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Old 12th April 2012, 12:22 AM   #81
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Default TU-875 on battery power?

Victor, I wonder if you could ask Mr. Fujita if it possible to run the TU-879 on battery power. There are two possible choices without regulation:

LiPo: These cells are 3.7 volts each, so a 2-cell pack in series would be 7.4 volts. That is the peak voltage. Under load, they will be closer to 7.2 or so.

LiFePo: These cells are 3.3 volts each, so a 2-cell pack would be a maximum of 6.6 volts.

I see that the TU-875 switch mode power supply specifies an output of 7 volts at 2.5 amps. The actual voltage present at the connector plug is a little over 7.2 volts.

Simple example using a 2500 mAh LiFePo 2 cell battery pack:
-- Fully charged: ~7.4v (3.7v per cell)
-- 2.5A current draw from a 2500mAh pack = 1C discharge rate
-- At 1C discharge rate, pack voltage will hover around nominal: 6.6v (~3.3v per cell)
-- At 2.5A current draw, the pack would be exhausted in 1 hour.

So, if we want 6 hours of running, and assuming that the unit actually draws 2.5A, we will need a 15Ah battery pack.

The question for Mr. Fujita (or you, if you are confident of the answer) is will the unit run on voltage as low as 6.6 or as high as 7.4 volts? What are the upper and lower limits without damaging the unit?
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Old 12th April 2012, 01:24 AM   #82
vkung is offline vkung  Canada
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I don't know how to answer your question but I will forward your question to Mr. Fujita
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Old 12th April 2012, 02:54 AM   #83
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Victor, please note my mistake in the first sentence. I am asking if the TU-875 preamp can be run on battery power, not the TU-879... Thanks for forwarding to Mr. Fujita!
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Old 12th April 2012, 02:59 AM   #84
vkung is offline vkung  Canada
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Here is the spec of TU-875's SWITCH ADAPTOR
MODEL 3A-161WU07
7V 2.14A PSE

http://pdt.static.globalsources.com....5003100017.pdf

Last edited by vkung; 12th April 2012 at 04:17 AM.
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Old 12th April 2012, 03:07 PM   #85
Gobble is offline Gobble  India
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Quote:
Originally Posted by autoformer View Post
I spent quite a lot of time rolling tubes on the TU-879 and finally arrived at my favorites: Current production Tung Sol 6L6G and Tung Sol 12AX7. I am still using the stock Electro Harmonix 12AU7s in the preamp, but they seem to be quite good. I may try some Tung Sols in there as well.
Hi Autoformer
How did you find the change after vitamin-Q? Mine are lying in the cupboard, waiting for a suitable day when I feel like opening up the system again.
Did you also change the potentiometer at the same time or one after the other with some listening in between? How was the new volume pot?

And lastly how did you find the stock EH 6l6GC compared to Tungsol?

Thanks
--G0bble
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Old 12th April 2012, 03:43 PM   #86
w5jag is offline w5jag  United States
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Quote:
Originally Posted by Gobble View Post

The Elekit TU-879S is built on an elegantly modified Williamson circuit, and will accept a myriad of upgrades.
Wait ... what?

Isn't the classic Williamson Amplifier push - pull? The TU-879S is basic two stage single ended pentode with a big negative feedback loop around the amplifier.

The schematic is published in the manual - at least in the home market japanese manual. It's the next to last page, IIRC.

I have the schematic scanned into my computer with some notes and measurements from when I did the 6V6 conversion on my TU 879S, but I assume its protected by copyright or other restrictions on dissemination.

Win W5JAG
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Old 12th April 2012, 03:50 PM   #87
w5jag is offline w5jag  United States
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Quote:
Originally Posted by autoformer View Post

Since the TU-879 was so easy and so much fun to build with such a great sound, I decided to order a TU-875 preamp as well.
I have a TU-875 as well that I ordered from VK Music, but I've never gotten around to building it. Glad to hear that you like it!

I'm trying to justify a reason to buy the little Elekit 6BM8 amp or the 5670 headphone amp as they are just such nice looking kits. Thanks to VK Music for putting these on the market here! Wish I'd bought the CD player!

Win W5JAG

Last edited by w5jag; 12th April 2012 at 03:54 PM.
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Old 12th April 2012, 05:13 PM   #88
Gobble is offline Gobble  India
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Quote:
Originally Posted by w5jag View Post
Wait ... what?

Isn't the classic Williamson Amplifier push - pull? The TU-879S is basic two stage single ended pentode with a big negative feedback loop around the amplifier.

The schematic is published in the manual - at least in the home market japanese manual. It's the next to last page, IIRC.

I have the schematic scanned into my computer with some notes and measurements from when I did the 6V6 conversion on my TU 879S, but I assume its protected by copyright or other restrictions on dissemination.

Win W5JAG
You may be right. I only quoted a web article as a hint.

--G0bble
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Old 12th April 2012, 09:39 PM   #89
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I installed the Vitamin Q and the TKD potentiometer at the same time, so it's hard to distinguish the effect of either. But the effect of the upgrades is undeniable. To my ears, and using the stock tubes as reference, the sound is richer and more detailed than stock.

As to the tubes, I wrote my impressions here:
Tung Sol 6L6G with Elekit TU-879S!


Quote:
Originally Posted by Gobble View Post
Hi Autoformer
How did you find the change after vitamin-Q? Mine are lying in the cupboard, waiting for a suitable day when I feel like opening up the system again.
Did you also change the potentiometer at the same time or one after the other with some listening in between? How was the new volume pot?

And lastly how did you find the stock EH 6l6GC compared to Tungsol?

Thanks
--G0bble
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Old 13th April 2012, 04:55 AM   #90
vkung is offline vkung  Canada
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Location: Vancouver BC Canada
[QUOTE=autoformer;2982007]Victor, I wonder if you could ask Mr. Fujita if it possible to run the TU-875 on battery power. There are two possible choices without regulation:"



Mr. Fujita is on a business trip. He will answer your question next week

Victor
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