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-   -   miniblok 1 voltage problem (http://www.diyaudio.com/forums/tubes-valves/175441-miniblok-1-voltage-problem.html)

chopchip 16th October 2010 01:34 AM

miniblok 1 voltage problem
 
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i built this amp a while ago and all the voltages checked out, i had 215 volts B+ but now the voltage has bumped up to 250 for some reason and i cant determine why that is. i guess there isnt enough voltage drop across R1 so that means that the tube isnt pulling up enough current, im not sure where to go from here. maybe i can just increase the value of R1 but that doesnt really solve the mystery...

any ideas?
thanks

Cassiel 16th October 2010 01:10 PM

Quote:

any ideas?
Yes, leave it alone.

chopchip 16th October 2010 01:44 PM

Quote:

Originally Posted by stalker (Post 2334427)
Yes, leave it alone.

is that supposed to be a joke?:soapbox:

Cassiel 16th October 2010 01:54 PM

No. No need to worry.

Brit01 16th October 2010 02:17 PM

I guess if the tube's parameters are within optimum working levels then all should be ok?

Any change in current or sound? Has R2 or R3 drifted?


Have you measured the cathode voltages/current?

If R3 is pulling less current, the B+ is likely to rise.

Frank Berry 16th October 2010 02:30 PM

The tube characteristics have changed for some reason. The output triode is pulling less current than it pulled originally. Perhaps it's gassy. Have you tried another tube?

chopchip 16th October 2010 02:55 PM

Quote:

Originally Posted by Brit01 (Post 2334488)
I guess if the tube's parameters are within optimum working levels then all should be ok?

Any change in current or sound? Has R2 or R3 drifted?


Have you measured the cathode voltages/current?

If R3 is pulling less current, the B+ is likely to rise.


could it be the bypass cap (c8) next to r3? maybe it's voltage rating is too low because i have the same problem with the other channel's amp.

the sound has become distorted. im going to install a 1ohm resistor from the cathode to ground to measure current.

chopchip 16th October 2010 02:56 PM

Quote:

Originally Posted by Frank Berry (Post 2334497)
The tube characteristics have changed for some reason. The output triode is pulling less current than it pulled originally. Perhaps it's gassy. Have you tried another tube?


i tried a different tube and the result is the same. i guess ill just start switching out parts until i hit the fawlty component

Frank Berry 16th October 2010 03:08 PM

Is the bias voltage correct?

Brit01 16th October 2010 03:24 PM

Give us some measurements.;);)

Do you have a DMM?


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