High voltage driver for AB2 operation GU81m tubes - Page 28

Alexontherocks · 13th August 2012, 12:46 PM

and his is exactly why I love this forum!

your input is much appreciated. I will send an email to epcos and ask.

What would you suggest as a more reliable approach? Tube based device maybe?

I need something which is available at a reasonable price.

Thanks!

FLT · 13th August 2012, 03:35 PM

Quote:

Originally Posted by Alexontherocks

Damage from the opt

Inviato dal mio GT-I9001 con Tapatalk 2

Maybe the sharp edges of the soldering joint are a starting point for
partial discharge and lead to the flashover.

regards

FLT · 13th August 2012, 03:41 PM

Quote:

Originally Posted by Alexontherocks

The Core is large and the transformer heavy. What would be an inexpensive way of dessicating and potting the OPT?

Thanks

Not inexpensive but the way transformer companys do it:

Drying in the oven, then put into a tank where vacuum is applied and
potted in this tank under vacuum...

regards

Alexontherocks · 13th August 2012, 04:10 PM

Isn't there a tube which could somehow replace the gdts?

Inviato dal mio GT-I9001 con Tapatalk 2

Alexontherocks · 16th August 2012, 08:53 AM

No ideas?

Are there an other, none tube, devices which might work better than gdts?

Inviato dal mio ASUS Transformer Pad TF300TG con Tapatalk 2

Alexontherocks · 2nd September 2012, 06:12 AM

What about using a high power thyratron operated so that the peak voltage across the opt exceeds maximum inverse voltage?

Something like this perhaps.... if i were to find a cheap lot could it be a solution?

http://www.ebay.com/itm/TG1-2-5-4-TG...item3a68ef134f

Inviato dal mio ASUS Transformer Pad TF300TG con Tapatalk 2

tubelab.com · 3rd September 2012, 02:23 PM

Alex,

Unfortunately a thyratron works much like a GDT, in fact it IS a GDT with a control grid. Once the gas inside the thyratron ionizes the only way to shut it off is to remove the plate voltage. There were some speciallized devices that could be shut off, but I don't remember any that could work at this power level.

I have thought about this issue quite a bit and I haven't got an answer.

I experimented with several ways to avoid frying the OPT in the case of operating an amplifier without a load. The worst case is a guitar amp operating at full crank when the speaker fails to an open.

I had best luck with GDT's, MOV devices and even Transorb diodes, but they were all attached to the secondary to clamp the voltage at about twice the expected maximum. These work on mid powered amps, but they just fry in a 300 watt guitar amp.

Your amp should have enough power to melt about any type of clamp device. Any device attached to the primary of the OPT will try to clamp the B+ which has enormous stored energy, and it will discharge that energy through the OPT.

Alexontherocks · 3rd September 2012, 03:23 PM

thanks for your post!

Unfortunately the fact that you haven't found a solution makes it almost impossible for me to stumble across one by myself.

I found a good lot of thyratrons (the model I linke to above). a hefty piece of glass!

My concern is that what i witnessed is not a random event (allbeit caused by an solvable issue) but may be related to the interaction between the amp and the huge inductance of the opt. If this is the case I think a solution may be required for the amp to reliably work in the future.

My though is the following:

two tg1 - 2,5/4 are placed across the opt primary section. The insulation for the opt will be upgraded to above 4kv. In case of a spike the reverse voltage barrier is punctured and the thyratron turns on. The problem would be how to turn the device off and remove the bypass.

I am trying to read as much as I can and found this..

http://www2.l-3com.com/edd/pdfs/crow...tionnote.6.pdf

seems an intteresting read.

Alexontherocks · 4th September 2012, 01:36 PM

What about a string of thyratron + resistor + ptc thermistor to rapidly quench the current draw and lift the clamp?

Inviato dal mio ASUS Transformer Pad TF300TG con Tapatalk 2

Alexontherocks · 5th September 2012, 08:53 PM

while waiting for opt repair, thyratron and some other stuff I have worked on the driver board.

I cannot measure beyond 390vpp as the scope clips so I connected the probe to the common cathodes of a single 6bl7 tube. Adjusting persistence and display i managed to get a clear view at the sine wave (while cranking the signal beyond the 390v barrier)

if ccs are set differently the peaks are not alligned to the voltage markers.

Unfortunately I cannot tell what vpp is produced but it *should be almost 430/450 vpp.

Sine was ok but square was bad.

without fb, high voltage swing and possibly a not high enough probe impedance this may be acceptable but it seems to me almost every anomaly one can find in a square wave test is infact there!

Observations?

