I just picked up a used Pignose G40 and it hums a lot. So I'm thinking of putting a rectifier on heater supply. But then I look at schematics of other amps and they are not using DC heater supplies and are quiet.
The heater wires are not twisted together, so I'm wondering if replacing them with a twisted pair will be sufficient in getting rid of the hum. Any opinions?
Thanks,
-FunkyE9th
DC vs AC heater supply
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skyboltone
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Re: DC vs AC heater supply
I've never looked in one so it's kinda hard to make a general statement. There are a variety of ways to fight hum. Some of them can be found on Randal Aiken's pages http://www.aikenamps.com/ check the tech info section. There is also a lot to be learned from the tech sections of any tube manual. You can also look at http://www.ax84.com/ The crazy thing about it is, with this bunch anyway, you may not get a direct answer because the focus here is on gettin' smartened up. That's what makes it so darn much fun. Be forwarned. It's addicive.
The short answers to your question though is 1) It's really tuff to get 6.3 VDC out of a 6.3VAC transformer winding. Not saying it can't be done but it's tough. You have diode losses and regulator losses that will drop too much voltage and you end up with about 5 volts on the filaments. Not quite enough. Check with a cat named Paulster (on the board here) from the UK, he can fix you up with a board that will do it for the preamp section. 2) There have been one zillion amps and radios and transmitters and preamps and other stuff made that work just fine off AC filaments. It's about lead dress as you've already discovered. So go ahead and twist them, either run them flat to the chassis or fly them above the sockets. Just make sure that they cross signal wires at 90 degrees. Don't let them run parallel to signal wires. Also, check to make sure your cathode capacitors are in good shape. An open one will cause hum as will one that has drifted way low. Hum can also originate in the main power supply if you've got bleed through on the main filter caps.
In other words, it's time to dive in deeper than you thought.
There you have it. My
1000th post
The short answers to your question though is 1) It's really tuff to get 6.3 VDC out of a 6.3VAC transformer winding. Not saying it can't be done but it's tough. You have diode losses and regulator losses that will drop too much voltage and you end up with about 5 volts on the filaments. Not quite enough. Check with a cat named Paulster (on the board here) from the UK, he can fix you up with a board that will do it for the preamp section. 2) There have been one zillion amps and radios and transmitters and preamps and other stuff made that work just fine off AC filaments. It's about lead dress as you've already discovered. So go ahead and twist them, either run them flat to the chassis or fly them above the sockets. Just make sure that they cross signal wires at 90 degrees. Don't let them run parallel to signal wires. Also, check to make sure your cathode capacitors are in good shape. An open one will cause hum as will one that has drifted way low. Hum can also originate in the main power supply if you've got bleed through on the main filter caps.
In other words, it's time to dive in deeper than you thought.
There you have it. My
1000th post
The Last of the World's Great Human Beings
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Seek immediate medical attention if you suddenly go either deaf or blind.
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Re: DC vs AC heater supply
Really depends on the gain you are using. For Vintage gain, AC heaters proper grounding and good tubes there is no reason to use DC heaters.
Should be pretty much silent.
You can also float the CT of the Heater center tap to 60~90 VDC this helps a lot and costs 2 resistors and a small cap.
Many preamp tubes have bad hum, so make sure you are not chasing your tail for the sake of a hum cured with a simple tube swap.
If you like gain and want to get rid of ALL low freq hum, you cant beat DC heaters. I would recommend 12.6VDC since you are running half the current and use an added transformer, and a regulator. You can float a 12V with a diode to get 12.5VDC. You dont need to run the Phase inverter on DC, just the other preamp tubes. Now this is brute force these days so for easier solution that can handle much more current.... for $25 you can get a switching Power supply from Digikey, and it is relatively small for what it is, requires no transformer, just hook it up to AC and you are off any running ! AC 100~240 supplys 12.6 VDC at 5.4A! 2"x4"x 1.25" again this is complete and turn key, no additional transformer or parts and has a trim adjuster so 12.6 is no problem. So my attitude is for $25.... why not !
Should be pretty much silent.
You can also float the CT of the Heater center tap to 60~90 VDC this helps a lot and costs 2 resistors and a small cap.
