DHT Heater using VCCS - PCB or Kit (Possible Group buy)

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

Post 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.
jc123
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#1112 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by jc123 »

Thanks RhythMick, what is the least voltage input for normal operation on Andrews board for 300B ?
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#1113 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

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

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

Post by Andrew »

Got more PCB on the way, had run out.
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pre65
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#1116 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by pre65 »

Andrew, did you ever get the higher power versions up and running ?

10V @ 10A would be nice. :)
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#1117 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

Post by Andrew »

Not yet, I never got a round tuit, sorry.

It's on my list, but life keeps getting in the way.
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#1118 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

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

Post by simon »

You got Doris Day's Greatest Hits too G-Popz? :-D
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#1120 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

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

Post by simon »

I'll take that as a rhetorical question :-)
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#1122 Re: DHT Heater using VCCS - PCB or Kit (Possible Group buy)

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

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

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

Post 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.


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