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Request for 3Q5GT Single Headphone amp schematic
Request for 3Q5GT Single Headphone amp schematic
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Old 10th November 2017, 09:53 PM   #11
supernut is offline supernut  Thailand
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Dear Dragon lord,

Your book seems very old. I guess you are old guy too.

But very cool and valuable book.
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Old 10th November 2017, 10:16 PM   #12
Dragon Lord is offline Dragon Lord  China
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哈哈,其实我是个在校大学生啦,那本书确实很老,是1958年出版的,几年前在旧书店里看到并买下,是一本 很好的书,虽然已经60年过去了,但是它至今还是中国电子管爱好者重要的参考资料之一

Haha, actually I am a university student, that book is really very old, is published in 1958, a few years ago in the old bookstore to see and buy, is a very good book, although it has been 60 years, but it is still the important reference for China's vacuum tube enthusiasts.
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Old 10th November 2017, 10:20 PM   #13
Dragon Lord is offline Dragon Lord  China
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Quote:
Originally Posted by Mooly View Post


English only please


对不起,我的英文水平非常差,我借助翻译软件进行交流,同时附上中文原文,可以吗?

Sorry, my English is very poor, I use the translation software to communicate, but also attached to the Chinese text, can it?
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Old 10th November 2017, 11:03 PM   #14
supernut is offline supernut  Thailand
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Is it 8K OPTs Mr. Dragon?

How much capacitor value?
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Old 10th November 2017, 11:15 PM   #15
audiowize is offline audiowize  United States
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An 8K:32 transformer is a 16:1 step-down. How much gain will you get from the tube? You'd really want to use some feedback since you're planning to use this tube as a pentode, and that will cost you a little more gain.

In the end, you'll put 1V into the circuit and get less than 1V out.
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Old 10th November 2017, 11:28 PM   #16
Dragon Lord is offline Dragon Lord  China
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Quote:
Originally Posted by audiowize View Post
An 8K:32 transformer is a 16:1 step-down. How much gain will you get from the tube? You'd really want to use some feedback since you're planning to use this tube as a pentode, and that will cost you a little more gain.

In the end, you'll put 1V into the circuit and get less than 1V out.

手册上给的是单元运用,那个图只是功率级,一般放大器都不止一级,正常使用还要在这个的基础上加一个前级做 电压放大,如1N5GT和1H5GT就是个不错的选择,阻容耦合可以很方便的自由组合,当然也可以加一个升 压变压器做输入,这样就不会有增益不足的问题了

The manual is for unit use, which is just power level, general amplifiers are more than one level, the normal use of the base on this plus a front-level do voltage amplification, such as 1N5GT and 1H5GT is a good choice, resistance coupling can be very convenient combination of free, of course, can also add a step-up transformer to do the input, So there will be no gain problem.
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Old 11th November 2017, 05:15 AM   #17
supernut is offline supernut  Thailand
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It seem this tube might not suitable for Headphone amplifier

but rather suit to do preamplifier with 6SJ7 as Xindak VP2 Pre amp

specification seem good

S/N Ratio ≥100dB
THD 10V - 0.5% 2V - 0.13% 600mV - 0.03%~0.06%
Input Impedance 100kΩ
Output Impedance 600Ω
Number of Channels 2
Tubes 6SJ7*2, 3Q5GT/G*2, 5Z4P*1
Frequency Response 10Hz/-0.5dB ~ 100Khz+/-2dB


Headphone amp might be more suitable to use 6V6 as E400 Headphone amp.

or 6SN7 as E200 Headphone amp.

Last edited by supernut; 11th November 2017 at 05:33 AM. Reason: Final detemine
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Old 12th November 2017, 12:26 AM   #18
PRR is offline PRR  United States
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3Q5 is a perfectly good headphone amp, WITH a transformer!!

It is really a "beach radio" power tube. 15 years ago I wrote:

We did take tube-radios to the parks and hills and beaches. The last time I saw one was on the beach in California (before the first time Nixon ran for President) so I call them "Beach Radios". They were heavy because they were about half batteries and you usually needed new batteries every time you went to the beach. And the speaker wasn't very loud. But they did the job.

The same amount of audio power in headphones would be deafening; we could design for lower voltage and less battery drain.

The wiring on a battery-filament design is very strange to eyes that are accustomed to separate cathodes. Because all the heaters must be connected together, all the cathodes are grounded. That makes the usual form of self-bias cathode resistor impossible. These tubes were designed to work with some tricks.


The 3Q5 (or similar 3V4) will make well over 200mW in a 8K load. To do that it needs 4.5V peak or 3Vrms, more than many preamps, DACs, iPods deliver. However headphones will be happy with 1/4 of 200mW, so we only need half this audio voltage.

The attachment shows a Beach Radio, and a cut-down with just the power stage.
Attached Images
File Type: gif 3V4-3Q5-HP-amp.gif (50.0 KB, 50 views)
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Old 12th November 2017, 12:32 AM   #19
supernut is offline supernut  Thailand
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Oh my goodness, I don't know before Thank you so much Mr.PRR
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Old 12th November 2017, 02:39 AM   #20
audiowize is offline audiowize  United States
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200mW isn't actually enough for many headphones available today, though it's more than enough for some.

The bigger concern is what a zero feedback pentode wired single ended amp is going to sound like.
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