Heath SP2717A Only Giving 150V, not 400V - diyAudio
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Old 20th January 2013, 02:04 AM   #1
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Default Heath SP2717A Only Giving 150V, not 400V

I got a used SP2717A off an auction on ebay for a reasonable price. The seller was not super knowledgeable about the product, so I knew I had my work cut out for me. After completely disassembling it and replacing the front panel pots, switches, and power cord, the power supply only outputs 150V. The adjustment pots on the main circuit board do nothing when adjusted, but checking them with my multimeter, I see a change in resistance. Could the adjustment tube be shot but still outputting a 150V on the B+ supply? The C- supply works perfectly...
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Old 20th January 2013, 03:45 AM   #2
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Here is a link to a schematic and manual.

HEATHKIT SP2717A 0..400V,0.1A,0..-150V VALVE STABILISED POWER SUPPLY 1982 SM Service Manual free download, schematics, eeprom, repair info for electronics
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Old 20th January 2013, 05:03 AM   #3
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I gave it a look, and I tried the calibration steps, but tweaking the adjustment pots gave no indication that it was doing anything. The pots test ok with my multimeter, I'm worried if there is something wrong with the adjustment tube, and if there's any way to check that...
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Old 20th January 2013, 10:27 PM   #4
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Check the voltage from pin 3 and 4 on the 6l6 to common . Be very careful pin 3 should be at about 600 volts dc . pin 4 at about 269 . That is lethal voltage act like and show it respect . We can go from there.
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Old 20th January 2013, 10:44 PM   #5
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Quote:
Originally Posted by Triodethom View Post
Check the voltage from pin 3 and 4 on the 6l6 to common . Be very careful pin 3 should be at about 600 volts dc . pin 4 at about 269 . That is lethal voltage act like and show it respect . We can go from there.
Aren't pin's 3 and 4 the heater pins? http://park2.wakwak.com/~happy/123/vacuum/6AU6.gif
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Old 21st January 2013, 02:26 PM   #6
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Quote:
Originally Posted by supersonik319 View Post
Aren't pin's 3 and 4 the heater pins? http://park2.wakwak.com/~happy/123/vacuum/6AU6.gif
Sorry on the 6l6 series tube .
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Old 21st January 2013, 08:29 PM   #7
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if you live in a country w/ 120v mains, did you check that it's not set up for 240v ?
range set to 400v ?
when you say 150v, does that mean adjustable between 0...150v or just 150v regardless of voltage dial settings
tube heaters glowing ?
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Old 21st January 2013, 10:29 PM   #8
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All measurements were taken after waiting 30 seconds from a cold start. Test lead clips were used to clip measurement points to a Radio Shack multimeter.

On the first tube, on the left hand side looking at the schematic, pin three goes off the scale of my multimeter, which maxes out at 600V, when I switch it off it quickly falls to around 590V before dropping to zero, so I assume its around 600V.

Pin 4 hovers around 243V when the B+ knob is full counterclockwise (minimum voltage), and it goes up to 460V when the knob is all the way on the right. If I leave it alone, the voltage drops to about 420V after a minute.

On the right hand side tube, pin 3 and 4 show identical behavior.

I checked against the manual, it's set for 120V.

I tried fiddling with the adjustment pots, but I don't see any changes in the max output, despite the pots being good (I tested by turning the power supply off and clipping leads to the wiper and one leg and turning the pot back and forth)

Adjustable between 0-150 using the front face knobs.

All three tube heaters are glowing.

Thanks in advance for helping me out with this; I'd love to get this up and running to play with the small collection of tubes I have growing
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Old 22nd January 2013, 10:37 AM   #9
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look at the schematic and check the res. r15,16,17,18 they all should be 27k . with unit off . Then r11 ,r 13 and r9. Having voltage of 600 plus on the6l6 is good the voltage on the screen in the range .
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Old 22nd January 2013, 06:44 PM   #10
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If the minus -300volts (i.e. pin3 = lower leg of the 400v adjust pot) is off spec - say just -225v or so, this would limit the output voltage to around 150volts.
It would also explain why the adj. pots have no effect ...
Check the -300v.
If it is indeed low, check zeners ZD6 to ZD10 ...
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Last edited by payloadde; 22nd January 2013 at 06:48 PM.
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