The "$250" Amp? - 6LU8 Compactron SE, UL

[Kegger]

Yes, just removing the second choke, keeping that large cap so you end up
with like 220uf or so of capacitance then after that first choke in the supply.

Also this was designed as stereo amp, the power supply IS for both channels.

So it is 1 supply feeding both channels, both channels being the same as the
amp schematic just copied identical per channel and used as left and right.

 

[sled108]

Well, it's Tube Weather now...And, until Evan posts Pics of his Cake Pan Amp, I've finally gotten around to getting a Shot of the 'Mighty Compactron'...Just for Something to Look At...With the 'Big Edcor' OPT's, and the Tubes a Glow..

 

[Angler]

That's too cool sled108!

Al

 

[Evan110185]

here's some pics: http://imgur.com/a/If29A
Sorry, the inside pic is a little blurry.

8" cake pan from walmart
Edcor transformers
Hammond chokes
5V4G rectifier (Zenith)
2x Sylvania 6LU8

B+ is 322.7

I highly recommend using 9" or larger cake pans...

 

[sled108]

Wow Evan...Now that's a 'Mighty Compact Mighty Compactron' amp...Good work, and one Hella job of Packaging. You take the Cake with That, mine is on a 10" pan. What are you using to Drive It?

 

[Evan110185]

To drive it, I'm using a Technics SL-1700 with a crappy phono stage.

With my current temporary speakers, I have to turn it up to max for it to be loud. I'm not sure if this is because of the speakers or the weak phono preamp, but I plan on replacing both soon.

Also, how precise should the voltages be for V1_A and V1_B? I'm getting something like 37.5v and 2.5v.

 

[Evan110185]

crap... I accidently bridged one of the heater pins with the output pin on the rectifier(Pin 1 on 5V4G) and now there isn't any B+, including before or after the chokes. Getting around -1.18v at B+ and output pin. Is it possible that this "fried" my rectifier tube?

getting 305v for each input pin(and heaters still work), so i know the PT is fine.

 

[sled108]

Ouch, I did not think that you Could Fry a 5V4G that Fast...You must ask Greater Minds than Mine about That...But, What My Feeble Mind Knows is...You need to Drive this Amp Hard to have Sweet, Heavy Output....

 

[sled108]

Hey, so Evan...I have been Running mine, with the 100K Alps Stereo Pot Wide Open...And, even Then it Needs a Lot of Punch to Really Sing..I Hit Mine with a 6V6 Pre-Amp at least 12:00 to make It Start to Come On...If you're only running a Phono Amp in, then you're Missing 1/2 your Output Enjoyment...

 

[Kegger]

Also, how precise should the voltages be for V1_A and V1_B? I'm getting something like 37.5v and 2.5v.

That's just fine..

 

[Kegger]

crap... I accidently bridged one of the heater pins with the output pin on the rectifier(Pin 1 on 5V4G) and now there isn't any B+, including before or after the chokes. Getting around -1.18v at B+ and output pin. Is it possible that this "fried" my rectifier tube?

getting 305v for each input pin(and heaters still work), so i know the PT is fine.

Yah sounds like a fried rectifier, or possibly bad center tap ground for the B+.

 

[Evan110185]

Just tried it out with a 2nd 5v4g... still nothing for pin 1

If I'm getting 305v for both pins 4 and 6, and 610v across both, my center tap should be fine, right?

The first cap in the power supply, 10uf for me, is going from Pin 1 to the same point I'm using for the center tap. I assume this is correct.

5.3v at the heaters. I assume this is within tolerance of 5v.

I guess its possible this 2nd 5v4g is bad too, but i doubt it... got it on eBay, NOS but untested. Everything was working great until i bridged those 2 pins together, so that must have caused the problem... I cant think of anything that would have effected besides frying the rectifier.

 

[Kegger]

Without the rectifier in:

What do you measure resistance wise from ground to each pt HV leg? (ground to pin 4 and 6 on rectifier)
(amp unplugged and off)

Then still no rectifier what do you measure AC V from ground to each pt HV leg? (ground to pin 4 and 6 on rectifier)
(amp plugged in and turned on)

 

[Kegger]

Just tried it out with a 2nd 5v4g... still nothing for pin 1

WAIT A MINUTE!

PIN 1?

NO, pin 8 is the output of the rectifier not 1..
(that's your issue, use pin 8 and should be set)

 

[Evan110185]

Im confused... This diagram says pins 2 and 8 are for the heater.

http://www.r-type.org/pdfs/5v4g.pdf

 

[Evan110185]

Without the rectifier in:

What do you measure resistance wise from ground to each pt HV leg? (ground to pin 4 and 6 on rectifier)
(amp unplugged and off)

Both are 28ohms, with rectifier either in or out.(and power off)

Then still no rectifier what do you measure AC V from ground to each pt HV leg? (ground to pin 4 and 6 on rectifier)
(amp plugged in and turned on)

both are 306.8v

 

[Kegger]

Look what else 8 is connected to..

It's the cathode as well as the heater, this type rectifier
has the heater connected to the cathode indirectly there.

See this pic, pin 8 is also connected to the cathode, which
is where all the DC voltage comes out of the rectifier tube.

.(pin 1 is just a shield, most tubes nothing)

 

[Evan110185]

So just leave pin 2 empty? and connect pin 8 to the ouput and the heater? I don't need to do anything else special?


EDIT: Ok, I just did this. Looks like this solved all of my problems. B+ is now 317v.

 

[Kegger]

Hook up your heater as normal, pins 2 and 8.

THEN take your B+ output from pin 8 to your supply caps and chokes/etc.
(I know it can seem odd, but that's how these rectifiers work)

 

[Alex Kitic]

Pins 2 and 8 should be connected ONLY to the heater for the rectifier tube.
Pin 8 is internally connected to the cathode, therefore the DC output should be taken from pin 8 (not necessarily, actually).

Pins 4 and 6 should be connected to the two secondary wires, while the CT is connected directly to ground.

Pin 1 should NOT be connected to ANY OF THE ABOVE!