Many preamp tubes have bad hum, so make sure you are not chasing your tail for the sake of a hum cured with a simple tube swap.
If you like gain and want to get rid of ALL low freq hum, you cant beat DC heaters. I would recommend 12.6VDC since you are running half the current and use an added transformer, and a regulator. You can float a 12V with a diode to get 12.5VDC. You dont need to run the Phase inverter on DC, just the other preamp tubes. Now this is brute force these days so for easier solution that can handle much more current.... for $25 you can get a switching Power supply from Digikey, and it is relatively small for what it is, requires no transformer, just hook it up to AC and you are off any running ! AC 100~240 supplys 12.6 VDC at 5.4A! 2"x4"x 1.25" again this is complete and turn key, no additional transformer or parts and has a trim adjuster so 12.6 is no problem. So my attitude is for $25.... why not !
Last edited by drz400 on Wed Mar 12, 2008 6:45 pm, edited 1 time in total.
Re: DC vs AC heater supply
I must assume you can hear the hum with no guitar plugged in. Does the volume and tone controls affect the hum?
There are two types of hum. There is the low organ note type that comes from the raw line frequency and there is the buzz type that is two times the line frequency (usually). That comes from a bad filter cap or bad ground in the power supply or other possible causes. Many amps have a little of both.
Here's a simple test that works on most amps. Strum a cord and flip the standby switch to off. The volume should fade out over a period of a couple of seconds. If it doesn't, the test won't work. Turn the amp back on so you can hear the hum. Flip the standby off. Does the hum stop immediately or does it fade out? If it fades out, it's probably coming from the heater supply or as pointed out above, it could be a bad tube. If it stops immediately it's some other power supply issue, not the heater supply and/or wiring.
There are two types of hum. There is the low organ note type that comes from the raw line frequency and there is the buzz type that is two times the line frequency (usually). That comes from a bad filter cap or bad ground in the power supply or other possible causes. Many amps have a little of both.
Here's a simple test that works on most amps. Strum a cord and flip the standby switch to off. The volume should fade out over a period of a couple of seconds. If it doesn't, the test won't work. Turn the amp back on so you can hear the hum. Flip the standby off. Does the hum stop immediately or does it fade out? If it fades out, it's probably coming from the heater supply or as pointed out above, it could be a bad tube. If it stops immediately it's some other power supply issue, not the heater supply and/or wiring.
Re: DC vs AC heater supply
LOUDThud,
Yes I can hear the hum with no guitar plugged in. The amp has no standby switch, so can't do the test you suggested. One of my to do's is add a standby switch later.
Anyway, I did some tube swapping and it seems this piggy does not like Electroharmonix or Sovtek 12AX7s for V1. I put a generic Chinese 12AX7 and no hum. Need to look more into it...
drz400,
What do you mean by "You can also float the CT of the Heater center tap to 60~90 VDC this helps a lot and costs 2 resistors and a small cap". I'm a noob.
-FunkyE9th
Yes I can hear the hum with no guitar plugged in. The amp has no standby switch, so can't do the test you suggested. One of my to do's is add a standby switch later.
Anyway, I did some tube swapping and it seems this piggy does not like Electroharmonix or Sovtek 12AX7s for V1. I put a generic Chinese 12AX7 and no hum. Need to look more into it...
drz400,
What do you mean by "You can also float the CT of the Heater center tap to 60~90 VDC this helps a lot and costs 2 resistors and a small cap". I'm a noob.
-FunkyE9th
Re: DC vs AC heater supply
Drz400 might be talking about "standoff DC" as Kevin O'Conner puts it in his "TUT" books.
I have had some success creating a 6V3 DC supply by making a full-wave bridge and using a filter cap that's about 1500-2200uF (25V or 35V rating). At first I tried 200uF and was surpised that this amount of filtering didn't bring the voltage up much higher than the unfiltered 5V I was getting initially. I tried 2200uF next and that brought it up to about 6V9 DC. If you're still unhappy with the amount of hum you're getting, I think it's worth your effort to give the DC heater supply a try.
I have had some success creating a 6V3 DC supply by making a full-wave bridge and using a filter cap that's about 1500-2200uF (25V or 35V rating). At first I tried 200uF and was surpised that this amount of filtering didn't bring the voltage up much higher than the unfiltered 5V I was getting initially. I tried 2200uF next and that brought it up to about 6V9 DC. If you're still unhappy with the amount of hum you're getting, I think it's worth your effort to give the DC heater supply a try.
