High voltage

[pendergast]

Hi!

Got the basic CRACK kit and started to build it.  I had some weird measures, so I left everything on the side in order to rework at it with a quieter mind.

So this morning I resoldered many of the connections, etc.

Resistance check is A-1 everyone.

Voltage is a different story...

terminal  voltage
1              118
2              281
3                0
4              281
5              118
6                0
7              168
8                0
9              165
10              0
11              0
12              0
13            280
14              0
15            316
19            146
20                0

A1            117
A2                0
A3              2.5
A4                0
A5                0
A6            118.5
A7                0
A8              2.5
A9                0

B1            118.5
B2            282
B3            169
B4            118
B5            281
B6            166
B7                0
B8                0

Indeed, terminal 19 and 20 are totally off, but elsewhere, I have double the voltage...  Suggestions?

 

[grufti]

That looks like you accidentally built a voltage doubler PSU ... or else your transformer is funky.

Check the AC [!] voltage coming out of the transformer. It should be 130 V AC +/- 10%.

Then check everything about the power supply diodes: placement .. are they connected in the right places, orientation ... location of the stripe, solder joints ... the leads of the diodes are thicker than those of most other parts in the kit. They need a bit more heat to solder up properly.

Then check placement, orientation and wiring for the power supply electrolytic capacitors.

 

[Paul Birkeland]

Something is wrong with your meter. The A socket measurements indicating over 2.5 volts across the LED's is extremely unlikely. They are 1.5v devices essentially regardless of current drawn through them.

Perhaps try borrowing another meter or double check that you have all the correct settings on yours.

 

[Paul Birkeland]

Oh, by-the-way, based on the strange voltages you got, you're probably good to go listening-wise, but it'd still be good to sort out that meter.

One good check would be to measure a fresh D cell and 9 v battery.

The D cell measurement and A3/A8 should be an identical voltage.

 

[pendergast]

I was afraid of listening to it but...  My Goodness!  It is fantastic!  I'll look for another meter and check the numbers again, but this seems to be fine. There is a slight ground noise at 2o'clock, but I don't listen to such levels.  I use Grado SR 225.

That will sound clich

 

[tdogzthmn]

Today I re-did a resistance check and got correct readings for all the terminals except the centerpin which got a reading of zero ohms, not 90-100k like it should.  I also powered it up and did a a few voltage checks and found my numbers way off.

Terminal

1- 240
2- 241
3- 236 (should be zero)
4- 0.006
5- 239

I have no idea why my new voltage readings are so off.  I looked again to make sure its wired correctly so it must be either a poor connection or a failing component.  I have been so eager to listing to my amp but I might end up having to send it in for professional repairs.

 

[Doc B]

Hey tdog,

I'm kinda seeing different directions in your threads about the readings on different forums. I don't have an idea of exactly what is wrong based on what you have posted so far. This is not our usual policy, but since in this case we may have exhausted getting this sorted via the forum I would be willing to have a look at it for you and get it running. You can contact us tomorrow about sending the amp to us and we'll get it running.

 

[Dyna Saur]

The maximum DC voltage, across the first 220 uF cap, should be around 210VDC, and the 6080 plate voltage should be around 170VDC.    IIRC the power trannie's HV secondary voltage is approx 160VAC.

If there was actually 2.5V across the HLMP6000s, they would immediately  become SEDs (Smoke Emitting Diodes)  ;-)

Presuming that you have assembled/wired it  correctly, I'd suspect that your meter might have a problem. My  vintage Fluke 87 DVM is dead-nuts-on for DC voltage and current,  and resistance readings, but sometimes it reads about 10% low on RMS AC voltage measurements, this is an intermittent situation, and I haven't yet tried to figure out the cause of this problem.  (I suspect that the rotary mode selector switch might have a dirty contact or minor corrosion)



/ed B in NC

 

[Paul Joppa]

Just a thought - make sure the jmeter is on DC voltage, not AC voltage. Some meters will work but give incorrect readings when on the wrong setting.

 

[Doc B]

As a followup here - we have the unit on the bench this afternoon. It appears that the problem is not enough heat from the soldering iron, as Shawn found about a dozen solder joints that looked cold and could well be intermittent like the original description indicated. He's reflowing every solder joint with a Hakko, and I imagine that will get it running.

update - after a reflow we determined that one LED was bad, which was also indicated as a possibility by the original description of the problem. Replaced it and she fired right up. While here she had Speedball installed and is on her way back home tomorrow.

 

[tdogzthmn]

Wow Doc thanks for the update!  I knew I should have waited to get a better iron before I started the build.  I will definitely be getting a nice Hakko before I start my next build.  Thanks for getting it up and running with the speedball installed.  I will be heading to Yosemite on Tuesday to hike Halfdome.  If I dont fall off I will be looking forward to hearing the amp. 

 

[pendergast]

Hi,

I had to leave the project on the bench since June, and finished it today after installing my second speedball upgrade (I blew up the first and found too late that I had mixed 2 transistors).

Anyway, it is completed and it works very well!

I'll be looking at other tubes soon. It really provides a nice sense of accomplishment to build, troubleshoot, and repair ourselves.  Really grateful for this.