DHT Heater Group Buy notes.

[Andrew]

I should add that I have not had any reports of the non-epoxy cap breaking on the PCBs in the field. Doesn't mean it hasn't happended but I've not heard about it....if it has.

[Mike H]

Fascinating.

[izzy wizzy]

The diodes DSB10I45PM are hard to get or on long back order from Farnell
https://uk.farnell.com/ixys-semiconduct ... w%2Fsearch.

I found these
https://uk.farnell.com/stmicroelectroni ... dp/2325859

I know they're duals so I figured I could use 3; the common cathode being used for the positive leg of the bridge and use them as singles for the negative leg. I thought they were close in spec to the originals if I'm looking at the right things; a low Vf fer instance.

These are a small signal schottky like the originals. What is the difference between a small signal schottky and a schottky rectifier?

If these were OK, they have a low Vf and I'm using only 5VAC in for 2.1V out to 4P1L
https://uk.farnell.com/stmicroelectroni ... dp/9803360

Cheers,
Stephen

[Nick]

I use these all the time

https://uk.farnell.com/stmicroelectroni ... t=STPS1045

Slightly higher Vf, but don't know if 60mv matters.

[izzy wizzy]

I use these all the time
https://uk.farnell.com/stmicroelectroni ... t=STPS1045
Slightly higher Vf, but don't know if 60mv matters.

Thanks Nick. I've gone with these,

[Andrew]

Yep, Nick's suggestion should be fine

[Ray P]

The parts that that are best not substituted include the 470nF surface mount caps and the carbon comp resistors, please get the exact ones listed in the BOM.

It looks as though the carbon comp resistors listed in the BOM are now obsolete - I substituted similar of good quality.

[Ray P]

I'm assembling a couple of boards for my Bartola 2P29L preamp project and need an output of 9.3V - would prefer to populate Rx & Ry rather than using a trim pot but I'm not sure how to derive the values?

I'm upgrading the filter caps to accomodate the higher AC voltage Tx I'll need to use.

[Ray P]

So I found this on the main thread;

(i) what values of Rx , Ry should I be using for 20V-out on the big boards ?

Its basically Vout = 2.5v(1 + Rx/Ry), something like 6k8/1k might be a good place to start.

It's all in here. http://www.ti.com/lit/an/slva445/slva445.pdf

[Ray P]

Using the information in the previous post I should get 9.3V out with Rx=6K8 and Ry=2K5

I'm assuming the use of a 12VAC or 15VAC Tx. 2P29L was designed for battery use so filament current is only 120mA so I'm not anticipating heat dissipation issues.

I'll be using the 'large' PCBs because of the lower physical profile.

[Ray P]

I also tracked down in the main thread the mechanical drawing of the 'large' PCB so posting it here for reference.

I measured the corner mounting holes pitches as 38.5mm and 74mm

[IslandPink]

Here's a link to the original thread about the development.
Just putting it here because it took me a while to find it, just now :

https://www.audio-talk.co.uk/phpBB3/vie ... php?t=4729