I just got a pair of 300B monoblocks, which each use a pair of 6sn7s as the input tubes.
My problem is my house AC is on the high side.
Powered them up yesterday, and checked some voltages.
The 6SN7's had 6.96 VAC across the heater wires, according to my meter, did not put a scope on the lines.
The 300B's had just under 6 VDC on the heater lines.
I know both numbers are high, am I going to burn out my tubes by running them like this?
So far, I only ran the amp for maybe 15 minutes like this.
I was thinking about getting the tentlabs filament supplies for the 300b's, with a seperate transformer for it.
For the 6SN7's, I was thinking about making a regulated DC heater. If I rectified the AC, I would end up with just under 10VDC, so I have about 3.5 volts of headroom, before the regulator.
B+ is 520 VDC.
One of the 6SN7's has 297 VDC from the plate to cathode, which seems like it's on the high side too.
One other unrelated issue. I tried driving the amp last night with a modifed squeezebox. The squeezebox has the DAC, a PCM1748 connected to the output via a coupling cap, with no op amps. I hooked it up to an old pair of speakers, and barely got any sound out of it. When it started to get to a somewhat reasonable volume, it would start distorting
This morning, I hooked up my portable player, a Rio Karma, with the headphone output going to the 300B input, and it sounded much better, more volume without the distortion.
So, I am either running out of current or voltage, but I have not figured out which one.
Any advice would be appreciated.
This is my first DHT SET amp.
Randy
My problem is my house AC is on the high side.
Powered them up yesterday, and checked some voltages.
The 6SN7's had 6.96 VAC across the heater wires, according to my meter, did not put a scope on the lines.
The 300B's had just under 6 VDC on the heater lines.
I know both numbers are high, am I going to burn out my tubes by running them like this?
So far, I only ran the amp for maybe 15 minutes like this.
I was thinking about getting the tentlabs filament supplies for the 300b's, with a seperate transformer for it.
For the 6SN7's, I was thinking about making a regulated DC heater. If I rectified the AC, I would end up with just under 10VDC, so I have about 3.5 volts of headroom, before the regulator.
B+ is 520 VDC.
One of the 6SN7's has 297 VDC from the plate to cathode, which seems like it's on the high side too.
One other unrelated issue. I tried driving the amp last night with a modifed squeezebox. The squeezebox has the DAC, a PCM1748 connected to the output via a coupling cap, with no op amps. I hooked it up to an old pair of speakers, and barely got any sound out of it. When it started to get to a somewhat reasonable volume, it would start distorting
This morning, I hooked up my portable player, a Rio Karma, with the headphone output going to the 300B input, and it sounded much better, more volume without the distortion.
So, I am either running out of current or voltage, but I have not figured out which one.
Any advice would be appreciated.
This is my first DHT SET amp.
Randy
randytsuch. quote: "I know both numbers are high, am I going to burn out my tubes by running them like this?"
Not immediately but tube life will be shortened. If you lower the filament supply by what ever method you still have the high HT to lower. Best solution would probably be to shave off some of the mains voltage and fix two problems at once. I suggest using a mains step down transformer.
Not immediately but tube life will be shortened. If you lower the filament supply by what ever method you still have the high HT to lower. Best solution would probably be to shave off some of the mains voltage and fix two problems at once. I suggest using a mains step down transformer.
Note that regulated DC supplies are not required for heaters (of course that depends on what you call regulated). All that matters is that the RMS voltage across the filament be stable at the rated voltage.
On using a transformer - better to avoid autotransformers - an "open neutral" problem as it is known can cause the full input voltage to appear at the output defeating the purpose of the transformer.
Another interesting fact - relative to the earth pin, the live and neutral are different for different countries. If yours is the "wrong" way and you are using a plug adapter, then the device sees the mains voltage between earth and neutral rather than earth and live (ouch) and it can instantly blow up any voltage stabilizer you put in the middle that is expecting earth to be at neutral potential!
On using a transformer - better to avoid autotransformers - an "open neutral" problem as it is known can cause the full input voltage to appear at the output defeating the purpose of the transformer.
Another interesting fact - relative to the earth pin, the live and neutral are different for different countries. If yours is the "wrong" way and you are using a plug adapter, then the device sees the mains voltage between earth and neutral rather than earth and live (ouch) and it can instantly blow up any voltage stabilizer you put in the middle that is expecting earth to be at neutral potential!
At first I had a brain fart, and could not figure out how to find the right transformer. Then I figured I just need to find one that would output 100V, for 110v input. Then, I found that hammond makes what I need, they even have multiple taps, something like the 168e, but they are not cheap either.fredex said:
So, I am going to start watching ebay, see if I can find something there.
