• Disclaimer: This Vendor's Forum is a paid-for commercial area. Unlike the rest of diyAudio, the Vendor has complete control of what may or may not be posted in this forum. If you wish to discuss technical matters outside the bounds of what is permitted by the Vendor, please use the non-commercial areas of diyAudio to do so.

B+ voltage drift?

I've been putting some hours on my new TSE 300B amp to break in the Psvane Treasure MKII 300B's. My power transformer is an Edcor XPWR131-120. It has 660 volts, center taped. I have an 8.2uf cap in C4 position. When I power up the amp my B+ is 374 to 375 volts. As it warms up the B+ drops. It seems to stay around 370 volts for a while, then continues to drift down. After about 5 hours it has dropped to about 366 to 367 volts. Today, I turned it on, and B+ was 380 volt. After an hour it is now down to 375 volts. It's all within a decent range. So I'm not worried about ruining anything. I am just curious if this is normal with a new amp where everything is breaking in. Oh, I have about 71 hours on the amp now, and about 55 hours on the new tubes. Oh, the 300B's bias current drifts down as they warm up also. Although they are drifting less as they get more hours on them.Thanks all for all your help.:spin:
 
Last edited:

cbutterworth

Member
2006-10-03 11:02 pm
Valves do not "break in". They have issues like poor regulation for the bias voltage or have not been set up properly.
Question; Do you expect a new car to improve after use? I doubt it.


Cars do have a break-in period. They can improve, one example being in the Prius in which gas mileage gets more efficient.

People swear that caps break in. I can't say I've noticed, but that doesn't mean it does not happen.

Charlie
 
The power transformer is not getting hot. It gets warm. And the drift seems to be a steady, slow downward drift the longer I leave the amp on the lower it drifts. Not like the mains voltage was changing. But about 366 volts is the lowest it's gone so far, so its not to bad. Today it didn't seem to drift as low as fast, but I only ran it for 2 hours. I'm waiting on some resistors to come in the mail, to get my filament voltage correct for the 5842. Then I'll continue testing and see if its settling in yet.:confused:
 
The power transformer is not getting hot. It gets warm.
Is this a joke?
Both words refer to exactly the same parameter: temperature.


Although they are drifting less as they get more hours on them.

see if its settling in yet

NONE of that applies to an amplifier or to electronic circuits; those terms are at home in a car mechanic shop or similar places where moving mechanical parts are the main object.

Electrons work in a very different way.
 
Is this a joke?
Both words refer to exactly the same parameter: temperature.







NONE of that applies to an amplifier or to electronic circuits; those terms are at home in a car mechanic shop or similar places where moving
Electrons work in a very different way.




Yes this is correct. I know that the 300B tubes do break in and sound better after time. But the electronic circuit should be stable. The only thing I can figure is as Triplej has said. Although the power tranny is not getting really hot, Maybe it does loose some efficiency and drops voltage a little as it warms up.
Both pairs of 300B tubes that I have had the bias drift when new. This seems to become less as I get some hours on the tubes. So this doesn't bother me. I was just wondering about the B+. Now the 380 volts at start up yesterday, that could of been line voltage.
Also, I know that when you up the bias current on the 300B tube the B+ should drop. But the B+ drops as the amp gets warmer, and at the same time that the tubes Bias current is drifting downward also. The tubes are drifting less as they get more hours on them so I expect them to settle down soon.
 
If the transformer is not overheating, the filter caps or bleeder resistor could be suspect, or rectifier tube. Or your mains voltage could be suspect, but it seems odd that the variance would always be down. If it were that, you'd think it would drift up once in a while.

I can see a new tube, or a tube that has not been used in long time, needing a few hours for the cathode to come up to full emission, but after that, it should be stable.

Win W5JAG

edit: have you looked at what the bias voltage is doing? if the bias voltage is also declining, off the top of my head, that would seem to suggest a transformer problem.
 
Last edited:
The B+ and the B- voltage drift downward as the unit warms up. The B+ seems to drift more then B-. I have a confession to make. I don't have any electrolytic caps in the B+ or B- supplies. C4 is a 8.2uf clarity cap. C5 is a 200uf Mundorf Poly Tube Cap, C6, and C7 are both 100uf Mundorf Poly Tube Caps. They are connected to the brd. by 2" to 3" twisted pair wires, except C4 which is connected directly to the brd. by its leads. This should not make a difference, and it improved the sound.
So I'm left to think that the power tranny is drifting a little as it warms. Could C4's value be drifting as it warms up inside the chassis. Would it have to drift a lot to make a 10 volt drop in B+ in 5 hours. Funny thing. Usually when I turn her on in the morning when she is cold the B+ usually starts out at 375 volts, and then drifts down as it warms. Yesterday when I turned her on B+ started out at 380 volts, and drifted slower then usual to 375 volts and seemed to stay there. But I only had her on for 2 hours. Today when I turned her on, it was the same. It started at 380 volts and is very slowly drifting down. She has been on for 1 hour and it had dropped to 376 volts. I have monitored my line voltage recently, and it is a pretty steady 120 volts AC. The filament voltage for the 5842 is steady. Same transformer. Different winding. The power transformer also has a 520 volt center taped winding that I caped off the wires with shrink tubing and tied them off. I think I covered everything. I really don't want to have to try a different power transformer, at this point. Any thoughts? Thank you all.:confused:
 
