6LU8 Compactron Amp - Completed

[prelius]

Hi Folks,

It took me a looooong time to finish this amp. Pics are attached... The two additional tubes you see there are for a separate headphone amp, based on Russian 6F5P TV tubes.

I will bring it to Markus this Saturday..

Cheers, Paul.

 

[vinylkid58]

The two additional tubes you see there are for a separate headphone amp, based on Russian 6F5P TV tubes.

Very interesting and unique.:thmbsp:

jeff

 

[whoaru99]

Looks nice! What do you think about the sound?

 

[Redboy]

Very nice, Paul! Did you use Front Panel Express for the aluminum plate, or are you extraordinarily good with metal? :scratch2:

 

[Kegger]

Very Cool!

You did some great work, pretty compact build as well..

 

[prelius]

Looks nice! What do you think about the sound?

I built it to be used in the office either at low volume or with the headphones. Overall, I like the sound. Very solid tight bass. In fact, I ended up reducing the size of the interstage caps from .33mkf to .1 mkf. The channel separation is very good, and listening to speakers at close range is very good and not tiresome. Mids a bit flat, and no too exciting; highs are clean and sound fresh, although my wife say they are too bright for her... I am using Scott S17 speakers in the office, and KLH 12 at home.

This is the first time I've built a compactron amp, and I think compactrons have their place in the auido world. So far I am enjoining it. I will hook it up to the scope to take measurements, but it might take a while before I get to that. I built an RH84 sometime ago, and subjectively comparing the two amps I'd give RH84 an slight edge for quality of the sound. But the 6LU8 is not too far behind.

Thank you, Paul

 

[prelius]

Very nice, Paul! Did you use Front Panel Express for the aluminum plate, or are you extraordinarily good with metal? :scratch2:

Thank you Nate...
The plate came from a piece of disposed network gear, biggest challenge was to cut it at a straight line... But aluminum is soft and files are your best friends in this case. I was just careful not to scratch the surface .

BTW, your mechanical skills outshine anything I've seen in DIY world!!! I've been drooling over your EL84 SE's... And TT!!! Did you actually milled/lathed all the parts?!?!?!


Cheers, Paul.

 

[Redboy]

Thanks Paul, but you need to look around a bit more... my "skills" are pretty amateur.

I built the EL84 monos, but a friend built the turntable. I can do simple stuff with aluminum plate, but I don't have a mill/lathe of my own. Someday, perhaps. For now, I fake it with a drill press and some files.

Anyway, that's some nice work with on your amp - it looks great!

 

[1MOR]

Very nice! :tresbon:

 

[prelius]

Update - the amp needs more work...

After listening to in at Markus, using KLH 23's and his WE SE as a reference, it became clear:
1. My KLH 12's are still in need of work.
2. The amp needs tuning.
It look like my cathode voltages are off... I wonder if the headphone amp is affecting it.
Anyway, it is going back to the bench today...

Cheers, Paul.

 

[Kegger]

If you'd like any help and wanted to post the voltages we can figure what is what.

 

[prelius]

Kegger,

Thank you very much!!!

Voltages are as follows:

Left Ch
B+ 297V
Pin 11 2.01V
Pin 2 168V
Pin 9 31V

Right Ch
B+ 295V
Pin 11 2V
Pin 2 151V
Pin9 31V

My power supply is a SS diodes ->22mkF -> LC-RC-RC filter for each channel. My cathode resistors are 560Ohm+120Ohm in series at 5W (did not have single one in range).

It looks like I need to check R3 for left channel and R7s in both channels...

Thank you, Paul.

 

[audiozaz]

Good job, I like the looks of it!

az

 

[Kegger]

Kegger,

Thank you very much!!!

Voltages are as follows:

Left Ch
B+ 297V
Pin 11 2.01V
Pin 2 168V
Pin 9 31V

Right Ch
B+ 295V
Pin 11 2V
Pin 2 151V
Pin9 31V

My power supply is a SS diodes ->22mkF -> LC-RC-RC filter for each channel. My cathode resistors are 560Ohm+120Ohm in series at 5W (did not have single one in range).

It looks like I need to check R3 for left channel and R7s in both channels...

Thank you, Paul.

Do me a favor, switch the 6LU8's to opposite sides an take readings again.

Make sure to note the voltages from same side of the amp as before, what
this will tell us, does the voltage reading track the tubes, or the circuit per
channel they are being used in.

Then we can go from there to figure any issues..

Also I take it the B+ readings you have there are the plate voltage of each
output tube per channel and not just the power supply voltage?