1967 Bandmaster AB763 Rebuild Log

[dbishopbliss]

I shared some of this information in other posts, but since I have started my build I thought it might be helpful to people in the future to keep a log of my project.

I originally bought my bandmaster head around 1992.  I had never done any electronics before and probably should never have even tried, but I was young and stupid.  I read an article in Guitar Player magazine about someone modifying an old Fender and thought I would try.  I immediately realized that I didn't know what I was doing so instead of giving up, I bought some "mod kits" from a dealer that is still in business today.  I won't name any names because when I do people generally have negative reactions.

I tried to modify the amp so that it would use EL34 tubes, have a master volume, an extra gain stage and a "brown sound" tone stack (whatever that means).  In the end, I ended up with an amp that I could only play while standing on a rubber mat without getting shocked.  I lost interest and it went into the basement.

Years later, I started building audio amplifiers.  I have built a number of single ended 2A3, and 300B amps.  I designed my own SE6V6 amp as well as a preamp.  All of these amps were built using tags strips.  While cleaning out the basement I came across the old bandmaster.  I figured it was time to bring this thing back to life.

[dbishopbliss]

While researching the best way to restore this amp, I came across some sites that sold replacement eyelet boards as well as boards with turrets. This lead me to another site that sold Hoffman AB763 boards. This reminded me that I bought some turrets and a staking tool from Doug around 10 years ago, but never actually used them.  After doing some more reading I decided that I would use Doug's layout or at least something similar. 

The first problem is the two channel Hoffman board is too wide to fit in the Bandmaster.  This is because the Bandmaster does not have reverb.  The second problem is board was designed for different size parts than those that I wanted to use.  I have a bunch of the blue molded capacitors originally used in Fender amps but the leads are of varying length so I'm not sure I could get them to easily fit.  In the end, I decided to go with Mallory 150 capacitors instead but regardless, I decided to adjust the spacing on the Hoffman board to fit the larger parts I was using.

[dbishopbliss]

While I'm at it, I may as well post the schematic I'm using as well.  I redrew the schematic using a font that is similar to the font that Fender used on their originals.  It is actually a font based on antique legal documents, but it looks almost exactly like Fenders.  I modified the schematic to include the same Tremolo/Vibrato circuit that Doug included in his AB763 board.  In addition, I decided to make Channel 1 use values from a Tweed era circuit rather than the Blackface era.  This will give me some variety.  I assume my schematic is correct and will work, but I'm not a designer so I may have missed something.  I will have to let you know when I finish my build.

[dbishopbliss]

I used the Turret Board Design Program to make my own board.  This was very easy to use.  I did follow Doug's instructions and printed out the scale turret board template.  I then entered my holes, and printed out the board I designed and re-checked that I had all the holes I intended.  I then checked it again.  In the end, I still forgot two holes, but they were for the standoffs so no big deal.

One thing I discovered is that the holes I included for the standoffs were too small so I had to enlarge them.  For some reason I thought the board material was going to be much more difficult to drill through, but it was very easy.  It took about 2 seconds with a hand drill.  After enlarging the standoff holes I placed the board in my chassis and used it as a guide for drilling holes in the chassis.  Again, this was easier than I expected.  I used the drill bits I had in my garage (Dewalt) and an electric hand drill (Ryobi).

Because my board includes holes that will not contain turrets I decided to mark the holes to make it easier when installing the turrets.

[dbishopbliss]

After marking the holes I installed the turrets using the Press Method Two.  Actually, I started using the first method, but this was a lot of work.  Load the turret into the bottom tool, line up the board (which was hard to do since I could not see my mark), pull the drill press handle, remove the board, repeat.

Method two is much easier. I recommend getting a stool or something so that your view of the drill press looks like the photo below.  This way I was able to easily see the turret and line it up with the bottom of the staking tool.  I installed the turrets one row at a time going down the length of the board so all I had to do was press then move the board to the left, then press, then move to the left, repeat.