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Bernardduur
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Re: DC vs AC heater supply
I had a small discussion last night with a HiFi maniac (tube HiFi) and he claims that heating tubes on DC is poisoning tubes. They work but don't last as long as AC heated tubes and they sound worse.
Dunno if that is common good or new; he has a high standard when it comes to tubes
Dunno if that is common good or new; he has a high standard when it comes to tubes
Re: DC vs AC heater supply
On directly-heated cathodes I'd be inclined to agree, but I'd be very sceptical that it makes any noticeable difference to sound or longevity on indirectly-heated cathodes like we tend to use.Bernardduur wrote:I had a small discussion last night with a HiFi maniac (tube HiFi) and he claims that heating tubes on DC is poisoning tubes. They work but don't last as long as AC heated tubes and they sound worse.
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CaseyJones
- Posts: 856
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Re: DC vs AC heater supply
Let's back up a whole bunch of steps...
We all assume that a technical question is addressing an issue in the general area of the root cause. What if the actual problem isn't the amp at all?
Rule one of technical writing is to know your audience, that way you're not wasting an expert audience's time with unnecessary information or on the other end baffling beginners with material that's way over their heads. Stick that in yer wiki!
Without further preamble:
Is the ground really the ground? In my area we get amps in all the time where if they had a grounded plug to begin with someone has broken the ground lug off the cord to plug the amp into antiquated wiring. Next check, if a ground lug is present do a quick continuity check to make sure the ground is actually connected from the plug to the chassis, the ground pin is the first one to break internally when someone trips over the cord. Finally does your outlet ground to a water pipe in the basement like it's supposed to? Not sure? Bring the amp into the bathroom and plug into the ground fault protected outlet in there. Modern electrical codes stipulate that there must be a ground fault protected outlet in the kitchen and in the bathroom. If you have old wiring or flourescent lights you'll just have to hum along.
One of the latest things I see on eBay in hand built amps is "we stood the filaments up to eliminate any possibility of hum." You did, did you? Well Fender did that in the '60s probably because it was a production expedient not because it was a good idea. The usual theme in vintage mil-spec gear is to keep the filaments tight to the chassis and twist the wires. Just because some website wonder tells you that "standing up filaments elimates hum" doesn't mean it works. In some circuits standing up the filaments routes them right over the signal path on the circuit board due to space constraints. In that case standing the filaments up promotes the possibility of hum rather than eliminating it no matter what the current fad or glowing bullshit hype would lead you to believe.
KISS That stands for Keep It Simple, Stupid. Well it ain't simple and I ain't stupid but I can fake it! The simplest possible filament scheme is straight AC filaments with a center tap, virtual ground or a hum balance pot. 3.2 volts on either side of the ground isn't much. Regular old plain vanilla 6.3 volt AC filaments can be made to work with no audible hum. If you want to be a psycho about it crank the sensitivity of your scope way up and go ripple hunting.
We all assume that a technical question is addressing an issue in the general area of the root cause. What if the actual problem isn't the amp at all?
Rule one of technical writing is to know your audience, that way you're not wasting an expert audience's time with unnecessary information or on the other end baffling beginners with material that's way over their heads. Stick that in yer wiki!
Without further preamble:Is the ground really the ground? In my area we get amps in all the time where if they had a grounded plug to begin with someone has broken the ground lug off the cord to plug the amp into antiquated wiring. Next check, if a ground lug is present do a quick continuity check to make sure the ground is actually connected from the plug to the chassis, the ground pin is the first one to break internally when someone trips over the cord. Finally does your outlet ground to a water pipe in the basement like it's supposed to? Not sure? Bring the amp into the bathroom and plug into the ground fault protected outlet in there. Modern electrical codes stipulate that there must be a ground fault protected outlet in the kitchen and in the bathroom. If you have old wiring or flourescent lights you'll just have to hum along.
