#1
Hello fellow amp gurus,

I'm a Senior here at Purdue University in the Electrical Engineering department. My Senior design proposal has been focused on inventing a battery powered tube amp. I was wanting to see if I could get some feedback from this community on my project. I was thinking of using a lithium ion battery, a switching boost power supply to get the crazy high B+ voltage, an E88CC preamp tube because of the 90V voltage, an ECC83S power tube for its low heater power, and was thinking about a 1 Watt output.
I put a post up a few weeks ago when the idea got into my head and got some great information. I am using space charged tubes to reduce power and am only looking at 1 Watt output. I have been in contact with AX84 forums as well as others online. I have a great block diagram going for the project, now I need to find some specifics for the project.
So far I have a general idea about how to approach this project, but I have very little exact info on things such as calculations and part numbers. I am trying my hardest to learn how to play with tubes in an amplifier. I have been using op amps and MOSFET's my whole college career.
I figured this community would be eager to help a kid out with your experiences and sources. My bookmark folder has 25 different pages where I have been doing research. Any info would help guys.

Thanks in advance.
Peavey VK112
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........Uber Noob Skillz
#2
Quote by jewbaby667
I was thinking of using a lithium ion battery,
make it a big one. you need a good bit of power, just to heat the tubes. this thing could be a waste, if your battery capacity is low.

Quote by jewbaby667
a switching boost power supply to get the crazy high B+ voltage,
crazy high? not necessary. about 100v should do okay. 200v would be better.

remember, even with perfect efficiency in your transfer, if you need 20 mA on your B+ @ 120v, that would require 200 mA @ 12v from your battery. and power transfer is never 100%

Quote by jewbaby667
an E88CC preamp tube because of the 90V voltage,
I'm curious why you chose that tube. typically a E66CC/6922/CV2492 would be used in a circuit that uses a LOT of idle current. about 10~15 mA per triode. sweet tube, but power sucker. also, the heater requirements are not as flexible as those of a ECC83/7015/12AX7. it can only run on 6V, 12 is not an option. the current is the same as a 12AX7 with parallel heaters. and the mu is lower. about 33 instead of 100.

what are you hoping to gain, here.

Quote by jewbaby667
an ECC83S power tube for its low heater power, and was thinking about a 1 Watt output.
1W is a very reasonable expectation from a 12AX7. are you planning on push-pull or single ended?
Meadows
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#3
Quote by SomeoneYouKnew
make it a big one. you need a good bit of power, just to heat the tubes. this thing could be a waste, if your battery capacity is low.

crazy high? not necessary. about 100v should do okay. 200v would be better.

remember, even with perfect efficiency in your transfer, if you need 20 mA on your B+ @ 120v, that would require 200 mA @ 12v from your battery. and power transfer is never 100%

I'm curious why you chose that tube. typically a E66CC/6922/CV2492 would be used in a circuit that uses a LOT of idle current. about 10~15 mA per triode. sweet tube, but power sucker. also, the heater requirements are not as flexible as those of a ECC83/7015/12AX7. it can only run on 6V, 12 is not an option. the current is the same as a 12AX7 with parallel heaters. and the mu is lower. about 33 instead of 100.

what are you hoping to gain, here.

1W is a very reasonable expectation from a 12AX7. are you planning on push-pull or single ended?


Thank you for such detailed questions. The 12AX7 heats both tubes inside up with 1 element?

My power calculations from this data sheet http://lib.store.yahoo.net/lib/thetubestore/JJ-ECC83-S.pdf put the heater at 12V @ 150mA which is 1.8Watts. The plate would then consume 250V @ 1.2mA which is 300mA. That totals to 2.4Watts of power to supply. It does not seem like that would require such a large battery.

I was thinking of using something like a 50 Amp/hr laptop battery.

I hadn't decided on pushpull or single ended, but was leaning towards single ended. Don't pushpull require phase splitters? A guy a semester ahead of me is doing a 100Watt tube amp and says Class AB push pull is a bitch and I should just go single ended Class A.

The main part of my project is the battery charger and battery monitoring system. The amp is just something to do with it hehe, but I am the most interested in this part.
Peavey VK112
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Jackson Warrior JS30 upgraded EMG 81/85
Epiphone Silverburst 1966 Reissue G-400
Washburn D12N

Playing since 03-11-07
........Uber Noob Skillz
#4
searchbar, a couple of months ago a guy on here built a similar amp usin space charge tubes, it was pretty awesome....but it didnt use a battery...could still be useful tho

EDIT: here ya go. https://www.ultimate-guitar.com/forum/showthread.php?t=924380&highlight=space+charge
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Last edited by AngusJimiKeith at Oct 30, 2008,
#5
Quote by AngusJimiKeith
searchbar, a couple of months ago a guy on here built a similar amp usin space charge tubes, it was pretty awesome....but it didnt use a battery...could still be useful tho

EDIT: here ya go. https://www.ultimate-guitar.com/forum/showthread.php?t=924380&highlight=space+charge


