With the transformer, then a/some RC filter within the signal stuff.

What kind of thermal paste does everyone use for heatsink mounting? I was thinking of using Aavid Thermalcote, but not sure it doesn't have

https://www.chemtronics.com/p-699-circuitworks-heat-sink-grease.aspx

http://www.amazon.com/dp/B0007Y836W/ref=pe_385040_128020140_TE_3p_dp_1

http://www.amazon.com/dp/B0007Y836W/ref=pe_385040_128020140_TE_3p_dp_1

 

Is this a different Arctic Silver from the one about which

Edited May 19, 201511 yr by gepardcv

According to the Arctic silver website, ceramique "does not contain any metal or other electrically conductive materials. It is a pure electrical insulator, neither electrically conductive nor capacitive."  So it should be OK.

^ this.

I learned the hard way.

http://www.mcmaster.com/#3883k24/=x8q3rf

Perfect, thanks everyone!

 

Next, a question about heatsinks. I've been comparing various Aavid models, and found three models with identical footprints:

 

- http://www.aavid.com/products/standard/530002b02500g(2.5" height, 2.6 thermal resistance)

- http://www.aavid.com/products/standard/529902b02500g(2.0" height, 4.5 thermal resistance)

- http://www.aavid.com/products/standard/529802b02500g(1.5" height, 3.7 thermal resistance)

 

The largest sink has the best thermal resistance; seems reasonable. But the 1.5" has a better thermal resistance than the 2.0"? How can this be? They seem to be made of the same material and look otherwise the same.

Look at the graphs provided, that data looks more plausible

I used 2" sinks as that's what I had.  It's what I'd use though when doing it again. 

Thanks luvdunhill

Is there a source for matched 2SK170 transistors other than AMB? AMB says those JFETs are all reserved for people buying his own boards (which I'm not). I don't fancy getting buying dozens from bdent just to get a handful of matched pairs. Do you trust eBay sellers who claim to have matched (like this or this)? 

Take a look at the for sale section...

Spencer may be able to help...

 

http://www.fetaudio.com/archives/category/shop

Is there a source for matched 2SK170 transistors other than AMB? AMB says those JFETs are all reserved for people buying his own boards (which I'm not). I don't fancy getting buying dozens from bdent just to get a handful of matched pairs. Do you trust eBay sellers who claim to have matched (like this or this)? 

FWIW I've bought from "alweit" and his parts look good to me. Service was good too.

 

//UFN

I've just done precisely that.  I needed four quads each matched to 10mA +/-0.25mA and he said no problem.  Since his prices seem so good, there is no major loss if they turn out to be duds.  But with 100% positive feedback I have some modest hope they will be OK.

I bought J74BL's from him a month or so ago with tight matching.  Excellent service, and warp speed shipment.  But he was about out of K170's when I ordered the J74's.

 

Spencer may be able to help...

 

http://www.fetaudio.com/archives/category/shop

Edited May 24, 201511 yr by Craig Sawyers

J109's at least for me a bigger problem to source.

Linear Systems LSJ109 is fairly easily available.  In the UK https://www.micross.com/ecommerce/for about UKP1.30

He's referring to the 2SJ109, the dual J74.  Not that easy to find. 

He's referring to the 2SJ109, the dual J74.  Not that easy to find. 

 

Indeed. Need a few of the GR grade ones. Don't wish to pay $40-50 for a pair as I'll be damn broke for the amount I need. Also don't wish to go down the route of buying 100+ J74's and trying to match them to the tightest tolerance.

 

Wish there was a modern day equivalent.

He's referring to the 2SJ109, the dual J74.  Not that easy to find. 

Ah - goddit.  Must have had brain fade.  Alternative way of doing it is to get matched pairs from Spencer and mount them in an isothermal housing.  Something like the old 2SJ75 package of two discrete matched J74 that predated the funky plastic packaged dual 2SJ109.  I just got four J74BL quads matched to 10mA.  Each quad is matched to the second decimal place, so easily good enough for a roll your own 2SJ109.

 

2SJ75GR available from the usual source, but at $32.

 

Or buy a bunch of LSJ74 and match.  Not cheap at $6 each.

 

Basically the cheapest way is to buy matched from Spencer at $9 each and then pair them to give a cost of $18 per pair.

Just curious - has anyone been brave enough to try the new, V2.0 Khozmo attenuators?  I say that PE is now stocking them (in some values) and that more are available direct from Khozmo.  At ~$400 for a quad w/ upgraded resistors it would appear to be a pretty good value as long as it's not as fragile as the earlier ones.

 

http://khozmo.com/products_dale_shunt.html

I've just sprung for an LDR passive attenuator, having looked at and tried various standard rotary (TKD etc), switched resistive attenuators, and flirted with tapped transformer attenuators without trying them.  We'll see once I get them boxed up.

Edited May 26, 201511 yr by Craig Sawyers