Just put in new batteries a few weeks ago, thanks for the advice anyway.Jeff Yourison said:
Would that work for AC heating?rdf said:
For the DC heating for the 300b's, I am really leaning to get the tentlabs filament heater, even if I solve this problem another way.
Randy
I really think some of the solutions noted here are a "dirty" fix to a problem that should be fixed in a "proper" way.
Really...given that your mains voltage is prone to wandering, some of the fixes noted here won't deal with an opposite 'problem' that might crop up later.....a voltage sag.
Note that you are from Los Angeles USA...which has very good codes for proper wiring...here in Argentina we don't even have grounds wired up, and chassis grounds of all my gear here has a "biting" voltage floating about.
You really should have all voltages regulated...It's really easy to do, granted you will have to redesign/recalculate your PS but it will absolutely nail your intended voltages, get you a nearly pure Thevenin source, clean up any and all sources of hum and once in place you won't have to worry about it.
Use one 317 (TO220 case) for each 6SN7 and one each 317K (TO3 case) for the 300Bs. The 317Ks for the 300Bs of course won't have the voltage variation capacity that the heater filiments will, but they will suffice quite nicely.
________________________________________Rick..........
Really...given that your mains voltage is prone to wandering, some of the fixes noted here won't deal with an opposite 'problem' that might crop up later.....a voltage sag.
Note that you are from Los Angeles USA...which has very good codes for proper wiring...here in Argentina we don't even have grounds wired up, and chassis grounds of all my gear here has a "biting" voltage floating about.
You really should have all voltages regulated...It's really easy to do, granted you will have to redesign/recalculate your PS but it will absolutely nail your intended voltages, get you a nearly pure Thevenin source, clean up any and all sources of hum and once in place you won't have to worry about it.
Use one 317 (TO220 case) for each 6SN7 and one each 317K (TO3 case) for the 300Bs. The 317Ks for the 300Bs of course won't have the voltage variation capacity that the heater filiments will, but they will suffice quite nicely.
________________________________________Rick..........
Attachments
Randy..... do you have a schematic readily available for your amp?? Can we see?
I was just thinking how a regulator would deal with your B+ if it is tube rectifyed......the heaters would power up fully on switch on but the B+ will be ramping up and the HT regulators would be dropping out until they "Broke out" and HT would hit full on....need a schematic to sort this out.
Not a good idea to use the "existing" 6.3 VAC winding of the TX as the voltage would be too close to regulator 'drop-out' a 9VAC TX for a regulated heater would be much better....you could use that other winding for a 12VDC cooling fan however, 9VDC would make for a very quiet fan.
Jeez...I gotcha changing out everything don't I?
___________________________________Rick............
I was just thinking how a regulator would deal with your B+ if it is tube rectifyed......the heaters would power up fully on switch on but the B+ will be ramping up and the HT regulators would be dropping out until they "Broke out" and HT would hit full on....need a schematic to sort this out.
Not a good idea to use the "existing" 6.3 VAC winding of the TX as the voltage would be too close to regulator 'drop-out' a 9VAC TX for a regulated heater would be much better....you could use that other winding for a 12VDC cooling fan however, 9VDC would make for a very quiet fan.
Jeez...I gotcha changing out everything don't I?
___________________________________Rick............
For the 300B, I believe that even 5.3V is too much, given that the life of the valve will be reduced - by an amount that varies with the quality of the build.
Don't forget that at 6V the cold-filament inrush current will be dangerously high - may be enough of a jolt to cause mechanical damage. And since a very frequent failure mode of 300Bs is broken filament, you really don't want that!
It's an expensive valve, and the filament should be treated carefully, especially if you turn it on & off a lot. This duty is a long way from the original ON continuously duty found in telecom repeaters, where the 300B was first aimed.
DC heating with passive regulation does little for inrush, and requires a lot of filtering to sound acceptable. DC with IC regulator voltage control is usually worse than passive dc, unless a lot of time is spent with additional filtering. AC heating is worst for inrush, and is second-worst for sound (only unfiltered dc is worse). In fact - the way to tell if you are heating your DHTs properly, when you build a new amp, is to quickly compare the sound to ac heating from a separate 5V trafo. If your new design is not hugely better in every way within 10 seconds listening, you need to improve it!
Using current drive, like the Tentlabs is kindest treatment of the filament, and sounds dramatically better than ac or any kind of voltage controlled dc.
The increased lifetime of expensive 300Bs should easily payback the cost of the modules if you stick with DHTs.
and since this is DIY, why not build your own:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=38248&perpage=30&highlight=&pagenumber=2
Don't forget that at 6V the cold-filament inrush current will be dangerously high - may be enough of a jolt to cause mechanical damage. And since a very frequent failure mode of 300Bs is broken filament, you really don't want that!
