Hoffman Bias Current Checker

[SoundCarver]

Hi,
Hopefuly a quick question. I built a bias current checker that will not read current (ma). I put it together using Dougs plan, with one difference. I used sheilded cable twin conducter and used the two wires instead of the braided shield and one wire . Could this be the problem? I am checking el34's into a Fluke 23
dmm set to 200ma. The amp is a Laney AOR 100 combo. Thanks for any help in advance.

[sluckey]

You can't use a dual banana plug with that meter to measure milliamps. You need individual banana jacks (or hacksaw that dual plug). Your bias checker must be plugged into the 300ma jack and the common jack on your meter.

Or, you could put a 1Ω resistor across the banana plug. Then plug it in just as if you were going to measure voltage. Set your meter to read milliVOLTS. The number of millivolts you read across the 1Ω resistor is also the same number of milliAMPS flowing thru the resistor.

[SoundCarver]

Thanks for the reply Sluckey. I should have mentioned that I did use individual banana plugs due to the configuration of the Fluke 23. I have also ohmed the connections to pin 8 all checks fine that's why I am baffeled as to what the problem could be.

[tubesornothing]

Using shielded cable or individual wires wont make a difference.  If you are not reading any current, but the amp still works, you probably have a short.  Measure the resistance between the two banana jacks, with the tester unplugged.  Should read very high or infinite ohms.  If it reads 0.2 ohms or something small, you have a short and will have to rebuild it.

ToN

[SoundCarver]

Thanks tubesornothing. I have checked the ohms they are infinity. I have checked every  problem that i know. I guess thats why it is so baffiling. Looking at the pin wiring configuration the #1 pin is wired to the #8 pin and then to ground.
I am not an expert only a novice but this seems strange to me. Maybe this is why the bias current checker is not working.

[sluckey]

EL34 typically has pins 1 and 8 tied together.
You should be able to play thru the amp with the bias checker/meter plugged in. Do you get normal sound?

Did you try bridging a 1Ω across the meter leads and checking milliVOLTS?

[SoundCarver]

Thanks sluckey. I can play through it and get normal sound (4 EL34's). I haven't tried the 1 ohm resistor yet (don't have one handy). I will try as soon as I can thanks.

[sluckey]

Do you have confidence in your meter? A simple test would be to connect a 9v battery, 300Ω resistor, and your meter in series. You should get about 30ma. Use whatever resistor value you have.

[SoundCarver]

Thanks sluckey. I performed the test you described. I did not have the 300ohm resistor but had another value and read 50ma on my meter.

[sluckey]

OK. Now check your bias dongle. Short the two banana plugs together. Then check for zero ohms from the female plug pin 1 to the male plug pin 1. Repeat for all 8 pins. All readings should be zero. Are they?

[SoundCarver]

 Thanks Sluckey . Yes, all pins check zero pin to pin with the banana plugs together.

[sluckey]

Should work. What are we missing? Got another meter?

Try this. Connect the dongle as if you were going to check bias but DON'T CONNECT BANANA PLUGS TO METER. Just leave the banana plugs open.

Can you play guitar and make a sound thru the amp like this?

[SoundCarver]

Thanks Sluckey. I disconnected the dongle from the meter and the guitar still plays trough the amp. I have also tried another DMM still does not work. I am truly baffeled by this. According to everything I have read this should work perfectly. I have tested every point #1-#8 the socket is wired correctly. A quick question has become a short story :)

[sluckey]

I disconnected the dongle from the meter and the guitar still plays trough the amp.

Well, that's just wrong! It can't be wired right. You have continuity from pin 8 to pin 8 somehow. You didn't tie pin 1 to pin 8 inside the dongle, did you? What's your shield connected to? Hopefully nothing.

Take it apart and look for the culprit.

[SoundCarver]

Thanks sluckey. I am looking at the bias checker connections right now #8 pin clockwise from the alignment pin same for the top. I can ohm the banana plugs and it indicates infinity zero. Could it be the design of the old Laney amps. this just doesn't make sense.

