• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

some questions about an ECL82 SE amp

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totaltmega

Member
Joined 2012
Hello, I have been given to me a box containing a kit of a radio (LW/MW/KW...) Its from the 60s, I was glad to find 10 mostly different tubes and some transformators. 2 of the tubes is ECL82 which i hope still works :) so I will try to build a small SE amp.
I found this Single Tube amplifier as they did in this old thread http://www.diyaudio.com/forums/tubes-valves/66020-se-ecl82-amp-build.html The problem was the PSU. They said it should be a full wave bridge.
The powertransfomrator is rated:
Primary: 220V
Secondary: 205V
Filament: 6.3V
Questions: My mains in Sweden is 230V which gives the Secondary: 214V and Filament: 6.6V, will the tube filament handle 6.6V and how should I build my PSU. and modify the circuit to 214V? some ideas? Im a bit noobish on analog circuits
Tried PSU Designer II but that didnt made me smarter.:no:
 
G

gingertube

Member
Joined 2004
Just use the circuit as shown in the "Single Tube amplifier" link you posted.

All tube circuits can be considered as at least +/- 10% tolerance on voltage levels.

Build it as shown - there will be no problems with either the sligtly higher B+ voltage or the slightly high heater voltage.

Cheers,
Ian
 
E

Eli Duttman

Member
Joined 2004
Contact Jeff Yourison and ask him to provide you with info. on the Dirt Cheap SE amp, which uses the 6BM8/ECL82. That project is based on an old Mullard design. Unfortunately, the AudiophileTalk site got "hacked" and the descriptive forum thread is lost. :crying:

An inexpensive Triad N-68X isolation trafo is Greinacher doubled to get the B+ rail. With its dual primaries, the N-68X works well for people in both "120" and "240" VAC zones.
 
T

totaltmega

Member
Joined 2012
Today i built one channel and the PSU of the amp from Single Tube amplifier, and it works! yay. But reading the DC voltage from the PSU should be 200-215V it is 306V with no load and 280V with load.... and the Filament is 7.2 Volt True RMS with load. Secondary PT voltages is ok tho, something must be wrong with the PSU schematic as its ~65V off.
Tried to disconnect one secondary and then the PSU gave me 265V(load).
 
V

v4lve lover

Member
Joined 2010
measure . the DC resistance of the transformer (disconnected from mains and from rectifier/cap

use the duncan amp PSU designer . choose a 204 Rms winding whit the measured indepedance. solid state bridge your chosen cap size . and use a constant current load . load it whit one channel first then step the load up. this will give you a fine estimate of the DC voltage under load .


works like a charm.:D

v4lve .
 
T

totaltmega

Member
Joined 2012
v4lve lover said:
measure . the DC resistance of the transformer (disconnected from mains and from rectifier/cap

use the duncan amp PSU designer . choose a 204 Rms winding whit the measured indepedance. solid state bridge your chosen cap size . and use a constant current load . load it whit one channel first then step the load up. this will give you a fine estimate of the DC voltage under load .


works like a charm.:D

v4lve .
Click to expand...

will try that right away sir. And as for the filament I tested both tubes at the same time and the voltage was 7.0 max is 6.9 from a datasheet so will order four 1.5ohm resistors, 2 in parallel and series with each filament. to get it near 6.5V
 
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