Behringer vintage tube monster

[whomeno]

I seen today the tube is not lighting up. so I pulled it apart to measure the voltages to the tube. here is what I came up with
pis 1=0
pin 2 = 0
pin 3 = 0
pin 4=8.76
pin 5=8.77
pin 6 =0
pin 7 =0
pin 8=8.01
pin 9=8.79
put it back together plugged it in and still works.
Maybe the tube is just for show?
or is there something wrong with the pedal?

[thermionix]

There have been products in the past (some rack-mounted preamps IIRC) that had a tube just for show.  I've never heard of the Behringer, but googling it says it has a 12AX7.  In that case, your voltage readings don't make much sense.  Just to light it up, there should either be 12.6V (AC or DC) between pins 4 and 5, or 6.3V between pins4+5 and 9.  There really shouldn't be any voltage on pin 8 in that situation unless you have a H-K short.  Is it a JJ brand tube?  Those are the only 12AX7s I've ever seen develop a H-K short.

[anotherjim]

There are schematics out there if you search, but I don't know how accurate they are. It appears to be a version/clone of the Ibanez tk-999.
Anyway, it looks to me like there is a disconnection for 0v supply somewhere. A blown or cracked pcb track or solder joint.
As Therm said, it may have been caused by a tube fault.

[whomeno]

the tube is ok,tried a new tube same thing.

[teemuk]

It is extremely rare that some device would feature a vacuum tube solely for the aesthetic purpose and nothing else. If there's one it most likely has a purpose in the amplification chain, usually also a serious one. Least that one can expect is that the tube operates as a "transparent" gain stage and the signal passes the tube circuit's signal path, even though remaining practically unaltered.
That's furthest extreme of my experience about designs employing tubes "for show". Usually when there's one it's for good reason.

Behringer effect is - as mentioned already - a clone of the Butler "Tube Driver" starved plate voltage tube effects. I have a faint memory that Butler even designed the Ibanez pedal (which Behringer clones) and it's pretty similar to other of his designs in same category. Gain stages built around the dual triode tube introduce primary source of signal clipping distortion, solid-state stages are used for overall signal boosting and recovery. Starved plate designs are not that good for "HiFi" applications of tubes because they feature very low headroom and introduce high amount of inherent harmonic distortion due to significant non-linearity at region where they operate. All that is great for producing nothing but distortion, though, so this one's not a "gimmick" design even though tubes are not operated at customary high plate voltages.
Also, I expect you should actually measure a bipolar voltage supply there, that's at least customary for this design category.

Do not worry about filament glow because it indicates basically nothing. Filament is not that great light source to begin with, especially that of a tiny "preamp" tube. Also, there are huge differences in tube architectures and some of these basically hide the filament from sight so you're not even supposed to see any distinct glowing. Nowadays designers practically have to fit several LEDs to tube equipment because people believe the thing must be broken unless it looks like a damn Christmas tree.
The important question to ask and verify is: Are filament terminals actually receiving (correct) voltage?

Nope. Never seen Behringer units where tubes would be just for show. I remember one incident though where people falsely believed this to be true just because a certain Behringer effect had those LEDs enhancing the inherently dull glow of filaments I mentioned about. That effect unit in question happened to incorporate very clever triode tube-based distortion circuit.

[whomeno]

teemuk,
Thanks for explaining that to me. The power pack they send with it sends out 8.88v. so going through the circuit it drops to 8.77 to 8.79.
I think you are right "Gain stages built around the dual triode tube introduce primary source of signal clipping distortion, solid-state stages are used for overall signal boosting and recovery."
That would explain why it is still working.
Thanks

[thermionix]

It is extremely rare that some device would feature a vacuum tube solely for the aesthetic purpose and nothing else.

Extremely rare indeed.  I was just saying that it has happened, I don't think that's the case with this Behringer.  I looked for a schematic last night and couldn't find one, but pics of the innards show more than 2 wires going to the tube daughter board.

Behringer effect is - as mentioned already - a clone of the Butler "Tube Driver" starved plate voltage tube effects.

