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New design: 12V push-pull tube amplifier
New design: 12V push-pull tube amplifier
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Old 20th September 2007, 01:54 PM   #1
engels is offline engels  Israel
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Wink New design: 12V push-pull tube amplifier

I was fiddling with spacecharge tubes for a while and I'm very exited about them. Now I've finally found a suitable small OPT with CT primary (not made for tubes but should withstand this). So, I'm planning a pushpull guitar amp with 12V power transformer.

The problems are - of course - the PI and the power stage. The preamp is not a question, it already worked in SE design.

Click the image to open in full size.

From my experience all the 12V tubes work (sound) better with grid-leak bias, that's why the output stage looks so stupid and I'm shure I'm missing something here.

Datasheetz::::

12AJ6 - hi-mu triode
12FM6 - medium-mu triode
12DU7 - output tetrode
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Old 20th September 2007, 02:13 PM   #2
EC8010 is offline EC8010  United Kingdom
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There's no way you will get 15V from a 7815 supplied from a 12V transformer. You need at least 15VAC and a bigger reservoir capacitor.

Don't space charge output valves draw grid current? If so, your concertina will be in trouble.
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Old 20th September 2007, 02:18 PM   #3
engels is offline engels  Israel
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Unhappy oops!

sorry, I forgot the coupling caps between the PI and the power tubes...
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Old 20th September 2007, 04:02 PM   #4
Tom Bavis is offline Tom Bavis
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I agree that a higher-output phase inverter is needed - I'd probably use a pair of 6GM8 dual triodes and a pair of 12K5s - since I have 'em. G1 is usually at 12V and G2 used as control grid - I wonder about that 12DU7 data sheet...

At 15V, some cathode bias may be necessary on the outputs - the 12K5 has a more complete data sheet, and says there is -2V bias (from rectified signal) with 2.2 meg grid resistor, and draws 40 mA with no signal.

Sounds like a fun project - I'd run it from a 12V gel-cell battery, of course!
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Old 21st September 2017, 12:15 PM   #5
efeemeka is offline efeemeka
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Hello, engels...

Where go this condenser into PI and power tubes?.

What is PI or where go this condenser's?

I am spanish and not understand good the site of this condenser's

This is one interesting idea, i have some run amps whit single 12k5, and i see for one probe whit two spacecarge in phushpull for more power.

The power of this in phush pull is...? Aproximate?

Thanks.

Last edited by efeemeka; 21st September 2017 at 12:28 PM.
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Old 21st September 2017, 03:57 PM   #6
smoking-amp is offline smoking-amp  United States
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Push pull power with the 12DU7 is probably around 0.1 Watt.

With 12K5 outputs, something like 0.14 Watt.

For more power 26A7GT, 0.5 Watt output, but needs more B+, 26.5V:
http://tubedata.milbert.com/sheets/049/2/26A7GT.pdf

50V B+ and conventional 12HL7 and 21LG6 tubes could get you 1.7 Watts.

(and 200V B+ with 12HL7 and 21LG6 could get you 70 Watts)
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Old 21st September 2017, 06:02 PM   #7
stocktrader200 is offline stocktrader200  Canada
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6922 also works quite well on 12 - 20v B+
I was testing my cct with 135v on it and tried a 9v for the b+ supply.
The gain was about half but the sound was still good.
at 46v B+, The + VAS stage rail, the output levels are identical to the 135v supply.
I did not do any distortion tests at the different B+ voltage levels
I would use a voltage doubler and RC filter for the 15v supply as current is very low.
you could then easily get 25v for the amplification stages

Last edited by stocktrader200; 21st September 2017 at 06:08 PM.
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Old 21st September 2017, 06:05 PM   #8
kevinkr is offline kevinkr  United States
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New design: 12V push-pull tube amplifier
Necrothread or not off it goes to Instruments & Amps since it is a guitar amplifier..
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Old 22nd September 2017, 09:17 PM   #9
leadbelly is offline leadbelly  Canada
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New design: 12V push-pull tube amplifier
Quote:
Originally Posted by EC8010 View Post
There's no way you will get 15V from a 7815 supplied from a 12V transformer. You need at least 15VAC and a bigger reservoir capacitor.

Don't space charge output valves draw grid current? If so, your concertina will be in trouble.
If space charge tubes draw grid current, what distinguishes them? If so, they basically act the same as 6GM8 or 6922 for example.
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Old 22nd September 2017, 09:33 PM   #10
dmfraser66 is offline dmfraser66  Canada
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The power output of this will be so tiny to barely bother with. It would be useful as an tube sound emulator to sweeten the sound of an instrument before feeding the output to a big clean power amplifier.
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