3rd September 2012, 02:23 PM	#277
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	Alex, Unfortunately a thyratron works much like a GDT, in fact it IS a GDT with a control grid. Once the gas inside the thyratron ionizes the only way to shut it off is to remove the plate voltage. There were some speciallized devices that could be shut off, but I don't remember any that could work at this power level. I have thought about this issue quite a bit and I haven't got an answer. I experimented with several ways to avoid frying the OPT in the case of operating an amplifier without a load. The worst case is a guitar amp operating at full crank when the speaker fails to an open. I had best luck with GDT's, MOV devices and even Transorb diodes, but they were all attached to the secondary to clamp the voltage at about twice the expected maximum. These work on mid powered amps, but they just fry in a 300 watt guitar amp. Your amp should have enough power to melt about any type of clamp device. Any device attached to the primary of the OPT will try to clamp the B+ which has enormous stored energy, and it will discharge that energy through the OPT. __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
High Voltage BjT's for Pre-driver stages of High Power Amplifier - Overview	tiefbassuebertr	Solid State	38	30th May 2011 07:37 AM
Why high voltage Fets when low voltage types gives less distortion?	Circlomanen	Pass Labs	21	9th December 2009 09:43 PM
Wanted - High Power, High Voltage, Audio Frequency Transformer Manual.	kimbal	Tubes / Valves	4	11th May 2009 08:05 PM
A high voltage drive fully differential driver/op amp	Russ White	Pass Labs	21	18th July 2007 10:14 PM
gu81m	ik3ssj	Tubes / Valves	4	4th March 2007 03:41 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

13th August 2012, 12:46 PM	#271
Alexontherocks Account disabled at member's request Join Date: Jul 2009	and his is exactly why I love this forum! your input is much appreciated. I will send an email to epcos and ask. What would you suggest as a more reliable approach? Tube based device maybe? I need something which is available at a reasonable price. Thanks!

13th August 2012, 04:10 PM	#274
Alexontherocks Account disabled at member's request Join Date: Jul 2009	Isn't there a tube which could somehow replace the gdts? Inviato dal mio GT-I9001 con Tapatalk 2

16th August 2012, 08:53 AM	#275
Alexontherocks Account disabled at member's request Join Date: Jul 2009	No ideas? Are there an other, none tube, devices which might work better than gdts? Inviato dal mio ASUS Transformer Pad TF300TG con Tapatalk 2

2nd September 2012, 06:12 AM	#276
Alexontherocks Account disabled at member's request Join Date: Jul 2009	What about using a high power thyratron operated so that the peak voltage across the opt exceeds maximum inverse voltage? Something like this perhaps.... if i were to find a cheap lot could it be a solution? http://www.ebay.com/itm/TG1-2-5-4-TG...item3a68ef134f Inviato dal mio ASUS Transformer Pad TF300TG con Tapatalk 2

3rd September 2012, 03:23 PM	#278
Alexontherocks Account disabled at member's request Join Date: Jul 2009	thanks for your post! Unfortunately the fact that you haven't found a solution makes it almost impossible for me to stumble across one by myself. I found a good lot of thyratrons (the model I linke to above). a hefty piece of glass! My concern is that what i witnessed is not a random event (allbeit caused by an solvable issue) but may be related to the interaction between the amp and the huge inductance of the opt. If this is the case I think a solution may be required for the amp to reliably work in the future. My though is the following: two tg1 - 2,5/4 are placed across the opt primary section. The insulation for the opt will be upgraded to above 4kv. In case of a spike the reverse voltage barrier is punctured and the thyratron turns on. The problem would be how to turn the device off and remove the bypass. I am trying to read as much as I can and found this.. http://www2.l-3com.com/edd/pdfs/crow...tionnote.6.pdf seems an intteresting read.

4th September 2012, 01:36 PM	#279
Alexontherocks Account disabled at member's request Join Date: Jul 2009	What about a string of thyratron + resistor + ptc thermistor to rapidly quench the current draw and lift the clamp? Inviato dal mio ASUS Transformer Pad TF300TG con Tapatalk 2

5th September 2012, 08:53 PM	#280
Alexontherocks Account disabled at member's request Join Date: Jul 2009	while waiting for opt repair, thyratron and some other stuff I have worked on the driver board. I cannot measure beyond 390vpp as the scope clips so I connected the probe to the common cathodes of a single 6bl7 tube. Adjusting persistence and display i managed to get a clear view at the sine wave (while cranking the signal beyond the 390v barrier) if ccs are set differently the peaks are not alligned to the voltage markers. Unfortunately I cannot tell what vpp is produced but it *should be almost 430/450 vpp. Sine was ok but square was bad. without fb, high voltage swing and possibly a not high enough probe impedance this may be acceptable but it seems to me almost every anomaly one can find in a square wave test is infact there! Observations?