Variacs

cantskienuf · 5th September 2006, 09:34 PM

I'm troubleshooting a new tube pre-amp that I just finished and am finding voltage after the diode bridge a bit high. It looks like my PS transformers are 115v input and my line voltage is 124v. Thinking about a Variac. I can get a 3-amp Staco from Mouser for $86 or a 5-amp Payne Engineering from Newark for $90. The Staco appears to be a traditional variable transformer, but the Payne calls itself a solid-state variable voltage control with a remote potentiometer that "replaces variable transformers." I'm looking at the 18TBP-1-5 product described somewhat at http://www.payneng.com/ptbp.htm . It has a curious note 4 which says "These controls are not recommended for use on inductive loads." Newark does some explanation of the device at http://www.newark.com/NewarkWebComme...D121/5773.html

Any idea just what this thing is and whether it would accomplish my goal?

Thanks
John

lndm · 5th September 2006, 11:38 PM

Could it be a glorified light dimmer? Hopefully it's not as noisy as one

Fortunately, there are other options for lowering your B+

tool49 · 6th September 2006, 12:31 AM

I have no clue about the solid state one, but the following one might be worth a look

http://www.mpja.com/directview.asp?product=15162+TR

It's good for almost 5A and is only 49.95USD

The next one up is good for almost 20A and is 104.95USD

http://www.mpja.com/directview.asp?product=15163+TR

Hope this helps!
*By the way I'm not affiliated with MPJA*
Sébastien

poobah · 6th September 2006, 01:54 AM

Probably should avoid that solid state gizmo... Your power supply already has a narrow conduction angle. Your PSU voltage may go from 50% to 100% just by turning the control from 4.5 to 5 (just as an example).

Is your overvoltage causing problems? Are there some resistors or perhaps inductors you could change to burn some voltage?

mrshow4u · 6th September 2006, 02:00 AM

I'd go Iron based. Smoov, simple, delicious

cantskienuf · 6th September 2006, 10:27 PM

After a little more reading, it appears that the electronic gizmo is comprised of something called a triac. I think that is somewhat akin to an overgrown dimmer, so is probably too noisy. Thanks for the tip Indm.

Poobah, I'm not sure if the overvoltage is causing me a problem. I'm using tube regulation for the B+ and the regulator is correcting the overvoltage to the desired amount, but I'm also starting my initial troubleshooting effort to find the source of an unacceptable distortion. I don't know if overworking the regulator is a source for the problem. A schematic for the PS is at http://www.diyaudio.com/forums/attac...amp=1051169517

If I tried to burn off some of the voltage, would it be best to do that before the diode bridge or after? Is it better to add resistance to AC or DC? Right now I'm reading about 405v at the 350V measurement point upstream from the 6CW5 tube. Recommendations appreciated. Now I'm leaning towards other than a variac, maybe an RC or LC insertion?

poobah · 6th September 2006, 10:35 PM

yeah... 405 instead of 350 seems a little hot. I'll look at your power supply...

Have you posted your amp schem as well? The best way to burn some voltage should probably consider how your amp "uses" current... SE PP etc...

poobah · 6th September 2006, 10:47 PM

You know, as long as you not over loading the EL86, or the cap immediately after the bridge you should be alright.

I am not an expert wth this type of regulator. It could be the extra Va-k affects the regulation... I doubt that is your distortion source though.

Are you getting the 305 (+/- 20V) VDC from circuit? If so, it is stable and quiet under load (music)?

cantskienuf · 6th September 2006, 11:07 PM

I did get the 305VDC, but I wasn't measuring it under load.

poobah · 6th September 2006, 11:11 PM

I would guess then that your distortion problem is coming from somewhere else. Do you have a scope?

BTW, the voltage issue may warrant digging into further. As long as the plate of the '86 is not glowing; you're OK for the now. Do you know your amps total current draw from the PSU?

SE or PP?

