a.c. heaters

[emrr]

The cheap fix on a transformerless amp is:

1) hit a thrift store, buy a used hair dryer.  Not an antique; see below. 

2) cut the cord off as long as possible. It has a GFCI built into it.  Replace the amp cord with it. 

The reason for this route is that one can't really buy an affordable GFCI as a standalone product, you'd have to wire a box with an outlet.  Guys servicing old radios like this approach, as budget is usually low. 

Show me an electrician or electronics repair person who's never been shocked, and I'll say we've found someone in management, or a tech who hasn't done very much. 

 

[Kingston]

Show me an electrician or electronics repair person who's never been shocked, and I'll say we've found someone in management, or a tech who hasn't done very much.

But then, each time at least a professional electrician gets shocked they need to get checked: heart filmed for irregular beat and curve. There are even laws in some countries about this since its a professional hazard. Because these guys know each time is potentially lethal. You may not die on the spot, but in your sleep due to a very irregular one-shot pace maker.

Now tech repair guys might be different. The kind of gung ho attitude does shine through on this forum as well.

 

[CJ]

well, how many people die each year from electrocution?

500?

probably all were drunken electricians,

never heard of anybody getting zapped to death by a tube chassis,

cancer gets about 7 million a year, drunken drivers kill about 16,000 a year in the US,

i get zapped about once a week, for the last 40 years, at this point it is the least of my worries,

ever read anything by Dan Torres?
puts out amp kits, instruction manual is way overkill on safety, 5 pages of warnings and 1 page of instructions, he must have got zapped pretty good at one time,  you can keep a hand in your pocket if you are young, kill two birds with one stone,  ;D

now watch, tomorrow i will be convulsing on the carpet with a Music Man amp on top of me, 

 

[mjrippe]

Hopefully not, CJ!

I've had 120VAC across the chest exactly once and will never make that mistake again. 

Mostly I worry about high voltage DC in tube amps and always remembering to discharge caps.  But there are always those surprises - the Altec 322C limiter with high voltage across the meter, the Magna-Tech 31B transistor compressor with 145VDC on the heat sinks of the transistors, etc. 

While it is part of the job to work around these dangers, being cavalier about it is not conducive to our longevity.  As a wise man once said "Electricity is nice, just don't get any on you"!

Oh, and back on topic - AC heaters are fine if well implemented!

 

[Kingston]

I think this getting shocked as a badge of honor attitude may be a passing phase with historical roots in ye olde times. Lead paint and asbestos were common until quite recently.

We know better now. Well, some here do anyway.

Because in this thread alone shocks were used to "feel more alive" and their lack directly correlated with lack of experience. Thank goodness bus and taxi drivers don't feel this way with accidents, let alone airplane pilots! But I also understand CJ may wish to die with his boots on. Standing on firm ground.

 

[abbey road d enfer]

i get zapped about once a week, for the last 40 years

That explains everything...  ;D

 

[Gus]

When I built a tube microphone power supply the DC heater part is what I spent the most effort on.  When you get the noise down you can sometimes hear the diode turn on as low level ticks.  There are simple fixes for tube microphones with one heater.

 

[bluebird]

Sorry, didn't mean to offend Kingston. My comments may have been a bit irresponsible so I'll remove them. I'm really not a macho man, stupid maybe,

Just being a tech trying to connect with other techs by sharing experiences. You know just trying to be one of the guys…

So for younger dudes who aren't brain dead and close to the end anyhow…

Keep one hand in your pocket when working on live circuits!

Unplug your equipment and discharge all large filter caps with a low value resistor and some clip leads before you start soldering!

Voltage as low as 42V can be lethal!

Getting shocked IS NOT COOL!

we good?

 

[buildafriend]

I saw the best ball of plasma a few weeks ago.  - was about 1.5 inches when I tapped 120V Neutral to the earth pin. the size could have been wrong.. that was from the black orb it left in my vision. I'm not sure if an arc welder could have compared.  No more late night attempts at PSU configuring. Mains = have coffee first.