I'm not sure about that.  There seems to be two similar Behringer products, a VT999 Vintage Tube Monster and a VT911 Vintage Tube Overdrive.  Searching for the 999 schematic last night brought up mostly results for the 911.  The 911 seems to be based on the Butler "patent application" schematic (running on 9V) rather than an actual Butler production unit (running on +/-12V).  Just stuff I read late at night, I honestly don't know.

That would explain why it is still working.

I'm still confused.  The schematics of *whatever* that I saw last night would require the tube to be working in order to get sound through the box.  You would have to have some DC voltage on the plates.

[whomeno]

double checked the plates pins 1 & 6 no voltage at all. but still works.
I think teemuk got it right "Gain stages built around the dual triode tube introduce primary source of signal clipping distortion, solid-state stages are used for overall signal boosting and recovery. "

[thermionix]

Yes but is there a path for the signal to get around a tube that isn't conducting?  From Teemuk's description, I imagine a SS (opamp) stage before and after the tube, but you still need the middle link.  All just speculation though wihout a schematic.

[teemuk]

We don't really need exact schematics for basic troubleshooting. We know basics of "Tube Driver" circuitry so that should provide us enough clues, whether there are minor differences in the Behringer circuit or not.

It looks like Ibanez units actually employ basic unipolar supply and at least the TK999 features moderately high supply voltage for the tube section. According to schematics the supply voltage for solid-state circuitry is approximately 10 volts (unipolar), out of which they naturally derive the 10V/2=5V OpAmp bias reference. Basically, we don't really care if that supply voltage is 8 volts or 12 volts, we primarily care that it exists.

Power supply section of TK999 shows transformer with two primaries. One primary supplies filaments and (after a regulator) the OpAmp and other solid-state circuitry (the "Vcc" supply). I guess you should measure something around 15 - 8 volts there depending on design. The voltage will drop a bit after the regulator. If you don't measure any power supply voltage or filament voltage there's a fault somewhere.

You should probably get that reading at every transistor collector (they are primarly just "buffers") and at every opamp pin #8. If you don't measure any voltage (in close range) at such places you have found a fault. Every OpAmp pin #4 should show 0V. Inputs and outputs of the OpAmps should have DC offset, which is the same as opamp bias voltage, approximately half of "Vcc".

If the supply happens to be bipolar then you should measure something (e.g. 6VDC - 15VDC) at every opamp pin #8, and same voltage (but negative polarity) at every pin #4. Inputs and outputs in such case should read around 0 volts.

See, we can troubleshoot this far just by making few educated guesses about the circuit. It's basic electronics so far...

The TK999 schematic shows that the tube circuit's power supply (B+) is derived from another secondary of the PT. In TK999 the voltage is a bit over 100 volts, and its then regulated to approximately 100 volts. Naturally you do not measure that voltage at the tube plates (pins #6 and #1) but something less, probably something like 50 volts or something in that region. Then, follow the signal path and locate the plate load resistors. Verify that B+ connects to them properly. You should measure around 100 volts (B+) at the other terminals of those plate load resistors because they connect to B+.

What if the B+ supply is something else than 100V in Behringer design? Again, we don't really care for sake of troubleshooting, we only care that there is supply voltage and that it is supplying the circuit. Point is that the circuit is just two basic common cathode amps so it's bread and butter to troubleshoot. Both gain stages have plate load resistors that connect to B+ supply, are you measuring a B+ supply there? Basically any voltage in the range of 9V - 400V will do. Do you also measure dropped voltage at the plates?

Effectively we don't really care what B+ voltage the design employs. If B+ and plate voltages exists, but are lowish, then the stage just has lower headroom. If those voltage exists, and are high, then headroom is higher. Nevertheless, regardless of voltage value, the tube circuit should work and pass some signal. ...BUT if those woltage's don't exists then we have pinpointed a fault.

See, again we got pretty far in troubleshooting just by making educated guesses.

You can likely trace the circuit down from plate resistors to the B+ supply. Filter capacitor voltage there should give some clue what voltage you're expected to meaasure. e.g. if Voltage rating is >100V then there's likely moderately high B+ voltage employed, ratings like 10 - 25 VDC would indicate "starved", lower B+ voltage. If the measured B+ voltage doesn't seem to match those ratings (e.g. you measure 10 volts B+ but filter capacitors are rated for 100VDC) then it indicates a fault somewhere.

