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Underp4ntz 26th March 2012 12:20 AM

Project: Small 6C33 / Hybrid Stereo Headphone Amplifier
Hello People, Questions & a little story!

Little About myself:
I'am Chris and I'am searching, reading, learning on this forum for a while so I registered because I need get my mind updated again.
I was a fan of vacuum tubes since I was a kid and also finished a electronics school before I went very sick. I don't want to get into detail with this.
But because of that I had limits :wchair: and had to change my love of work and did industrial / media design.
Until today! Now days I'am a Product "look" and media/game/commercial designer.

I wan't to get back into the Amplifier Design World and love music. "Can't live without it".
But Because I had to re-school again. I did not spent time into schematics anymore.
And forget how to schematic to pcb / wire it. But I still know the use of Components etc.

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Please dont say its overkill for a Headphone Amplifier or its a Home Heater.
We Like the tubes. We have a lot of these tubes and a lot of amazing NOS/NIB Russian Components like Capacitors, Resistors and more!

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6c33 Burn-in? How to connect the Heaters in DC or AC "I like to use DC because my lab psu.
I read lot of people burns the heaters for 24 hours.
We also want to burn those tubes but sadly we can't get the heaters to work!

DC Heater Tryout:
I tried a 5-7A 13v DC Lab Power Supply. "voltage tuned down to 10v DC with a resistor.
Hooked the heaters in Series. Seems It's not Glowing.

AC Heater Tryout:
So I Used a "TENPAO Donut AC Input & AC Output Transformer" 13v AC output. Tuned down to 9-10v AC with a Resistor.
Hooked the heaters in Series Nothing Glows....

What I'am missing? Whats wrong? "Maybe the resistor is the bad part?"

On some pictures I see people having capacitors on the heaters leading to Ground"EARTH".
Some Designs do not have the heaters on Ground"EARTH".

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Amplifier Goal!
My goal / and friends goal is getting a Hybrid 6c33 headphone amplifier and maybe driving some 20watts speakers to.
I like to use the 6c33 as pre-amps and mosfets as power amps to power a headphone or 15-20watts speakers.
If I need to use a 12au7 tube i will hide it in the chassis.

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Amplifier "LOOK" Design Limits:
The Design will be very and yes VERY compact / small.

1. Max 2x 6c33 Vacuum Tubes.
2. Max 2x Small as Possible Transformers. "If needed a External PSU" so it can be hidden."

1. Max 2x 12au7 or 12ax7 Double Triodes. The 12xx7 tubes will be hidden in the chassis.

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Amplifier "GUTS" Design:
So far I seen designs and schematics that looked easy but also for a very compact design.

1. Susan Parker: Zeus SE Triode Preamp PP MOSFET Power Amp Tests
Susan seems to use MOSFETS for the Power-Amplifier and 6c33 as Pre-Amplifier

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2. I found a little Schematic about a small looking 6c33 headphone Amplifier.
Sadly I cannot find more about this.

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3. And also a Germany guy build a small looking 6c33 Amplifier.
So far looks small for a Amplifier but we don't want to use the 6SL7 tubes. This makes the amp chassis 50% smaller.
6C33C - PP-Amp von Ernst Roessler

Thanks and I really hope some people would like to help out!

kevinkr 26th March 2012 12:26 AM

Filament pins probably not wired correctly .. Recheck basing diagram and rewire if necessary.

And there is no such thing as a "ultra small" amplifier with the 6C33, the heat output of the filaments alone precludes that possibility.

I'd use something like the 6N6 or its big brother the 6N30P instead..

Good luck! :D

Underp4ntz 26th March 2012 01:17 PM


Thanks! Yea Ultra Small... Maybe a bad statement but small as possible.
Trying to get smallest cool awesome looking 6c33 hybrid / tube amp.
Hybrid seems more easy and less power consuming.

We will use a plate voltage not above 160v and not below 90v.

