some questions about an ECL82 SE amp - diyAudio
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Old 4th April 2012, 09:58 PM   #1
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Default some questions about an ECL82 SE amp

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 Which SE-ECL82 amp to build? 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.
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Old 5th April 2012, 12:20 AM   #2
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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
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Old 5th April 2012, 12:45 AM   #3
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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.

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.
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Old 5th April 2012, 09:55 PM   #4
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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).
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Old 6th April 2012, 03:17 AM   #5
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no - once you load it with two channels, the B+ voltage will drop further
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Old 6th April 2012, 08:23 PM   #6
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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.

v4lve .
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Old 6th April 2012, 10:04 PM   #7
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Quote:
Originally Posted by v4lve lover View Post
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.

v4lve .
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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Old 6th April 2012, 10:11 PM   #8
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Have a search for an ECL82 amp by member "shoog" here. I heard that amp and it was just lovely. I think one of the issues is the high gain, and I think shoog dealt with this using an interstage transformer..... I once had the link bookmarked, but have since lost it.


Fran
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