My board has around 100 turrets and I was able to get them all installed in about 20 minutes.  It is certainly easy enough that anybody can do it. 

[plexi50]

I think photos and documentation is as rewarding as building an amp itself. Looks great

[dbishopbliss]

I laced together the various turrets, and busses last night.  So far, this has been the most difficult task.  Not really hard, but a little frustrating.  I had in my mind that the laces would be perfectly straight and perfectly level.  In reality they are sort of straight and not level at all.  Of course, you can't really tell that they aren't level when viewing from above.  In practice it won't matter at all.  I checked continuity on all the connections and there are no issues.  I didn't really expect any, but I thought just maybe one of the wraps wouldn't be tight enough or something.

The trickiest part of lacing the turrets (for me) was getting the wire to stay taut.  At first, when I laced a turret it would seem taut, but then when I pushed the wire down it would loosen up.  The technique I found that worked for me was to wrap almost all the way around the first turret.  Then I pulled the wire as straight as possible and around the next turret.  This I had to do in stages because I would pull, then lift to get over a nearby turret, then press the wire down, then lift over another nearby turret, the press down, repeat.  If I simply tried to wrap around the turret there was a lot of slack so the mechanical connection was not as good. 

For the last lace, I picked up the board and rotated it rather than keeping it in one place and moving the wire around.  I think this actually worked better but its hard to say because it was my last lace.  I'll have to try it when I build another amp.

[dbishopbliss]

I started populating the board but it is going a little slow for two reasons:

First, the resistors I have are 1 Watt so the leads are thicker than the 1/2 Watt resistors normally used in these builds.  This means I can get only one lead into a turret at a time.  I have tried using a tool to make the hole bigger, but there is just no way.  In general, this isn't really an issue except for the parallel components.  For those I wrapped the capacitor lead and put the resistor lead through the hole - simple.

That said, I do have some 1/2 watt resistors from other builds (not the right values) that I tried.  While these work for putting two resistor leads in a single turret, I was not able to get a mallory 150 lead and a resistor lead in the turret.  Am I missing something?

The other issue is that I forgot to buy a 25uF capacitor.  The build needs five and I ordered four. 

More pictures coming soon.

[Willabe]

I was not able to get a mallory 150 lead and a resistor lead in the turret.  Am I missing something?

Yes and no. It depends what you want to do with the turret. You can also think more 3D layout with turrets.

Guys do use the through hole for putting in parts but for the best strength of solder joint you wrap them around the turret.

If you look in the tools section IIRC there's at least a couple of vid's on getting military spec solder joints.

I've seen a few guys who refuse to use the center hole in a turret because of the strength issue.

You can put the thicker lead in the turret whole and then wrap the thinner lead around the other lead right at where it goes in the turret.

I know some like the look of turrets better than eyelets but if your only going to use the center hole why not use eyelets? Unless you want the added strength that wrapping a turret gives over an eyelet solder joint.

Turrets are nice to lift a part up and over another part but to do that you have to wrap the bottom part so it lays on the board and lift the other over it by using the center hole.

Turrets are much harder to tweak an amp (if you wrap the lead around the turret) then using eyelets.

I like to use a turret when making a galactic ground star point like Kevin O'Connor and Merlin use to tie the B+ filter/ripple caps ground to all the circuit part grounds fed from that B+ filter/ripple cap. I also like to use them for modern radial filter caps.


           Brad        

[dbishopbliss]

I finally got the board loaded.  It look me longer than I expected.  Some of this was because of the part I forgot to order, some if it was because the parts were more difficult to load because multiple leads didn't fit in a turret, but mostly because of work (always getting in the way of projects). 

One thing that occurred to me when soldering the parts is that my solder joints don't look like many that I've seen in pictures.  Specifically, I see a lot that fill the turret and dome on top.  Mine don't do that.  The solder would run into the turret.  I don't think it really matters because I've tested the continuity on all the joints using my DMM touching the probes to the leads of adjacent components.