You mean use 6N6P instead of the 12xx7 tubes?
Because we need to use the 6c33 tubes.

Anyways Here is how i hooked the heaters of the 6c33.
I did both on AC and DC and nothing glows. I checked pictures of people wired the Heaters and what I did are same as them and also tried different methods.
So far in my theory the resistor cannot be the problem or is it?

The AC donut transformer is a unknown spec as the goes for amperes.
But it is scrapped from a 1000watts audio system. "big heavy donut!".

The DC psu has 5 to 7 amperes.

Koifarm 26th March 2012 04:56 PM

Just fotget the resistors. 13V is just right.10V is to low.

Underp4ntz 26th March 2012 09:43 PM


Originally Posted by Koifarm (
Just fotget the resistors. 13V is just right.10V is to low.

Alright. I connected the tube heaters in series direct into DC 13.4volt. As measured from the power supply.

No glow at all but when I measure the voltage on the tube heater pins voltage drops to zero. The filament"heaters" are also connected inside the tube so its not damaged or death so far I measure.

So my understanding is the heaters work on DC or/and AC right?:confused:
On the image above is exact thing how i wire them up to the DC or AC donut.

aardvarkash10 27th March 2012 08:35 AM

wow - this is worrying.

You need to go back to basic electrical theory lessons. The testing you are doing and your descriptions indicate a VERY limited knowledge and a high capacity for self immolation.

I am trying not to sound negative here, but unless you can confidently work out for yourself what is going on in the heater circuit, you will be in deep trouble as you get into high voltage stuff.

Take a look through some of he basic stuff in the education section of the forum - it will start to help you understand what is happening and why. More to the point, read the safety section and get a good understanding of what you are dealing with.

Just to get you started, the heater is drawing 3.3amps at 12v (nominal) as you have it configured. You should have 12v at pins 1/7 (top diagram) or 2/6 (bottom diagram).

If you do NOT have that voltage at those points, but there is the correct voltage at the power supply itself, you have a poor or open connection in the supply circuit - probably at the connector in the tube base. Systematically test to find this break in the circuit.

If you DO have the correct voltage at the pins of the tube and the heater is not functioning, the heater is faulty OR you have an open circuit in your link wire between the heaters.

rotaspec 27th March 2012 07:45 PM

I'll bet the current draw is too high for the power supply to cope with......

Underp4ntz 27th March 2012 10:17 PM

Hey Aardvark:
Thanks for the information. Yes we know about the safety. Before my sickness I work'd with high current electricity Like Generators and Marine Gas dryers and strange looking equipment with extremely high temperatures and very very deathly powered machines.

And yes I will read the instructions and information on the tube education sections carefully since safety is first in my house and friends house.

Thanks Aardvark for your call! We will put all the info on my topic on paper and learn.

Yea maybe the supply is bad. When I put my multimeter on the supply.
I measure 13.40volts and 13.40volts on the + - side of the tube socket. "without tube".

When I turn on the supply with the tube. It breaks to 1 volt. on supply itself and tube heater pin sockets.
My thougts are yes a supply that cannot draw a 3+ amp current.
I'am 100% sure tubes have no short inside of them. These are high quality Military tubes and very strong including the insides of it. If they shorted it can be measured so far I know of my old electronics teacher.
Only the heater pins are connected if i test on shorted circuits. Anyways Ill try out another tube maybe its faulty but the heaters are linked together when i test on shorted.

Again Thanks! We are currently getting the heater working / testing. No even using the complete tube yet.
In the meanwhile of burning we still researching.

UPDATE: SEEMS PSU CAN NOT HANDLE THE HEATERS! Drops on 1 volt on 6 tested tubes!

aardvarkash10 28th March 2012 12:51 AM

cool - you have restored my confidence somewhat! Now you need a bigger supply... A car battery makes a very good 12V nominal heater supply and will EASILY deliver the current

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