Last edited:
.... I have a confession to make. I don't have any electrolytic caps in the B+ or B- supplies. C4 is a 8.2uf clarity cap. C5 is a 200uf Mundorf Poly Tube Cap, C6, and C7 are both 100uf Mundorf Poly Tube Caps. They are connected to the brd. by 2" to 3" twisted pair wires, except C4 which is connected directly to the brd. by its leads. This should not make a difference, and it improved the sound.

.....

Any thoughts? ...

Well, if you have not already, I'm thinking it might be a good idea to try the parts specified in the bill of materials and make sure it works properly with those.

Otherwise, you have no baseline to work from.

After that, you could substitute parts. I've never heard of the parts above ^^^^ ( that doesn't really mean anything ) but I would consider the possibility that they may not be cutting the mustard for the purpose you are using them.

Win W5JAG
 
Hey w5jag,
The Mundorf Poly Tube Caps are Big polypropylene Caps designed for Tube power supplies. The Clarity Cap is a standard for electronics Capacitor.
I've tried different rectifier tubes. Still Drifts.
I have a fan inside the unit, and the drift is slower when the fan is on. So I'm pretty sure its a thermal problem with a part. I've ordered a new cap for C4 position, since C4 value effects the voltage.
By the bleeder resistor do you mean the resistor from the B+ rail to ground (R30) ? If so I will try that next.
Thank you for all the help.
 
Do you have another DMM? If so, try it and see if you are seeing the same pattern of drift.

It's a possibility, remote perhaps, that your meter is drifiting, but might as well eliminate that before you start changing parts.

Win W5JAG



Changed DMM. Same Drift. Started at 379 volts. After 10 hrs. of play it dropped to 369 volts, with the fan running.
 
I'm still studying what's going on. But I'm starting to think that The downward drift of the Bias current of the 300B tubes corresponds to the downward drift of the B+ voltage. Seems like after 4,or 5 hours, with the fan on the B+ settles at around 370 volts. I say the because it will bounce between 370 and 371. Sometimes after a few more hours it sometimes drops to 369 volts. But when it's settled and bouncing between 370 volts and 371 volts, the bias current stops dropping also and bounces between 68 ma and 682ma. So I think as the B+ drops it brings the Bias current down also.
Any ideas as to what to look for? I have a replacement coming for C4. I'll keep my fingers crossed. Thank you all.:xfingers:
 
Tale of two meters!

I have 6 DMM's. Two good Flukes, and 4 cheap flee bay meters. I had one of the cheapo meters on the AC line voltage in my shop, which is a small steel building, powered by an extension cord from the garage. It read 120 Volts steady. So I figured it was the same in the garage, where I have the amp and speakers playing now, to break in the tubes. Well, that meter craped out on me so it got retired. I took one of my flukes and put it on the AC line voltage.
I have a 8.2uf cap in the C4 position. And it seems my line voltage is high. It starts out in the mornings at about 123 volts, and slowly declines all day to 121 volts at night.
So it seems like when its cold and the AC is 123 volts it starts out with about 379 to 380 volts B+. As it warms up it seems like the voltage drops faster then the AC drops. After about 30 min or so it has dropped to about 375 volts B+. Then it seems to follow the AC voltage. The AC voltage drop isn't a straight linear decline. As it drops over the day it fluctuates up and down, but gets lower as the day goes on. The B+ volts follows the AC voltage up and down.
It seems about .3 volts change in the AC voltage equals a 1 volt change in B+ voltage. At about 10 PM yesterday she was at about 122 volts AC, and about 369 volts B+.
So my conclusion is that when cold the B+ is a little high. As it warms up that corrects it self, and then the B+ follows the AC line voltage decline. So I think its working as it should. I can't hear any change in the sound as the voltage changes. I'm only talking about a 1 to 2 volt change in the AC voltage. So I think I'm good to go.:p
 
The drift was mostly AC line voltage changing, but also it seemed to drop faster the first 20 minutes. I was using a Sovtek 5AR4 rectifier tube. I changed that to a NOS Mullard 4 notch 5AR4/GZ34 tube and the voltage drop as the tube warms up stopped or is a lot less. It seems to just follow the AC voltage now.

My 300B TSE has been doing the exact same thing. It starts out at about 379ish and as it warms up over thirty minutes to an hour, it gets to about 368. My guess is it has to do with the silicon somewhere.

Also, for those saying that tubes don't drift a pretty good bit in the first few hours, I don't where you're getting your tubes, but mine varied considerably for at least the first 5-10 hours. I've finally got them dialed in now and the bias rises to the same point and the two 300B's seem to stay pretty even. But in the beginning, they drifted up to 10-20mA.