More Heater stuff -- trying DC Heaters: currently at 65 VDC?

[Mook]

So, I successfully wired my heaters in VAC using two 100R to fake the ground.    But, getting lots of hum.    Want to return to DC Heaters.    I did have DC Heaters, but I think it was done wrong.   

So, currently, I have both green wires from the Heater secondary (3.15V-0V both) wired to a bridge on the "S" poles.    I have the "-" pole of the bridge wired to ground, and I read 65 VDC off the "+" pole.

Is this correct?

If so, guess I need to drop the voltage with a resistor, but why is the voltage so high?        Shouldn't I be expecting 6.3 volts x 1.4 (for the diodes in the bridge) to be about 8.8 volts?

Thanks all.

Mook

[kagliostro]

65v DC seems really odd

if you have a transformer with CT (3.15v-0-3.15v) try connecting the CT to ground and the two extremities to the tube pin (for AC heater)

if you don't have a CT (0-6.3v) you can try with two 100R or 220R resistors (or an humdinger) as to have a virtual CT

but if you have a CT don't use the resistors for a virtual CT if you also connect the real CT to ground

if you want to go DC and you have a CT and you connect it to ground, you must rectify with only two diodes not a bridge

if you want to rectify using a bridge you must use it in junction with a winding that is without CT, if a CT is present you must not connect it to

ground if you use a full bridge and connect to ground the - (minus) of the bridge

K

[jjasilli]

Yes, you don't actually state whether there is a CT or not.  For a picture of what kaliostro is saying checkout the bottom of this page:  http://www.valvewizard.co.uk/heater.html

[Willabe]

Why do you think the hum is from the heaters?

There's lots of things that can cause hum in an amp. Wiring/lead dress, grounding, layout of circuit, placement of PT/OT/choke on chassis, noisy tube(s), etc.

To rule out the heaters as a hum source get a 6v lantern battery hook it up in place of the PT heater wind. (If you try this be very careful to tape off and safely stow the loose heater wires before you fire up the amp for testing.)

If the hum goes away it's the heaters, if it doesn't go away it's something else.

Most guys here who have tried this have found that it was not the heaters. Very few (if any?) have found it to be the heaters.


             Brad   

[Mook]

65v DC seems really odd

if you have a transformer with CT (3.15v-0-3.15v) try connecting the CT to ground and the two extremities to the tube pin (for AC heater)

if you don't have a CT (0-6.3v) you can try with two 100R or 220R resistors (or an humdinger) as to have a virtual CT

but if you have a CT don't use the resistors for a virtual CT if you also connect the real CT to ground

if you want to go DC and you have a CT and you connect it to ground, you must rectify with only two diodes not a bridge

if you want to rectify using a bridge you must use it in junction with a winding that is without CT, if a CT is present you must not connect it to

ground if you use a full bridge and connect to ground the - (minus) of the bridge

K

I am thinking the exact same thing.     I'll prolly use 2 100Rs and create a virtual ground and use 2 diodes, instead.


Thanks!

[Mook]

Why do you think the hum is from the heaters?

There's lots of things that can cause hum in an amp. Wiring/lead dress, grounding, layout of circuit, placement of PT/OT/choke on chassis, noisy tube(s), etc.

To rule out the heaters as a hum source get a 6v lantern battery hook it up in place of the PT heater wind. (If you try this be very careful to tape off and safely stow the loose heater wires before you fire up the amp for testing.)

If the hum goes away it's the heaters, if it doesn't go away it's something else.

Most guys here who have tried this have found that it was not the heaters. Very few (if any?) have found it to be the heaters.


             Brad   

in this case, it *is* the heaters as that's the ONLY thing I've changed on the amp.

I did have DC Heaters (or, what I think was DC heaters) working......at least, *something* was working.     I decided to try AC heaters, and got the hum.

[Willabe]

You also had a problem with the LED and a shorted wire from the 6.3acv twisted pair.

Between fixing the LED problem and changing from dc to ac heaters what wires did you move?

That might be the problem, heater wiring layout/lead dress.

And if this amp is the PSE amp they are pron to hum from to little B+ filtering.

Can you post any gut shot pictures so the guys can have a look? They might see something that your not at this time.


            Brad      

[kagliostro]

BTW have you DC elevated heaters or only DC heaters ?


65v could be in the case you have DC elevated heaters


K

[Mook]

BTW have you DC elevated heaters or only DC heaters ?


65v could be in the case you have DC elevated heaters


K

no, not elevated.    Was simply using both 3.15 windings to create 6.3 VAC and then using a bridge to try to get DC.

[Mook]

You also had a problem with the LED and a shorted wire from the 6.3acv twisted pair.

