundorfs.   This is unlikely to occur, however, because they sound great! 

So what can we do to cool the interior?  I'm thinking a lot more airflow, perhaps even forced?  I don't want to get too complicated but surely there is a nice 12v DC fan that could be added in some reasonable manner to increase airflow.  I really want to try the Mundorfs in the Paramounts without too much worry.

Best,
John

Reading my note again, I may not have been very clear. I meant that the temperature of the wire inside the transformer, and the temperature of the silicon chip inside the transistor, would be kept below 100C. Inside the chassis the air temp is of course much lower - hotter than room temperature, cooler than 100C.

We have been adding ventilation slots in the chassis plates, gradually, as products get revised. This allows thermally-driven airflow, taking it in below the wood base frame and exhausting through the slots.

Cooling air from a fan or other cause does not need to flow very fast, but it does need to flow over the heat sources and then out of the chassis. Components don't sweat, so a fan inside the closed chassis won't cool anything - you need that cross ventilation!

 

[earwaxxer]

I have Mundorf SIO in my Eros, it is up on spikes increasing ventilation.  I have the same caps in my FP 2 and the base doesn't even have feet on it.  I'll probably put spikes on it too after Paul's post.

I liked the recent picture of a custom Bottlehead product, can't remember which, with a grill at the back of the base and a fan that snuggles up to the grill to increase cooling.  Using a 12V fan on a 9V or 6V supply will decrease the speed, lower the CFM rating and make it very quiet.

Edit:  Found the pictures.

http://www.bottlehead.com/smf/index.php/topic,3046.0.html

Granger - nice build! - 'those pretzels are making me thirsty!' - sorry - couldnt resist the Seinfeld quote!

 

[intojazz]

Hello Debra,
I've found this site http://humblehomemadehifi.com/ to be most helpful in describing specific qualities of various capacitors. There are also useful recommendations on bypass caps. I hope this helps.
John

 

[debk]

Thanks john, I have actually seen that site before.  A lot of information.

I think what I may do is build the 2a3 paramount with the stock capacitor, and then put a temperature probe  next to the capacitor and see what I measures

Debra

 

[Grainger49]

Eric,

I can't take credit, it isn't mine.  But isn't that gorgeous wood?  I really like that finish on the Oak.

Debra,

Try bypassing with two pair of jumpers.  It took me quite a few swaps the first time I did it.  I decided to leave the KK Teflons in my Ack! dAck!

 

[InfernoSTi]

Reading my note again, I may not have been very clear. I meant that the temperature of the wire inside the transformer, and the temperature of the silicon chip inside the transistor, would be kept below 100C. Inside the chassis the air temp is of course much lower - hotter than room temperature, cooler than 100C.

We have been adding ventilation slots in the chassis plates, gradually, as products get revised. This allows thermally-driven airflow, taking it in below the wood base frame and exhausting through the slots.

Cooling air from a fan or other cause does not need to flow very fast, but it does need to flow over the heat sources and then out of the chassis. Components don't sweat, so a fan inside the closed chassis won't cool anything - you need that cross ventilation!

Thank you, Paul.  Adding additional vent holes in the right spots and/or adding a small, slow fan (such as running a silent 12v DC fan at 6v) to create greater cross ventilation is the goal, then.  If ambient is around 25C and max temp is 100C, and cap max is 55C, then it should be possible to get there, perhaps.  I just love my Mundorfs....

Best,
John

 

[InfernoSTi]

Well a couple of things.  First, I've drilled a few vent holes above where the parafeed cap are located.  I drilled six 7/32" holes. Since I'm painting the top plates, I think they will simply disappear to a great degree.  I'm also planning on using Herbie's Tenderfoot 1/2" feet which should allow a lot of air to get in underneath the amps.  Each of these is done with the hope that this well allow better crossflow ventilation.

Also, I realize I picked up a set of Mundorf Supremes, not the SIO (and paid appropriately and with full and proper disclosure by the seller...just misspeaking on this thread).  So I'm going to get a new set of SIO for the cap and will probably allow them to hang a bit low where they can get good air flow around them.

Best,
John

 

[InfernoSTi]

So I thought about this some more and added a few more holes above the parafeed capacitor (9 total). I also added some holes around where the cathode resistors mount (7 total), figuring this was where Paul said there was a significant source of heat.  I have painted with black lacquer with a clear lacquer top coat.  I'm not the best craftsman around...the flaws are obvious...but I'm happy with the result and think the extra vent holes will keep the air flowing better.  Oh, and I decided to get the 3.9uf Mundorf SIO...I bi-amp and am not worried about bass extension.

Best,
John

 

[InfernoSTi]

One last post for this thread...here are the Mundorf 3.9uF Silver In Oil caps installed with a bit of an air gap to allow free flow of air to the extra vent holes above.  Remember, heat rises (which is down in the photo).

Best,
John

 

[InfernoSTi]

As an update to this thread, the hottest place I measured on the surface of my Paramounts was 56 degrees C. with most areas within 1/2 inch away being 53 degrees C or lower.  Underneath, the cathode resistors are at 80 degrees C.  The Mundorf SIO are measuring at 43 degrees C. maximum (they are rated at 55 degrees C max).

Remember, I mounted mine "low" and have extra vent holes drilled.  While I would like to see more than 10 degrees from max, I'm not too worried.  I'd love to see what others are measuring in their Paramounts, particularly if they are mounting the caps "high" and didn't add additional vent holes. 

Best,
John

 

[earwaxxer]

Those Mundorfs are a thing of beauty! Just proves it... 'cap lust' is real, although tubes are always going to be prettier.

 

[ranger3]

Newbie question.

I will be replacing the Solen 3.3 Para Feed caps.  I have Mundorf silver in oil and have a couple of questions.

Do I need to bleed off the Solen's before un-soldering them?  If so, what's the best way to handle this.

Any advice on safely performing this task is appreciated.

Thanks.

 

[Doc B]

Any advice on safely performing this task is appreciated.

Thanks.

Simply use your voltmeter to measure across the cap and see if it has any voltage. If it does, connect a 10K ohm resistor across the leads to drain it off. You will be able to see the voltage drain off on the meter.