It's an expensive valve, and the filament should be treated carefully, especially if you turn it on & off a lot. This duty is a long way from the original ON continuously duty found in telecom repeaters, where the 300B was first aimed.
DC heating with passive regulation does little for inrush, and requires a lot of filtering to sound acceptable. DC with IC regulator voltage control is usually worse than passive dc, unless a lot of time is spent with additional filtering. AC heating is worst for inrush, and is second-worst for sound (only unfiltered dc is worse). In fact - the way to tell if you are heating your DHTs properly, when you build a new amp, is to quickly compare the sound to ac heating from a separate 5V trafo. If your new design is not hugely better in every way within 10 seconds listening, you need to improve it!
Using current drive, like the Tentlabs is kindest treatment of the filament, and sounds dramatically better than ac or any kind of voltage controlled dc.
The increased lifetime of expensive 300Bs should easily payback the cost of the modules if you stick with DHTs.
and since this is DIY, why not build your own:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=38248&perpage=30&highlight=&pagenumber=2
Here's an even easier solution:
Take a filament transformer... anything with 5 amps secondary rating, or more.
Connect the primary across the voltage from the wall... with a wall cord.
Connect one lead of the secondary to one lead of the primary, and measure the voltage difference between the other secondary lead and the other primary lead. If the voltage is HIGHER than the wall voltage, REVERSE the secondary leads until the voltage is LOWER (and it should be by the voltage rating of the secondary of the transformer... i.e, if it's a 6.3 volt filament transformer, it should be lower by about 6.3 volts or so). Once you've done this, connect the second secondary lead to one side of an outlet socket, and the second primary lead to the other side of said outlet socket.
By doing this, you're creating a small bucking transformer... it would be easy to just mount this in a small box, with a line cord and an outlet socket mounted to the box. Then, if the voltage is high, plug it in... and if you ever have a day or a location where the voltage is NOT high, you can just unplug the box (and plug the amp directly into the wall)...
This would work for any low-voltage transformer... if you wanted to drop 12 volts, just use a 12 volt secondary transformer... and so on. And, this solution, unlike the resistor/coil/cap solution above, has the advantage of NOT adding unwanted extra impedance into the primary (which can impede bass response and dynamics)...
Regards,
Gordon.
Take a filament transformer... anything with 5 amps secondary rating, or more.
Connect the primary across the voltage from the wall... with a wall cord.
Connect one lead of the secondary to one lead of the primary, and measure the voltage difference between the other secondary lead and the other primary lead. If the voltage is HIGHER than the wall voltage, REVERSE the secondary leads until the voltage is LOWER (and it should be by the voltage rating of the secondary of the transformer... i.e, if it's a 6.3 volt filament transformer, it should be lower by about 6.3 volts or so). Once you've done this, connect the second secondary lead to one side of an outlet socket, and the second primary lead to the other side of said outlet socket.
By doing this, you're creating a small bucking transformer... it would be easy to just mount this in a small box, with a line cord and an outlet socket mounted to the box. Then, if the voltage is high, plug it in... and if you ever have a day or a location where the voltage is NOT high, you can just unplug the box (and plug the amp directly into the wall)...
This would work for any low-voltage transformer... if you wanted to drop 12 volts, just use a 12 volt secondary transformer... and so on. And, this solution, unlike the resistor/coil/cap solution above, has the advantage of NOT adding unwanted extra impedance into the primary (which can impede bass response and dynamics)...
Regards,
Gordon.
First off, thanks to everyone for the suggestions.
I was already doing some research here for heater circuits, so I know there are many opinions on heaters, and I see some of that in the responses.
I measured my AC line this morning, and it measured 122.1-122.6 VAC with my Fluke meter.
I don't think it fluctuates much during the day, but I will check it again at night to make sure. I would guess that this is still within code, although on the high side.
I do have the schematic, but this is a current production amp, so I don't think I can post it. The amp was bought as a project, with the understanding that I would need to put some effort in to make them work, and make them the same, so the schematic was also provided.
But, I think I can provide some circuit details.
It is diode rectified for the B+. As I already said, AC heaters for 2 6SN7 tubes, and DC heater for the 300B. It is a monoblock amp.
There is some room inside to add more things, I would prefer not to add stuff to the top. Inside bottom, I am limited to about 2 inches of height.
Rod
I ran across you design a few days ago, but I was not sure I wanted to tackle it. Looking again, I think I could do it, and it would be way cheaper than tentlabs. I may skip RT2, and put a CMC/cap filter in front of RT1 instead, mostly because of space.
Gordon
Thanks for that idea. It is would be relative cheap to try it.
