Elekit TU-879S 6L6GC

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autoformer

Member
Joined 2011
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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Gobble

Member
Joined 2010
autoformer said:
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.
Click to expand...

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
 
W

w5jag

Member
Joined 2007
Gobble said:
The Elekit TU-879S is built on an elegantly modified Williamson circuit, and will accept a myriad of upgrades.
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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
 
W

w5jag

Member
Joined 2007
autoformer said:
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.
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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
 
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G

Gobble

Member
Joined 2010
w5jag said:
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
Click to expand...

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

--G0bble
 
A

autoformer

Member
Joined 2011
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:
http://www.diyaudio.com/forums/elekit/203026-tung-sol-6l6g-elekit-tu-879s.html


Gobble said:
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
Click to expand...
 
A

autoformer

Member
Joined 2011
Thanks Victor. Today, I completed a linear power supply for the Squeezebox Touch and it has made a remarkable difference for the better. I have asked the people at Welborne Labs if they can provide a power supply for the TU-875. It is already a good-sounding preamp and the only complaints some people have is a slightly compressed soundstage. What do you want to bet that a good linear power supply makes a huge difference on TU-875?
 
vkung

vkung

Member
Joined 2005
autoformer said:
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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Mr. Fujita is back to his office today and here is his reply regarding TU-875 power by DC (battery) instead of switch adaptor:
================================================================================================
There is no problem to operate TU-875 with battery. However voltage of TU-875 is 7V and it is not appropriate for smooth operation for it.

If you replace R83 (0.47ohm) to jumper wire, you could operate it with 6V battery.

Approx 2 ampere constant current flows when you use 6V battery.
So please be aware of the capacity of the battery when you use it.

======================================================================================================
 
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A

autoformer

Member
Joined 2011
Victor, thank you very much for making this inquiry with Mr. Fujita. I have tested the TU-875 with a 1500mAh 2-cell LiFePo pack at 6.6v output. I could only run it for a short period of time (around 30 min) as the TU-875 does indeed seem to draw its rated 2A.

The results of my test are honestly quite dramatic. The TU-875 on battery power sounds completely different. First of all, the soundstage is much larger. Small details in recordings start to emerge in a startling way. Separation of individual instruments improves in an obvious way. Dynamics are way up and yet the sound is less fatiguing. Even poorly recorded classic 70s rock is easier on the ears. Bass is stronger, high frequencies are smoother and more open. The general demeanor of the TU-875 on battery power is that of a much more refined preamp. It is clear to me that TU-875 is a sleeping giant that only needs better power to reach its full potential.

I have ordered a linear power supply from Welborne Labs that will supply 7V at a 2A current draw. I think that should provide most of the same magic as I heard with the battery power supply.

I am also going to look into building a LiFePo battery power supply that will supply the TU-875 for around 6 hours and shut off before the batteries are drained to zero and thus damaged. Also, with an integrated charger that can be taken out of the circuit when the preamp is being powered.
 
vkung

vkung

Member
Joined 2005
Cubdriver said:
Bah!! Of course I join this forum and find this thread shortly AFTER ordering the kit from Tube Depot. I guess I'll have to see how it goes with the supplied power transformer and then go from there.

This has been an enlightening thread!

-Pat
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Hi Pat

Yes, your TU-879S has an aftermarket R-core. If you are not happy about your aftermarket R-core. I have an original Japanese R-core in stock.
 
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