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Old 15th April 2019, 05:56 PM   #1
790rivers is offline 790rivers  United States
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Default Can I run the Elekit TU-8600R with 2A3 tubes?

This is my first post, after building the little ampcampamp and being thrilled with the results on my VOTT horns. Now I'm considering Elekit TU-8600R. I have a good supply of NOS RCA 2A3 tubes and would like to avoid buying 300B's if I can. Is there an option or a built-in modification, or maybe even internal switching, that would permit using 2A3s instead?
Thanks!
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Old 15th April 2019, 07:10 PM   #2
paczeltf is offline paczeltf  Hungary
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Almost certainly not. There is a good chance that you kill the tube, and maybe the amp as well.

You can obviously modify the amp for 2A3 but that would include many components including probably the power transformer.
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Old 9th May 2019, 10:06 PM   #3
790rivers is offline 790rivers  United States
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Default Question about the ELEKIT TU-8600R 300B

I posted this question in the Elekit thread and did not get much of a response. But I'm reposting here because I think that with many other modern SET tube kits of the past 30 years or so, it was not unusual to have the same amp use either 2A3 or 300B tubes, by dropping plate and grid voltages and using alternate taps on transformers...I think. So, I'm asking again: does anyone know if and how the ELEKIT TU-8600R 300B POWER AMPLIFIER might be fitted with 2A3 tubes instead of 300Bs?
Many thanks
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Old 9th May 2019, 10:18 PM   #4
planet10 is offline planet10  Canada
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Question about the ELEKIT TU-8600R 300B
A good question. From what Stereophile says it is not your classic 300B circuit. Check out their description: Gramophone Dreams #27: EleKit TU-8600R amplifier kit | Stereophile.com. It might help.

Of the few amps i have sampled, i have a preference of the 2A3 over the 300B but i suspect that comes down to what is around it. I think the 8600R would be a cheap way to try out the Elrog tubes… i have great respect for Thomas Mayer.

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Old 10th May 2019, 07:37 AM   #5
6A3sUMMER is offline 6A3sUMMER  United States
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The 300B filament is 1.25A @ 5V. 2A3 filament is 2.5A @ 2.5V.

Can the TU-8600R deliver 2X the filament current (5 Amps)?

Getting 2.5V instead of 5V is the easy part. 1 Ohm Resistors can drop the voltage from 5V to 2.5V. Getting rid of the extra heat of the dropping resistors may be a problem. 2.5V drop x 2.5A is 6.25W, 12.5 Watts for two 2A3 tubes. You should use resistors that are rated for 3x to 5x the heat in the resistor, they are bigger, and so dissipate heat easier, and run cooler (but still the same total heat).

But the real problem is going to be the extra heat in the filament winding(s) of the power transformer. I do not know what the circuitry is that powers the 300B filaments. You might be able to power one 2A3 filament, and add a second filament transformer to power the other 2A3 filament.

If the filaments on the TU-8600 are DC, you also have to consider the rectifier current, etc.

Or . . . you might be better off to start with an amp chassis and parts that can easily run 2A3s.

Last edited by 6A3sUMMER; 10th May 2019 at 07:53 AM.
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Old 10th May 2019, 09:29 AM   #6
paczeltf is offline paczeltf  Hungary
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Quote:
Originally Posted by 790rivers View Post
I posted this question in the Elekit thread and did not get much of a response.
I responded and said "no", which is the fact and also the likely reason why no further comment has been posted.

It is basically the power supply that does not support this, neither the B+ nor the heater as it was explained above.

Even if it worked, the OPT would not operate under optimal parameters in terms of load impedance and core saturation, and both the auto-bias circuit and the global negative feedback would require adjustments. Especially the second part cannot really be done without lab equipment.
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Old 10th May 2019, 10:19 AM   #7
jazbo8 is offline jazbo8
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Question about the ELEKIT TU-8600R 300B
Duplicate threads on the same topic have been merged.
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Old 10th May 2019, 07:27 PM   #8
6A3sUMMER is offline 6A3sUMMER  United States
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790rivers,

If you really want a 2A3 stereo or 2A3 mono-block amplifiers, there are plenty of threads and examples and advice on the Tubes part of this forum.

As you can see, the TU-8600R is not going to work as a basis for a 2A3 amplifier.

Since it will no longer be a vendor product, perhaps the moderators will allow you to start a new thread in the Tubes section of the site.
If not, just pick up an old 2A3 thread in that part of the forum, and we will respond.

Darn . . . I have some 2A3 tubes, and I may want to build another 2A3 amp.
See what you started.
I used to have some 2A3 Amps, but I no longer do.
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Old 10th May 2019, 08:14 PM   #9
Natural Sound is offline Natural Sound  United States
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If you want a nice 2A3 kit, Bottlehead has a sale on the Stereomour II. The offer expires on May 17.
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