I need some help from you guys who are more familiar into DIY stuffs.
My pre-amp PS has gone wild. The pre-amp tubes 2x6922 were very bright and when I did the measurement, heater supply went up to 12V. I did some measurement on components and found this regulator GL317 shorted. I replaced with LM317 and tuned the desired voltage 6.3V for the filament but, it can only run for less than a minute then it shut-off. The regulator turns very hot when loaded with the tubes.
My x'former secondary output 10.3Vac to the bridge rectifier 100V/6A and measured 12.96Vdc after filtering section and serves to be my input to LM317.
Any idea how can I fix this???
Thanks a lot for your halp.
My pre-amp PS has gone wild. The pre-amp tubes 2x6922 were very bright and when I did the measurement, heater supply went up to 12V. I did some measurement on components and found this regulator GL317 shorted. I replaced with LM317 and tuned the desired voltage 6.3V for the filament but, it can only run for less than a minute then it shut-off. The regulator turns very hot when loaded with the tubes.
My x'former secondary output 10.3Vac to the bridge rectifier 100V/6A and measured 12.96Vdc after filtering section and serves to be my input to LM317.
Any idea how can I fix this???
Thanks a lot for your halp.
With 6.3V across the filaments and about 2.5V across the 317, the simple solution is to make a pi filter by adding a series resistor in the PS and a second filter cap to bring the voltage at the input to the 317 to about 9V. Calc's out to 6.6R and about 10W.
I don't like series stringing tubes, esp when the voltage is a bit high. You can never tell exactly how they will line up in terms of voltage across each individual filament, so one may end up > 6.7V and shorten it's life.
Heatsink the 317 really well.
I don't like series stringing tubes, esp when the voltage is a bit high. You can never tell exactly how they will line up in terms of voltage across each individual filament, so one may end up > 6.7V and shorten it's life.
Heatsink the 317 really well.
The LM317 has a trim pot connected to the common pin to (B-). This where I tune the ouptut voltage to 6.3V and a 150ohms resistor connected between commom to ouput pins.
It will only runs hot if the load is present. I did tried to load only 1 tube since my pre has 2 6922 tubes, but still hot. The regulator shuts-off after reaching a certain temp.
how????
It will only runs hot if the load is present. I did tried to load only 1 tube since my pre has 2 6922 tubes, but still hot. The regulator shuts-off after reaching a certain temp.
how????
JOE DIRT® said:The Lm 317 is rated for 1.5 amps with a modest heatsink
I would measure what each heater is drawing there could be a chance you have a bad tube
also is there a current limiting resistor going to each heater>???...if so that could be the culprit
DIRT®
Exactly. He had a system that worked, no it doesn't anymore, blows the reg. Logically, that points to a (partially) shorted heater wire (or series R, if there is one). So, advise on a complete redesign is not what he needs, because it wouldn't work anyway without getting rid of the cause.
jan Didden
Hi,
Me neither...unless we're talking a single block using //ed valves you still have a real risk of signal breakthrough between cathode and heater.
Anyone ever capcoupled a heater supply and listened to it?
Powersupplies?
Cheers,
I don't like series stringing tubes, esp when the voltage is a bit high.
Me neither...unless we're talking a single block using //ed valves you still have a real risk of signal breakthrough between cathode and heater.
Anyone ever capcoupled a heater supply and listened to it?
Powersupplies?
Cheers,
Thanks guys for all your suggestions. But, I am a bit lost where to start. Roughly, I may need ~8Vdc without the load. It will be just nice maybe for 6.3V.
What is the best step now? Bring down the input voltage to ~9Vdc?
Any other design I can DIY with my existing 10.33Vac for the filament?
thanks again...
Billy
What is the best step now? Bring down the input voltage to ~9Vdc?
Any other design I can DIY with my existing 10.33Vac for the filament?
thanks again...
Billy
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