[Lifthanger]

Hi fellow EHHA builders. My GJA kit arrived months ago, but I was out with a broken clavicle. The sigma22 is done now. But it only reads 28.5V unloaded. Is this common? Used the parts for the 30V build.

 

[digger945]

Depending on one resistor and one zeners accuracy, and the output of your transformer, I would say your probably right on the money for your build.

 

[johnwmclean]

Lifthanger yes is fine, expect some variation in tolerances within the D5 zener diode and resistors.

Beat me to it digger945.

 

[MrMajestic2]

Ok, I'm finally gearing up to order my first EHHA kit. Fully balanced with the PSU section in a separate case. Only a few questions to answer first:
6.3V or 12.6V heater supply?
Delay circuit for the heater supply?

For the heater supply I'm thinking of going with H-PS-1 from Glassware, seems like a good kit. What are the pros and cons of the respective voltages?

I know I saw a ready made delay circuit, but I cant seem to find it again. What are you guys using?

 

[Lifthanger]

thanks

 

[jjazzyj]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif In my opinion, those heat sinks are woefully small. Also, the fin orientation doesn't help much either. I would not run the devices anymore than half their max junction temperature, as stated above. I know for example Nelson Pass has been known to quote the same estimate, and it's a good one. There are a few flaws in your calculations. You aren't considering the thermal resistance of the isolator and/or thermal compound. Also, the thermal resistance of the heat sink is not constant across its operating temperature. Thus, you may need to derate the quoted spec, depending at what ambient temperature it was given. Here is one manufacturers derating curve: If you're looking for a number, I'd recommend something in the 0.5 C/W range, per channel. Perhaps you can inquire what size Conrad heat sink Farrari is using, it looks to be about the right size and fin orientation.

That picture doesn't really show how large those heatsinks are. They are 12" long 5 3/4" wide and 2" thick. They weigh around 2lbs each.

I am taking the isolation compound into consideration, that's Rcs=.9C/W according to the Aavid Thermalloy specs.

 

[dBel84]

Quote:

Originally Posted by MrMajestic2 /img/forum/go_quote.gif ...Only a few questions to answer first: 6.3V or 12.6V heater supply? Delay circuit for the heater supply?

This amp is designed for the 6GM8 , you can use the 6DJ8 or 6H30. Thus 6.3V is the choice for parallel, 12.6V if you want to run them in series. Take note of the current requirement of the heaters before deciding what you want.

I will let others answer your delay circuit Q as I use manual delay

..dB

 

[sachu]

Quote:

Originally Posted by MrMajestic2 /img/forum/go_quote.gif I know I saw a ready made delay circuit, but I cant seem to find it again. What are you guys using?

Here you go...Tube B+ delay kit

 

[runeight]

Gents, I am finally able to pay more attention to this thread.

First, jjazzyj, I want to apologize for the previous post. Whoever put on the EHHA website that 2.5" heatsinks were adequate for speaker duty is an idiot. The best explanation I can offer is that I wasn't really paying attention.

You guys have mostly sussed this out, however. At 18W into 4R each mosfet will burn about 18W itself. This is they typical effiency for class AB (mostly B) operating condition.

If we can live with a 40C temp rise over a 25C ambient this will put us at 65C, ten degrees less than the halfway point to 150C.

Now I know we won't have ambient but just to get a ballpark number this is 40C / 18W or about 2C/W. Given all the various thermal barriers between the junction and the air I think that Marc's recommendation that the heatsink itself needs to be 0.5C/W is a good one.

And, of course, only off-board heatsinks can do this.

 

[MrMajestic2]

Quote:

Originally Posted by sachu /img/forum/go_quote.gif Here you go...Tube B+ delay kit

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif This amp is designed for the 6GM8 , you can use the 6DJ8 or 6H30. Thus 6.3V is the choice for parallel, 12.6V if you want to run them in series. Take note of the current requirement of the heaters before deciding what you want. I will let others answer your delay circuit Q as I use manual delay ..dB

Great, thanks guys.

 

[johnwmclean]

Quote:

Originally Posted by dBel84 /img/forum/go_quote.gif This amp is designed for the 6GM8 , you can use the 6DJ8 or 6H30. Thus 6.3V is the choice for parallel, 12.6V if you want to run them in series. Take note of the current requirement of the heaters before deciding what you want.

So what are the pros and cons for in series vs parallel?
I've lost it here...

 

[luvdunhill]

Quote:

Originally Posted by johnwmclean /img/forum/go_quote.gif So what are the pros and cons for in series vs parallel? I've lost it here...

My opinion is that when you can run lower current heaters, do it. That means you have some sort of choice via a center tap heater. Otherwise, there isn't much you can really do.

 

[sachu]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif My opinion is that when you can run lower current heaters, do it. That means you have some sort of choice via a center tap heater. Otherwise, there isn't much you can really do.

Humbly suggest the opposite, atleast for the EHHA..Run it in 6.3 volt configuration so you can use the 6H30 which has a fuller sound all around albeit a bit rolled off at the top compared to the 6GM8..doesn't cost all that much more to up the heater supply circuit to handle the extra current.

You can always play around with the NFB to get taht top end back with the 6H30s

 

[luvdunhill]

Quote:

Originally Posted by jjazzyj /img/forum/go_quote.gif That picture doesn't really show how large those heatsinks are. They are 12" long 5 3/4" wide and 2" thick. They weigh around 2lbs each.

how do you plan to attach the devices to the heat sink, via angle bracket? That's how I'd do it... Don't forget to add that in. But really, the fin orientation is the big hurt with those... Now, how can you measure the thermal resistance? I'd tell you, but it was a scarring experience that started when I got in between my wife and the oven in the kitchen

 

[luvdunhill]

Quote:

Originally Posted by sachu /img/forum/go_quote.gif Humbly suggest the opposite, atleast for the EHHA..Run it in 6.3 volt configuration so you can use the 6H30 which has a fuller sound all around albeit a bit rolled off at the top compared to the 6GM8..doesn't cost all that much more to up the heater supply circuit to handle the extra current. You can always play around with the NFB to get taht top end back with the 6H30s

er? What I meant is, either you have a center tap to work with or you don't. When you do, use the lower current option (assuming you are willing to change the heater voltage when you roll in new tubes, perhaps that's what you're getting at).