Bach on sparks!

[pentode]

There doesn't seem much interest in VTTCs here, only one thread, but...….

I've just built VTTC using 2 GU81 valves. 2 MOT's in parallel. Full wave rectification.
Sec coil 750 turns.
Getting a HV variable capacitor in order to  tune the primary.

Will be modulated to play Bach's Toccata and Fugue, not for organ but for sparks !

Have tested it with a 555 astable osc so far and it sounds OK.

[oneKone]

Welcome to the forum.

vttc have always interested me, hopefully one day i will get around to building one. Does yours follow a standard construction or is it your own design?

looking forward to seeing more of this coil.

[pentode]

Just cobbled together off the net.
Mostly here...….http://www.danyk.cz/vttc1_en.html
But added full wave smoothed EHT as I wanted a non mains frequency sounding spark.

I  made a SGTC recently, rather noisy so looked around for something quieter
and VTTC fitted the bill. 
I love big glowing valves, hence this new rig.

[Mads Barnkob]

Welcome to HVF!

What is your plate voltage?

Did you struggle with balancing feedback between the two tubes? I had quite some trouble to get two 811A tubes to share the load evenly.

I have built 2 VTTCs and got a QB5/2000 tetrode waiting for a future project

[pentode]

Mads, It's just over 2kv. DC
Glad to see someone is still into VTTCs....nothing to beat the glow of big valves.

The tank coil and cap not yet tuned. 
 I have not checked for any imbalance. Not sure I would know how to 

But I do have 100 w bulbs as the grid resistors for each valve and they both glow equal brightness
if that is any indication of balance?
A single feedback coil serves both valves.

I am using DC because I do not want any AC interference on the sound of the modulated spark.

The basis of my rig has been taken from here............
http://www.danyk.cz/vttc1_en.html

[Mads Barnkob]

Mads, It's just over 2kv. DC
Glad to see someone is still into VTTCs....nothing to beat the glow of big valves.

The tank coil and cap not yet tuned. 
 I have not checked for any imbalance. Not sure I would know how to 

But I do have 100 w bulbs as the grid resistors for each valve and they both glow equal brightness
if that is any indication of balance?
A single feedback coil serves both valves.

I am using DC because I do not want any AC interference on the sound of the modulated spark.

The basis of my rig has been taken from here............
http://www.danyk.cz/vttc1_en.html

Imbalance issues first started showing when I pushed the tubes near their voltage rating and here is the lovely thing with tubes, they dont explode in million pieces if you do something wrong, they just start to red plate a bit and if you are pushing it further you get orange spots in the plates and suddenly it melts or the glass melts.

I tapped the feedback coil so that one tube used 22 turns and the other 23 turns, that was the best way to share the load, at first I tried to change the resistors, but they are of-course not changing to the load, but the feedback coil voltage is

[pentode]

My GU81s will never be over run .  There is no need.  It's not spark length I am after
but good sound without AC interference.

Bach's Toccata and fugue will soon be sparking, after tuning the tank etc...….I hope.

Thanks for your comments.   Hope your anodes forever stay cherry red