The photo does not have the bias pot installed.  I am waiting on that until I have all the leads to the pots, sockets and jacks wired up.  I guess that's next.

[Willabe]

One thing that occurred to me when soldering the parts is that my solder joints don't look like many that I've seen in pictures.  Specifically, I see a lot that fill the turret and dome on top.  Mine don't do that.  The solder would run into the turret.

Looks real good!

If you want the nice round dome on top of the turret end go back after they have cooled off a little and hit them a 2nd time. Just don't heat them too much or the solder will run back down the turret center hole just like the 1st time. Our host Doug posted how he does this to get the nice round dome.

It takes a little practice not to heat them up too much the 2nd time but you'll get it.


                  Brad      

[dbishopbliss]

Progress has been slow. This has been the most difficult task so far.

I finally figured out how I wanted to make the ground bus.  I was having trouble getting a single bus wire to solder to the back of the pots and past the bright switches.  Perhaps I could have bent the wire a little to clear the switches, but I didn't like the way it looked.  Instead, I followed (sort of) what sluckey suggested and I have the bus floating above the pots connected using either resistors or wire to the back of a pot.

Once I had the whole thing soldered (the photos are pre-solder), I installed the pots, jacks, etc. on the inside of the chassis.  I have a questions now... Should I extend the ground bus to a separate ground lug bolted to the chassis near first input jack, or is terminating the ground bus at the input jack good enough?  (I hope that makes sense)

[sluckey]

Here's what I like to do. Look closely at this pic. The buss bar terminates at the input jack. See the short black wire connected to the buss near the input jack? The other end is soldered to a ground lug bolted to the chassis.

http://home.comcast.net/~seluckey/amps/revibe/revibe_03_big.jpg

Sometimes I vary slightly from this technique. Just depends on the particular project. And sometimes I don't even use a buss bar.

[dbishopbliss]

What does the ground lug provide that the input jack does not?  As I've been thinking about it more it seems that both are bolted to the chassis, just in different ways.  Just curious.

[sluckey]

It's just a secure chassis connection that will not become loose after you insert a plug into the input jack 1 million times.

[dbishopbliss]

Snow day so I got to finally spend time finishing up my amp.  Just about to wire up the standby switch when I noticed that the Hoffman layout has the first filter cap (actually two capacitors in series) AFTER the standby switch while the original Fender schematic shows the capacitors BEFORE the standby switch. 

I have my layout and wiring run for the Fender style of layout.  Will there be a problem if I follow the Fender layout going from the rectifier diodes to the 100uF capacitors in series, then to the standby switch?

I hope this makes sense, I don't have my computer with image editing software to better explain my question.

[sluckey]

Will there be a problem if I follow the Fender layout going from the rectifier diodes to the 100uF capacitors in series, then to the standby switch?

That will be fine.

[Willabe]

It can make a difference if you use a tube rectifier.

If you add extra filter cap uF's with a tube rectifier they can pull more B+ current at 1st turn on and blow the rectifier tube. So to make it easer on the rectifier tube you put the 1st B+ filter cap(s) before the standby switch so the rec. tube only has to charge them up. Then when you hit the standby now the rec. tube charges up the rest of the B+ filter caps.

The guys will correct me on this if I'm wrong but if you use a time delayed warm up rec. tube I think that will limit the B+ current draw at start up like GZ34? 


             Brad      

[dbishopbliss]

Solid state rectifier in the bandmaster so no worries about blowing the tube.  I'm getting close now.  Just gotta finish wiring the the mains, output transformers and heaters.

[Ed_Chambley]

Snow day so I got to finally spend time finishing up my amp.  Just about to wire up the standby switch when I noticed that the Hoffman layout has the first filter cap (actually two capacitors in series) AFTER the standby switch while the original Fender schematic shows the capacitors BEFORE the standby switch. 