I think electricians are just more at risk. One guy I knew had a lady in a school turn the breaker back on on him. He had 240V burn a big black hole through his shoulder.

Glad I work in a TV production facility behind some quartz routers.

 

[shabtek]

getting off topic;
here is me disconnecting a ground on 'de-energized gear'
as bad as it gets in the hum department
one hand in pocket, insulated tool and distance is required

View My Video

 

[PRR]

> shocks, is this stray capacitance through the transformer or is this having to do with a hot chassis

Amp with one 6V6 is "surely" not literal hot-chassis.(*)

Your shocks may be the "small" stray capacitance in the PT.

Or it could be failed insulation in the PT.

WHY haven't you installed a proper modern 3-pin plug already??

You know you should.

It would divert stray-capacitance current.

If you have a hard-fault in the insulation (some people hardly notice straight 110), the 3rd-pin would blow a fuse and PROVE you have a problem. (Minor, since any Champ replacement PT will do the job.)

Hot-chassis guitar amps have tubes like 50L6, 50A6, 25L6, 35L6--- the two biggest tubes will be 25V-70V heater, the first two digits. While such a line-up "could" still be transformer isolated, the whole reason for such oddball voltages is so they (and you) can be strung-up directly across the 110V wall outlet.

CJ's toy is odd in that ONE of the tubes "is" transformer isolated heater. This is not even a half-assed attempt at Safety (maybe third-assed). I believe this type was made UnApproved as soon as UL could re-write their standards to keep-up with over-clever designers and marketers.

 

[PRR]

I still have nerve-damage in my finger 40 years after a tube-amp shock.

I am very glad it is my finger and not my heart or central nervous wiring.

Don't Get Shocked!! It is unpredictable, and can be permanent.




> each time at least a professional electrician gets shocked they need to get checked: heart filmed for irregular beat and curve.

I am quite sure no electrician within 200 miles of me gets-checked after each shock.

(I've had two EKGs and each time seemed to be the first time for the EKG tech. They certainly do not do a lot of EKGs, not like they had electricians coming in often.)

Even in states with more extensive regulations, I do not think it is common in the US in general electric work.

Does seem like a good idea. And in the near future we may be able to get an EKG with an iPad app, get a robot interpretation instantly and some low-paid yet qualified doctor to read the record within 48 hours. (One problem is that the robot-readers must err on the side of excess positives, scaring both patient and personal doctor.)


CJ does have a point. Electrocution is rare compared to other causes of death. But electrocution is incredibly preventable.


Remember that the White wire is not ground, and the green wire is not ground either. (At my house I always have several Volts from wiring to dirt/concrete, and I have seen more around an unsuspected fault.) While several volts is not lethal through skin, it can throw enough current through a finger-ring to burn your flesh to the bone.

 

[CJ]

if you use AC heaters, you can try to cancel any residual hum by injecting hum on purpose, or by swapping tube heater pins, and fun stuff like that,

you can practice safety but accidents will still happen, so we use damage control techniques, which can be learned by experience, unfortunately, experience comes after you need it,

being an electronics teacher in the old days must have been stressful, 35 high school students playing with high voltage Heathkits all day long, year after year, playing tricks on each other like leaving charged caps on the bench for the next class, that was a two week suspension if you got caught,

had a drunken TV shop boss back in 72, used to scream loud when he got hooked up to 30,000 volts from the anode supply on a 25" Zenith,

do they still use electro-shock treatment today? putting high voltage on somebody's brain on purpose, seems kind of weird, and why pay for it when you can do it yourself? 

 

[DerEber]

Do any people care of wiring all heaters of a unit from the same side of the tansformer tap on each tube?
I thought about this a while ago.

Usually one is having a pair of twisted wires of the same color and randomly connect them.
Now as I think of it, it seems to me that in some (maybe rare) cases it could be also benificial to run heater current in antiphase. E.g. push-pull pairs.
On the other hand randomly connection and a pot to ground should lead to a random good results.
If it´s working fine in countless desingns it´s maybe piontless to discuss. It´s just what pops up in my head.

