Filament supply modules.

[Mike H]

PS good act, that Shirley.




 

[pre65]

DHT DC Heater V12-B parts list -
for each separate module:

Ref. Description
C1 electrolytic, 10,000 uF, 35V - or 2 x 4,700 uF 35V Rapid 11-3770

IC1 L78S12, 12V 2A, TO-220 case, Rapid 47-3304
Q1 BC547B, transistor, npn, Rapid 81-0468
TR1 TIP142, power darlington, npn, TO-247 case 125W, Rapid 81-0190
BR1 Bridge rectifier GBU8A, SIL, 50V 8A, Rapid 47-2956

R1 resistor, 1R, 1% 2W metal film, Rapid 62-7265
R2 resistor, 2K, 5% 0.5W carbon film
R3 resistor, 120R, 5% 0.5W carbon film
R4 resistor, 1K, 5% 0.5W carbon film

VR1 25-turn cermet preset PV36W (top screw), 500R, Rapid 68-1944

-- stripboard 64 x 95mm, Rapid 34-0505

-- TO-220 insulating kit
-- TO-247 (plastic TO3) insulating kit
^ preferred: silicone rubber type + a dab of heatsink paste on both sides

-- metalwork, heatsinking, M3 fasteners etc.

Suitable transformer type may be toroidal 12 @ 2A or 15 - 18V @ 1A

Edit: ^ that is filament current not exceeding about 1 - 1.2 Amps

Note generous heatsinking required, might get away with the "usual" board mounting size if there's a separate one for each power device (L78S12 & TIP142), but not absolutely sure about that.

The 500R pot number you have quoted is actually for a 2K pot !

[Mike H]

OK I boo-booed. Does happen.

Not even the same type should be Murata, 68-1154


Must have read it off the plastic bag label for the other one, as they are currently out of stock of the 2k Murata ones so it wasn't even a Murata.


Original list has been edited.


 

[pre65]

The 500R pots on mine are fiddly to adjust.

I thought about a remote pot on the end panel and in my box there are two 1K Vishay precision 10 turn pots.

Can I turn it into a 500R by putting a 1K resistor across the two non wiper terminals ?

[Mike H]

Actually no, between the wiper and whichever end is, well, the other end!


In what way fiddly?



 

[Nick]

I would worry about introducing hum into the regulator if it was me.

[pre65]

I would worry about introducing hum into the regulator if it was me.

Is that because the pot would be 4" from the board or because of the extra resistor ?

[pre65]

Actually no, between the wiper and whichever end is, well, the other end!

In what way fiddly?

Because of A) the position of the module and B) the way it is mounted on the tag strip.

Would using a 1K pot be a problem ?

[Nick]

Because of the extra length.

using 1k would just let you use the first half of the travel. Mike would know how much of 500R is actually used.

[Mike H]

Up to about half as far as I can judge, for 1.2A anyway. Might be a bit more. More resistance means more current output, but also reduces the gain of the control transistor, as it's in its emitter path.

Pretty sure hum won't be too much a problem as it's all low impedance around there.


 

[pre65]

So, now these "modules" have been tested, and found to work OK, is anyone else thinking of giving them a try ?

[Mike H]

They are a bit fiddly to make, really needs a PCB to make it easier.



 

[Rod Coleman]

They are a bit fiddly to make, really needs a PCB to make it easier.

That's true! So I made some after all, and with a long qualification programme behind them, they're reliable, and made to suit a wide range of DHTs. Low priced kit available!

[simon]

Hi Rod, good to see you here. Would the board in the photo be the proto for my KRs?

[ed]

Hi Rod

ditto

I got lost in the diyaudio thread a while back..is there a summary of how to get the boards and how much and what transpired with the heavier curremt version.