Couple of questions for a VK1 P-T-P build...

[JayDubrek]

I'm part way through building a VK1 point to point style although I have made a pcb to provide regulated 6.3v DC from a 9VAC trafo...
On power up I'm getting the 6.3v for the heaters but after a couple of minutes this is disappearing along with the LM350 regulator getting very hot... Is the regulator shutting down because of an insufficient heat sink?
The heaters on the 6BZ7's and 6AL5's glow as you would expect but there's nothing from the 12AT7's...I've double checked the heater wiring and it's all bang on...
Last of all has anyone built one of these using Edcors...10k/10k on input and 10k/150 on the output? Just thinking about cheaper options to the Sowters that usually go in this...
Thanks
Jay

 

[SKJGProject]

i'm also part way through building one although i got one of the "faulty" purusha boards...the project is that much black listed that you won't even get support from the gurus even if you pretend to do it p2p (maybe it's true for you)

i already got some cheap ll1540 from ebay but will order the sowter outs because i asked the same questions like you and nobody wanted to help!

thx maarten for setting up this page otherwise there would be way more of unfinished units  ;D ;D

http://www.tubefreak.com/varimu.htm

 

[dmp]

On power up I'm getting the 6.3v for the heaters but after a couple of minutes this is disappearing along with the LM350 regulator getting very hot... Is the regulator shutting down because of an insufficient heat sink?

I would say so - heaters take quite a bit of current. You can look this up on the datasheet and see if your regulator can provide the necessary power. For instance, for an 12at7 the I_f=300ma and for the 6bz7 I_f=400ma. Add up all the If for all the tubes to get total I_f, which is probably about 1Amp / channel. The more current being drawn, the higher heat dissipation necessary. If your DC voltage in to the regulator is 9v and output is 6.3v, the required power dissipation in Watts is (9v-6.3v)*HeaterAmps. you can check the heat dissipation of your heatsink by looking it up on the datasheet.
I recall trying to set up DC heaters on my VK1 build, but switched to AC because I was having the same problem you are. FWIW, mine is dead quiet with AC heaters. I used Sowters.

 

[JayDubrek]

Thanks for the quick replies chaps!
SKJG Project- I noticed your request for VK1 parts in the Black Market...I've not had chance to see if Sowter are still making the trafos for this- have you tried them? I'm aware of 'dodgy' boards etc but it looks like a simple fix... I steer of PCBs for my tube projects and the VK1 is relatively straightforward. I'd be interested to hear how you get on with your build!

DMP- thanks for confirming my suspicions...I'll  pop a new regulator in with a bigger heatsink. I'd like to stick with the power trafo I've got so if I were to change this to AC heaters what's the easiest way to drop from 9VAC to 6.3VAC? Will this be why the heaters on the 12AT7's aren't on either, they're both new and connected correctly...hmmm!

 

[SKJGProject]

they are listed on the sowter page for 70 £ a piece so i think they are still available

 

[EvLoutonian]

i'm also part way through building one although i got one of the "faulty" purusha boards...the project is that much black listed that you won't even get support from the gurus even if you pretend to do it p2p (maybe it's true for you)

i already got some cheap ll1540 from ebay but will order the sowter outs because i asked the same questions like you and nobody wanted to help!

thx maarten for setting up this page otherwise there would be way more of unfinished units ;D ;D

http://www.tubefreak.com/varimu.htm

Was the faulty boards issue just about separately wiring the heaters on the bottom side of the board?
Or are there other issues to address on those PCB's?

 

[radardoug]

If you wire your heaters to 4 and 5 of the 12AT7, then they are only getting half voltage. Wire 4 and 5 together, and use 9 as the other terminal