[rafe]

This may be stupid , but here goes....this is what you stated
"I am looking at the bias checker connections right now #8 pin clockwise from the alignment pin same for the top."
If that statement , that you made is literal .....then your connections are wrong ....They should mirror each other. one clockwise from indicator , one counterclockwise .....
I know you probably know that , but just in case
You also said
 "I can ohm the banana plugs and it indicates infinity zero"

That is a bit confusing too ...which is it infinity or 0

[jhadhar65]

I've got some questions just to be sure we're on the same sheet of music:

Did you build only one dongle?  I assume so since it sounds like you talk about it in singularity.

The AOR-100 is a four tube amp.  So, when you tested to see if the amp still played with the banana jacks disconnected, you had the dongle in one socket with a tube plugged into that, and then three other tubes simply in their respective sockets.  Is that right?

Now, when you built the dongle, did you use a socket for the female connections and a tube base for the male connections?

And are the female (socket) connections directly wired to their respective male (base) counter parts, except for Pin 8?  This means that Pin 1 socket is wired only to Pin 1 base, Pin 2 socket is wired only to Pin 2 base, etc.

Pin 8 should not be wired across like this, but rather one wire from your twisted pair lead should connect to the Pin 8 socket and the other should connect to Pin 8 base and their respective ends should terminate at individual banana plugs.  Is that what you have?  That's what it should be, but it seems that yours can't be like that.

Does the subject tube's heater light up when the dongle is in use and the amp's on?

With the dongle completely unplugged from everything at both ends (meter end and amp end), double check continuity between each dongle socket pin and it's respective base pin.  Each pin should read zero resistance from socket female to it's respective base male underneath, except for Pin 8.  So, you'd measure from female Pin 1 to male Pin 1, and repeat for each pin pair around the dongle.  The Pin 8 pair should read open or infinite.

Last question... what did you do with the shield?

[sluckey]

It's too simple for the grief you're having. Are you sure you don't have pins 1 and pins 8 confused? Looking into the male end of the dongle, pin 8 is CCW of the key notch and pin 1 is CW of the key notch. And, looking at the female end, pin 8 is CW of the key notch and pin 1 is CCW of the key notch.

If it's wired like this, it should work unless maybe you have some goofy EL34s that have pin 1 and 8 jumpered internal to the bulb.


Hoyt made some good points, especially about being able to play thru the amp with the meter disconnected.

[SoundCarver]

Thanks everyone for the input. OK here goes. looking from the top of the female socket, starting from the alignment pin going clockwise pin 1,2,3,4,5,6,7,8. Looking at the male socket from the bottom from the alignment pin going counterclockwise pin 1,2,3,4,5,6,7,8. If I ohm the banana plugs there isn't any resistance. Checking the pinouts 1-8 all check good indicating resistance. One wire connects to the top of pin 8 female, one wire connects through pin 8 male
soldered to the bottom of the pin. The shield wasn't used. I have built only one bias checker and my amp is a four tube model. When I use the bias checker the heater lights up on the tube it is being used on. The #8 pin does read open through the banana plugs. I am using standard el34 made by Ruby Tubes.

[rafe]

No    You need to look at the bottom of the female (where the connectors are ) you may have one or both backwards

If you look from the top of the female the first one clockwise would be #8 not #1

you look from the inside, the connection side.....is that what you did ?? and remember the male end is CCW from inside

[sluckey]

Thanks everyone for the input. OK here goes. looking from the top of the female socket, starting from the alignment pin going clockwise pin 1,2,3,4,5,6,7,8. Looking at the male socket from the bottom from the alignment pin going counterclockwise pin 1,2,3,4,5,6,7,8.

NO NO NO! That's backwards. You actually have the banana plugs connected to pin 1 on the tube.

[sluckey]

Well, now that you have a clue to the solution, have you fixed it? Please don't say you put epoxy in it!   :'(

[SoundCarver]

Hi Sluckey,
I took the unit apart and resoldered. You were correct, I had the #8 pins connection soldered to the #1 pin. The male base does no have numbers on it. I took an old el34 tube that does have numbers on it and compared. All is working fine now . Thanks for your help. This is the best forum on tube amps out in cyberspace.