5th September 2006, 09:34 PM	#1
cantskienuf diyAudio Member Join Date: Dec 2003 Location: Denver, CO	Variacs I'm troubleshooting a new tube pre-amp that I just finished and am finding voltage after the diode bridge a bit high. It looks like my PS transformers are 115v input and my line voltage is 124v. Thinking about a Variac. I can get a 3-amp Staco from Mouser for $86 or a 5-amp Payne Engineering from Newark for $90. The Staco appears to be a traditional variable transformer, but the Payne calls itself a solid-state variable voltage control with a remote potentiometer that "replaces variable transformers." I'm looking at the 18TBP-1-5 product described somewhat at http://www.payneng.com/ptbp.htm . It has a curious note 4 which says "These controls are not recommended for use on inductive loads." Newark does some explanation of the device at http://www.newark.com/NewarkWebComme...D121/5773.html Any idea just what this thing is and whether it would accomplish my goal? Thanks John

6th September 2006, 02:00 AM	#5
mrshow4u diyAudio Member Join Date: Jul 2006	I'd go Iron based. Smoov, simple, delicious __________________ ".........These go to eleven"

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5th September 2006, 11:38 PM	#2
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Could it be a glorified light dimmer? Hopefully it's not as noisy as one Fortunately, there are other options for lowering your B+

6th September 2006, 12:31 AM	#3
tool49 diyAudio Member Join Date: Apr 2003 Location: Montreal	I have no clue about the solid state one, but the following one might be worth a look http://www.mpja.com/directview.asp?product=15162+TR It's good for almost 5A and is only 49.95USD The next one up is good for almost 20A and is 104.95USD http://www.mpja.com/directview.asp?product=15163+TR Hope this helps! By the way I'm not affiliated with MPJA Sébastien

6th September 2006, 01:54 AM	#4
poobah diyAudio Member Join Date: Nov 2005	Probably should avoid that solid state gizmo... Your power supply already has a narrow conduction angle. Your PSU voltage may go from 50% to 100% just by turning the control from 4.5 to 5 (just as an example). Is your overvoltage causing problems? Are there some resistors or perhaps inductors you could change to burn some voltage?

6th September 2006, 10:27 PM	#6
cantskienuf diyAudio Member Join Date: Dec 2003 Location: Denver, CO	After a little more reading, it appears that the electronic gizmo is comprised of something called a triac. I think that is somewhat akin to an overgrown dimmer, so is probably too noisy. Thanks for the tip Indm. Poobah, I'm not sure if the overvoltage is causing me a problem. I'm using tube regulation for the B+ and the regulator is correcting the overvoltage to the desired amount, but I'm also starting my initial troubleshooting effort to find the source of an unacceptable distortion. I don't know if overworking the regulator is a source for the problem. A schematic for the PS is at http://www.diyaudio.com/forums/attac...amp=1051169517 If I tried to burn off some of the voltage, would it be best to do that before the diode bridge or after? Is it better to add resistance to AC or DC? Right now I'm reading about 405v at the 350V measurement point upstream from the 6CW5 tube. Recommendations appreciated. Now I'm leaning towards other than a variac, maybe an RC or LC insertion?

6th September 2006, 10:35 PM	#7
poobah diyAudio Member Join Date: Nov 2005	yeah... 405 instead of 350 seems a little hot. I'll look at your power supply... Have you posted your amp schem as well? The best way to burn some voltage should probably consider how your amp "uses" current... SE PP etc...

6th September 2006, 10:47 PM	#8
poobah diyAudio Member Join Date: Nov 2005	You know, as long as you not over loading the EL86, or the cap immediately after the bridge you should be alright. I am not an expert wth this type of regulator. It could be the extra Va-k affects the regulation... I doubt that is your distortion source though. Are you getting the 305 (+/- 20V) VDC from circuit? If so, it is stable and quiet under load (music)?

6th September 2006, 11:07 PM	#9
cantskienuf diyAudio Member Join Date: Dec 2003 Location: Denver, CO	I did get the 305VDC, but I wasn't measuring it under load.

6th September 2006, 11:11 PM	#10
poobah diyAudio Member Join Date: Nov 2005	I would guess then that your distortion problem is coming from somewhere else. Do you have a scope? BTW, the voltage issue may warrant digging into further. As long as the plate of the '86 is not glowing; you're OK for the now. Do you know your amps total current draw from the PSU? SE or PP?