[looser101]

Quote:

Originally Posted by sachu /img/forum/go_quote.gif yeah the way i have my heater wiring laid out, they pretty much go past the signal wires..hence i went with a LDO reg DC supply.

Even better. How are the 6H30's?

 

[TimJo]

Quote:

Originally Posted by TimJo /img/forum/go_quote.gif I've been looking at the options and in reading what Morgan Jones had to say about heater supplies, he brought up the topic of cathode poisoning. Since it sounds like the recommended startup sequence on this amp is to preheat the cathodes before B+ is applied, it seems like cathode poisoning may be relevant here. He lays out a fairly simple heater supply that uses an LM317T regulator and Schottky diodes, but is configured to output ~4 V on standby, and then kick in to 6.3 V when B+ is applied. He says that running the heater's at 63% of full power will reduce any ill effects during warmup. Any thoughts on this, or practical experience in any other tube amps?

Quote:

Originally Posted by adamus /img/forum/go_quote.gif I really wouldnt bother with the low voltages on offer here.

Quote:

Originally Posted by looser101 /img/forum/go_quote.gif x2 on Adamus comment. My understanding is that delaying the B+ is only necessary at much higher voltages.

Thanks for the input guys - it's a great thing having this forum to bounce ideas around.

It's interesting that both of you mention high voltage being a factor. As Morgan Jones explained it, cathode poisoning is a function of running the heaters at full power with no current passing through the tube. Basically the electrons on the cathode are excited, but they have nowhere to go, and so the surface of the cathode becomes altered. As described, it would seem this effect can take place on any tube, independent of plate voltage. On the other hand, maybe it's effects are more pronounced at high voltages - I'm not sure...

 

[adamus]

typically people delay the B+ to stop 'cathode stripping'.

why would you be warming up with no B+ (forgive if this is the case with the ehha)

 

[smeggy]

Given how inexpensive tubes are I'll buy a few and not worry about it. I can just swap out to see if anything is deteriorating, if not, back in they go until they're toast.

 

[wiatrob]

Inexpensive 6GM8s or 6H30s? Can I get your source

 

[wiatrob]

Not authoritative but informative: Cathode Stripping vs. Poisoning vs. Bombardment

 

[wiatrob]

Just got the parts to repair my blowed up EHHA board (~12 transistors. TRIPLE check before hooking up polarized voltage after a looong day

)

 

[smeggy]

Good luck, no more sparks and pops.

And tubes.. inexpensive whatever Jeff sells with the kits

 

[sachu]

Quote:

Originally Posted by smeggy /img/forum/go_quote.gif Good luck, no more sparks and pops. And tubes.. inexpensive whatever Jeff sells with the kits

yeah..but he's got a limited stock i belive and intended for EHHA kits.

 

[TimJo]

Quote:

Originally Posted by adamus /img/forum/go_quote.gif typically people delay the B+ to stop 'cathode stripping'. why would you be warming up with no B+ (forgive if this is the case with the ehha)

Well, my understanding is that there is a risk in starting the EHHA amp boards with cold tubes in that the servo may swing to one of the rails before stabilizing. So, it is suggested that the tube heaters should be powered up for about a minute before the the B+ power supply is powered. Maybe Alex or Don can shed some light here.

Quote:

Originally Posted by wiatrob /img/forum/go_quote.gif Not authoritative but informative: Cathode Stripping vs. Poisoning vs. Bombardment

Thanks, I'll read what they wrote about it.

Just for clarity, what I was referring to from the Morgan Jones book was poisoning, rather than stripping.

If a cathode is kept at full operating temperature, but little or no current is drawn, a high resistance layer of barium orthosilicate forms at the interface between the barium oxide emissive surface and the nickel cathode structure. The interface resistance eventually reduces emission, but more significantly, it increases the noise generated by the valve.

I guess a common design to prevent this is to have the LT heater supply default to a lower voltage in 'stand-by' mode, and then go to the rated voltage when the amp is powered up. He says that the default value is 63% of the rated heater voltage, based on the design of color tv cameras that used tube sensors.

I may just build the PS this way for the fun of it.

 

[Lifthanger]

Hey all

This might be the wrong thread to ask this, but I was looking to build my first hybrid.
Till now I leaned towars the millet maxed or the SOHAII, but now I found the EHHA.
Main criteria is performance Phones will be HD595 and HD650...
Any pointers?
Thanks.

 

[sachu]

Quote:

Originally Posted by Lifthanger /img/forum/go_quote.gif Hey all This might be the wrong thread to ask this, but I was looking to build my first hybrid. Till now I leaned towars the millet maxed or the SOHAII, but now I found the EHHA. Main criteria is performance Phones will be HD595 and HD650... Any pointers? Thanks.

The first headphone I ever listened to with the EHHA was the HD580 and I was floored. I have been in 'love' with this amp ever since.
The SOHA2 is an easier build compared to the EHHA..but the EHHA will be that much sweeter once you have it going.

 

[Lifthanger]

Quote:

Originally Posted by sachu /img/forum/go_quote.gif The first headphone I ever listened to with the EHHA was the HD580 and I was floored. I have been in 'love' with this amp ever since. The SOHA2 is an easier build compared to the EHHA..but the EHHA will be that much sweeter once you have it going.

That's what I wanted to hear

.
Just wanted to make sure because I thought the SOHA2 was better.
Millet Max < SOHA2 < EHHA sound quality wise I guess?

 

[digger945]

I'de say study them both and pick one to build now with the intent of building the other one eventually so you can compare them later. You can print out the BOM for both and maybe order parts for both, maybe saving a little by buying for both.

Wow, I'm a lot of help, ain't I

 

[wiatrob]

I do agree with Digger (and I have built both, including proto'ing the SOHA II - which is quite good with all Senns).

I won't get into SQ comparisons here, as that's for another thread! But-

The SOHA 2 is an easier build - all parts specified and fits in a standard case. The EHHA will require some knowledge of component selection and casing skills.

I will say that the reward is certainly there if you are up to it...