I have my layout and wiring run for the Fender style of layout.  Will there be a problem if I follow the Fender layout going from the rectifier diodes to the 100uF capacitors in series, then to the standby switch?

I hope this makes sense, I don't have my computer with image editing software to better explain my question.

I believe after the standby switch the filter caps will drain.  I am guessing this is why Doug wires it this way.  I usually do the same and you can hear the caps draining at shutdown.  I think it will also allow for a slower buildup of current since the filter caps are not receiving current until the standby is flipped.  I may have this all wrong, but it keeps you from having to keep the standby switch on while the amp is off if that makes sense.

[Willabe]

I believe after the standby switch the filter caps will drain. 

Yes but all you have to do is leave the standby ON when you turn off the amp and the filter caps will drain off their dcv.


              Brad     

[Ed_Chambley]

I believe after the standby switch the filter caps will drain. 

Yes but all you have to do is leave the standby ON when you turn off the amp and the filter caps will drain off their dcv.


              Brad     

That is what I was trying to say in the last sentence.

keeps you from having to keep the standby switch on while the amp is off if that makes sense.

But dang it, you said it better.

[dbishopbliss]

I finally managed to finish all of the soldering on my Bandmaster... well almost.

When I first turned it on I got horrible buzzing sounds.  As the amp warmed up they got louder and louder so I turned it off.  Then I realized I forgot to connect the ground bus of the board to the chassis.    Temporarily, I used a wire with alligator clips to connect the bus to ground.  When I turned the amp on again there was no buzz (well there is a faint one but I think that is your typical heater hum). 

However, when I plugged a guitar into the amp, no sound coming out of either channel. This is my first guitar amp and first amp I have ever built that did not make any sound... where do I start?

I read somewhere (might have been here) about using a separate amp and a probe to trace the signal.  The idea was plug a guitar into the input and have someone start strumming (or use a looper pedal).  Then connect the probe to the input so you can hear it the sound in the debug amp.  Then you move the probe to the next point and listen, then to the next point, etc.  This seems like a good way of figuring out where the sound stops, but I'm not sure if there a special probe required, special amp, etc.  Does anyone recall reading something like this and can you point me to the link?

Thanks!

[eleventeen]

You're referring to a "signal tracer" [real name] or what Doug calls a "listening amp". The absolute cheapest and easiest way to achieve such a thing is to find a junk set of powered computer speakers (preferably at a thrift store or yard sale) and 1: figure out some way you can make the 1/8" plug into a probe sort of thingy...you could go as Fred Flintstone as using a BIC pen type of thing...and most importantly, figure a way to insert a blocking capacitor into the signal lead so that when the 200-300-400 volts of your Bandmaster head collides with the 6-12 volts of the computer speakers you don't get a big smoke release. You also need to pull the ground wire out of the shielded input cable to the speakers and hopefully fashion a long wire with an alligator clip that you chomp onto the amp chassis. There's your ground.

detailed here: http://el34world.com/Forum/index.php?topic=15893.0

The blocking cap is what's important. It can be just about any value but should be a 600 volt rated cap. A .05 would be fine, a .01 would be fine. Anything. You should be able to power up such a pair of speakers (really, you only need/want one of them, the one with the amp in it) and touch the tip of the input plug and get a mild hum just like on a guitar amp.

Instead of worrying about strumming a guitar plugged into the amp input, which is always a kind of dicey situation because the strings are (in 99.9% of cases) grounded and....what are you going to do....hold the guitar, left hand on strings/frets to steady the thing while you reach into the amp with your right hand? Very likely you'll zorch yourself. Right across your heart! Do not do that! Get a radio or CD player signal w/proper adapters and run the audio into the input of your amp as your "test" signal.

The beauty of the computer speakers is: 1: they're already built. 2: They cost $2. 3: They have pilot light, on-off switch, even a jack to drive a bigger speaker if you need such a thing 4: They are completely insulated 5: If you blow them up accidentally, the next set is $1-2 as well.

