Priceless tube tester

[gui_tarzan]

So I built the Priceless tube matcher and tried testing some tubes but I'm not getting anything measuring V, mv or ma on my meter.

Is there something I'm overlooking in this circuit?

[xtian]

This is as simple as any tube amp is simple...Start from the beginning. Is your power supply working? What's your B+? What about your bias supply? What's your bias voltage? Etc.

[gui_tarzan]

Yeah I know it should be that easy. Is it because there is no output transformer load on them?

B+ 394v before the diodes, 270v after. ??? Shouldn't that be higher once it is converted to DC?

-50v bias.

[ampdoc1]

I don't think you have a complete schematic. You'll notice on the attached schematic there are a number of connections, etc that are not shown on your drawing.

a'doc

[gui_tarzan]

Hm, are you sure? It looks the same to me.

[gui_tarzan]

Duh... I forgot to hook up pins 3.

[gui_tarzan]

Same results. No reading.

[Phil_S]

Time to show us a picture or 2. This is going to be something obvious, just not to you. It happens to everyone.

[gui_tarzan]

Here we go.

[gui_tarzan]

I used a 6-0-6v filament transformer because the PT only gives me 3.2v when it's hooked up to this pair of V+ in, otherwise the alternate primary lead gives me 7.2v and 800v on the filament and B+ respecitvely, and I only wanted to use the 400V option.

[gui_tarzan]

The small black, red, green, blue wires go from pins 1/8 to the four-way switch for the meter connection.

[Phil_S]

Please excuse me if I am telling you stuff you already know. I'm only trying to be thorough and I hope this is coherent.

I think you have wired the tube side of this correctly. I am not particularly liking the construction -- more on this later. I think the problem is in the power supply picture. I'm not convinced it will work by just addressing the power supply. Here goes.

I am having difficulty seeing clearly the power supply picture. To the left of the fuse holder, there are two larger caps in series, each strapped with a resistor. I don't follow where these are connected and how they are supplied. I want to confirm, these are the B+ supply?

There is another pair of smaller caps oriented vertically. These are the bias circuit? You are taking the bias supply from the HT winding before the string of 3 diodes and using a Marshall style dropping resistor? I am thinking the voltage divider is not present for the bias circuit and you are missing one resistor.

I assume HT supply is the pair of twisted red.

Here's what I don't see, don't follow:
-- There should be two strings of diodes, one for each red wire. I only see one.
--Where is the HT center tap wire? That needs to be grounded. Can't see it.
--No connection at the negative side of the lower cap.
--I don't understand the twisted bundle (white, yellow, purple) from the bias feed to the switch.
--At the upper right of the PT I see 2 red, 2 green and 1 smaller red. The green are unused filament? Are there really 3 red wires? Where exactly do these go?

On the bias supply, if there is a separate bias feed, it goes directly into a diode with the stripe oriented towards the PT. (The 470R shown on the schematic between the PT and the diode is OK and should be used if needed to drop voltage.) If there is no separate bias feed, use a 100K-220K resistor (depending on the feed and desired voltage) between one leg of the HT secondary and the diode. Simplify this. You only need one cap, not two. (Can't see the value in use, but it isn't critical.) Bias is a very low current circuit. Attach the diode to the neg side of the cap and ground the + side of the cap. Strap two 10K resistors in series across the + and - of the cap. The bias feed comes from the junction of the two 10K resistors. Hook this directly to one tube socket at pin 5. There should be jumper wires to the other sockets' pin 5 and I think that is done. Remove the bundle to the switch. (Maybe you explain that bundle and I'm not correct?)

On the power supply, each HT red wire feeds into a separate string of 3 diodes (total of 6 diodes.) The diode stripe is away from the PT. The one string I see looks right. I don't see the other string of diodes. Join the two diode strings at the + side of the upper filter cap. The - side of the lower filter caps goes to ground. The + side of the filter caps connects to pin 3 on the first tube and it looks like the rest of what you built will work.

Wiring the B+ filter caps. Strap a 220K from each + to -. Ground one - (the lower one in the picture.) It looks like you have a jumper from the lower + to the upper - and that's correct.

Not liking what I see on the tube side. There are many flying leads and uninsulated joints hanging in the air. I am concerned this is unsafe. I'd clean this up by running terminal strips.
--On each socket run a jumper between pins 1 and 8.
--The 1R should be soldered directly to #8 pin (not #1).
--Terminate the other side of the 1R on a terminal strip.
--Run a ground wire to the ground side of each 1R (daisy chain) and ground the chain.
--Run the 1K directly from pin 3 to pin 4 on each socket.
--Run the B+ feed to the first socket. Run jumpers from the 1st socket pin 3 to the other pins 3. This will get rid of the flying connections.

As an alternative, you can supply the B+ to a terminal strip and use that as a star style distribution point.

Make sure the Vtest wires are all hooked to pin 8 of the respective sockets and terminate cleanly to a lug on the switch.

[gui_tarzan]

Please excuse me if I am telling you stuff you already know. I'm only trying to be thorough and I hope this is coherent.

I think you have wired the tube side of this correctly. I am not particularly liking the construction -- more on this later. I think the problem is in the power supply picture. I'm not convinced it will work by just addressing the power supply. Here goes.

The construction is not optimal, that is true, but I can and probably will clean that up later.

I am having difficulty seeing clearly the power supply picture. To the left of the fuse holder, there are two larger caps in series, each strapped with a resistor. I don't follow where these are connected and how they are supplied. I want to confirm, these are the B+ supply?

Yes.

