Voltage Measurements Off & One Diode Out Post Speedball

[dubiousmike]

I finished attempting the install of my speedball this evening, but unfortunately something seems to have gone awry.  Kind of depressing to have taken my stock build that was sounding so good - only to turn it into something that presumably doesn't work at all...   The tubes light up, but a number of voltages are off (listed below).  Also, while I could have sworn it lit up when I first powered the amp on, the back diode on the 9-pin socket (from the center pin to A8) is now out.  Given the location, I'm feeling a bit overwhelmed about how I should be attacking this if it needs to be replaced...

Here are the funny voltages, in order:

Terminal:

A8 - reads 13 [should read 1.56]
B1 - reads 176 [should read 75]
B3 - reads 176 [should read 100]

Could this all possibly be the result of my somehow disconnecting/blowing the diode at A8?  I had to maneuver things a bit to get the vertical stand-offs in and maybe I just knocked it loose (although it doesn't look loose)?  Or is it likely that I've got bigger issues?  Any advice would be greatly appreciated!

edit: Just noticed the speedball manual correction sticky.  So terminals 19-21 are okay afterall, but A8, B1, and B3 are still off.  

[Grainger49]

Without looking at the schematic it sounds like one tube or one half of a tube is not conducting.  If the LED (diode you mention) is in the cathode position of the driver and it broke when you moved it then the high voltage doesn't pass.  That causes the voltages on the plate of the tube to be way too high and that is probably what you have on B1 and B3.

Test the LED.  Take your meter, set on resistance or diode if you have it, and measure across it.  Swap the leads and measure again.  Most likely this is the only problem.

[Jim R.]

Yes, those are the cathode bias LEDs, and as Grainger said, without that, everything will be way off and not work.

I'm afraid, unless you have a bad solder joint, the LED will most likely have to be replaced.

-- Jim

[dubiousmike]

Thanks for the quick responses Grainger and jrebman!  My meter doesn't have a diode mode unfortunately, so I tried it set on resistance.  The front diode [A3 - center] lights up if my read lead is on A3/black lead on center, and my meter set to 200 or 2,000 ohm sensitivity.  If my meter is set any higher, nothing happens.  At a setting of 2,000 ohms, with red on A3/black on center, the led comes on and resistance reads but then jumps off the scale in a fraction of a second.  Resistance measures infinite with my leads in the opposite orientation.   

The rear diode [center - A8] does not light up, and does not measure anything less than off the chart resistance, in either orientation of my test leads. 

I unscrewed the two side boards on the speedball and was able to move them out of the way.  Both diodes are actually firmly attached and do not appear to be physically damaged.  Does this all support that replacing the rear diode my best first step in troubleshooting?

If so, do I need another HLMP-6000, or can I use something like this 3mm diode from RatShack: http://www.radioshack.com/product/index.jsp?productId=2062552

[Jim R.]

Measure the voltage across the diodes and they should both be about 1.6 v.  Don't substitute the diodes -- these are a specific type chosen for this application and just any ol' LED won't work, or sound good.

-- Jim

[Grainger49]

Jim means with the amp turned on measure the voltage across each.  It is DC and I suspect the A8 will be all screwy.  A call to Eileen, the Queen, will get you one in the mail today if you call early enough.

[dubiousmike]

Thank you both for the further input!  I spoke with Eileen this morning, and a couple of replacement LED's will be heading my way soon. 

I'll keep my fingers crossed in hopes that simply replacing this LED on the 12au7 socket will do the trick.  But the more I stare at the schematic and instructions, the more I worry that there must be some other issue with my speedball to account for the excessive voltages I'm seeing at B1 (grid?) and B3 (cathode?) of the other tube. 

[Jim R.]

Not necessarily.  This is a direNot necessarily.  This is a direct coupled amp and the wrong bias on the va tube will definitely play havoc with the second stage.

If you can, test the 9 pin tube socket connection on pin 8 and also look for potential solder bridges to pin 9.

-- Jim

[dubiousmike]

Work picked up and will probably prevent me from doing much more with my amp until the weekend, but I will definitely be taking more measurements on the 9 pin socket at that time.  

Jim, when you suggest testing the connection on pin 8, do you just mean that I should take a resistance measurement between A8 (on the bottom of the chassis) and the hole of pin 8 up top?  (I can safely confirm that there aren't any solder bridges or other connections between A8 and A9 on the bottom side of the socket.)  

Thank you both so much for your continued help in troubleshooting my build!  As soon as time allows, I'm also planning to retest A6, the plate on the same channel with the bad LED (per post No.2 by Grainger), in hopes that it shows excess voltage.  In my initial testing, I thought A6 measured consistent with the numbers in the manual, but this seems difficult to reconcile with the voltages I'm getting at B1 and B3, given the schematic.

(sorry, we don't publish our schematics on the web and I have removed it from the post- Doc B.)

[Jim R.]

Hopeful,

Yes, just to make sure there is continuity between the pin connection underneath the plate and the pin hole on top.  But I also meant to plug the tubes in, power it up, and read the voltage across each of the diodes of the 9-pin socket.

I have a pair of paramour IIs here that you can't see any problem with when looking at the driver tube socket, and the tube plugs in just fine, but inside the socket, pin 2 -- the grid -- is not making contact with the tube pin.  I tried to fix it temporarily, and did so, but it only held for a couple of hours and now I can't establish the connection again.  From what I can feel in that socket hole, the metal appears to be broken off inside the socket.

I also know another guy who had a problem with the 9 pin socket in his crack kit.

First thing though it to make sure there is contact with the tube pin from the bottom side of the socket, because if that's not there, then the LED could be fine, but not lighting because there's no connection to the tube.

One other thing you could do to test this is have the amp powered on and wiggle the tube and see if the led blinks as you do so.

-- Jim

[dubiousmike]

I'm delighted to report that my crack + speedball are up and running!  All voltages read exactly as they should, and it sounds absolutely fantastic.  I've never heard Billy Holiday's "Songs for Dintingue Lovers" sound so good.

Many thanks again for all your help Jim and Grainger.  The new LED at A8 did the trick.  Cheers!

[Jim R.]

Hopeful,

Excellent!  Glad that was the problem and that you were able to fix it easily enough.

Glad to be of some help.

-- Jim

[Grainger49]

Just glad you are now listening to music!