Between fixing the LED problem and changing from dc to ac heaters what wires did you move?

That might be the problem, heater wiring layout/lead dress.

And if this amp is the PSE amp they are pron to hum from to little B+ filtering.

Can you post any gut shot pictures so the guys can have a look? They might see something that your not at this time.


            Brad   

My problem with the short happened as I was switching from DC to AC heaters.     In other words, I created that short when I started the mod.



Before, however, instead of connecting the "-" to ground, I used it as the negative side of the heater run.      So, I had each 3.15V winding connected to the "S" poles of the bridge, then the 10,000 cap was connected to the "+" and "-" poles of the bridge and running the heaters off the respective "+" and "-" sides.

I was getting DC voltage, but it was high -- 8.5V.     And, since it didn't look like any DC Heater schematic I've found, I thought I did it wrong.

[kagliostro]

That is OK if you don't connect the CT to ground, you must connect only the minus of the bridge to ground if you want to use a bridge


(of course you must drop the excess in voltage using a resistor)


K

[Willabe]

No that's not what I'm trying to ask or say.

When redoing wiring in an amp often wires get moved, not intentionally, and that can cause hum in an other wise working amp circuit.

I'm trying to say I don't think that going from dc heaters to ac heaters, if wired up/laid out/lead dress done correctly, by itself would cause hum in a guitar amp.

Some preamp tubes have heater/cathode leakage and dc heaters can stop that, but changing the tube for another will fix it too.

I'm betting it's something else or even a few things that are causing the hum. Sometimes you find 1 thing and it reduces the hum somewhat, then you find another and reduce it a little more until you track them all down. 


                        Brad   

[sluckey]

So, currently, I have both green wires from the Heater secondary (3.15V-0V both) wired to a bridge on the "S" poles.    I have the "-" pole of the bridge wired to ground, and I read 65 VDC off the "+" pole.

What amp are you talking about? Need schematic.

[kagliostro]

Are you sure about 65v read ? May be it was 6.5v ?


K

[Mook]

Are you sure about 65v read ? May be it was 6.v ?


K

No, it was certainly 65 V DC.    Checked it twice.   

[Mook]

OK, so currently, I have it wired with CT to ground, and two diodes from the 2 3.15V taps.     

I get 7.1 VAC, which is what I expect.

But, at the joining of the two 4001 diodes, I get 3 VDC.


I don't get it.....

Mook

[Willabe]

Rectified dcv needs a filter cap to ground at the 2x diode junction or the meter will be fooled.

Pop in a 10uF or 20uF @25v or so for now and take a new reading. Doug uses a 4700 @25v for the filter cap on his 6.3acv wind rectified to dcv for his relay power supply (PSU).


              Brad   

[Mook]

Rectified dcv needs a filter cap to ground at the 2x diode junction or the meter will be fooled.

Pop in a 10uF or 20uF @25v or so for now and take a new reading. Doug uses a 4700 @25v for the filter cap on his 6.3acv wind rectified to dcv for his relay power supply (PSU).


              Brad   

Yes, I understand, and with a 10K uf  cap, I get about 4.4 VDC.....still way off of what I'm expecting!


Any other ideas?


Mook

[Willabe]

You might have it wired wrong or a bad diode or a bad solder connection or you might have damaged the PT 6.3 wind when you had it wired up wrong for the dcv heaters.

If your sure you have it wired up correctly, with diode banded end facing away from the heater leads and connected to the filter cap, then I'd; 

Start by unsoldering the 6.3 leads and measure them, 1 meter lead to 1 heater lead and the other meter lead to the other heater wire.

If good then I'd retouch the solder joints and swap the diodes. 


              Brad   

[kagliostro]

Where do you connect your voltage meter ?

with CT connected to ground and two diodes (full wave rectify) you must connect it to the junction of the two diodes with the cap and ground

look to the image on the middle



if you measure there and you have less than 8.*v try to change the capacitor with one other (may be the one you are using is damaged)

K

[Mook]

Where do you connect your voltage meter ?

with CT connected to ground and two diodes (full wave rectify) you must connect it to the junction of the two diodes with the cap and ground

look to the image on the middle



if you measure there and you have less than 8.*v try to change the capacitor with one other (may be the one you are using is damaged)

K

According to this, I am testing correctly.     I tried to measure the diodes, and they both test the same....so I'm thinking they are ok.

I've tried 2 caps, as well.     Same reading.


Like I said, I get 7.1 VAC just fine, and if I measure each side of the windings, I get 3.6VAC, which looks fine.

I've re-melted all solder connections.   

At the junction of those two diodes, I should be reading about 7-8 VDC, right?

After all, I'm using the exact same method for the B+!!!



I wonder if I should just take a tap off the B+?    What do you think?


