Power Transformer

[taylorc315]

Hello,
I'm new at building amps and was wondering if any one could tell me the color code of a Hoffman 50 watt power transformer? I'm having trouble with the heater section and what and where the wires attach. there's blue,2 blacks one smaller gage, orange & brown that I have left. any info would be great.
Thanks
Tracy

[sluckey]

The little black wire is probably on the primary. The bigger black wire is probably one of the heater wires. Use your ohm meter to check for low resistance between the orange wire and a black wire. Whichever black wire shows low resistance is the correct heater wire.

Once you are sure which black wire belongs to the filament winding, the orange and black wires will become your filament string, and the brown (center tap) will usually connect to chassis. But if you are using a Hoffman board just tape off the brown wire and use the two 100Ω resistors on the board as an artificial center tap.

Page two of this pdf shows exactly how to connect all wires of the PT.

     http://el34world.com/Hoffman/files/Hoffman_Plexi50.pdf

[taylorc315]

This is great info.. there's a blue wire also is that the bias tap?

[sluckey]

This is great info.. there's a blue wire also is that the bias tap?

Look at page 2 again.

[taylorc315]

Ok sorry, I do have the blue hooked to the switch, the orange and black go to the board at the 100 resistors the smaller black goes to the filament which is?
Sorry I'm new at this and not the best schematics reader. I know that once I get this figured out (with help) I'll see the light.

Thank You
Tracy

[sluckey]

Did you use an ohm meter to check resistance like I suggested?

The smaller black wire is probably in the primary winding. Check for continuity between the small black wire and the blue wire to confirm this.

Now, if your mains AC voltage is 120V then connect the little black wire to the line cord white wire. Again, this is clearly shown on page two.

[taylorc315]

Thanks Again, I think that I have it, I will check everything when I get home. thanks for your patience and info.

[John]

I'm going to chime in and strongly suggest you build a lamp bulb limiter before you fire that transformer up the first time. Even as slap dash I can be about some things, I use mine religiously EVERY time I change anything. Especially if you're not dead sure you've got it wired right, that limiter will keep you from burning up the transformer. I put a 60W bulb in mine because I build mostly low watt amps. You'll probably need a 100W in yours.


And be careful, this is an addictive habit. 

[taylorc315]

Thank you. Yes the current limiter was the first thing I built, it already has saved me. I do have a question, the lamp in the unit I'm building is a neon lamp, it calls for 120v but the layout is calling for 6.3v I do see the hook up for the neon bulb but so far I have been struggling. I know it's right in front of me but the light switch has yet to switch on in my head. I will probably desolder everything and start from scratch. I am using a load station and plugging it into the speaker jack, is this correct? any info would greatly appreciated.

Thanks
Tracy

[sluckey]

Look at page 2 of this pdf again...

     http://el34world.com/Hoffman/files/Hoffman_Plexi50.pdf

One side of your neon lamp will connect to the blue wire at the on/off switch. The other side of your neon lamp will connect to the white wire of the power cord.

[taylorc315]

Thank You,
I have to be close, This is frustrating and exciting all at the same time. I really appreciate all of your input and sorry to say I will probably asking more questions.
Thanks Again
Tracy

[taylorc315]

What am I doing wrong? Everything looks good but for some reason the tubes will not heat up. Very frustrating.arrgghh

[John]

Well, this is probably the last thing you want to do (instead of actually working on your amp) but how about downloading ExpressSCH? It's a free download, pretty easy to learn, and it'll do a couple things. Learning how to read and draw schematics, IMO is crucial... maybe just because it's been such a huge help to me.


It will also let you draw your schematic "as built", the way you have your PT hooked up, and let us see where the problem is.


Anyway, to get back to this

What am I doing wrong? Everything looks good but for some reason the tubes will not heat up. Very frustrating.arrgghh

You've got your heaters wired wrong. They're so dead simple you'd think it's impossible, but I did just that on my current build. I hooked up the filament wires on the wrong side of the 100 ohm resistors that go to ground, and so gosh, they just wouldn't glow with about 2 volts going through them. (in case anyone wonders how on earth, I had the 2 resistors going to the humdinger pot for a "safety fuse"... one more duhhh moment for me)


Anyway, it's something simple. Don't get frustrated, it's all part of the fun!

[taylorc315]

Thank you very much.. Schematics are an Achilles heal for me, I will check out the download, If I have to I will start from scratch, like I said before this is exciting and frustrating all at the same time. Kind of like golf.

Thanks Again
Tracy 

[sluckey]

Do you have a meter?

[taylorc315]

Yes I have meters and oscilloscopes, it's got to be something simple that I'm just not seeing. :{ 

[sluckey]

Yes I have meters and oscilloscopes, it's got to be something simple that I'm just not seeing. :{

Does your neon lamp turn on and off with the power switch?

Check some AC voltages on the PT.  What do you measure BETWEEN the orange and black filament leads? What do you measure BETWEEN pin 2 and pin 7 of each EL34 tube socket?

[taylorc315]

I've got the tubes to light up. Yeah.yeah.yeah. yes the lamp turns on it seems that I've got that part of the problem solved. I've got 6.5 or so depending on the bias.. I have a couple of other issues that I have to check out. I think I need to go through the input jacks. If it ain't one thing it's another. I do appreciate all your help and input I'm sure that I will be asking more questions.  Thanks again for everything.

[sluckey]

I've got the tubes to light up.

What did you do?

[taylorc315]

I ran wires from the heater to 7&2 on the tube socket is that correct?