                                                                               Soundcarver

[RicharD]

I am mildly dyslexic.  Thangs like this can be very frustrating for me.  To cope I usually use some sort of word association.  For tube-n-sockets, I use the phrase "counter top".

-Richard

[SoundCarver]

Gee Richard thanks for that helpful, somewhat insightful information.

Comment edited out by Tubenit

[tubesornothing]

The way I remember is that clockwise is normal for a tech.  The tube pins are always from the electronic technicians point of view - IOW soldering pins on a socket is 90% of our work.  So "normal" clockwise from the tech's point of view.  Rarely do I count pins on a tube, or play around with the top of a socket.  Its darn near always from underneath the socket.

ToN

[rafe]

It's all about visualization ! I have no advice on that, ( so please :-X) other than the old carpenters saying
"Measure twice , cut once."

Also on this board I have rarely seen any kind of insult , other than friendly banter between members that know each other. I'm sure it will remain this way!

[DummyLoad]

that was uncalled for.

glad to see you're having as much trouble with your silly little bias checker as your insulting nature suggests.

i use "clock bottom" to remember... i'm NOT dyslexic.

[RicharD]

Meh.....  I take no offense to his post.  Perhaps I'm as thick skinned as I am thick headed.  Someone has to be the village idiot and I've always been comfortable in that role.

-Richard

[Dynaflow]

 I'm a total 'tard' when it comes to 8 pin sockets, I eventually get it, but Gosh I sure like EL84's a lot better haha...

Regards,

Dyna

[jhadhar65]

I'll bet there was some sort of misunderstanding somewhere.  SC seems pretty polite and appreciative all the way through until that last post.  All of his eleven total posts are in this thread, so we don't know him yet anyway.  Since I've been a real bunghole before, you'd think I'd recognize one!  :-[  If I get that way again, hopefully one of you guys will come along and straighten me out right quick.

Regardless, 'countertop' is a pretty good memory word.  Now if I can just remember it when I need it...

[mick]

When in doubt about tube pin outs always reference the tube data sheets.   They will show the socket pin out.   It also helps to have a magnifying glass as some tube sockets are numbered. 

[jjasilli]

being dyslexic myself, I do appreciate that "counter-top" memory assistance.

I wouldn't criticize Buttery.  He really knows his stuff; is very helpful; and still has no qualms about seeking advice for his many inventive projects.

I think everybody wires something backwards once in a while.  You don't have to be dyslexic to do that. But it sure helps!  :D

[Greasehorse]

I'm a total 'tard' when it comes to 8 pin sockets, I eventually get it, but Gosh I sure like EL84's a lot better haha...

Regards,

Dyna

My vision not being what it used to be gives me a problem. I found some type of felt pin that was just right to wipe over the pin numbers on ceramic sockets but moved it and can't find it now...oh well...I wish my magnifying light had an LED adjustable spotlight on it for hard to see areas in an amp...like socket pin numbers, ect...

[madison]

I've screwed up more than once and wired pins wrong; pin one ends up being pin two etc.
I usually mark pin #1  socket base with a magic marker as a reference.

I learn things the hard way........no wonder my life has been a mess!

Word associations are great.
I use them often living over here in the Far East.

Buttery knows his stuff!

[bnchwrmr]

I'm new here and just saw for myself what quality
of character of heart the moderators and regulars
on this forum have....you did your best to smooth
out the "bump in the road" and not make things
worse with the negativity that I've heard about on
other forums. Thank you all for keeping this forum
a great place to learn from.
 The pin-out from an 8-pin DIP IC helps me to keep
tube sockets straight because they are so darn familiar
to me throughout the years.....both from the "IC socket"
point of view (top of tube socket), as well as the "PCB
foil" point of view (bottom of tube socket).

And my eyesight is bad from diabetes and from birth, too..
So I applaud anyone with any kind of handicap, big or small
who still pursues their dreams and goals in spite of them, or
even in the face of "uncalled-for" comments.

bnchwrmr