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2A3/6A3 tube preamp
2A3/6A3 tube preamp
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Old 14th February 2018, 03:02 AM   #1
reellike is offline reellike  Hong Kong
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Default 2A3/6A3 tube preamp

Hi
I want to DIY 2A3/6A3 preamp
I want to know my schematic is work or not
Attached the schematics of power amp and preamp
Please give some suggestions to me
Thank you !
Attached Images
File Type: gif 6A3-Preamp.gif (14.9 KB, 243 views)
File Type: gif 805-Poweramp.gif (13.7 KB, 240 views)
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Old 14th February 2018, 05:53 AM   #2
PRR is offline PRR  United States
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Quote:
Originally Posted by reellike View Post
...I want to know my schematic is work or not...
Work? Make sound? Yes, if built right.

Work? Be a good music playback system? I think it does not have enough gain to work in most systems.

The 417 stage does have good gain. The next 2A3 stage has very little gain to plate. The 2.5K:2.5K is unity gain. Then the 5K:16 plate transformer has voltage LOSS of 17:1. So two fancy tubes and two transformers for almost no overall gain.

Why a 16 Ohm output on a preamp?

Married to the power amp: the 805 grid needs a BIG driver. I'm not sure a single 2A3 will do. In any case the 2A3 will need about 45V peak at its grid to make full output. Since your preamp gain is 2.5 (maybe 3), this means you need a VERY large signal into your volume pot.

Are you looking at transformers in hand and trying to make something?
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Old 14th February 2018, 06:03 AM   #3
reellike is offline reellike  Hong Kong
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The power amp is working now with my 417A one tube preamp
I want to DIY new preamp (417A+2A3)
I have 2.5K:600 replace the 2.5K:2.5K
The preamp output transformer can replace by 5K:600 ?

The inter-stage transformer of the power amp is 2.5K:600

My first schematic
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File Type: jpg 417A+2A3 !@.jpg (27.2 KB, 216 views)
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Old 14th February 2018, 12:26 PM   #4
kodabmx is offline kodabmx  Canada
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Using 2A3 for a preamp is like using a V8 engine in a golf cart...
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Old 14th February 2018, 02:10 PM   #5
ColinA123 is online now ColinA123  United Kingdom
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Why are you trying to re-invent the wheel?
A google search for valve tube preamp circuit.
Will give you thousands of ideas that can be used or modified
within whatever budget you have.
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Old 14th February 2018, 02:16 PM   #6
JZatopa is offline JZatopa  United States
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Quote:
Originally Posted by kodabmx View Post
Using 2A3 for a preamp is like using a V8 engine in a golf cart...
Whats wrong with that?
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Old 14th February 2018, 02:25 PM   #7
kodabmx is offline kodabmx  Canada
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LOL It's a little overkill, no? Seems like a giant waste of a 2A3... Almost as daft as using a KT88.
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Old 14th February 2018, 03:30 PM   #8
JohnAtwood is offline JohnAtwood  United States
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Using a directly-heated output triode as a "preamp" tube will most likely become a nightmare of microphonics. Only try this if you shock-mount and/or enclose the tube to keep ambient sound away.

- John
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Old 14th February 2018, 04:14 PM   #9
JZatopa is offline JZatopa  United States
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Quote:
Originally Posted by kodabmx View Post
LOL It's a little overkill, no? Seems like a giant waste of a 2A3... Almost as daft as using a KT88.
Hmm KT88 preamp you say... Tell me more

Honestly if the pursuit for the ultimate in sound quality and enjoyment I believe nothing should be taken off the table. If someone were to build a 300B preamp (or 2A3 or KT88) and demonstrate that tubes of all kinds should be considered, I'm all for it.

Oh, and I should also say that sometimes I think we all should try something just for fun and to see what happens.

Last edited by JZatopa; 14th February 2018 at 04:17 PM.
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Old 14th February 2018, 04:51 PM   #10
kodabmx is offline kodabmx  Canada
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Oh of course. If the reason is "because I can" I'm all for it. I've built a 16 6P1P stereo amplifier :P
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