Hey thanks, if the power consumption turns out to be reasonable at 12V, that my really help. Thanks again
Peavey VK112
Fish&Chips EQ
Ibanez TS9DX
Jackson Warrior JS30 upgraded EMG 81/85
Epiphone Silverburst 1966 Reissue G-400
Washburn D12N

Playing since 03-11-07
........Uber Noob Skillz
#6
Quote by jewbaby667
Thank you for such detailed questions. The 12AX7 heats both tubes inside up with 1 element?
2 elements, three pins. you can run the heaters in parallel on 6v or in series on 12v.



connect one end of a 12v supply to pin 4 and the other end to pin 5 for the series connection.

connect one end of a 6v supply to BOTH pins 4 and 5 and the other end to pin 9 for the parallel connection.


Quote by jewbaby667
My power calculations from this data sheet http://lib.store.yahoo.net/lib/thetubestore/JJ-ECC83-S.pdf put the heater at 12V @ 150mA which is 1.8Watts. The plate would then consume 250V @ 1.2mA which is 300mA. That totals to 2.4Watts of power to supply. It does not seem like that would require such a large battery.
your calculations are a bit off.

- in a Single Ended amplifier, you need to be idling at 100% power.
with 250v on the plate, you'll need 4 mA. at any rate, figure 1 watt if you want to have a capability of 1 watt output.

- you've only calculated the power for a single 12AX7 regarding the heater requirement. you need to have at least 2 of them. one pair of triodes, bare minimum, for voltage amplifiers before the power amp. figure 3.8w for the heaters.

- your voltage amplifiers will be more similar to what you had estimated for the 12AX7.
with a 250v supply and 1.2 mA, 300 mW per triode.
lets figure using 3 voltage amplifiers. now you're at 900 mW.

- total for the heaters, 3 voltage amplifier stages and the output stage = 5.7 watts

- wait, we can't go there yet!

- 1 W for the output + 900 mW for the voltage amplifiers = 1.9 W

- with a 70% efficiency in the transfer from 12 volt to 250v, 1.9 W / 0.70 = 2.7 W

- add the 3.8 W for the heaters and you're at 6.5 Watts


Quote by jewbaby667
I was thinking of using something like a 50 Amp/hr laptop battery.
well that would get you 7 1/2 hours of use, assuming you can supply enough voltage all the way to the end of the 50 Ah capacity. Not always true.


Quote by jewbaby667
I hadn't decided on pushpull or single ended, but was leaning towards single ended. Don't pushpull require phase splitters? A guy a semester ahead of me is doing a 100Watt tube amp and says Class AB push pull is a bitch and I should just go single ended Class A.
yeah, phase inverters can be a royal pain, but a PP amp is rich in odd ordered harmonics. great tone when distorted. you get mainly even ordered harmonics from a SE amp. not nearly as interesting. for a first project, a SE probably makes more sense due to the simplicity.


Quote by jewbaby667
The main part of my project is the battery charger and battery monitoring system. The amp is just something to do with it hehe, but I am the most interested in this part.
k, koo.
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#7
OK SomeoneYouKnew, those thoughts really helped out. I am looking at a 12au7 for the power amp. So using a 12ax7 in a two stage preamp setup and a 12au7 as a Class A single ended power stage, my power budget is looking like this:

Preamp (12ax7):

Heater = 12V @ 150mW = 1.8W times 2 = 3.6W

Plate Voltage = 250V @ 1.2mA = 300mW times 2 = 600mW

Total = 4.2W from the preamp

Power Amp (12au7):

Heater: 12.6V @ 150mA = 1.89W

Plate: 330V @ 22mA = 7.26W

Total = 9.15W

My total power budget would then be 13.35W.

I want to consider the worst possible efficiency of my power supply and say it takes double the power to make this so, 26.7 is good. I will round to 30W. I need a 30Watt hour battery for 1 hour of operation. I am only speccing for 30 minutes of runtime, so this gives me a ton of headroom.

Thanks again man for helping me smooth out this operation.

See any flaws in my logic or power budget?
Peavey VK112
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Ibanez TS9DX
Jackson Warrior JS30 upgraded EMG 81/85
Epiphone Silverburst 1966 Reissue G-400
Washburn D12N

Playing since 03-11-07
........Uber Noob Skillz
#8
Quote by jewbaby667
See any flaws in my logic or power budget?
k, then. let's look it over:

Preamp (12ax7):

Heater = 12V @ 150mW = 1.8W times 2 = 3.6W
if your heater is in series (12v) you only need 120 mA for the whole tube. i was doubling that in the previous, when talking about a 12AX7 for the preamp and another one for the power amp.
1.8 W for the heater for this tube.