One of the latest things I see on eBay in hand built amps is "we stood the filaments up to eliminate any possibility of hum." You did, did you? Well Fender did that in the '60s probably because it was a production expedient not because it was a good idea. The usual theme in vintage mil-spec gear is to keep the filaments tight to the chassis and twist the wires. Just because some website wonder tells you that "standing up filaments elimates hum" doesn't mean it works. In some circuits standing up the filaments routes them right over the signal path on the circuit board due to space constraints. In that case standing the filaments up promotes the possibility of hum rather than eliminating it no matter what the current fad or glowing bullshit hype would lead you to believe.
KISS That stands for Keep It Simple, Stupid. Well it ain't simple and I ain't stupid but I can fake it!
The simplest possible filament scheme is straight AC filaments with a center tap, virtual ground or a hum balance pot. 3.2 volts on either side of the ground isn't much. Regular old plain vanilla 6.3 volt AC filaments can be made to work with no audible hum. If you want to be a psycho about it crank the sensitivity of your scope way up and go ripple hunting.That indicates to me that something may be wrong with your Sovteks. For diagnostic purposes it helps to have a tube set that's tested and certified as perfect. Nothing wastes time like chasin' a fault caused by a dud tube and assuming it's something else.FunkyE9th wrote:Anyway, I did some tube swapping and it seems this piggy does not like Electroharmonix or Sovtek 12AX7s for V1. I put a generic Chinese 12AX7 and no hum. Need to look more into it...
Re: DC vs AC heater supply
So even after putting the Chinese 12AX7, which brought the hum down significantly, I decided to replace all the heater wires and improve the grounding of the amp last night. I was up 'til 3AM doing this. The whole time I was wondering if I was wasting my time. But I figured it will be fun and will be a good learning experience. This is the most work I've done on an amp in one sitting.
So heres what I did...
1) I did not go DC on the heaters. Used twisted pair on the heater. 20AWG on the preamp tubes and 18AWG on the power tubes.
2) I lowered the heater voltage which was orginally at 7.5 when using a a 6V6s, 7.3 with a 6L6s. Now it's about 6.19 with a 6V6. This brought down the voltage down to 5.3 with a 6L6 though. Not so good, but I wanted to use convert the amp to 6V6 anyways...
3) Used 18AWG on the grounds.
4) The "virtual center tap" on the heater was originally grounded via the preamp ground. I cut traces and routed the ground into the chassis ground of power tube cathode.
5) The input jack ground wire was originally grounded directly onto the chassis and was also making contact with chassis via the sleeve. I routed the ground wire directly on onto the AC bypass cap ground of V1. It' still making contact via the sleeve. I did not have one of those isolated input jacks.
6) Oh and I added a trimpot for bias adjustment.
The Results:
The amp is dead quiet with the Master all the way up!!! It's significantly quiter compared to when I had the Chinese tubes in there. Now it's even useable with the noisy tube (i.e. the EH and Sovteks)I had earlier.
What did I leanrned:
I learned that I did not waste my time doing all this stuff! Though it might have been better if I did the changes one at a time to see which change gave me the most improvements.
I learned that I don't like working on small a chassis.
Thanks all!!!
-FunkyE9th
But I figured it will be fun and will be a good learning experience. This is the most work I've done on an amp in one sitting.So heres what I did...
1) I did not go DC on the heaters. Used twisted pair on the heater. 20AWG on the preamp tubes and 18AWG on the power tubes.
2) I lowered the heater voltage which was orginally at 7.5 when using a a 6V6s, 7.3 with a 6L6s. Now it's about 6.19 with a 6V6. This brought down the voltage down to 5.3 with a 6L6 though. Not so good, but I wanted to use convert the amp to 6V6 anyways...
3) Used 18AWG on the grounds.
4) The "virtual center tap" on the heater was originally grounded via the preamp ground. I cut traces and routed the ground into the chassis ground of power tube cathode.
5) The input jack ground wire was originally grounded directly onto the chassis and was also making contact with chassis via the sleeve. I routed the ground wire directly on onto the AC bypass cap ground of V1. It' still making contact via the sleeve. I did not have one of those isolated input jacks.
6) Oh and I added a trimpot for bias adjustment.
The Results:
The amp is dead quiet with the Master all the way up!!! It's significantly quiter compared to when I had the Chinese tubes in there. Now it's even useable with the noisy tube (i.e. the EH and Sovteks)I had earlier.
