6L6 for a beginner, plus ECL86/6GW8

jsp · 25th March 2007, 08:00 AM

Over time I have collected some bits and bobs and wish to make at first a simple mono amp. I have done some hunting around the net and reading up and I have very basic understanding of valve amps, and more than enough skill and tools to actually build one following instructions. I have done a search on the forum and have been reading up a bit, theres so much stuff here I would never be able to soak it all up!

I have a few OPT's and power trannies. PS's aren't an issue for me. I would like to try at first a PP 6L6, mainly as I have some nice 6L6GB's and lots of 12AX7's 12AU7's and 12AT7's.

I have found this circuit http://www.audiofanatic.it/Schemi/Ti...L6PP_12AX7.jpg and can follow most of it but I am not sure of the purpose of the 6.3v link through to the cathode? My OPT's don't have UL taps and most of the simpler schematics on the net seem to use these.

Also I don't seem to be able to hunt down many shematics for ECL86/6GW8 PP setups not using UL OPT's. I think I just got my terminology right

I picked up a faulty kreisler radiogram and would like to make something out of it for small PC speakers or something. The OPT's in it are 10k.

If I have broken any rules or reposted an allready asked question please let me know!

Thanks

dsavitsk · 25th March 2007, 08:23 AM

Quote:

Originally posted by jsp
but I am not sure of the purpose of the 6.3v link through to the cathode?

If it is what I think it is, it is to bias the heaters up to the same voltage as the cathodes. Typically you would just build a voltage divider off the PS to bias the heaters, but this could work too, I suppose, though it strikes me that it could inject some noise into the cathode?

SY · 25th March 2007, 11:17 AM

dsavitsk is correct, it's a cheap and easy way to bias up the heaters. That's really for the benefit of the input stage- the output stage will be far less sensitive to heater-induced noise because of the high level of signal and the suppression of common mode noise in the push-pull stage.

All that said, this circuit sucks. You can find better.

jsp · 25th March 2007, 01:23 PM

thanks for that, lots of other circuits I have looked at had the cathodes grounded by a resistor.

If this isn't a great circuit, what do you recomend?

I allready have a chassis to experiment with which has 3 octal sockets and 3 nine pin sockets. I have 390v to play with comming out of a 5AS4 in one socket.

The whole idea is to play around with one mono amp, and if I have sucess to build a stereo amp in the future based on what I have learnt, and to possibly drive my quad 57's, but thats probably a few years down the track

I also have one other design aim, and thats to have a few components as possible and to keep it very simple.

A family member interstate suposedly has some 6V6 valves I can get my hands on also so theres another option. But I think my current OPT is probably better suited for PP 6L6, its about 7.5K-8K hand wound, and I have a smaller 8K one from A&R Melbourne.

d1983 · 25th March 2007, 03:56 PM

Sy: If you don't mind me asking, why does the circuit suck? Is it the PSU, or is it just too simple of design? Would it sound ok?

sorenj07 · 25th March 2007, 04:02 PM

Quote:

Originally posted by d1983
Sy: If you don't mind me asking, why does the circuit suck? Is it the PSU, or is it just too simple of design? Would it sound ok?

I'm not quite as knowledgeable BUT I do know that a 12AX7 type tube alone probably doesn't have the current or voltage swing to drive a pair of 6L6's with any efficacy.

Another reason that this schematic is pretty miserable is that you don't have anything close to a regulated supply for the 6L6G screens, which you HAVE to have. I'm not fully boned up on SS regulators but a decent one shouldn't be too hard to find. The selenium rectifiers just add insult to injury.

SY · 25th March 2007, 06:41 PM

Quote:

Originally posted by d1983
Sy: If you don't mind me asking, why does the circuit suck? Is it the PSU, or is it just too simple of design? Would it sound ok?

More later when I have time, but in brief, it's a lousy input stage/phase splitter. A reasonable choice for 1955, but it's 2007 and we can do better.

Yvesm · 25th March 2007, 06:47 PM

Here are some ideas with 6L6 and 6GW8:

http://www.dissident-audio.com/Index.html

Yves.

sorenj07 · 25th March 2007, 07:31 PM

Barring the time constant issues, you could always go with the Williamson... you would need another dual triode per channel though.

leadbelly · 25th March 2007, 07:35 PM

Quote:

Originally posted by Yvesm
Here are some ideas with 6L6 and 6GW8:

http://www.dissident-audio.com/Index.html

Yves.

Great, I like the paralleled 6SL7 to drive the 6L6!

25th March 2007, 08:00 AM	#1
jsp diyAudio Member Join Date: Mar 2007	6L6 for a beginner, plus ECL86/6GW8 Over time I have collected some bits and bobs and wish to make at first a simple mono amp. I have done some hunting around the net and reading up and I have very basic understanding of valve amps, and more than enough skill and tools to actually build one following instructions. I have done a search on the forum and have been reading up a bit, theres so much stuff here I would never be able to soak it all up! I have a few OPT's and power trannies. PS's aren't an issue for me. I would like to try at first a PP 6L6, mainly as I have some nice 6L6GB's and lots of 12AX7's 12AU7's and 12AT7's. I have found this circuit http://www.audiofanatic.it/Schemi/Ti...L6PP_12AX7.jpg and can follow most of it but I am not sure of the purpose of the 6.3v link through to the cathode? My OPT's don't have UL taps and most of the simpler schematics on the net seem to use these. Also I don't seem to be able to hunt down many shematics for ECL86/6GW8 PP setups not using UL OPT's. I think I just got my terminology right I picked up a faulty kreisler radiogram and would like to make something out of it for small PC speakers or something. The OPT's in it are 10k. If I have broken any rules or reposted an allready asked question please let me know! Thanks

25th March 2007, 11:17 AM	#3
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	dsavitsk is correct, it's a cheap and easy way to bias up the heaters. That's really for the benefit of the input stage- the output stage will be far less sensitive to heater-induced noise because of the high level of signal and the suppression of common mode noise in the push-pull stage. All that said, this circuit sucks. You can find better. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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25th March 2007, 01:23 PM	#4
jsp diyAudio Member Join Date: Mar 2007	thanks for that, lots of other circuits I have looked at had the cathodes grounded by a resistor. If this isn't a great circuit, what do you recomend? I allready have a chassis to experiment with which has 3 octal sockets and 3 nine pin sockets. I have 390v to play with comming out of a 5AS4 in one socket. The whole idea is to play around with one mono amp, and if I have sucess to build a stereo amp in the future based on what I have learnt, and to possibly drive my quad 57's, but thats probably a few years down the track I also have one other design aim, and thats to have a few components as possible and to keep it very simple. A family member interstate suposedly has some 6V6 valves I can get my hands on also so theres another option. But I think my current OPT is probably better suited for PP 6L6, its about 7.5K-8K hand wound, and I have a smaller 8K one from A&R Melbourne.

25th March 2007, 03:56 PM	#5
d1983 diyAudio Member Join Date: Mar 2007	Sy: If you don't mind me asking, why does the circuit suck? Is it the PSU, or is it just too simple of design? Would it sound ok?

25th March 2007, 06:47 PM	#8
Yvesm diyAudio Member Join Date: Jul 2004 Location: Ardeche	Here are some ideas with 6L6 and 6GW8: http://www.dissident-audio.com/Index.html Yves.

25th March 2007, 07:31 PM	#9
sorenj07 diyAudio Member Join Date: May 2006	Barring the time constant issues, you could always go with the Williamson... you would need another dual triode per channel though.

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