[livewire]

answers for bhjazz................I forgot to include quotes from previous page.
 
There are always a few "scraps" on ebay - NOS 19j6 tubes (not matched), if you dont mind paying out the kazoo. ($15 to $30 ea)
 
As far as heatsinks go, two each - Digikey p/n: HS380-ND or equivalent should work fine. About $1.71 each + S&H.
 
Linky:  http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&KeyWords=hs380-nd&x=0&y=0
 

 

[Beftus]

Those 63mm tall heatsinks are a good choice. You can also use cheaper 50mm tall ones but they will get noticeably hotter. 

 

[bhjazz]

So the 63mm is what people are using for the 12AU7 builds?  After looking through the thread it's clear that the original ones are too small!
 
Thanks guys!

 

[Beftus]

A 12AU7 build needs to dissipate more heat than the original 19J6 build. Every bit of extra heatsink surface area helps to keep things from getting too hot to touch.

 

[digger945]

Ohmite makes a similar heatsink, sold at Mouser. About $2 each.
http://www.mouser.com/ProductDetail/Ohmite/FA-T220-64E/?qs=sGAEpiMZZMttgyDkZ5WiumlCfl50RTwzVA%252bY4U4BtvA%3d
 
The mosfet on the 19j6 amp would be trying to dissipate about 4.35 watts, the 12au7 about 5.31 watts.

 

[bhjazz]

Good deal.  I just wanted to make sure I had the minimum size to work with.  It looks like the dissipation factor isn't a giant leap, but definitely something I'll need to adjust for.
 
Thanks guys!

 

[the_equalizer]

As already pointed out by Beftus and livewire, the larger heatsinks are more appropriate for 12 volt heater tubes.
 
 Good to see that there are still builders interested in this great little amp!
 
cheers!

 

[videoman5]

Would a heatsink ripped from an old computer PSU be sufficient? I mean, those are often meant to handle higher heat loads.

 

[Ikarios]

Quote:

Would a heatsink ripped from an old computer PSU be sufficient? I mean, those are often meant to handle higher heat loads.

as long as you can mount it to the case/mosfets, sure. People have used heatsinks before.
 

 

[livewire]

Quote:

Would a heatsink ripped from an old computer PSU be sufficient? I mean, those are often meant to handle higher heat loads.

He is a pic of my MSSH build with a dual heatpipe CPU cooler rated at 30 watts.
I ripped it from a boat anchor outdated desktop box. Both of the mosfets are bolted to it from below.
(and electrically insulated, so no direct contact with the grounded metal of the heatsink.)
IIRC in this circuit, the mosfets each dissipate ~5 or 6 watts, so 12 watts total.
It runs warm to the touch. You want to avoid using a smallish heatsink that will run really hot.
 

 

 

[videoman5]

He is a pic of my MSSH build with a dual heatpipe CPU cooler rated at 30 watts.
I ripped it from a boat anchor outdated desktop box. Both of the mosfets are bolted to it from below.
(and electrically insulated, so no direct contact with the grounded metal of the heatsink.)
IIRC in this circuit, the mosfets each dissipate ~5 or 6 watts, so 12 watts total.
It runs warm to the touch. You want to avoid using a smallish heatsink that will run really hot.
 

 

as long as you can mount it to the case/mosfets, sure. People have used heatsinks before.
 

Thanks! PSU heatsinks are already mounted to MOSFETS, so I wouldn't have to modify them for them to work, and they come with a mounting kit to boot!

I am a computer tech, so I have tons of dead PSUs laying around. So this should shave 10 bucks or so off my 2 orders. My friend has a birthday coming up, and he recently got some DT880's. He ordered the 250 Ohm ones, but got the 600 Ohm ones instead. He went to e-mail the dealer about it, and dealer wanted him to ship back the headphones before he refunded him. My friend, not one to fuss, just sucked it up and said that he would just keep the 600 Ohm pair. Since he got me ~$50 of stuff on my birthday last year, I'd thought I'd make it up to him by building him one these amps for his new pair of headphones. Sort of ironic when you consider that I'm the Civil Engineering major, and he's Electrical Engineering major.

Anywho, I am using the modified 12AU7 design, and as soon as I get around to building them, I'll give back some insights on how it sounds. Hopefully they will drive my MB Quart 805HS's a bit better than my sound card. If it doesn't, well, it's quite the conversation piece!

 

[SpringHalo]

Comparing the schematics for the 17EW8 and the original 19J6, I've noticed everything is exactly the same, except for the pins on the tube. How hard would it be to just edit the PCB to support the new pin-out?
 
EDIT: Jesus, the pins are rather muxed up on the 17EW8.
 
EDIT v2: Sketching out a re-wired PCB right now. Might post them later. I'm trying not to move any components, but R1 is probably going to move. You want the least amount of parallel paths though, right?

 

[the_equalizer]

Quote:

Comparing the schematics for the 17EW8 and the original 19J6, I've noticed everything is exactly the same, except for the pins on the tube. How hard would it be to just edit the PCB to support the new pin-out?
 
EDIT: Jesus, the pins are rather muxed up on the 17EW8.

'Editing' the PCB layout for a different tube might seem simple but, as you just discovered, it's usually not. You might want to consider building tube socket adapters, which are certainly feasible, and use the same PCB layout.  There was talk about that in the thread some 2 years ago, I think. Search the thread for 'adapter' or some such thing.
 
cheers!

 

[Ikarios]

The 17EW8 is one of the few tubes that has been used as a replacement for the 19J6 (with some modifications, of course), the others being a 6J6, 12SR7 or 12SN7 (can't remember), and 12AU7. if you search back it should be there. equalizer I thought you built one?
 
FWIR the 17EW8 tube works as a drop-in replacement for the 12AU7 circuit as well, although I think the resistor change for the 17EW8 was suposed to be around 250k (instead of the 390k for the 12AU7).

 

[the_equalizer]

Quote:

The 17EW8 is one of the few tubes that has been used as a replacement for the 19J6 (with some modifications, of course), the others being a 6J6, 12SR7 or 12SN7 (can't remember), and 12AU7. if you search back it should be there. equalizer I thought you built one?
 
FWIR the 17EW8 tube works as a drop-in replacement for the 12AU7 circuit as well, although I think the resistor change for the 17EW8 was suposed to be around 250k (instead of the 390k for the 12AU7).

Indeed I built the prototype 17EW8 version, but it was a point-to-point build, not 'editing' the beezar PCB. As you very well said it has the same pinout as the 12AU7 so it CAN be used as a drop-in replacement for the 12AU7, but the heater voltage will not be optimum. As you pointed out too, some simple modifications (to the MOSFET biasing resistors) can put that voltage around the 17 volts that make the 17EW8 happiest.
 
Said modifications can be found earlier in the thread (a year ago, I think?? Time flies !)
 
cheers!