 

[dbishopbliss]

Thanks for the link.  I have a set of computer speakers at home.  Looks like I will be making a probe tonight.

[HotBluePlates]

There's a simpler way to do what you want (the signal tracer is a better all-around tool, though).

Measure voltage at all tube grids, starting with the output tubes. Clip the black lead of your meter to the chassis (or another ground point), and use only one hand for the red lead to probe tube grids.

You will hear a little "pop" when you touch the meter to the output tube grids. That's normal. You'll hear a slightly louder pop when you touch the probe to the phase inverter grids. The loudness increase is the additional gain of the phase inverter circuit. The pop will continue top get louder as you work backwards towards the input jack.

When you find a point where you stop getting pops (and you don't have the volume control all the way off), you've found an area of the circuit where signal is not passing. Investigate wiring in that area.

You can combine this with plate voltage measurements. You might measure plate voltage around the circuit area where you should have gotten a pop but didn't. If the plate voltage is supposed to be 250vdc but is 270vdc, that doesn't matter. You care if it is supposed to read 250vdc and reads either 400vdc or 0vdc (that is diagnostic of 2 different kinds of open circuit).

[dbishopbliss]

I just finished the "pop test".  The (sort of) good news is that I got pops all the way back until I got to V1 and V2 pins 2 and 7.  So, whatever I did is the same on both tubes. 

I checked the resistances from the input jacks to the grid (pin 2) on both valves and they are as expected.  That is, when I plug a guitar cable into Input 1 and measure between the tip and pin 2 I get ~34K, ground is 1M.  When I plug it into Input 2 I get ~68K hot and ~68K to ground.  I get similar values for both channels.  So, I expect that the signal is making it to the grid.

Looking at the photo, if I touch the probe to the top of the .022uF caps on channel 1 or the .1 and .047 caps on channel two I get loud pops, but if I touch to the bottom of the caps I don't get any sound.  I'm not sure if that is expected or not.

Please let me know what I should try next.

[eleventeen]

At the risk of stating the obvious, V1 ain't working, or if it is working, then its output isn't getting to where it should go. Either you don't have B+ going to that tube (easy to measure) or you're missing the coupling cap (or connection to it, or the cap is open [very rare]) from the output of that tube to your next gain stage. Missing jumper...? Missing jumper that carries B+ from the next 12a_7? Shielded cable from input jacks got overheated during soldering and shorted out? Are you sure you've taken the input signal off the correct pin on the 1/4" input jack?

If you have 170-200 volts on the plates of V1 and maybe a volt and a fraction on the cathode(s) then you know the tube is conducting. It's the cathode voltage that really tells the story, if you have 1.x volts there, the tube is definitely conducting in some way and its output signal just isn't getting to its intended destination, OR, you've shorted out the input signal in some way.

[dbishopbliss]

I think I got it figured out but cannot test until tonight.  I forgot to connect ALL the board ground buses to ground.   

The yellow lines in the attached photo shows where I intend to connect the grounds.  I'm thinking that should make things work.

[dbishopbliss]

It lives!  Ends up the grounds (or lack there of) were the problem.

While testing things out and measuring voltages I was concerned and disappointed about the BUZZ I was getting.  I took a lot of care to twist my heaters and install them Valve Wizard style away from the tube in the corner of the chassis.  I also tried to keep all AC wires twisted and in corners, not to mention having separate ground buses and grounded Hoffman style.  Then I decided it was time to go to bed so I turned off the mag light I use on my work bench - SILENCE.  So one little tip... don't test you amp with fluorescent light 10 inches above your amp!

The other thing I'm disappointed about is the tremolo is almost non-existent. Its there but it is so faint it almost sounds like my guitar is slightly out of tune instead of tremolo.  I'm going to try swapping some of the resistors as originally described on the Hoffman schematic.

