Been reading the forum again trying to get an answer to my problem. Just installed the Bias circuit kit from Dynakit and I cant't get the right (side) bias pot to adjust to 1.56....gets to about 1.38 and then stops even though I still have adjustment left in the pot. Left side works fine. Bad pot? Everything else seems fine.
2 posters
Bias help. One side not adjusting to proper voltage.
gjmess- Posts : 9
Join date : 2020-10-16
peterh
peterh- Posts : 1869
Join date : 2012-12-25
Location : gothenburg, sweden
- Post n°2
Re: Bias help. One side not adjusting to proper voltage.
by peterh Wed Oct 28, 2020 3:07 pm
It could be the tubes at the right side that is weak. Have your swapped right and left side tubes ?gjmess wrote:Been reading the forum again trying to get an answer to my problem. Just installed the Bias circuit kit from Dynakit and I cant't get the right (side) bias pot to adjust to 1.56....gets to about 1.38 and then stops even though I still have adjustment left in the pot. Left side works fine. Bad pot? Everything else seems fine.
If this is not the problem, pull the powertubes and the rectifier tube, turn on and
measure the voltage at pin 5 of the powertube sockets. There should be a negative voltage
here that changes when turning the bias pot.
Does both sides behave equal ?
gjmess- Posts : 9
Join date : 2020-10-16
- Post n°3
Re: Bias help. One side not adjusting to proper voltage.
by gjmess Wed Oct 28, 2020 4:42 pm
Swapped tubes...same result...negative voltage on all pin 5s and it does adjust....although the right pot makes no correction to the voltage for the last 1/4 of the turn...both with the bias and the negative voltage.peterh wrote:It could be the tubes at the right side that is weak. Have your swapped right and left side tubes ?gjmess wrote:Been reading the forum again trying to get an answer to my problem. Just installed the Bias circuit kit from Dynakit and I cant't get the right (side) bias pot to adjust to 1.56....gets to about 1.38 and then stops even though I still have adjustment left in the pot. Left side works fine. Bad pot? Everything else seems fine.
If this is not the problem, pull the powertubes and the rectifier tube, turn on and
measure the voltage at pin 5 of the powertube sockets. There should be a negative voltage
here that changes when turning the bias pot.
Does both sides behave equal ?
peterh- Posts : 1869
Join date : 2012-12-25
Location : gothenburg, sweden
- Post n°4
Re: Bias help. One side not adjusting to proper voltage.
by peterh Wed Oct 28, 2020 5:45 pm
Then check the pot by ohm reading from one end to viper. The pot might be bad.gjmess wrote:Swapped tubes...same result...negative voltage on all pin 5s and it does adjust....although the right pot makes no correction to the voltage for the last 1/4 of the turn...both with the bias and the negative voltage.peterh wrote:It could be the tubes at the right side that is weak. Have your swapped right and left side tubes ?gjmess wrote:Been reading the forum again trying to get an answer to my problem. Just installed the Bias circuit kit from Dynakit and I cant't get the right (side) bias pot to adjust to 1.56....gets to about 1.38 and then stops even though I still have adjustment left in the pot. Left side works fine. Bad pot? Everything else seems fine.
If this is not the problem, pull the powertubes and the rectifier tube, turn on and
measure the voltage at pin 5 of the powertube sockets. There should be a negative voltage
here that changes when turning the bias pot.
Does both sides behave equal ?
gjmess- Posts : 9
Join date : 2020-10-16
- Post n°5
Re: Bias help. One side not adjusting to proper voltage.
by gjmess Wed Oct 28, 2020 6:23 pm
ok....thankspeterh wrote:Then check the pot by ohm reading from one end to viper. The pot might be bad.gjmess wrote:Swapped tubes...same result...negative voltage on all pin 5s and it does adjust....although the right pot makes no correction to the voltage for the last 1/4 of the turn...both with the bias and the negative voltage.peterh wrote:It could be the tubes at the right side that is weak. Have your swapped right and left side tubes ?gjmess wrote:Been reading the forum again trying to get an answer to my problem. Just installed the Bias circuit kit from Dynakit and I cant't get the right (side) bias pot to adjust to 1.56....gets to about 1.38 and then stops even though I still have adjustment left in the pot. Left side works fine. Bad pot? Everything else seems fine.
If this is not the problem, pull the powertubes and the rectifier tube, turn on and
measure the voltage at pin 5 of the powertube sockets. There should be a negative voltage
here that changes when turning the bias pot.
Does both sides behave equal ?
gjmess- Posts : 9
Join date : 2020-10-16
- Post n°6
Re: Bias help. One side not adjusting to proper voltage.
by gjmess Thu Oct 29, 2020 9:16 am
Removed to pot....8.29K and the wiper goes from 6.1 to 8.29k Looks the the other pot is about the same although I only removed the one not both.gjmess wrote:ok....thankspeterh wrote:Then check the pot by ohm reading from one end to viper. The pot might be bad.gjmess wrote:Swapped tubes...same result...negative voltage on all pin 5s and it does adjust....although the right pot makes no correction to the voltage for the last 1/4 of the turn...both with the bias and the negative voltage.peterh wrote:It could be the tubes at the right side that is weak. Have your swapped right and left side tubes ?gjmess wrote:Been reading the forum again trying to get an answer to my problem. Just installed the Bias circuit kit from Dynakit and I cant't get the right (side) bias pot to adjust to 1.56....gets to about 1.38 and then stops even though I still have adjustment left in the pot. Left side works fine. Bad pot? Everything else seems fine.
If this is not the problem, pull the powertubes and the rectifier tube, turn on and
measure the voltage at pin 5 of the powertube sockets. There should be a negative voltage
here that changes when turning the bias pot.
Does both sides behave equal ?
peterh- Posts : 1869
Join date : 2012-12-25
Location : gothenburg, sweden
- Post n°7
Re: Bias help. One side not adjusting to proper voltage.
by peterh Thu Oct 29, 2020 10:57 am
If the removed pot behaves correct when measures from both sides ( one end to viper, then other end to viper) then adjust the surrounding resistors.
As the voltage is to high ( to low current in the tubes) you should reduce the bias voltage.
Identify the 10k fixted resistor that connects from one end of both bias pots to ground, solder
another 10k resistor across it, giving the effective resistance 5k.
This will affect both sides, turn down bias pot before power on.
As the voltage is to high ( to low current in the tubes) you should reduce the bias voltage.
Identify the 10k fixted resistor that connects from one end of both bias pots to ground, solder
another 10k resistor across it, giving the effective resistance 5k.
This will affect both sides, turn down bias pot before power on.
gjmess- Posts : 9
Join date : 2020-10-16
- Post n°8
Re: Bias help. One side not adjusting to proper voltage.
by gjmess Thu Oct 29, 2020 4:37 pm
well that did it....thanks for the help.peterh wrote:If the removed pot behaves correct when measures from both sides ( one end to viper, then other end to viper) then adjust the surrounding resistors.
As the voltage is to high ( to low current in the tubes) you should reduce the bias voltage.
Identify the 10k fixted resistor that connects from one end of both bias pots to ground, solder
another 10k resistor across it, giving the effective resistance 5k.
This will affect both sides, turn down bias pot before power on.
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