miniblok 1 voltage problem
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

 Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
chopchip
diyAudio Member

Join Date: Feb 2010
Quote:
 Originally Posted by Frank Berry Is the bias voltage correct?
is the bias voltage the -35 volts? i measured it at -37v. i guess that is pretty close. the heater voltage is good too. i changed out C8 that didnt make a diff. try C7 next

chopchip
diyAudio Member

Join Date: Feb 2010
Quote:
 Originally Posted by Brit01 Give us some measurements. Do you have a DMM?

without the tube the caps charge up good, C1 and C2 charge up to 160 volts and C3 up to about twice that much. the voltage on the B+ line is 330 volts.
the bias supply voltage is -37.5volts. heater voltage is 14.25

with tube plugged in B+ is 255v, bias is -37volts and filament voltage is 13.5v.

i will install a 1ohm resistor on pin 3 to ground to determine the current that is going through the tube. will a .5watt resistor suffice?

 16th October 2010, 04:08 PM #13 Brit01   diyAudio Member   Join Date: Jul 2008 What is the voltage on the plate? What tube are you using? 13.5 volts for the heater? Is it a 13 series? To measure current, just measure across the cathode resistor and divide that voltage by the value of the resistor (if it hasn't drifted: measure the resistance of R3 with power turned off to verify). How did you measure/calculate the bias?
chopchip
diyAudio Member

Join Date: Feb 2010
Quote:
 Originally Posted by Brit01 What is the voltage on the plate? What tube are you using? 13.5 volts for the heater? Is it a 13 series? To measure current, just measure across the cathode resistor and divide that voltage by the value of the resistor (if it hasn't drifted: measure the resistance of R3 with power turned off to verify). How did you measure/calculate the bias?
voltage at the plate is 230v on pin 2

pin 1 is 35.6v which is the bias voltage

its a 13em7.

i cant measure the current because there is no resistor from pin 3 to ground. someone said i should mod it with a 1ohm resistor to measure that current.

 16th October 2010, 04:52 PM #15 Brit01   diyAudio Member   Join Date: Jul 2008 Yes you can add a 1R resistor to measure current on Pin3 to ground. I'm doing the same on the cathodes of my OTL in work with a fixed bias. What current is flowing through R3? Has this changed? This could have also altered the B+. If the resistor has drifted down in value then it's going to be pulling more current dropping the B+.
chopchip
diyAudio Member

Join Date: Feb 2010
Quote:
 Originally Posted by Brit01 Yes you can add a 1R resistor to measure current on Pin3 to ground. I'm doing the same on the cathodes of my OTL in work with a fixed bias. What current is flowing through R3? Has this changed? This could have also altered the B+. If the resistor has drifted down in value then it's going to be pulling more current dropping the B+.

i think the voltages are actually within tolerance if i measure them right at the pins. maybe i can increase R1 by a few values.

i will put that 1ohm resistor from pin 3 and monitor the current there. .5 watt is good?

maybe stalker was right

Last edited by chopchip; 16th October 2010 at 05:19 PM.

 16th October 2010, 05:20 PM #17 Frank Berry   diyAudio Member     Join Date: Sep 2003 Location: Midland, Michigan The current through the input section of the tube shouldn't affect the B+ to this extent since the plate of the input stage is fed through a 47k resistor. The bias voltage is a bit high. I noticed that the 470uf filter capacitors on the bias supply are rated at 35 volts. They're under-rated. Should be at least 50 volts. You might want to bring the bias voltage down a little bit. That will increase the plate current and bring down the B+ voltage a bit. This is very puzzling. __________________ Frank
chopchip
diyAudio Member

Join Date: Feb 2010
Quote:
 Originally Posted by Frank Berry The current through the input section of the tube shouldn't affect the B+ to this extent since the plate of the input stage is fed through a 47k resistor. The bias voltage is a bit high. I noticed that the 470uf filter capacitors on the bias supply are rated at 35 volts. They're under-rated. Should be at least 50 volts. You might want to bring the bias voltage down a little bit. That will increase the plate current and bring down the B+ voltage a bit. This is very puzzling.

if i measure the B+ voltage right at pin 2 it is about 230 volts so i guess that is within tolerance. i was measuring it before the transformer so i guess the transformer drops the voltage by about 30v. kinda silly of me.

i guess it is actually operating properly, i just wasnt measuring the voltage at the right spot. it didnt occur to me that there would be voltage drop across the OT.

the sound was probably distorted because it was turned up too loud and i played some head games with myself.

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Site     Site Announcements     Forum Problems Amplifiers     Solid State     Pass Labs     Tubes / Valves     Chip Amps     Class D     Power Supplies     Headphone Systems Source & Line     Analogue Source     Analog Line Level     Digital Source     Digital Line Level     PC Based Loudspeakers     Multi-Way     Full Range     Subwoofers     Planars & Exotics Live Sound     PA Systems     Instruments and Amps Design & Build     Parts     Equipment & Tools     Construction Tips     Software Tools General Interest     Car Audio     diyAudio.com Articles     Music     Everything Else Member Areas     Introductions     The Lounge     Clubs & Events     In Memoriam The Moving Image Commercial Sector     Swap Meet     Group Buys     The diyAudio Store     Vendor Forums         Vendor's Bazaar         Sonic Craft         Apex Jr         Audio Sector         Acoustic Fun         Chipamp         DIY HiFi Supply         Elekit         Elektor         Mains Cables R Us         Parts Connexion         Planet 10 hifi         Quanghao Audio Design         Siliconray Online Electronics Store         Tubelab     Manufacturers         AKSA         Audio Poutine         Musicaltech         Aussie Amplifiers         CSS         exaDevices         Feastrex         GedLee         Head 'n' HiFi - Walter         Heatsink USA         miniDSP         SITO Audio         Twin Audio         Twisted Pear         Wild Burro Audio

 Similar Threads Thread Thread Starter Forum Replies Last Post chopchip Tubes / Valves 3 7th October 2010 04:57 PM 69CamaroSS396 Tubes / Valves 11 9th August 2008 08:37 PM pj_cow Tubes / Valves 2 5th March 2008 08:38 PM jtrompetter Tubes / Valves 8 16th February 2008 05:28 PM sith Tubes / Valves 10 7th January 2005 12:20 PM

 New To Site? Need Help?

All times are GMT. The time now is 10:08 AM.