Working on an amp right now that is giving me lower than expected B+ values and I want to know why. Here's what I have and what i'm getting:
PT Secondaries: 315 - 0 - 315 VAC
Rectifier: 5AR4
B+ (no tubes) : 444 VDC
B+ (w/ tubes) : 373 VDC
I'd expect to see somewhere in the 420-430 VDC range for the B+ under load, and i've checked with an online calculator to verify that. Anyone have ideas why my B+ is so low? Its a cathode biased amp, 2xEL34 push pull. Started with a 250 ohm shared cathode resistor, and the intent was to tailor that value as needed but I'm trying to get a grip on this B+ first.
B+ Quandary
Moderators: pompeiisneaks, Colossal
-
Dr Tony Balls
- Posts: 88
- Joined: Wed Jun 05, 2013 4:25 pm
- Location: Brooklyn, NY
- Contact:
B+ Quandary
I build effects and amps and do custom builds to order. Boom.
Site: http://ballseffects.com/
Site: http://ballseffects.com/
-
sluckey
- Posts: 3528
- Joined: Sun Jul 22, 2007 7:48 pm
- Location: Mobile, AL
- Contact:
1 others liked this
Re: B+ Quandary
2xEL34 running with cathode bias is a BIG current load. It's perfectly normal for the B+ to drop that much with most PTs. Now if you use a PT that's capable of delivering 500mA, the B+ drop will be much less, but using a PT that big would be insane for this amp.
You can increase the B+ by using a SS rectifier.
You can increase the B+ by using a SS rectifier.
-
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: B+ Quandary
Has that 5AR4 been been tested and is showing as good, which in my book for a cathode biased amp means testing out at 80% or better?
If it’s down to testing at 60% that will make for a big drop in output voltage!
If it’s down to testing at 60% that will make for a big drop in output voltage!
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!
-
Littlewyan
- Posts: 1944
- Joined: Thu Sep 12, 2013 6:50 pm
- Location: UK
2 others liked this
Re: B+ Quandary
Few things come to mind.
- Measure your wall voltage
- Test that rectifier as SteveM said
- Measure the current draw of your EL34s
The B+ sagging a lot under load could be due to poor regulation in the Power Transformer. Did you measure 315VAC unloaded or loaded? Or is that just the spec of the PT?
- Measure your wall voltage
- Test that rectifier as SteveM said
- Measure the current draw of your EL34s
The B+ sagging a lot under load could be due to poor regulation in the Power Transformer. Did you measure 315VAC unloaded or loaded? Or is that just the spec of the PT?
-
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: B+ Quandary
I would like to make a request that from this point forward we try like heck to not use the term B+ or minus, but use V+ And such.
I don’t know about you but on my many years on this rock I have never ran any of my amps on Battery.
I don’t know about you but on my many years on this rock I have never ran any of my amps on Battery.
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: B+ Quandary
B+ is standard notation, battery or not. We all know exactly what it means. Introducing V+ is like swimming upstream.
-
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: B+ Quandary
I guess some don’t remember that when you learn electronics in school it’s always V, remember good old VAC and +VDC and - VDC?
Anyone have a voltmeter, maybe even one thats over 60 years old that has a cable hole or a rotory switch labeled for B+ or B- ? Yup, I did not think so!
Anyone have a voltmeter, maybe even one thats over 60 years old that has a cable hole or a rotory switch labeled for B+ or B- ? Yup, I did not think so!
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: B+ Quandary
I agree with Phil…
If we want to get super nit picking we could argue about which direction electrons flow and the wisdom of “conventional current. I was very confused during the electricity chapters of the physics class I took because I took it after completing chemistry because the two disciplines viewed the flow of electrons oppositely.
If we want to get super nit picking we could argue about which direction electrons flow and the wisdom of “conventional current. I was very confused during the electricity chapters of the physics class I took because I took it after completing chemistry because the two disciplines viewed the flow of electrons oppositely.
-
pdf64
- Posts: 2932
- Joined: Sat Mar 12, 2011 9:23 pm
- Location: Staffordshire, UK
- Contact:
4 others liked this
Re: B+ Quandary
This discussion over B+ is becoming rather high tension 
https://www.justgiving.com/page/5-in-5-for-charlie This is my step son and his family. He is running 5 marathons in 5 days to support the research into STXBP1, the genetic condition my grandson Charlie has. Please consider supporting him!
-
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: B+ Quandary
Lol, no at all, just charged up for a debate!
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: B+ Quandary
Everyone uses B+ and everyone understands what B+ means if has a even only bit of knowledge, so I can't see why we should avoid it.
A+ and C+ are way less used, but B+ is seen everywhere.
A+ and C+ are way less used, but B+ is seen everywhere.
Re: B+ Quandary
We British dont understand B+ we use HT or +V or V+.
-
Stevem
- Posts: 5144
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
1 others liked this
Re: B+ Quandary
How about we meet in the middle and adopt these proper terms from the GE tube book?
You do not have the required permissions to view the files attached to this post.
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: B+ Quandary
Good luck with that
https://www.justgiving.com/page/5-in-5-for-charlie This is my step son and his family. He is running 5 marathons in 5 days to support the research into STXBP1, the genetic condition my grandson Charlie has. Please consider supporting him!
-
sluckey
- Posts: 3528
- Joined: Sun Jul 22, 2007 7:48 pm
- Location: Mobile, AL
- Contact:
2 others liked this
Re: B+ Quandary
Maybe you could start your own thread rather than hijacking Dr. Balls thread!