Finally, I gotta figure out how to bias this thing... Right now I adjusted the pot to the middle.  I have the 1 Ohm resistors installed, but when I connected my DMM the values jumped all over the place and would not settle in to give me a reading.  I also have a bias checker and it would not register any mA when using it.  Do I need a better DMM?

I realize that I was bad about taking pictures along the way (so much for my build log), but I will take some tonight and post them.

[HotBluePlates]

It lives!  Ends up the grounds (or lack there of) were the problem.

Sweet! The trick to good troubleshooting is figuring out a test that's diagnostic in that it rules out possibilities (hopefully in the fastest way possible).

Finally, I gotta figure out how to bias this thing... Right now I adjusted the pot to the middle.  I have the 1 Ohm resistors installed, but when I connected my DMM the values jumped all over the place and would not settle in to give me a reading.  ...  Do I need a better DMM?

Does your meter have a millivolts range? Does it autorange? Did you have it set for D.C.? Did you keep all volumes controls and trem intensity at zero when you measured the bias?

[SILVERGUN]

It lives! 

Congratulations Sir...this thread has been almost as interesting as your last, and you've got a nice looking build there!

Finally, I gotta figure out how to bias this thing... Right now I adjusted the pot to the middle.  I have the 1 Ohm resistors installed, but when I connected my DMM the values jumped all over the place and would not settle in to give me a reading.  I also have a bias checker and it would not register any mA when using it.  Do I need a better DMM?

Don't set the meter to mA....set it to DC volts and measure across the 1ohm resistor....you are taking a reading of the voltage drop across that resistor, and the reason for using a 1 ohm resistor is so that the math for ohms law is a 1:1 ratio...i.e., if you read a 35 millivolt drop, that is the equivalent of 35 milliamps of cathode current

[HotBluePlates]

Don't set the meter to mA....set it to DC volts and measure across the 1ohm resistor....

If he did truly measure mA, it would all turn out the same (with some minor error). The meter tries to act as a good-quality short-circuit to pass current through the meter for measuring.

That said, sometimes folks turn the dial to mA, and forget that their meter has a different set of jacks for the meter leads when measuring current.

[SILVERGUN]

sometimes folks turn the dial to mA, and forget that their meter has a different set of jacks for the meter leads when measuring current.

The meter tries to act as a good-quality short-circuit to pass current through the meter for measuring.

Some of my concern is derived from the reverse situation where you DO remember to switch it to the A jacks, but don't remember to switch it back to the V jacks before you go measuring plate voltage....it does make for a high quality short circuit

[HotBluePlates]

  Yep, I've popped a few meter fuses doing that. Fortunately, the home improvement stores had more of the same-value fuses on hand.

[dbishopbliss]

I got the bandmaster biased using the 1 Ohm resistors.  I think I must have still had the leads connected to the mA inputs of my DMM when I tried measuring earlier and this would explain why I did not get any value recorded.

I measured each tube separately.  Using the bias pot, one tube measures at 36.4mA and the other 38.0mA.  They were supposed to be a matched pair, I'm not sure if that qualifies or not but the amp sounds good.

If you recall, I used two different tone stacks in my build; Tweed and Blackface.  I can't decide if there is one I like better... instead they are different and respond differently to the pickups that are driving it.  I will make some recordings in the future so people can hear.

Before I do that, I want to get the tremolo working.  I think I hear something when I turn it on, but it is so faint that I can't really decide if it is there.  You know when you are tuning your guitar with harmonics and you hear the wah-wah-wah sound when they strings are slightly out of tune... the tremolo is more faint than that.  I'm not sure if I'm hearing tremolo or just wishfully thinking that I'm hearing something.

I have a friend with a Princeton clone that uses a similar tremolo circuit.  His amp is also very faint but much more obvious than mine.  Any ideas how to debug if my tremolo is working at all and how to make it more pronounced?

[HotBluePlates]

...  I think I hear something when I turn it on, but it is so faint that I can't really decide if it is there.  ...

