"Sub Zero" Low Voltage Submini Tube Push/Pull Amplifier Project

[Cliff Schecht]

I've finished designing the switcher for output voltages of 150 V and 175 V with a 9V to 15V input (12V nominal). I'll try to get it built and tested tonight and will then post my findings. My goal is to post schematic values for different output voltages and, if requested, I can post customized versions of the schematic. I'll post the results later tonight if everything comes together.

[frequencycentral]

I've finished designing the switcher for output voltages of 150 V and 175 V with a 9V to 15V input (12V nominal). I'll try to get it built and tested tonight and will then post my findings. My goal is to post schematic values for different output voltages and, if requested, I can post customized versions of the schematic. I'll post the results later tonight if everything comes together.

^
^


I'm so happy I could explode!

[markeebee]

Yeah, Cliff is da bomb!

[Cliff Schecht]

Hrmm.. My first build didn't go so well, the inductor I was using (2.7mH) saturated and smoked pretty quickly . I figured the part was too small but it was worth a shot. Hopefully I can find something tomorrow that can handle more current.

[Bigorno]

Hello,

Sorry to bother you with my question but what will happen if I only put 24 volts on a 12AU7? 

I'm new to tube and I'm trying to make my 1st project: EF86 preamp + 12AU7 power.
I want to use 24 volts or 35 volts.

Thanks for the help.

[frequencycentral]

Hello,

Sorry to bother you with my question but what will happen if I only put 24 volts on a 12AU7? 

I'm new to tube and I'm trying to make my 1st project: EF86 preamp + 12AU7 power.
I want to use 24 volts or 35 volts.

Thanks for the help.

Hi, with tubes volts = volume, so 24v or 35v won't give you much amplification. Not a useable amount IMO anyway.

[Bigorno]

Hi,

1 watt would be ok for me.

Do you think it's realistic with a 12AU7 low voltage for the power section?

Thanks.

[frequencycentral]

Hi,

1 watt would be ok for me.

Do you think it's realistic with a 12AU7 low voltage for the power section?

Thanks.

You won't get 1 watt with such low voltages. Have a look at DougH's Firefly over at the AX84 forum, it has a self split 12AU7 output stage running at 265 volts. The output is about 1.5 watts.

[robot797]

is it possible to stack the push pull tubes
instead of one push and one pull 2 push and 2 pull


like this

can someone confirm me?



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[frequencycentral]

^^^

Cheeky! ©

Yes stacking the output tubes will work. However, you can't use a 5676 as a phase splitter as the cathode is directly connected to the filament. But you could use an additional 5676 to imvert the phase of the 'pull' signal.

[robot797]

now we are going into dark sorcery

can you explain that for me
(in a circuit)

becaus i am learning by watching how stuff works

and i still have 38 tubes (5676)

[robot797]

never mind got it already



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[frequencycentral]

Your 'balance' control is a little off - you don't want to do that. Instead, take a direct feed from to anode to the next tube stage, via a cap and a voltage divider (just two resistors or a trimmer). You want to use this next tube stage purely as an inverter, not an amplifier, so you'll need to use a voltage divider at it's input to reduce it's gain down to unity with the non-inverted signal.

[amptramp]

Youu are still going to need a grid resistor for the inverter stage.

[robot797]

hello i have some updates
2 new versions

pleas correct me if i did something wrong






the 2nd circut i did 2 things wrong
1. the version code is wrong
2. the secont transformer should be 12-230 (that way it makes 115V)

[robot797]

a update again

[robot797]

(kind of a bump)
tomorrow after cleaning i will gatter up some parts here!
and start testing on my breadboard

[robot797]

i had build this a long long time ago
and it does not work
to make it work i would need indirectly heated tubes and penthodes in the end
if i were to use
ecc82 in the pre stage
and an el95 in the end
i would get around 5 a 7 W (it is a guess)

well gues what i will do with the already build circuit

[robot797]

long time no see
i had some projects and some other things in my live

soon i will rebuild my special version
with a battery power supply and a diverent negative circuit
the problem i had the firsth time was that my power supply wassent steady enough

[amptramp]

long time no see
i had some projects and some other things in my live

soon i will rebuild my special version
with a battery power supply and a diverent negative circuit
the problem i had the firsth time was that my power supply wassent steady enough

Your filament supply could be regulated with an LM317 with the regulation pin grounded.  That would give you a fixed 1.23 volts for the filament with the added bonus of current limiting and high temperature shutdown.  You could still have a resistor dropping some of the input votlage and a pair of series diodes just as a safeguard in case the LM317 shorts out.  Your negative circuit looks OK.

As for a steady B+ supply, a VR-150 or VR-105 would be an interesting addition and that pink argon glow would be a combined attention getter and pilot light.