Plate Voltage = 250V @ 1.2mA = 300mW times 2 = 600mW
okay

Total = 4.2W from the preamp
adjust the total

Power Amp (12au7):

Heater: 12.6V @ 150mA = 1.89W

Plate: 330V @ 22mA = 7.26W
maximum plate dissipation for a 12AU7 is 2.75 W per triode.
even if you put both triodes in parallel, you shouldn't exceed 5.5 W.
tbh, i wouldn't run anywhere close to that.
1 W is plenty loud. i'd design around that.
4 W is as far as i'd push a little tube like this.


Total = 9.15W
adjust this total

My total power budget would then be 13.35W.

I want to consider the worst possible efficiency of my power supply and say it takes double the power to make this so, 26.7 is good.
if you run your heaters at 12v and the battery is 12v, you don't need to use a transfer stage for them. that part will just be 1:1.
only your B+ requirements need to be doubled because of losses in your power supply.

I will round to 30W. I need a 30Watt hour battery for 1 hour of operation. I am only speccing for 30 minutes of runtime, so this gives me a ton of headroom.
30 minutes doesn't seem like much. but if that's all you need, so be it.


good luck.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#9
I wanted to thank everyone again for their insight and help. I have decided to use a 5W design off of the classic AX84 amp and power it at 1W. I had a meeting with a Professor and he helped get me a solution. He advised to design 10 times more power than you will be using due to the 3x crest faster of audio sign waves. So, I will be using my 1W design budget with a 5W design. I will be using the 12ax7 preamp tube and EL84 power tube to get my 1W out. He OK'd my power budget for a 30 minute runtime and advised turning down the B+ voltage as many here have. So my biggest amplifier experimenting will be trying to get the 1W I need with as little power as these tubes will take.

I really liked the idea of using the minitubes, but I could not find a solution to get my 1W output that was as easy as using existing designs. I wish I had the time to design my amp from scratch like this and make this project even more outstanding. I am going to have to keep my focus on the power supply and battery.

I will try and keep this thread updated with my trials and tribulations. It is defiantly bookmarked.

Wish me luck folks.
Peavey VK112
Fish&Chips EQ
Ibanez TS9DX
Jackson Warrior JS30 upgraded EMG 81/85
Epiphone Silverburst 1966 Reissue G-400
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Playing since 03-11-07
........Uber Noob Skillz
#10
there are battery powered tube amps. There was a guy selling them as a kit on ebay for $20. They used old russian radio tubes that were in aircraft I believe
Quote by -Atticus-

oh and btw how do u put a quote in ur sig??
#11
I'm also interested in your project, jewbaby667. It would require quite a few 12K5 tubes to produce 1W output. Each tube is only rated for about 40mW. You would need a hefty battery to provide enough current to power all of those heaters.

I think you're better off sticking with what you've come up with so far. Please post pictures following your progress. Good luck, and learn much!
#12
I am leaning towards using this amp http://www.ax84.com/static/p1/AX84_P1_080708.pdf . The community on those forums are familiar with the design and could help me troubleshoot the whole circuit. I am going to keep up with things here too and on my other threads, but I think the output I need will be right here and the help too.
Peavey VK112
Fish&Chips EQ
Ibanez TS9DX
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Epiphone Silverburst 1966 Reissue G-400
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Playing since 03-11-07
........Uber Noob Skillz
#13
Quote by jewbaby667
I am leaning towards using this amp http://www.ax84.com/static/p1/AX84_P1_080708.pdf .
life just got a bit more complicated.

re-check your power budget. that output tube is idling @ about 13 W.

and your filament current is .76 A @ 6.3v ... 4.8W

and this is a 6V heater, so it would probably make sense to use a 6v battery, rather than 12. the 12AX7 can run on 6V with the heaters in parallel.

if you stay with a 12V battery, you'll need a series resistor for the EL84 and turn another 4.8W into waste heat.
Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.
#14
Quote by SomeoneYouKnew
life just got a bit more complicated.

re-check your power budget. that output tube is idling @ about 13 W.

and your filament current is .76 A @ 6.3v ... 4.8W

and this is a 6V heater, so it would probably make sense to use a 6v battery, rather than 12. the 12AX7 can run on 6V with the heaters in parallel.

if you stay with a 12V battery, you'll need a series resistor for the EL84 and turn another 4.8W into waste heat.


I realize my power budget did change a bit with this design, but I overshot my budget so far last time and got 4 times as much time out of the batteries than originally designed for. These laptop batteries are like tanks with paper armor. They pack such a punch but they can be hurt really easy in heat and recharging.

I plan on keeping an eye on power concerns by messing with the plate and heater voltages a lot. i am going to play with these to get power down. I do not need the full 5W output and can try and run these tubes a little "lean".

I am writing my 20+ page proposal that is due next Monday right now. I will put up a pretty post of it when I am done hehehe.

Wish me luck on my toils.
Peavey VK112
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Playing since 03-11-07
........Uber Noob Skillz
#15
*wishes luck*

Meadows
Quote by Jackal58
I release my inner liberal every morning when I take a shit.
Quote by SK8RDUDE411
I wont be like those jerks who dedicate their beliefs to logic and reaosn.