Set you meter to d.c volts and measure the bias voltage of the output tubes at pin 5. Then set it to a.c. volts and measure the plate signal at the trem oscillator plate. Be sure the trem is turned on.

Hopefully, your meter will measure the oscillator plate voltage output. If it won't, try turning the speed as high as it will go, and try again. Worst-case, you'd use a VTVM set to d.c. volts and note the two extremes of the needle swing. That will give peak-to-peak output, and you can calculate peak output from there.

The oscillator output should be a very large percentage of the bias voltage for strong trem.

[dbishopbliss]

I haven't had time to diagnose the tremolo yet, but I gave the Bandmaster its first real workout last night for a couple of hours.  Plugged into lots of different cabs with different speakers.  Mostly British style speakers, I'm a little short on American.  The cabs included a 4x10 Marshall 1965A with celestions (bright and punchy), 2x12 Marshall 1966B with with WGS reapers (nice and full, well rounded tone), 2x12 Marshall 1936 with WGS Reaper and Green Beret (didn't like this one as much), 2x12 Sundown with WGS Green Berets (similar to 1966B but made out of MDF and heavy, sounds like rock & roll), 1x12 close back with Eminence Wizard (this was really nice), 1x12 close back with Weber Blue Dog Alnico (nice as well, but more compressed), 1x12 open back with Eminence Swamp Thang (eh).  I have a WGS Black and Blue and a Weber Blue Dog Alnico that I want to put in an open back 2x12 cab.  I might have to put them in the 1966B and leave the back off for testing.  I've realized that changing speakers makes way more of a difference than changing resistors from CC to MF.

Overall, its a pretty nice sounding amp.  You have to push it pretty hard and turn it up most of the way to get any read grind out of it, but I think that is typical of a Bandmaster.

There is a difference between the tweed and blackface channels, but not as much as I had hoped.  Really seems to depend upon the guitar you are playing.  There was a bigger difference with the Les Paul than with the Strat or the Les Paul Jr with P90s.

And... my bias checker still doesn't register any mA when plugged in.  I'm going to re-check to make sure there all solder joints are correct (I did this once before but that was before it ever had tubes plugged into it).  Might be a silly question, but can I measure mA another way to see if my meter is actually working?

[sluckey]

but can I measure mA another way to see if my meter is actually working?

Yes. If you just want to verify the current measuring function of your meter do this...

Solder one lead of a 100Ω resistor to the positive side of a 1.5V battery (D, C, AA, whatever). Now set your meter to measure CURRENT. Connect the red lead to the free end of the resistor (gator clip helps). Connect the black lead to the negative side of the battery. Your meter should indicate about 15mA. (OHMs LAW says 1.5V/100Ω=.015A)

But if you really want to check the tube current to determine bias, just set your meter to measure VOLTAGE and connect the black lead to chassis and connect the red lead to pin 8 of an output tube (or connect to the 1Ω resistor on the board).

[dbishopbliss]

But if you really want to check the tube current to determine bias, just set your meter to measure VOLTAGE and connect the black lead to chassis and connect the red lead to pin 8 of an output tube (or connect to the 1Ω resistor on the board).

I have biased the Bandmaster by connecting to the 1Ω resistor on the board.  I wanted to confirm the value with my the bias checker.  I really want to use the bias checker on my 1967 Vibrolux and a friend's Princeton. 

[sluckey]

I have biased the Bandmaster by connecting to the 1Ω resistor on the board.  I wanted to confirm the value with my the bias checker.  I really want to use the bias checker on my 1967 Vibrolux and a friend's Princeton.

OK, in that case you still need to know if your meter reads current properly. The battery/resistor test above will confirm that. If the meter reads properly then either your bias checker is faulty or your procedure is faulty.

There are several different bias checkers. Some require your meter to be set to measure amps. Doug's bias checker is in this group. Others have built-in 1Ω resistors and require you to set your meter to measure voltage. Some even have a built-in meter. Which do you have?