What did I leanrned:
I learned that I did not waste my time doing all this stuff! Though it might have been better if I did the changes one at a time to see which change gave me the most improvements.
I learned that I don't like working on small a chassis.
Thanks all!!!
-FunkyE9th
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skyboltone
- Posts: 2287
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Re: DC vs AC heater supply
How? Is there a voltage trim pot? I've read technical articles from the olden days on the effects of high voltage on filament/cathode life. Running 7 volts on filaments lowers tube life from 10,000 hours to a few hundred.FunkyE9th wrote:2) I lowered the heater voltage which was orginally at 7.5 when using a a 6V6s, 7.3 with a 6L6s. Now it's about 6.19 with a 6V6. This brought down the voltage down to 5.3 with a 6L6 though. Not so good, but I wanted to use convert the amp to 6V6 anyways...
-FunkyE9th
You really didn't need the #18 on the power tubes but if it dressed nice way to go.
Good on you anyway. See? You smartened us all up a little.
Dan
The Last of the World's Great Human Beings
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
Seek immediate medical attention if you suddenly go either deaf or blind.
If you put the Federal Government in charge of the Sahara Desert, in five years time there would be a shortage of sand.
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CaseyJones
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Re: DC vs AC heater supply
FunkyE9th wrote: 1) I did not go DC on the heaters. Used twisted pair on the heater. 20AWG on the preamp tubes and 18AWG on the power tubes.
2) I lowered the heater voltage which was orginally at 7.5 when using a a 6V6s, 7.3 with a 6L6s. Now it's about 6.19 with a 6V6. This brought down the voltage down to 5.3 with a 6L6 though. Not so good, but I wanted to use convert the amp to 6V6 anyways...
The Valve Junior nutcases know every Band-Aid fix in the book to make the wrong voltages into the right voltages, they stick power resistors inline to drop the filament voltage into the correct range. Me, I prefer minimum parts count and transformers that provide the correct voltages to begin with. It seems to be a waste to start with too much voltage and piss the excess away as heat. Make it work correctly from the get-go with less parts.skyboltone wrote:How? Is there a voltage trim pot? I've read technical articles from the olden days on the effects of high voltage on filament/cathode life. Running 7 volts on filaments lowers tube life from 10,000 hours to a few hundred.
Re: DC vs AC heater supply
For some reason the Pignose has high heater voltage, don't know why they did that. Here's good article that I found on how to lower the heater voltage... http://www.tubecad.com/july2000/ It worked like a charm!!!skyboltone wrote:How? Is there a voltage trim pot? I've read technical articles from the olden days on the effects of high voltage on filament/cathode life. Running 7 volts on filaments lowers tube life from 10,000 hours to a few hundred.FunkyE9th wrote:2) I lowered the heater voltage which was orginally at 7.5 when using a a 6V6s, 7.3 with a 6L6s. Now it's about 6.19 with a 6V6. This brought down the voltage down to 5.3 with a 6L6 though. Not so good, but I wanted to use convert the amp to 6V6 anyways...
-FunkyE9th
You really didn't need the #18 on the power tubes but if it dressed nice way to go.
Good on you anyway. See? You smartened us all up a little.
Dan
-FunkyE9th
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CaseyJones
- Posts: 856
- Joined: Fri Mar 17, 2006 1:29 pm
Re: DC vs AC heater supply
AFAIK: I don't know where it's built but it's an import. Same deal as the Valve Junior, they pulled a transformer off the shelf, used it, called it good enough.FunkyE9th wrote:For some reason the Pignose has high heater voltage, don't know why they did that. Here's good article that I found on how to lower the heater voltage...
Why resistors in the filament supply aren't such a great idea: The filament string usually connects straight to its own secondary on the transformer. It's a simple foolproof design, the filament windings are sturdier than the HT windings. Stick a couple resistors in there and you've added a couple more parts that can potentially fail.
Re: DC vs AC heater supply
I bought the amp as a learning platform. So I don't mind having to put a series resistor in there. If it fails, I'll just fix it again. My idea was to buy a cheap amp (got it used for $160) and play around with it and not really worry about frying it. I learned a lot this week from what I've done to this amp. Maybe some day I'll replace the PT.