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Old 27th February 2011, 12:42 AM   #1
Hoej is offline Hoej  Denmark
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Default Ultra Linear Push Pull Tube amp

Hi All

well i am looking for schematic to build a Ultra Linear Push Pull Tube amp with 250 - 300 Watt or more.... my thought was to do it with KT120 or KT88 and ouput transformator Hammond 1650W

Any idea ?

Best regards Allan
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Old 27th February 2011, 03:57 AM   #2
RTF671 is offline RTF671  United States
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Is that total or per channel? That's quite a lot of power, what kind of setup are you looking to get at?

Last edited by RTF671; 27th February 2011 at 03:58 AM. Reason: spelling error
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Old 27th February 2011, 05:47 AM   #3
Matt BH is offline Matt BH  United Kingdom
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Are you going to build one amp for musical instrument use? If this is the case then do you need UL?

For this kind of power you should check the Pete Millet Red Board amp:

Posted new P-P power amp design

Read through
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Old 27th February 2011, 09:39 AM   #4
Hoej is offline Hoej  Denmark
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Hi All ...

First thanks for your response.

What I seek is a tube amp for Hi Fi audio as a class AB.

Whether I'll need 8 pieces KT 88 or 6 KT 120 is unimportant, Output transformer supports 280 watts RMS and is OK.

The power supply, I will do it my myself, so there is a free choice with respect to current and voltage.

I have a set of old JBL L220 that I must have kicked started
As a preamp, I have a NAD T 163 which I am not so happy. there has been quite a few errors on it and in the near future I hope to have it replaced, it would be nice if I could do something with tubes
But it is somewhat difficult, since I also love watching movies and want DD / DTS, but it is a different matter, right now it is two pieces of mono block which is important.

Thanks to everyone who comes with a comment.

Best Regards Allan
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Old 27th February 2011, 09:59 AM   #5
SY is offline SY  United States
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How many tube power amplifiers have you built before?
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
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Old 27th February 2011, 10:13 AM   #6
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Location: Alps:Tube amp designs over 150W, SMPS guru.
Who's using KT120's ? (I'm not).
6X KT90 parallel p-p should see 300W... I'm currently using 575V+ with 4x KT90
@ 2K A-A which gives close 200W;..... 4x hard pressed KT88's give around 160W in same circuit and todays makes won't last long. The 575V+ is the lowest B+ for such output power and the issue becomes the power supply and keeping the weight down.

I took my 200+200W design with regards "wear and tear" using the lowest usable B+ quite seriously, designed with sufficient natural ventilation.

Having been disappointed by the high failure dropouts of the TungSol 6550 New Edit on a lower power variant,
My design emphasis has shifted to lowest B+ for a given power. Only my philosophy and approach.

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Old 27th February 2011, 12:30 PM   #7
Hoej is offline Hoej  Denmark
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Hi All...

# SY

Non.... hoever I have built MosFet Power amp, 2 stereo amp 150W @ 8 Ohm and 1 stereo 250W @ 8 Ohm.

My education is Elektromekanic and electronics technician, the electronic part is the same as an electronics engineer, but it was 15 years ago.

# richwalters

It sounds exciting I am not fixated on anything special besides I wanted to use Hammond 1650W as it would be pretty expensive to get a big output transformer shipped to Denmark and beyond what should I pay 25% VAT. : (

I'd like to see a schematic of the amplifier that you've built, it sounds exciting.

PS: Thanks for your interest in my forthcoming AMP
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Old 27th February 2011, 01:49 PM   #8
DF96 is offline DF96  England
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Don't start with 300W as your first valve amp. Too much scope for sparks and bangs and disappointment. Try 10-20W, and learn from your mistakes on a cheaper safer circuit.
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Old 27th February 2011, 03:01 PM   #9
Hoej is offline Hoej  Denmark
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Hi All

# DF96

Thanks for the recommendation, but I'm going to continue with a tube amp at 250 to 300 W

I have previously repaired Hig Power Transformer 10 K Volt 60 Amp, of prima side. a big boy I have also repaired the electronics industry for 15 years where the last 5 years I have repaired servo drive at component level. so there for I intend to continue, although my knowledge of tubes is limited.

So I'm ready to try, and hope it goes well

if not then I take it from there

Best Regards Allan
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Old 27th February 2011, 05:33 PM   #10
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Here is one well known example; 400 W with 10 KT88.
This can be quite easily modified for the power level you want.

The Wireless World Archive

Here is the book from GEC where the later version of the same contruction is described (from page 112...):

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