Page 75 of 79

#1111 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Sun Mar 08, 2020 7:25 pm
by RhythMick
I can also highly recommend Andrews boards. I run the standard boards (as opposed to the large) with 300B no issue. Make sure you size the transformer with plenty to spare - I had a buzz which eventually tracked back to toroidal overload.

#1112 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Mon Mar 09, 2020 3:50 am
by jc123
Thanks RhythMick, what is the least voltage input for normal operation on Andrews board for 300B ?

#1113 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Mon Mar 09, 2020 7:08 am
by RhythMick
Allow 4v for regulation. So for a 300B

(5v + 4v) is 9v peak, over 1.414 is 6.36v RMS

6.3v tx should be ok. 6v might be if your primary is 5% high. I went for a dual 7v toroidal with 4.4A secondaries to give plenty of headroom.

I also used the 63mm heatsinks for the 300B. These are onboard the smaller boards. I'm not using any forced air circulation and I regularly measure the temperature of both the heatsink and the transistor casings, usually about 60 degrees.

#1114 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Mon Mar 09, 2020 3:15 pm
by jc123
RhythMick wrote: Mon Mar 09, 2020 7:08 am Allow 4v for regulation. So for a 300B

(5v + 4v) is 9v peak, over 1.414 is 6.36v RMS

6.3v tx should be ok. 6v might be if your primary is 5% high. I went for a dual 7v toroidal with 4.4A secondaries to give plenty of headroom.

I also used the 63mm heatsinks for the 300B. These are onboard the smaller boards. I'm not using any forced air circulation and I regularly measure the temperature of both the heatsink and the transistor casings, usually about 60 degrees.
Thanks !

#1115 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Wed Mar 25, 2020 9:36 am
by Andrew
Got more PCB on the way, had run out.

#1116 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Wed Apr 22, 2020 10:09 am
by pre65
Andrew, did you ever get the higher power versions up and running ?

10V @ 10A would be nice. :)

#1117 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Wed Apr 22, 2020 12:32 pm
by Andrew
Not yet, I never got a round tuit, sorry.

It's on my list, but life keeps getting in the way.

#1118 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Wed Apr 22, 2020 12:40 pm
by pre65
Andrew wrote: Wed Apr 22, 2020 12:32 pm Not yet, I never got a round tuit, sorry.

It's on my list, but life keeps getting in the way.
Que Sera, Sera. :)

#1119 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Wed Apr 22, 2020 2:11 pm
by simon
You got Doris Day's Greatest Hits too G-Popz? :-D

#1120 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Wed Apr 22, 2020 2:30 pm
by pre65
simon wrote: Wed Apr 22, 2020 2:11 pm You got Doris Day's Greatest Hits too G-Popz? :-D
Perhaps, perhaps, perhaps Simon, who wouldn't ? :)

#1121 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Wed Apr 22, 2020 4:03 pm
by simon
I'll take that as a rhetorical question :-)

#1122 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Wed Apr 22, 2020 4:46 pm
by pre65
simon wrote: Wed Apr 22, 2020 4:03 pm I'll take that as a rhetorical question :-)
Whatever. (will be, will be) :lol:

#1123 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Sat May 16, 2020 10:46 pm
by pre65
Another question for Andrew.

I've no experience of your small boards, but I'm thinking of filament bias on a 12A (112A) which would require 256.2 mA @ 14v. Will they cope with this ?

If so, when will you have kits available ?

#1124 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Sun May 17, 2020 11:18 am
by Nick
Or 0.25A as the rest of the world would describe it. Some may argue you would need to adjust the current until you get 5v across the filament.

#1125 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Posted: Sun May 17, 2020 11:47 am
by pre65
Nick wrote: Sun May 17, 2020 11:18 am Or 0.25A as the rest of the world would describe it. Some may argue you would need to adjust the current until you get 5v across the filament.


I don't think I've done filament bias before so I'd been looking at how Rod Coleman did things. I printed off his fact sheet so I can understand the details. What you say about the filament voltage sounds right, although I have read that slightly starving filaments may be an improvement.

My plan, if this idea comes to fruition, was to test things out with a 20R resistor in lieu of the filament to see how close to 5V it gets.

Rod recommends a 20-23v transformer to power his modules and I have a pair of 22v toroids.


*