Mook

[2deaf]

You need to use a bridge as in Kagliosto's figure (c) above.  Your current setup and figure (b) will give you half the voltage that you want.

[Willabe]

I wonder if I should just take a tap off the B+?    What do you think?

The PT B+ winding won't have enough extra current to support the 6.3dcv for the heaters.

Somethings wired wrong or since you get the right acv at the PT heater leads, changed filter caps the only thing left are the diodes. (yes I know you tested them.)

What amp are you talking about? Need schematic.

                 Brad       

[Willabe]

Your current setup and figure (b) will give you half the voltage that you want.

I think your wrong, he's saying he's wired up a full wave not a half wave.


                    Brad   

Edit; I am wrong, sorry 2deaf.
 

[Mook]

You might have it wired wrong or a bad diode or a bad solder connection or you might have damaged the PT 6.3 wind when you had it wired up wrong for the dcv heaters.

If your sure you have it wired up correctly, with diode banded end facing away from the heater leads and connected to the filter cap, then I'd; 

Start by unsoldering the 6.3 leads and measure them, 1 meter lead to 1 heater lead and the other meter lead to the other heater wire.

If good then I'd retouch the solder joints and swap the diodes. 


              Brad   

Here's deal (and a bit more back story):     I started working on this amp 6 years ago.   Then, I had to move, and packed it in a box.    2 weeks ago, I opened the box and decided to finish it.

Memory is starting to recall, and I remember having this EXACT same problem 6 years ago, which is why I ended up with what I had.     Both ends of the 3.15 VAC tap measure equal and good (testing at 3.2VAC when ON), but again, both taps measure good.   AND, when CT'ed I do get double that value - 7.1 VAC.

So, I add 2 diodes (and they are oriented correctly, with the banded end TOWARDS the voltage rail) and even with a 10KuF cap, I only get a little over 4VDC.

So, what I ended up with was this:    I used a bridge.    I did *not* CT the heater coils.    So, each end of the heater tap went to the "S" pole of the bridge, and again, no CT.    Then, I used the "+" and "-" poles of the bridge accordingly:    "+" went to the plus side of the cap and pins 4,5 of the heaters, and "-" went to the common side of the cap and pins 9.

It *did* work, and I was getting DC voltage, but too high!    I was getting 8.8 VDC!    So, that's when I decided I had done it wrong and started again.   

Perhaps I should just go back to the bridge diodes when it was working, add a resistor to tame the 8.8VDC and be done with it??


Thanks for all your help so far!!


Mook

[2deaf]

I think your wrong, he's saying he's wired up a full wave not a half wave.

I never said anything about half wave.

OK, so currently, I have it wired with CT to ground, and two diodes from the 2 3.15V taps

He also said it's wired like his B+.

[Mook]

You need to use a bridge as in Kagliosto's figure (c) above.  Your current setup and figure (b) will give you half the voltage that you want.

YES!    My original setup was very similar to (c) in the picture.   Except, my voltage was a bit over 8VDC....so I should add a resistor (R2 in the picture).

I think I'll just do this and call it a day.....


Mook

[Mook]

I think your wrong, he's saying he's wired up a full wave not a half wave.

I never said anything about half wave.

OK, so currently, I have it wired with CT to ground, and two diodes from the 2 3.15V taps

He also said it's wired like his B+.

It should be a full wave, but it's *acting* like a 1/2 wave.     With the 2 diodes, i'm only getting 1/2 the voltage I should be.....


Mook

[Willabe]

It *did* work, and I was getting DC voltage, but too high!    I was getting 8.8 VDC!    So, that's when I decided I had done it wrong and started again.

No, you said you were getting 65dcv's, it's in the threads title.

Perhaps I should just go back to the bridge diodes when it was working, add a resistor to tame the 8.8VDC and be done with it??

That is OK if you don't connect the CT to ground, you must connect only the minus of the bridge to ground if you want to use a bridge

(of course you must drop the excess in voltage using a resistor)
           
      K

And is this from the same amp?

Ok....got my LED problem worked out.    Seems one wire in my twisted pair was touching ground.

              Brad   

[2deaf]

It should be a full wave, but it's *acting* like a 1/2 wave.     With the 2 diodes, i'm only getting 1/2 the voltage I should be.....

It's full-wave and it is acting like it should.  Only half of the heater winding is being used at any given time just like your B+. 

[2deaf]

Except, my voltage was a bit over 8VDC..

It will probably drop down with a load on it.
 
1N4001 diodes are only good for 1 amp and it won't take much for you to exceed that.

[sluckey]

I add 2 diodes (and they are oriented correctly, with the banded end TOWARDS the voltage rail) and even with a 10KuF cap, I only get a little over 4VDC.

