[Parafeed]

Quote:

Originally Posted by regal /img/forum/go_quote.gif Thanks what are your thoughts on battery powered DC filaments on DHTs like the 71a, is there still an issue of low AC filament impedance and the audio signal picking noise up from them.

Battery powered filaments - the downside being that batteries tend to be large and need charging.

My last foray into battery powered filaments with a car battery ended badly with a trip to A&E, when a certain imbecile removed the charger croc clips from the battery terminals, without switching the charger off from the mains. The resulting spark caused the battery to explode! After a day at A&E where I thought I might lose my sight, I spent the following day pulling up a carpet that was ruined with battery acid and hunting for small pieces of plastic battery casing, 15ft away on the opposite side of the room. Regulated DC supplies are less dangerous, for me at least!

EDIT: A&E == ER (A&E is an abbrev. for Accident and Emergency. Otherwise known as the Emergency Room by our North American friends. Someone just asked me!

)

 

[pabbi1]

Quote:

Originally Posted by Parafeed /img/forum/go_quote.gif Battery powered filaments - the downside being that batteries tend to be large and need charging. My last foray into battery powered filaments with a car battery ended badly with a trip to A&E, when a certain imbecile removed the charger croc clips from the battery terminals, without switching the charger off from the mains. The resulting spark caused the battery to explode! After a day at A&E where I thought I might lose my sight, I spent the following day pulling up a carpet that was ruined with battery acid and hunting for small pieces of plastic battery casing, 15ft away on the opposite side of the room. Regulated DC supplies are less dangerous, for me at least!

You, sir, are my hero.

Edit: Great example of why we need a DarwinIY Award here at HF... for the more spectacular arcy-sparkys amongst us.

I was able to listen to a battery powered chain (source, preamp, amp) about a month ago, and while nice, my non-battery source destroyed it (mutual observations), so DC power, in and of itself, is not the panacea.

 

[Parafeed]

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif You, sir, are my hero.

I can laugh about it now, but it wasn't very funny at the time. My wife is still in mourning for that pink carpet!

Her main concern at the time was the damn carpet, not the fact that I got a face full of sulfuric acid and couldn't even see to get to the shower room and get the stuff washed out of my eyes. Women.....

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif Great example of why we need a DarwinIY Award here at HF... for the more spectacular arcy-sparkys amongst us.

I'd probably win that with a picture of my right thumb. (Which I won't expand on for fear of regal getting the idea that I'm a totally incompetent fool! LOL)

 

[FrankCooter]

Quote:

Originally Posted by regal /img/forum/go_quote.gif I guess I've been drooling over Frank Cooters 71A design so much that I didn't even notice the lack of bypass caps, but you don't miss a thing!.

My 112A/71A amp does use bypass capacitors. If I omitted them in the schematic, it was an error. Sorry.

A two stage all DHT headphone can be a very worthwhile and rewarding project.
In a head-to-head competition using the same source, headphones, and even the same Electra-Print output transformers, the two stage DHT amp was universally preferred over a maxed out "spud" based on a Western Electric 418a.

I've been down the battery route. A few years ago I built a 350v B+ supply using 12v/20AH SLA batteries. Works well, but not enough difference to justify the cost and effort. I used 12v car batteries for my 46/211/gm70 speaker amp filaments. In this case, it was the best sonic solution, but again, not worth the effort. A small DHT like the 71a is a different story, particularly in a low level application. Definitely like these small DHT's on battery filaments. Again, I'm lazy, so ultimately I went with the Tentlabs boards. These days, I'm thinking of trying ultrasonic AC. Where I think batteries are unequaled is as grid supplies for fixed bias configurations.

Too bad Parafeed and I can't get together, I bet we have some good stories to swap.

 

[FrankCooter]

Forgot to add that the 30 and 31 are extremely microphonic. Probably not suitable for headphone use. Because they were designed for battery use, the filaments are as thin as possible, making them extremely prone to vibration of any sort. The 26 isn't much better. the 12a is the quietest small DHT that I've used.

Since this is a "fantasy" thread, I'll add one of my own: an all DHT electrostatic amp based on the Eimac 304tl.
l

 

[spritzer]

Now we are talking.

 

[nikongod]

The datasheet for the 304TL crashed firefox the first time I tried to load it. Clearly it is too extreme for me.

 

[spritzer]

125W filament draw and 3KV max plate voltage would do that.

 

[GWorlDofSPACE]

If we still want to make a group diy project,
please make a list of specifications.

 

[FrankCooter]

Spritzer, just saw your comments in the NY meet impression thread about Kevin's all DHT electrostatic amp. I understand your concerns about people ripping off the design so I won't ask any details. Just want to say that I wasn't entirely joking about the 304TL amp. Been thinking about a 1:2 input step-up, Eimac 3c24 choke loaded, 304TL in parafeed with phase splitting 1:2 output transformer. B+ a modest 1.2KV.

 

[pabbi1]

Those are some CRAZY California tubes... and, at almost 8" tall, that is gonna be one big case. There are even a few on eBay, but, uh, oy. That looks like something from a 1950's sci-fi B movie, without the word 'Krell' in it.

 

[FrankCooter]

Quote:

Originally Posted by pabbi1 /img/forum/go_quote.gif Those are some CRAZY California tubes... and, at almost 8" tall, that is gonna be one big case. There are even a few on eBay, but, uh, oy. That looks like something from a 1950's sci-fi B movie, without the word 'Krell' in it.

It's actually not as crazy as it first appears. The 304TL works great in class A, has a mu of 12, an rp about like a 2A3, and is fairly easy to drive. Plus, as you saw, they are fairly cheap and easy to obtain. If you're looking for large, linear, effortless voltage swing with a beautiful harmonic structure, this is very close to the ultimate audio device. Devil, as always, is in the details.

 

[jcx]

looks like about right for OTL for Grado or K701

 

[spritzer]

Quote:

Originally Posted by FrankCooter /img/forum/go_quote.gif Spritzer, just saw your comments in the NY meet impression thread about Kevin's all DHT electrostatic amp. I understand your concerns about people ripping off the design so I won't ask any details. Just want to say that I wasn't entirely joking about the 304TL amp. Been thinking about a 1:2 input step-up, Eimac 3c24 choke loaded, 304TL in parafeed with phase splitting 1:2 output transformer. B+ a modest 1.2KV.

This would certainly work and the heat output not much more then a T2 driven at full swing. Kevin's amp is a full, 4 phase design from input though output so one can just imagine the cost of such a beast.

I've also been toying with the idea of a single ended SS amp with a phase splitting 1:1 transformer for something completely different.

 

[atothex]

Skimmed this thread for fun.

I think the solution here is clear: OP needs to simply throw money at Ari until he's forced to build the amp of his dreams. Then, they'll be the best of bosom buddies forever and ever.