TU-8200 SE tube amp kit

[EWBrown]

This must be about the most complex and complicated SE amp design currently in existence, replete with lots of small multi-legged silicon based "life forms",and far too many multi-conductor connectors and seven separate circuit boards....

https://tubedepot.com/products/elekit-t ... lifier-kit

Instruction manual, large PDF file, 4.34 MB

LINK REMOVED AT BEHEST OF COPYRIGHT HOLDER

Don't even think about scrolling down to page 19, for a peek at the schematic ;)

/ed B

[Geek]

Victor Kung of VK Music, the importer of those is practically my neighbour

I worked on one (the predecessor to that one) and they are mindblowingly good for what's under the hood. The transformer winding is the secret as I understand it.

Tip: Toss out that 6L6 and drop in an EL34 for heaven

[Kyle K]

Gregg,

When you worked on the earlier model, did you notice what the plate to cathode voltage for the output tubes was? From the schematic, B+ for the new model is listed at 250 - 275 volts, but it now has that active auto-bias circuit so the cathodes are sitting at .4 to .6 volts.

Kyle

[EWBrown]

The cathode is at 0.4 to 0.6 Volts, across two paralleled 12 ohm resistors, this corresponds to cathode current between 66 and 100 mA.
This voltage, in turn, controls the "autobias" circuitry, which varies the G1 voltage between -12 and -24 VDC (derived from a -30 VDC source).
Essentially, it is a self-regulating, fixed grid bias topology. Think of EFB, but with a different technique.

The 2904 dual comparator serves to control the four opto-isolators, which will cut off the B+ voltages if the cathode / plate currents exceed a pre-determined value.

Depending on the OPT primary DCR, the plate to cathode voltage across the 6L6CGs would be approximately 250 VDC. Which is fairly low for these tubes, but
it does allow for operation at a higher current (66 to 100 mA). OPT primary is apparently 3.5K in this circuit.

/ed B in NC

[Kyle K]

Thanks, Ed. Is it possible to get the power output they claim running the tube at that voltage, even running higher current?

[Geek]

They are REALLY generous on power output ratings.

I was not able to duplicate the power output specs of the old kit with ANY tube, new, used or NOS at the voltage levels they used. Most likely they just parroted the tube datasheet output figure.

Maybe the new kit is more accurate, as its schematic is totally different.

[EWBrown]

I'd SWAG that they are stating peak output power, and not RMS power output. That would approximately "double" the true RMS output power.

/ed B

[Shannon Parks]

Mr Kung has kindly asked me to remove the manual link for copyright reasons.

Shannon

[EWBrown]

No Problem....

BTW, the information is still available, posted on the Tube Depot website:

https://tubedepot.com/products/elekit-t ... lifier-kit

Just dig a little deeper, It should not be too 'challenging" to find it...

/ed B

[Shannon Parks]

No Problem....

BTW, the information is still available, posted on the Tube Depot website:

https://tubedepot.com/products/elekit-t ... lifier-kit

Just dig a little deeper, It should not be too 'challenging" to find it...

/ed B

Looks like a reseller approved link to me, too, Ed!

Shannon

[battradio]

Maybe he just thinks we don't know how to read assembly manuals

[Kyle K]

Victor Kung (VK Music) was the original North American distributor for Elekit. When he started bringing in the TU-879 (the predecessor to the TU-8200) he included a power transformer specifically for 120V operation sourced from Kitamura Kiden of Japan, the manufacturer of the original power transformer and the originator of R-core transformer design. The kits he sold included both the 100V and 120V power transformers.

Correction - The 120V units were sourced from Phoenix in Japan.

Elekit allowed Tube Depot to also sell their amplifier kits, but they sourced the necessary 120V power transformers from India as I understand it. I don't know if the Kitamura sourced transformers were any better, but I'd bet they were more expensive. Tube Depot also pulled the original 100V units from the kits and that's the R-core transformer you see them selling separately on their website (discussed in another thread). They have a data sheet pdf, but I think the DC filament supply rating is bogus. I don't see how you can get 3A DC from a 3A AC secondary through a bridge rectifier.

[EWBrown]

I've tested the 100VAc primary TU879 transformers, with a 40 watt, 240V light bulb (approx. 160 mA) connected to the 260VAC secondary, and a 6080 filament load on the 6.3V secondary (2.5A) , and ran this for hours, even for days, and the transformer barely gets warm.
I used a toroidal step up/down autotransformer, with 120VAC input, 100VAC output.

Also tested them with 120VAC directly into the primary, similarly loaded, but with additional series resistance, in order to protect the light bulb and 6080 filaments..
About 160mA loading on the 260VAC winding, and 2.5A on the filament winding, this delivered approximately 310VAC and 7.5VAC, under these conditions, and the transformer remained just barely warm. That is a total of approximately 70VA, continuous operation.

/ed B