There is another pair of smaller caps oriented vertically. These are the bias circuit? You are taking the bias supply from the HT winding before the string of 3 diodes and using a Marshall style dropping resistor? I am thinking the voltage divider is not present for the bias circuit and you are missing one resistor.

Yes, that is the bias circuit. I am getting -44v currently and can adjust that with the 100k pot.

I assume HT supply is the pair of twisted red.

Correct.

Here's what I don't see, don't follow:
-- There should be two strings of diodes, one for each red wire. I only see one.

There are two rows like the schematic shows.

--Where is the HT center tap wire? That needs to be grounded. Can't see it.

That is grounded to a terminal strip under the board. There is a little over an inch of clearance under the board.

--No connection at the negative side of the lower cap.

That's got a ground wire under the board to the ground terminal strip.

--I don't understand the twisted bundle (white, yellow, purple) from the bias feed to the switch.

That is the set of wires going to the bias pot on the front of the unit.

--At the upper right of the PT I see 2 red, 2 green and 1 smaller red. The green are unused filament? Are there really 3 red wires? Where exactly do these go?

The two greens are unused filament. Yes, there are three red wires for B+, the red/yellow center wire is grounded.

On the bias supply, if there is a separate bias feed, it goes directly into a diode with the stripe oriented towards the PT.

Correct.

(The 470R shown on the schematic between the PT and the diode is OK and should be used if needed to drop voltage.) If there is no separate bias feed, use a 100K-220K resistor (depending on the feed and desired voltage) between one leg of the HT secondary and the diode.

I ended up using a 100K to drop it to a range that's usable.

Simplify this. You only need one cap, not two. (Can't see the value in use, but it isn't critical.) Bias is a very low current circuit. Attach the diode to the neg side of the cap and ground the + side of the cap. Strap two 10K resistors in series across the + and - of the cap.

The bias feed comes from the negative end of the diode to the pot, the other end of the pot goes to a 47k resistor which goes to ground as do the positive end of the caps.

The bias feed comes from the junction of the two 10K resistors. Hook this directly to one tube socket at pin 5. There should be jumper wires to the other sockets' pin 5 and I think that is done.

Correct.

Remove the bundle to the switch. (Maybe you explain that bundle and I'm not correct?)

The bundle of small wires goes to the four-way switch on the front panel.

On the power supply, each HT red wire feeds into a separate string of 3 diodes (total of 6 diodes.) The diode stripe is away from the PT. The one string I see looks right. I don't see the other string of diodes. Join the two diode strings at the + side of the upper filter cap.

Correct, polarity is also correct.

The - side of the lower filter caps goes to ground. The + side of the filter caps connects to pin 3 on the first tube and it looks like the rest of what you built will work.

These two caps are in series, the red wire goes from the negative end of the first cap to the positive end of the second cap, then the negative end of the second cap goes to a ground wire under the board.

Wiring the B+ filter caps. Strap a 220K from each + to -. Ground one - (the lower one in the picture.) It looks like you have a jumper from the lower + to the upper - and that's correct.

Yes, as stated above that's how it's wired.

Not liking what I see on the tube side. There are many flying leads and uninsulated joints hanging in the air. I am concerned this is unsafe. I'd clean this up by running terminal strips.

As said earlier I will clean this up later, this is a mock-up to make sure it works.

--On each socket run a jumper between pins 1 and 8.

That's already there.

--The 1R should be soldered directly to #8 pin (not #1).

If they're jumpered it shouldn't matter whether it's #1 or #8, they are tied together. For neatness sake I agree with you.

--Terminate the other side of the 1R on a terminal strip.
--Run a ground wire to the ground side of each 1R (daisy chain) and ground the chain.

They all go to the terminal strip which is grounded to the chassis cover.

Make sure the Vtest wires are all hooked to pin 8 of the respective sockets and terminate cleanly to a lug on the switch.

Now that I look at it again, I used the bias circuit from the "Judybox" tester which has the double caps and the yellow cap goes from B+ to ground per that Judybox circuit as well. Attached is the actual JB power supply schematic. My apologies, I was working off that at first, then did the tube socket wiring off the Priceless schematic.

[Phil_S]

it seems you've wired it correctly. IMO, it doesn't hurt to confirm this. The only question left is the bias pot. (Sorry, didn't see what this was, my bad.) Why so many wires? Two is the usual amount. The pot is wired as a variable resistor (wiper and one outer lug). It goes between the two 10K (or whatever.) In any case, at -44, it is working. When you turn the bias pot, is bias voltage responding? You see -44V at pin 5, so I'll ask to be sure you see the same on all 4 sockets?

I'm content to set aside the cleanup issues. I didn't realize its a rough prototype. I felt that I would have been remiss in not mentioning it.

This PT supplies 394VAC? Then with a FW rectifier, I'd expect 279VDC (394 * .707). 270VDC is certainly reasonable.

You say you aren't getting any readings with tubes in sockets. This is at the test points on the panel? Did you try getting readings at the tube sockets? Do this old school. Plug in a tube, clip your meter across the 1R and measure the mV. I recommend clips and not hand held to get an accurate reading. If you get nothing, your meter is bad (broken or battery), the 1R isn't grounded, or the 1R isn't connected to the cathode. While you have it open for live measurements, check screens and plates, too.

You caught my interest with this project. I think I would like to build one also. It is much simpler than I had imagined.

[gui_tarzan]

I have a 6L6GC in socket 1 right now and my leads across the 1 ohm resistor, it's reading .6mv on my meter. I will get a new battery and see if that makes a difference and try it again tomorrow, I'm off to a gig here in a few minutes.