Bad news with my 300B help needed.

[AnGar]

Hi to all.
today arrived another rec tube 5r (NOS) I tested the filament and seems ok, after installed it nothing happen, the meters (B+ and 300B K) didn't move at all.
after inspection (voltmeter) I found the filament stop working and the base was lose, long story short the filament contact was lose. every time I was moving the base the filament was connecting and disconnecting.(waste)
then I install my normal rec tube, powered up and the B+ dial was showing low voltage and the 300B about 60mA. I turned everything off.
any advice what could happen?
Note the drawing shows a 5AR4 but the final design is for a 5r4gyb

Thank you in advance

 

[AnGar]

chocks and caps are ok.
can I power up without tubes? I thinks I asked that before but dont remember.

 

[AnGar]

the main caps are showing the right capacitance and using a voltmeter shows charge and discharge.
but powering up the B go too high and after turn off the power the meter still showing high voltage. IMO one of the main caps left the chat.

 

[paul_b]

You said you had ~300V DC, but now you have B+ that's too high?

If the circuit isn't drawing any current, then your B+ will go to the moon.

 

[AnGar]

I checked the PT with no tubes.
all voltages are ok.
I installed a rec tube again, powered up and the rec tube spark (using a variac) the b+ as you say go to the moon, turn off everything.
Do you think the caps could be damaged?

 

[adnick]

I’m having a difficult time understanding the issue(s) Andre, maybe be a bit more specific in each case, with tubes/without tubes, giving numbers when possible and/or the measurement locations….

Also you said you are powering it via a variac? Have you checked the output voltage of the variac?

 

[AnGar]

I’m having a difficult time understanding the issue(s) Andre, maybe be a bit more specific in each case, with tubes/without tubes, giving numbers when possible and/or the measurement locations….

Also you said you are powering it via a variac? Have you checked the output voltage of the variac?

Andy!
Thats true.
The last test was without tubes but rectifier.
The variac start at 100vac slowly going up until the filament get incandescent, 119vac then sparks all over. The B+ jump high more than 500 then goes down but at that moment I turned off everything. I do t want cause more posible damage that I have.
Powered without any tube. All PT voltages are normal.
Feel free to ask by now I have no idea how to start troubleshooting.

 

[paul_b]

You could try a 5AR4 for slower warmup.

 

[AnGar]

You could try a 5AR4 for slower warmup.

Using the 5AR4 starting with 100VAC until 120VAC the B+ reach the 450VDC and then start going up (no any other tube installed)
Should install the rest of the tubes and try?
what is not normal as before after the voltage reach the 500VDC and I turned off the system, the B+ meter slowly goes down, before the failure, it was going down way quicker.
for any further test do you recommend to disconnect the OT?

thank you in advance for your help.

 

[AnGar]

Another symptom observed is the when the B+ reach the proper working voltage there is a spike and then start going up.
AG.

 

[adnick]

Another symptom observed is the when the B+ reach the proper working voltage there is a spike and then start going up.
AG.

What did it rise to?

 

[paul_b]

With a 5AR4, just plug the amp into the wall and turn it on. I would not power up an amp like this with only the rectifier tube in. It's a good idea to have the 300Bs in there to provide some load to the power supply.

No, don't disconnect the output transformer.

 

[AnGar]

Hi Paul.
the B+ is moving slow and then jump to more than 500VDC the 300B cathode 30mA the rec tube is arcing.

 

[RonSSNova]

His supply uses a 1200vct transformer. Choke input configuration. Not good for a 5AR4.

It’s virtually identical to the Altec supply I copied for my PP300B amps. Except I use 2 5R4’s per channel.

I’m a bit confused Angar. Do you have any known good 5R4’s?

 

[AnGar]

His supply uses a 1200vct transformer. Choke input configuration. Not good for a 5AR4.

It’s virtually identical to the Altec supply I copied for my PP300B amps. Except I use 2 5R4’s per channel.

I’m a bit confused Angar. Do you have any known good 5R4’s?

I use a 5R4GYB on it, the 5AR4 was for test only.
thanks for your help

 

[AnGar]

His supply uses a 1200vct transformer. Choke input configuration. Not good for a 5AR4.

It’s virtually identical to the Altec supply I copied for my PP300B amps. Except I use 2 5R4’s per channel.

I’m a bit confused Angar. Do you have any known good 5R4’s?

yes I have known good 5R4GYB, I am afraid to fry it also.
Andre.

 

[AnGar]

What did it rise to?

more than 500VDC the needle is going til the end of the scale.

 

[paul_b]

Looking at the drawing, the thermistor position on the power transformer isn't correct.

30mA through the 300B on 500V of B+ isn't correct. You should see at least twice that.

You can certainly pop in some solid state diodes temporarily to check things.

The arcing in the rectifier could be from too much capacitance following that choke, or it could be from some excessive DC current demand from the power supply. Having higher B+ than expected would tend to indicate that there isn't a huge draw on the power supply.

As always, you can simulate your power supply in PSUD and have a look at the current through the rectifier tube to be sure the peak current rating isn't exceeded.

 

[AnGar]

Looking at the drawing, the thermistor position on the power transformer isn't correct.

30mA through the 300B on 500V of B+ isn't correct. You should see at least twice that.

You can certainly pop in some solid state diodes temporarily to check things.

The arcing in the rectifier could be from too much capacitance following that choke, or it could be from some excessive DC current demand from the power supply. Having higher B+ than expected would tend to indicate that there isn't a huge draw on the power supply.

As always, you can simulate your power supply in PSUD and have a look at the current through the rectifier tube to be sure the peak current rating isn't exceeded.

the thermistor is just in the drawing, was never installed there.
using SS diode will increase the B+ drastically. is that safe for the rest of the components?

My question what could possible happened after I install the failed rec tube?

 

[paul_b]

It's reasonable to run the amp with solid state rectifiers and the 300Bs installed in the sockets. Yes, the voltage will be a little bit higher, but the 300B will still be operating in a safe area.