Randy
I was already doing some research here for heater circuits, so I know there are many opinions on heaters, and I see some of that in the responses.
I measured my AC line this morning, and it measured 122.1-122.6 VAC with my Fluke meter.
I don't think it fluctuates much during the day, but I will check it again at night to make sure. I would guess that this is still within code, although on the high side.
I do have the schematic, but this is a current production amp, so I don't think I can post it. The amp was bought as a project, with the understanding that I would need to put some effort in to make them work, and make them the same, so the schematic was also provided.
But, I think I can provide some circuit details.
It is diode rectified for the B+. As I already said, AC heaters for 2 6SN7 tubes, and DC heater for the 300B. It is a monoblock amp.
There is some room inside to add more things, I would prefer not to add stuff to the top. Inside bottom, I am limited to about 2 inches of height.
Rod
I ran across you design a few days ago, but I was not sure I wanted to tackle it. Looking again, I think I could do it, and it would be way cheaper than tentlabs. I may skip RT2, and put a CMC/cap filter in front of RT1 instead, mostly because of space.
Gordon
Thanks for that idea. It is would be relative cheap to try it.
Randy
Agreed...we all seem to providing solutions for a problem that shouldn't be happening in the first place...IE line voltage variations.
First off what is the rated primary?....it would seem US ratings have been creeping up over the decades...look at the ratings over the years 110, 115, 120, 127...Who gets what?...is it regional??
What happens when one TX is set for say 110 and the utilities are cranking out 126.769 volts...where does that set the secondary on said TX?.
We have 222.7....tad high, note the one hand.
First off what is the rated primary?....it would seem US ratings have been creeping up over the decades...look at the ratings over the years 110, 115, 120, 127...Who gets what?...is it regional??
What happens when one TX is set for say 110 and the utilities are cranking out 126.769 volts...where does that set the secondary on said TX?.
We have 222.7....tad high, note the one hand.
Attachments
I read your post concering the 'highish' AC wall voltage. This is very common in today's power grid, to have 123 VAC to 125 VAC.
My solution to this problem, especially as I have about 1 dozen Vintage amplifiers and Preamps was as follows.
After building the Transcendent Sound Balanced Power unit, the AVEL toroid that was included in the kit caused an alarming 131 VAC when I loaded the unit with about 4 amperes.
Writing Transcendent, I received a dry recommendation to implement a 'bucking' transformer solution on the primary of the Balanced Power kit.
Not satisfied with a 'hardware-patch', I found the AVEL web site and purchased a toroid that was the next step down on the product line. The Y236954, that provides 55-0-55 balanced power on the secondary, vs 60-0-60 from the one included in the kit, which is the Y236959.
This replacement tamed the high AC voltage. I now get anywhere from 121 VAC (no load), down to about 117 VAC (close to full load).
It's a definite tube amp saver. Anyoned can put together this unit as it has few parts. I can draw up a schematic is you like that is different from the Transcendent but does the same thing.
In this manner you achieve full isolation from the wall outlet, balanced power operation and a reasonable control of that pesky 123 VAC making the tube amps run much more relaxed.
Currently I have an Aikido 6SN7 DIY preamp, a pair of Atmasphere M60's and assorted sources.
A higher quality toroid can be sourced from Plitron at about 2x the price if you prefer a potted center of the donut and slighty better performance. The AVEL works like a charm.
Let me know what you think.... Regards, Richard
My solution to this problem, especially as I have about 1 dozen Vintage amplifiers and Preamps was as follows.
After building the Transcendent Sound Balanced Power unit, the AVEL toroid that was included in the kit caused an alarming 131 VAC when I loaded the unit with about 4 amperes.
Writing Transcendent, I received a dry recommendation to implement a 'bucking' transformer solution on the primary of the Balanced Power kit.
Not satisfied with a 'hardware-patch', I found the AVEL web site and purchased a toroid that was the next step down on the product line. The Y236954, that provides 55-0-55 balanced power on the secondary, vs 60-0-60 from the one included in the kit, which is the Y236959.
This replacement tamed the high AC voltage. I now get anywhere from 121 VAC (no load), down to about 117 VAC (close to full load).
It's a definite tube amp saver. Anyoned can put together this unit as it has few parts. I can draw up a schematic is you like that is different from the Transcendent but does the same thing.
In this manner you achieve full isolation from the wall outlet, balanced power operation and a reasonable control of that pesky 123 VAC making the tube amps run much more relaxed.
Currently I have an Aikido 6SN7 DIY preamp, a pair of Atmasphere M60's and assorted sources.
A higher quality toroid can be sourced from Plitron at about 2x the price if you prefer a potted center of the donut and slighty better performance. The AVEL works like a charm.
Let me know what you think.... Regards, Richard
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