[taylorc315]

I decided to start from scratch, I was not happy with the way I had everything wired.trial and error I've found to be the best way for me. Thanks for all your help, I'm sure I will be asking more questions.

[taylorc315]

OK everything looks good, I have the brown wire taped off I still have the thinner black wire that has 110 v coming out of it can't find where it goes. Am I blind?

[sluckey]

Read this thread again.

[taylorc315]

The little black wire is in with the heater wires bundle it should be connected to the neutral side of power?

[taylorc315]

It looks like the black wire goes to ground... That's not right is it? That is a dead short right?

[sluckey]

READ THIS THREAD AGAIN.

You had it working at one time.

[taylorc315]

Yes I have the tubes lighting up, maybe I have more than one problem. like I said everything looks good now, but no sound from the amp:( I've double checked the input and output jacks they seem ok, I will continue to troubleshoot everything and hopefully find an issue. Thanks again

[sluckey]

Which amp you are building and who's layout are you following? Make some voltage measurements. AC voltages out of the PT, B+ voltages on each filter cap, and tube pin voltages. Post your voltage readings here. Post some hi-rez pics also.

[EL34]

Wiring diagrams are in the library for all the transformers I sell
The links are right next to every transformer on the page you were on when you ordered the transformer

http://hoffmanamps.com/MyStore/catalog/Transformers.htm

[taylorc315]

I will do that as soon as I get home, I am using the 50 plexi Hoffman layout thanks again for all your input I know it's probably frustrating believe me but I really do appreciate your help.

Thanks
Tracy

[EL34]

Wiring diagrams are in the library for all the transformers I sell
The links are right next to every transformer on the page you were on when you ordered the transformer

http://hoffmanamps.com/MyStore/catalog/Transformers.htm

By the way
There is no such thing as this

Hoffman 50 watt power transformer

Go to the page link above and find the transformer you have and follow the wiring diagram link

[taylorc315]

blue wire 110 volt AC. black wire 110 volt AC. Red wire number 1 317 volt AC. Red wire number to 290 volt AC. Large black wire 3.2 volts ac. Orange wire 3.2 volts AC. Brown wire 0 taped off send black wire 64 votes ac.power tube number 1 0 volts AC 0 volts DC pin number 2 3.2 volts ac zero volts DC.pin's 3-6 zero volts ac pin 3 -.929vdc pin 4 -.930vdc. Pin 5  -.656 vdc pin 6 -.645 vdc. Pin 7 has 3.2 vac zero volts DC. Pretty much the same for tube 2.... I am only getting 1 volt or so out of the filter caps, that don't seem right does it? I have all the preamp tube numbers if you want them,but I think we already have an issue with the filter caps. Thanks for your help

[sluckey]

Recheck your wiring. Time for some good hi-rez pics.

[taylorc315]

I will take them asap!

[taylorc315]

I'm having trouble attaching pics i will try to send from my phone to my computer and see if that will work. I'm trying to send from my phone and it's not working for me.

[Willabe]

Here's a couple of links with info on how to add attachments and how to shrink the size of pictures.

http://el34world.com/Forum/index.php?topic=4207.0

http://el34world.com/Forum/index.php?topic=464.0


                     Brad   

[taylorc315]

I know this is not the best, but I will get better at this stuff

[taylorc315]

More pics

[EL34]

Hard for me to see much in the pictures.
They are pretty tiny on my 23 inch onitors


They are 250 pixels wide
You can make your pictures 1024 pixels

[taylorc315]

I knocked them down to 250 in the pixel maybe to much?

[EL34]

1024 pixels is much better for everyone

[taylorc315]

Thank You

[taylorc315]

More Pics

[sluckey]

You just took your tiny pics and digitally blowed them up then resaved as jpg! That ain't hi rez. The big pics are even worse than the original tiny pics.

[taylorc315]

What do you suggest? I tried to load them without adjusting them but it wouldn't let me upload them.

[taylorc315]

Do you have a e-mail address that I could send the pictures to you?

[sluckey]

What do you suggest? I tried to load them without adjusting them but it wouldn't let me upload them.

I suggest you start with the original BIG pics and downsize them to an acceptable size for the forum. Never take a small pic and upsize it. Too much detail will be lost.

Even better, upload your BIG pics to one of the photo sharing sites and just post a link to the actual BIG pics.

[EL34]

What ever program you used to reduce the size must have let you set the size?


Just set the size down to 1024 pixels, not 250 pixels wide

[John]

Hi Taylor, not to overload you with advice, but if it were me I'd unhook all connections from that PT. If you know which 2 get hooked to the wall voltage, hook those up, let everything else free. Tape off the ends of all them except the ones you're going to measure with your voltmeter.


Then, using extreme caution and  alligator clips, take measurements of wires you think are pairs, like the secondary high voltage, etc. Hook up your test leads first, then apply power. With everything hooked up to filter caps and all that, it's pretty easy to get confused. Be very careful and look at everything twice before you throw the power switch on. Do not forget the "one hand behind your back" rule.


 I assume when you said Hoffman 50 watt, you meant this one, the Marshall 50 watt?


Another thing I think you may be doing, just by looking at your voltage measurements, is forgetting to switch between AC and DC reading on your meter. Hope this helps, stick with it, and be slow and careful!

[taylorc315]

Thanks John, I will do that also yes it is the Marshall 50 watt. yes I have been switching from ac to dc but I'm still learning where the dc volts are and where the ac volts should be. still studying the schematics slowly getting it. I will keep trying to get some pics loaded. and about the advice I need to be overloaded

Thanks