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Old 4th February 2014, 03:10 PM   #1
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Default Checkout problem TSE.

The final checkout according Checkout | Tubelab doesn't mention any B+ or B- values wich should be measured at the different stages (with or without tubes).
My understanding of schematics is very limited so these values would be a big help in the checkout procedure.
My configuration is:
300b version (shungang)
transcendar opt 5K
5ar4 rectifier
4852 tungsol
a custom power transformer image attached
The sockets are raised of the board by 6cm with copper rods.

I did have a problem with the final checkout of my tse. The first item i encounterded was that c3 cooked within a few seconds of powerup. After replacement with a 4700uF 16v (4700uF 6.3V electrolytic capacitor) one the specified check worked fine until i checked the filament supply it measured over pin 1 and 4 11 volts, the specs for 300b it should be around 5v.
B+ without tubes is -00 without tubes and 430v with rectifier.
The bias of the 4853's is about 175v.
I hope someone can give me a hint where to look.

Greetings Mark
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Old 4th February 2014, 10:46 PM   #2
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The TSE is more of an intermediate level project, so the instructions are a bit less detailed. George's "Tubes and Applications" page gives an idea what to expect for B+ voltages.

Tubes and Applications | Tubelab

With no load, that B+ sounds reasonable. You also have the 5842s setup correctly, so that is a good sign. Your filament voltage is way too high, obviously. It seems like you have an error in that part of the circuit. Perhaps there is a short or U1 is fried. Can you measure the voltages across C1, C3, and R1? Also check you bias voltage while you are at it (45 tube pin 3 to ground).
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Old 5th February 2014, 08:45 AM   #3
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I took some additional measurements this morning:
All with rectifier and pre-tubes in place.
B+ 408
B- -247

300b tube pin 1-4 filament supply 15,5 volt
Tube pins to ground
1 filament + = 15,4v
2 Plate = 26,1 & 33v
3 Grid = 415 (positive?)
4 filament neg= 0

Across C1= 15,7v
Across C3 = 15,02v.
Across R1 = 0 removed from pcb and resistance measures ~ going to replace it.
I hope this will do the trick and the filament supply will return to normal.
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Old 5th February 2014, 12:05 PM   #4
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Nope, changed R1 (for 500ohm) no change in filament supply at the output tube sockets. At plate pin, i have now -143v so that has changed.
At the filament supply on the pwt output 2x 6 vac.
from the iron tip of the d1 to gnd a 15,5 vdc.
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Old 5th February 2014, 03:52 PM   #5
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Do not install the 300B's until you get this fixed.

15.5 volts is way above the maximum spec for the filament regulator. The chip is probably blown.

The filament winding on your power transformer is 12.6 VCT volts which is too much. You need a 6.3 VCT transformer. Since you are using 300B tubes you should be able to use half of the winding for 6.3 volts. Connect the center tap to T1-7 and one of the 6.3 volt terminals to T1-8. Make no connection to T1-6 or the other 6.3 volt terminal on the transformer. The voltage across C1 should now be around 7 volts. If the voltage on C3 is not 5 volts your regulator chip is probably dead.

Do not install the 300B's until you get this fixed.
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Old 5th February 2014, 04:19 PM   #6
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To late. Installed them yesterday, luckily a cheap chinese set. They are probably dead.
thank you for the info. I will fix it first.
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Old 6th February 2014, 01:52 PM   #7
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Hi. I did as instructed and i have 7.5v over c3. So i will need a new voltage regulator. Has anyone a source for sharp PQ5EV5 in europe. With mouser or digikey i have to pay $18.00 shipping and here 21 % tax over the total invoice. Ridiculous.a set 300b from china just $60.
Already many thanks.
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Old 20th February 2014, 10:32 AM   #9
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Installed a new pq5ev5 at u1 and still have 7.93v at fillament on socket without tubes. Any suggestions?
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Old 20th February 2014, 02:35 PM   #10
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And a new D1 still 8v fillament.
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