Elekit TU-8900 2A3\300B Single Ended DHT Tube Amp - Build, Impressions, and Review

The general consensus, I think, is series resistors = bad, parallel resistors = not really a problem.

 

Very useful information!

 

Well underway!

Do you think it is okay to use the leftover wires from the big 5W resistors as jumpers, or is a copper wire preferrable?

See image: https://flic.kr/p/2mW86mR

 

Resistor leads are fine.

 

Noted!

I am installing some audio note mylar coupling capacitors to replace the stock ones. In the instruction, it says "For those capacitors wrapped with a film make sure to connect the outer side of the electrode to the lower impedance side of the pin (anode side)...

I can see which pin this is on the main unit board, but how do I go about doing this? I can seem to find any good pictures of others that have done this. Maybe I am misunderstanding something?

 

"Directionality

As you can see from the above pictures, each of our signal capacitors is marked with a line on the right; this marks the start of the foil. It is our experience that the Audio Note (UK)™ capacitors perform best when the start of the foil is "facing" the incoming signal."

https://www.audionote.co.uk/foil-signal-capacitors

 

Got ya!

I thought the idea was to add a cable somehow, but it's just about direction.

Thanks a ton

 

EagleWings, is the position of the yellow jumper sockets in the image you showed where it needs to be for your mod?

 

@Joskus , in that config, it doesn’t matter where the yellow jumper is, in fact you don’t even have to have it plugged in.

But I came up with an idea just last week, which will allow us to easily swap between ‘with-parallel-resistor’ config and ‘without-parallel-resistor’ config, by swapping the jumper. All you need to do is, put the 15R resistors in the R129/229 positions instead of the R123/223 positions. Now by swapping the yellow jumper between LZ-L and HZ-H positions, you will be swapping between ‘with-parallel-resistor’ and ‘without-parallel-resistor’ configs respectively.

 

Ah wow! That's perfect.

And I just finished... the amp worked AMAZING for 20 min then suddenly the right channel dropped out..

gutted!

Edit: My Sylvania tubes measured almost 5V different. Is that bad?

 

Solved and fixed: problems with a capacitor.

Already it sounds stunning. This is my first DIY audio project and my first tube amp!

Thanks kindly for all the support, tips and tricks

 

I'm glad you were able to get it fixed. As for your question about the tubes, I am not familiar. Hopefully someone else can chime in.

 

I get a electric tingling from touching the chassis. Its quite pronounced. I wonder why.. grounding issue of sort perhaps?

I also get it when touching it, even when its off (especially the front aluminium pannel)

 

Test voltage with a multimeter, DC and AC, from a non-anodized surface to ground. Screw head on the front panel would be ideal.

 

When the amp was ON:
Measuring from ground (water tubes in house) to screw head on front panel I get a reading of 52 Vac. For Vdc the reading was to erratic to gauge any spesfic value.

When the amp was OFF, but still plugged in:
Reading of 52 Vac. Reading of 0 Vdc.

 

Yeah, you need to pull that amp from the wall immediately, you have something in the power supply shorting to the chassis.

[EDIT] I re-read you post and funky things can happen when you measure ground to plumbing. It's probably accurate, but just measuring to signal ground is probably better.

The chassis anodising might be the only thing preventing you from popping a fuse or getting a *real* zap.

 

That's very concerning. I have checked all the values internally, and all seem within margin. The values for the two power tunes varied by 5 V, but other than that all was good. The wires from the power supply does not touch anything they shouldn't. I really have no idea where to start.

I have a feeling it might have something to do with the coupling capacitors, as I had to cut the silver leads and resolder them as the inital instalment crashed with the top plate of the chassis. (long story, pictures are coming).

Also the build is with the Lundahl transformers.

I will pick it apart and send pictures later today.

Thanks a lot

 

Just keep in mind, I don't have this amp, no circuit diagram, no ability to go through instructions. But voltage that high on the chassis, enough to give you a tingle, is concerning.

That said, I'd start at the power switch, mains entry, and check you aren't pinching wires from the transformers when the chassis went together.

 

Keep in mind that the exposed metal on the top of electrolytic capacitors will carry a voltage. If you're using metal standoffs for the circuit boards, check them to see if any are making contact with traces on the boards.

 

Well finally it's fixed.. it must have something to do with the cable management from the power supply, as suggested by Beefy. Now none of the wires from the Lundahl transformers touch the power transformer NOR the casing itself. I made paddings of electrical tape at every point where the wires touch the casing.

The biggest problem was likely that I taped some of the cables to the case itself, in order to guide the cables and avoid crosstalk between the power transformer and the output transformers.

I think the measurements I did using the waterpipe as ground was way off. As Beefy pointed out, waterpipes does not necessarily provide reliable ground. I measured it against the ground in my kitchen, and the multimeter shows 18.3 Volts! Does this mean I can charge my phone off the watertubes?! I need to have this checked out.

Anyhow... the amp sounds sweet like nectar and is not threatening to kill me anymore. Again, thanks for all your support!