But don't overlook the fact that with a properly designed DC supply, and that's what I'm talking about here, the regulation is excellent. My heaters get 6.3V every day. If line voltage drops 20 percent tomorrow, my heaters will get 6.3 volts.
Experiment time!
Ok...sounds like an experiment is in order....lets' run two 2A3s Output on regulated Dc and the other on AC......someone build an amp with this setup with two 6SN7 as drivers also with AC & DC........pretty funky, have it run on a radio station music , 24/7 and we might know the answer sometime next year OR.......Two thousand and ??
____________________________________Rick.................
Ok...sounds like an experiment is in order....lets' run two 2A3s Output on regulated Dc and the other on AC......someone build an amp with this setup with two 6SN7 as drivers also with AC & DC........pretty funky, have it run on a radio station music , 24/7 and we might know the answer sometime next year OR.......Two thousand and ??
____________________________________Rick.................
As a data point, I have been running both DC and AC heaters in various tube gear for about 40 years and have NEVER seen a single heater failure.
Data..
Sounds good enough for me!
AC or DC take your pick!
_____________________________________Rick...........
Sounds good enough for me!
AC or DC take your pick!
_____________________________________Rick...........
Cycline3 said:
Not always. Particularly with DHT's run well below their max current ratings. Also, most idht's are spec'd +/- 10% of the nominal value. So 6V for a 6.3 heater is not "starved".
http://members.aol.com/sbench102/dht.html
I have found that 801's in my amp have the best distortion profile (descending amplitude and lowered higher order harmonics) at around 6- 6.1 volts, as compared to the nominal 7.5V. Very stable so far.
Sheldon
There are a lot of terms used to describe the hum on the output of amplifiers but so far this thread contains just a single number: 4mV hum on the output for AC heating.
Here's another one for a DC heated 300B amp: 0.08mV (-82dBV) hum & noise on the output. Granted, I used a CRC filter and a VCCS but I think a level of hum this low would be impossible to achieve with AC heating.
Here's another one for a DC heated 300B amp: 0.08mV (-82dBV) hum & noise on the output. Granted, I used a CRC filter and a VCCS but I think a level of hum this low would be impossible to achieve with AC heating.
I know how to build well, but with very HE speakers, I find DC removes the last bit of hum. My house up north also has very vague mains; the voltage is dependent upon all sorts of factors, but my heaters are always at the correct voltage.
These next builds I'm going to try MJ's 6.3/4V standby using the regulators. DC adds some complexity and cost, but it's not exactly difficult to engineer a design well for these.
These next builds I'm going to try MJ's 6.3/4V standby using the regulators. DC adds some complexity and cost, but it's not exactly difficult to engineer a design well for these.
DC makes a build idiot proof - but at what cost.
All my amps, with the exception of my phono amp, use AC and are absolutely quiet with my sensitive system. I'm even thinking of trying AC on the phono amp. No DHT though. My headphone amp has a tiny bit of hum but i'm certain that is a wiring issue and could be eliminated if I was at all bothered by it,
I assisted a fellow member to eliminate hum from a 5687 preamp. He went DC on the heaters and the hum went away. I had built exactly the same design and used AC and there was no hum. The DC was masking an instability issue which hadn't been resolved. I urged the builder to carry on debugging and get rid of the DC. He rebuilt in the end.
I also choose to run all of my heaters slightly starved at 6V, no issues so far after a number of years of running.
Shoog
All my amps, with the exception of my phono amp, use AC and are absolutely quiet with my sensitive system. I'm even thinking of trying AC on the phono amp. No DHT though. My headphone amp has a tiny bit of hum but i'm certain that is a wiring issue and could be eliminated if I was at all bothered by it,
I assisted a fellow member to eliminate hum from a 5687 preamp. He went DC on the heaters and the hum went away. I had built exactly the same design and used AC and there was no hum. The DC was masking an instability issue which hadn't been resolved. I urged the builder to carry on debugging and get rid of the DC. He rebuilt in the end.
I also choose to run all of my heaters slightly starved at 6V, no issues so far after a number of years of running.
Shoog
Shoog said:
By using a DC heater supply on sensitive lo noise tube front ends, the AC hum-null pot often found across the AC 6.3V heater supply in many early amps can be removed. It makes it one component less to adjust.
Most of the problems of using DC are caused by unstable reggies and poor layouts. Sensible decoupling is obvious.
Morgan Jones does like DC heater supplies. browse p.361++ 3rd edit. Can't be wrong ....eh ?
richj
I have not build a tubeamp, yet...but have done some thinking, and due to unstable mains I suppose I would use regulated supply all the way
A little bit of money and some time. I almost always use seperate filament Tx's anyway.Shoog said:
I still don't see how a proper DC supply could do anything less than outperform an AC supply in this situation.
Also, if you have gone through the trouble of building an amp, why is building a regulated 6V supply so hard?
The best sounding tube amplifiers I have ever heard were the ones I spent years building, they all had tightly regulated DC supplies for all the heaters. They sounded awesome. They were also rated class "A" components by a leading magazine. My good friend that designed the circuits regulated all he could (our big monoblocks had 6 seperate regulated DC supplies in each one)....
I dunno, it just always seemed to work real good....
Also, if you have gone through the trouble of building an amp, why is building a regulated 6V supply so hard?
The best sounding tube amplifiers I have ever heard were the ones I spent years building, they all had tightly regulated DC supplies for all the heaters. They sounded awesome. They were also rated class "A" components by a leading magazine. My good friend that designed the circuits regulated all he could (our big monoblocks had 6 seperate regulated DC supplies in each one)....
I dunno, it just always seemed to work real good....
I have to admit that I am surprised by some of the old guys (Some I believe are mods even) that are asking for proof of the fact that DC causes heaters to fail earlier.