That's exactly what you should get with a two diode full wave rectifier. 1.414 x 3.15 = 4.45

...I used a bridge...It *did* work, and I was getting DC voltage, but too high!    I was getting 8.8 VDC!    So, that's when I decided I had done it wrong and started again.

And that's exactly what you should get with a full wave bridge. 1.414 x 6.3 = 8.9v

[Willabe]

Ok, I'm lost.   

Sluckey do you have the mooks quotes flip/flopped with you math?


              Brad   

[Mook]

It *did* work, and I was getting DC voltage, but too high!    I was getting 8.8 VDC!    So, that's when I decided I had done it wrong and started again.

No, you said you were getting 65dcv's, it's in the threads title.

Perhaps I should just go back to the bridge diodes when it was working, add a resistor to tame the 8.8VDC and be done with it??

That is OK if you don't connect the CT to ground, you must connect only the minus of the bridge to ground if you want to use a bridge

(of course you must drop the excess in voltage using a resistor)
           
      K

And is this from the same amp?

Ok....got my LED problem worked out.    Seems one wire in my twisted pair was touching ground.

              Brad   

I must admit, the 65V was somewhere in the *deconstruction* of what I had before......dunno what the circumstances were, but I did measure 65 V.   

I'm going to re-wire it like I had it before, and start all over.      I'll check in later today or tomorrow.


Mook

[sluckey]

Sluckey do you have the mooks quotes flip/flopped with you math?

Yes! My math was flipped. It's fixed now. Bet that added to the confusion. 

[Willabe]

Yes! My math was flipped. It's fixed now. Bet that added to the confusion. 

  Yes it did for me.


                Brad   

[Willabe]

@ 2deaf, I was wrong and edited my post to correct it, sorry.

            Brad   


(I think I need to change my light bulb.           )

[sluckey]

Mook threw us a dirty bone with that "and I read 65 VDC off the "+" pole." statement.

Here's an interesting statement from the valve wizard...

"A 6.3Vac transformer supply, after rectification and accounting for losses and diode drop, will yield about 6.5Vdc. You can of course adjust this to something closer to 6.3V with a dropping resistor, but this is rarely necessary. Another important thing to be aware of is that rectifying AC to DC in this way introduces a power-factor loss of about 0.5, which loads down the transformer more. In other words, to supply a heater with 300mA of DC the transformer actually has to deliver about 600mA of AC, So be careful not to overload the transformer. "

[Willabe]

Huh, that's good to know. Thanks.


             Brad   

[kagliostro]

I apologize, I was inattentive on my previous post

using the second option with CT and two diodes strarting from 3.15v-0-3.15v AC you have ~4.*v

the correct connection will be the third (on the bottom) with no CT and 4 diodes bridge with the minus of the bridge floating

however, if you have few AC current (the bare essentials) is to be applied what Sluckey says, you have a great loss in current

may be you can arrange the DC heater only for V1 or V1 & V2 only, leaving the rest of the amp AC





K

[mresistor]

Mook - how about a photograph or two? (A picture is worth a thousand words) And what amp is this?

[Mook]

Ok....I went down to Radio Shack and bought this 400V 4 Amp Bridge.    It's hot glued to the board.     Right now, I have the EL34s (2) and the pilot light running AC correctly, and i *am* getting 6.2 VDC between the "+" and "-" poles.....so....

as of now, I am having success.    I wonder if the bridge I was using before was defective?   

btw, I'm using the *exact* schematic that Kagliostro posted....

Mook

[Mook]

Welp......I've had limited success.

The amp is up and running again (albiet with lots of hum -- prolly due to re-routing the EL34 heaters)....BUT....

under load, the AC is 6.9 and the DC is 7.6



Mook

[Mook]

So, if I need to drop the voltage from 6.9 to 6.3 = .6volts and my entire current load is 4 amps, right?   (2 EL34s plus 3 12ax7)....



so, .6/4 = .15 resistor?     Is this correct??


Thanks!


Mook

[kagliostro]

To me .............. no

you must drop the DC voltage of 7.6v to 6.3v DC

so

1.3v DC of drop

you can achieve the result via resistors or using 2 diodes in series (each diode drop is ~0.7v)

K

[John]

If you're wanting to go from 6.9 to 6.3'ish AC, then 2 diodes on one filament wire, reverse parallel, will drop ~ .7 vac. Use the high current ones Doug sells, I think they're 5148s?. You need the reverse parallel because the current is alternating and needs that return path.


If you're wanting to drop the DC voltage, then K is correct, and they only have to point 1 way. (well, as far as I know anyway)


Hope this helps!
Hope I'm right, too! 

[Mook]

Cool!    Thanks, Guys!