Tube filament connections are pins #9, #5 and #4. The filaments can be connected in series or in parallel depending on design. If the heaters are in series you measure voltage potential between pins #5 and #4, pin #9 would be disconnected. If the heaters are in parallel you measure two voltage potentials between pins #5 and #9 and pins #4 and #9. Series filament voltage should be in the range of 9 - 12 V, parallel connection uses about half of that. Either way, voltage across each filament section should be the same. Some exact voltage reading is once again unimportant (filaments will work as long as the voltage is in the ballpark range), we only really care that the filament supply actually is there and that it is somewhat in the proper range. If you measure too low or too high readings then there's a problem somewhere, but whether the filament voltage is actually 10 volts or 8 volts doesn't really matter.

So, verify that the power supply is operating and that it actually also supplies each circuit section. Looking at the readings in first post indicates that there is a fault somewhere.

[teemuk]

Yes but is there a path for the signal to get around a tube that isn't conducting?

There may be. But it is not primary signal path of the design.

So, if there's clear indication of a fault somewhere in the circuit then there is a fault somewhere in the circuit. Period. Let's fix that first. Why even care if the tube circuit "bleeds" signal in that fault condition, it's a fault condition no matter what. Whether signal passes the tube section or not we already know the section is not working properly.

Just passing signal indicates nothing. For example, the tube stage may bleed low amplitude "cleanish" signal in fault condition but what exactly is the importance of that if in a properly working circuit we expect to see higher amplitude and distorted output signal?

I reckon that if the thing operated like it was supposed to do we wouldn't even be having this conversation.

[whomeno]

I am talking to customer care. it is still under warrenty ( hope they don't mind the bit mo mod)

[thermionix]

I reckon that if the thing operated like it was supposed to do we wouldn't even be having this conversation.

put it back together plugged it in and still works.

Dunno.  Only complaint in the OP was the tube not lighting.  Reported voltages won't light a 12AX7 filament, nor will they pass any audio signal through a 12AX7.

[whomeno]

Got this email today from behringer.


Dear Robert,

Regarding your inquiry: Warranty Request.
Please note that this is a confirmation email only.
We will be replacing your unit - VT999. It was just ordered and you'll receive the replacement in about a week & you DO NOT have to send your original faulty unit back to us. 

If you wish, you can email/call me on Monday & I should also be able to get tracking on the shipment for you!

Product and Serial Number: VT999 s/n S1708xxxxxxxx

Return Authorization Number: 35xxxx

Also, you do not have to register this new unit, the warranty actually takes over from the original units’ purchase date.

Warranty is covered for any manufacturing defects within the first year from the date of purchase from an authorized MUSIC Group dealer.  Your warranty includes parts and labor as well as return shipping to you after the repair is completed.

If you have any questions or problems regarding your warranty service, please don't hesitate to contact us.  Please use email address:  carecrea@music-group.com  Anyone in Customer Care will be glad to assist you.

Thank you again for contacting us and please let me know if you have any further questions or if I can be of further assistance. Alternatively please visit our website for support and further information.

Kind regards

Kyle Johnson
Your Specialist, Care
MUSIC
Tel:
Web: www.musictribe.com

This email is intended exclusively for the addressee(s) named above and may contain privileged and confidential information. If you are not (among) the intended recipient(s), you may not copy, utilize or distribute any of the information contained herein. If you have received this email in error, please notify us immediately via return email and delete the original from your mailbox. Thank you.


____________________________________

So looks like it is all good

[anotherjim]

Wow, so that means you still have the original to fix and soon to have a working one to compare it with?

[whomeno]

Here are some pics of the bad vt999. still think it is a starved tube setup. No transformer to up the voltage.
from left to right
ICs 1-2-3- 5 are 074 JRC Y51015P
UC 4 is V2164M

[whomeno]

YUP, sounds to good to be true right. I sent them the voltages of the tube. They would not give me the specs on it?.