It makes me think of 2 things. 1. None of my DC operated equipment has failed. And 2. Every major tube manufacturer of the 20th century published DC will cause failures before the same tube with AC heater.
Who am I to argue? Some things you just accept and move on.
My point was, in a normal hi-fi amp, there is zero difference in hum levels, so why even bother with something that the tube manufacturers say can shorten tube life? And it's easier?
Now, point 2 I wanted to make is, I have fallen to the "need DC myth" and used DC at slightly undervoltage to power my filaments by rectifying the normal AC heater. It is single handedly one of the worst mistakes I have ever made. It made a huge difference in power and tone of my amps.
For most people, and especially newbies, AC out of the tranny is better than having to design and create an accurate and reliable 10A DC regulator.
Oh which reminds me of, aren't tube guys supposed to know that less is more? Again, if the problem doesn't need it as a solution, it's pointless. Move on...
It makes me think of 2 things. 1. None of my DC operated equipment has failed. And 2. Every major tube manufacturer of the 20th century published DC will cause failures before the same tube with AC heater.
Who am I to argue? Some things you just accept and move on.
My point was, in a normal hi-fi amp, there is zero difference in hum levels, so why even bother with something that the tube manufacturers say can shorten tube life? And it's easier?
Now, point 2 I wanted to make is, I have fallen to the "need DC myth" and used DC at slightly undervoltage to power my filaments by rectifying the normal AC heater. It is single handedly one of the worst mistakes I have ever made. It made a huge difference in power and tone of my amps.
For most people, and especially newbies, AC out of the tranny is better than having to design and create an accurate and reliable 10A DC regulator.
Oh which reminds me of, aren't tube guys supposed to know that less is more? Again, if the problem doesn't need it as a solution, it's pointless. Move on...
Please give me a reference for this. Just one from a major tube manufacturer will do, you don't have to cite "every" one.
I did two projects, one with DC heaters (6J5 -> 6SL7 LTP splitter -> 6SN7 grid drivers -> 807 PP finals) and another (6BQ7A cascoded LTP -> 6FQ7 grid driver -> 6BQ6GTB PP finals) with AC heating, including wiring the screen reg. heaters in parallel with the signal path VTs (all connected to a 6.3V secondary of the power xfmr) and got no noise problems with either scheme. Given the input sensitivity (~1.0Vp for both designs) it's looking like DC heater power is a waste of time, especially since I really didn't do anything uber special with the 6BQ6 amp, other than twist the heater leads, and pay attention to lead dress so's AC carrying lines were well away from signal-carrying lines.
I also made sure that both designs used semi-star grounding (i.e. all DC returns from the circuit boards to the DC neutral of the power supply by lead, and not the chassis). Get very little noise at the outputs, and basically the only way to see if they're on is if the heaters are glowing and the panel LEDs are lit.
DC maybe for ultra low level signals such as a front end for a SW xcvr, or something like a phono/mike/mag. pickup where your signal level is way down in the milli (or micro) volt level. Otherwise, no.
"I have to admit that I am surprised by some of the old guys (Some I believe are mods even) that are asking for proof of the fact that DC causes heaters to fail earlier."
Yeah, me too. Headlamps, tail lights, and every other light bulb in a car operates off DC, and these don't seem to burn out at a faster rate than AC powered bulbs. Perhaps it's the other way 'round. VT heaters don't operate anywhere as hot as a light bulb filament.
I also made sure that both designs used semi-star grounding (i.e. all DC returns from the circuit boards to the DC neutral of the power supply by lead, and not the chassis). Get very little noise at the outputs, and basically the only way to see if they're on is if the heaters are glowing and the panel LEDs are lit.
DC maybe for ultra low level signals such as a front end for a SW xcvr, or something like a phono/mike/mag. pickup where your signal level is way down in the milli (or micro) volt level. Otherwise, no.
"I have to admit that I am surprised by some of the old guys (Some I believe are mods even) that are asking for proof of the fact that DC causes heaters to fail earlier."
Yeah, me too. Headlamps, tail lights, and every other light bulb in a car operates off DC, and these don't seem to burn out at a faster rate than AC powered bulbs. Perhaps it's the other way 'round. VT heaters don't operate anywhere as hot as a light bulb filament.
I did a quick search of Langford-Smith fourth edition and came up with nothing. It is possible that there is some treatment of this subject hidden somewhere in there. I'm not about to read it cover to cover to find out, but nothing so far...
I should read more than just selected chapters of this book, though. It's the best book from the era when big R&D money was spent on tubes. Page 1196 treats causes of hum internal to the tube, for those who have it.
I'd also like to see some references. A quick glance at mine show no such comments I saw.Cycline3 said:
When you have very high eff speakers as I have/had, then it's far more noticeable than you'd imagine when compared to the common 90dB boxes.Cycline3 said:
There have been arguments for and against DC heating on this thread, but I did not see any comparison of the sound character of the two methods. I suspect there should be some sonic difference (less is more, as Cycline3 wrote) but has anybody done a direct comparison? I tend to believe DC heating with it added complexity, especially involving semiconductors and electrolytic capacitors _should_ sound inferior to AC heating, even if it is not directly in the signal path.
Miles Prower said:
45th year of tube stuff and haven't had a tube heater fail in normal use beit AC or DC. Even in TV's where notorious supply practises were used, tubes didn't always fail because of heater faults but sheer overworking and set being physically abused.
Anyone with electronics knowledge should be able to knock-up a very low noise 6.3V DC reggy either from discretes or i.c. Bear in ind, the cold resistance of a tungsten filament can easily 4x the current and knock out a pass transistor without current limiting.
My arguement for DC for low noise front ends is without doubt and there is no proof that DC ruins filaments. in fact a slightly slower warm up is beneficial.
richj
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