Hot Rod Deluxe - Very Low Bias
Moderators: pompeiisneaks, Colossal
Re: Hot Rod Deluxe - Very Low Bias
Disconnect CR3 and see if the bias reading increases.
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Stevem
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Re: Hot Rod Deluxe - Very Low Bias
yeah, at this point it would seem to be a shorted socket or shorted circuit board trace issue, yet he makes no mention of smoke or fire!?
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Hot Rod Deluxe - Very Low Bias
Correct. Removing the OT's center tap from B+ did not raise it back to 431V. It went from about 360V to around 380V.sunnydaze wrote:If I read your responses correctly, pulling the power tubes causes B+ to reach the specified 431 volts. But you also said no to Steve M's question of whether disconnecting the OT CT from B+ caused the voltage to go back to 431? Did I read that correctly. Finally, through all that, no change in bias current.
Pulling power tubes - voltage returns to spec.
So, indicates powertubes drawing huge current causing big voltage drop.
However, disconnecting the plates from B+ by disconnecting OT CT has no effect. All the while, bias current in minimal.
Would seem to leave only the power tube screens, but rolling tubes has no impact either. Maybe the tube socket is shorted. Try pulling the power tubes and checking for continuity where there should be none on the tube socket. In particular look for a short on the screens.
Best regards,
Mike
I have done this already with no positive results.sluckey wrote:Disconnect CR3 and see if the bias reading increases.
No burnt components or any traces of such anywhere in the amp. I know, it's weird. I have done continuity tests between the pins in the sockets and the PCB and also between the pins on the sockets. I even removed the sockets completely and the measurements did not change. I have inspected the sockets thoroughly and see no signs of shorts or anything like that, however, at this point I'm kicking myself for not just replacing the sockets when they were out just for the hell of it. I will probably do this on Saturday when I am back in the shop.Stevem wrote:yeah, at this point it would seem to be a shorted socket or shorted circuit board trace issue, yet he makes no mention of smoke or fire!?
Re: Hot Rod Deluxe - Very Low Bias
For anyone that is interested, the first filter cap in the power supply was bad. I replaced it and that fixed all issues. Obviously my method of checking high voltage capacitors is not reliable. Thanks to everyone for your help!
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groovtubin
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HRD
pull the diodes on PLATES of power tubes, don`t need them.. also check the diode and one ohm on cathode
I`ve worked n modded a zillion of these..... HTH`s!!
jim@Omegaamps.com
I`ve worked n modded a zillion of these..... HTH`s!!
jim@Omegaamps.com
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Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: Hot Rod Deluxe - Very Low Bias
X2 to the above removal of diodes!
If you care to you can pull that bias check resistor at the end of the output board, cut the pin 8 traces and install a 1 ohm 2 watt 1% resistor from each cut trace to ground and then check the bias current for each output tube directly with a dc voltmeter.
If you care to you can pull that bias check resistor at the end of the output board, cut the pin 8 traces and install a 1 ohm 2 watt 1% resistor from each cut trace to ground and then check the bias current for each output tube directly with a dc voltmeter.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Hot Rod Deluxe - Very Low Bias
BungleSim wrote:For anyone that is interested, the first filter cap in the power supply was bad. I replaced it and that fixed all issues. Obviously my method of checking high voltage capacitors is not reliable. Thanks to everyone for your help!