I also wounder about DC tube mic heater supplys. I often see heater ground and signal ground bound together for sharing the same wire in the Mic cable. This is not what I´d do by intuition.
I haven´t thought about this in greater lengh, but I need to build a Tube mike PS soon.
So my mind is slowly preparing  ;D

Gus: If I understood you right you encountered diode switching noise issues in your tube-mic work
Did in your experience this noise find this way in the audio rather over the power transformer or due to the regulation...... Or one of the other ways one could imagine.

Getting zapped in the US...... we are having double Mains Voltage here
Lately worked on an tube amp with 550V B+.
I was super carefull.
I installed one new wire and the wire insulation zapped through to chassis......
Always gaining new experiences

 

[Dr Gris]

Do any people care of wiring all heaters of a unit from the same side of the tansformer tap on each tube?
I thought about this a while ago.

I have a silverface bassman as a mod plattform. The original heater wiring was sloppy so I redid it and
made sure that one wire went to pin 7 of both the power tubes, then on to all pin 9 on the preamp tubes.
And the wire from pin 2 of the power tubes to pin 4&5 on the preamp tubes.
This was not the case when I first checked the wiring. I also dumped the hum balance pot and put two 100 ohm resistors as a center tap insted.
The amp became more quiet after that but I also replaced all elyt caps at the same time and that could also be a reason for it to hum less...

Cheers
//M

 

[CJ]

got zapped three times today, Marshall JCM 900,

500 volts the hard way, attached bleeder resistor to HV caps, but ground wire from cap to ground was broken, thus, bleeder does not bleed, only me, 

never know how you are going to get it, voltmeter would do no good measuring from chassis to cap, so measure across the cap itself,

 

[abbey road d enfer]

Do any people care of wiring all heaters of a unit from the same side of the tansformer tap on each tube?
I thought about this a while ago.

Usually one is having a pair of twisted wires of the same color and randomly connect them.
Now as I think of it, it seems to me that in some (maybe rare) cases it could be also benificial to run heater current in antiphase. E.g. push-pull pairs.

Push-pull pairs is precisely the case where wiring heaters in-phase is beneficial, because it is a common-mode signal, which is actually cancelled in the push-pull operation.

On the other hand randomly connection and a pot to ground should lead to a random good results.

That is not a valid concept, because most of the noise performance of any unit is dependant on the first (input) stage.

 

[Brian Roth]

FWIW....been working on a Drip "forty seven" build recently.  The Kit came in several years ago, but just getting around to working with it.

I had to rotate the Hammond power xfmr to "null some hum", but still unacceptable hum noise floor,

On a Whim, I connected my variable voltage DC supply onto the filament leads, and essentially ALL hum went away.

Sooooo...I did a Sim with the Duncan PSU app to see what I could do with the "6 Volt" heater winding.

Schottkey diodes and "two pi" filters.  Looks good in the Sim.  Mouser parts are on the way.


Bri

 

[kambo]

DC heater is way easy... 4 diodes, 2 caps, and a 25. no hum, no noise. great but no fun.
AC heater is fun to mess and experiment  with

 

[abbey road d enfer]

FWIW....been working on a Drip "forty seven" build recently.  The Kit came in several years ago, but just getting around to working with it.

I had to rotate the Hammond power xfmr to "null some hum", but still unacceptable hum noise floor,

On a Whim, I connected my variable voltage DC supply onto the filament leads, and essentially ALL hum went away.

Sooooo...I did a Sim with the Duncan PSU app to see what I could do with the "6 Volt" heater winding.

Schottkey diodes and "two pi" filters.  Looks good in the Sim.  Mouser parts are on the way.


Bri

That is quite surprizing, since the REDD47 was originally on AC heaters. Are you sure that the heater supply does not interfere with the audio ground?
The various descriptions of "improvements" on the Drip site make me wonder if they really know what they're doing with "grounds".