EL34 SE amp schematic

[lquintas]

I want to build a EL34 SE amp for my daughter and I am hesitating between:

http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg

and

Stereo Single-Ended EL34 Hi-Fi Amplifier

I think that the Fostex FE127e drivers (not decided in which enclosure yet) could match.

Jute's amp is very simple, but Angela's seems better. Does it worth it?

Thanks

 

[Ezequiel (kel)]

has another option that is using pre SRPP ok? ai is a very good schematic.


1.000.000 de Circuitos Eletrônicos Audio: SRPP 12AU7 / EL34 SE

 

[lquintas]

Thank you Ezequiel. I have never built a SRPP amp, perhaps it is the opportunity to do it

 

[Eli Duttman]

Assuming the SRPP is set up well, switching from the 12AU7 to the 6FQ7/6CG7 will kick things up somewhat. Just make sure you have the extra 300 mA./bottle of heater current.

FWIW, I am not alone in disliking 12AU7 voltage amplifiers, as there are serious linearity issues. A properly designed 12AU7 circuit will work just fine, if the more linear 6FQ7/6CG7 is substituted. Obviously, the Octal 6SN7 and Locktal 7N7 can be used too.

 

[lquintas]

Thank you Eli. Do you suggest me to go on with Angela's amp? By the way, connecting both 6SL7 sections in parallel, does it mean that they share the same anode and cathode resistors, and that the bias current is half in each section?

 

[Eli Duttman]

Do you suggest me to go on with Angela's amp?

No, build the SRPP exactly as shown, but substitute a member of the 6SN7/7N7/6FQ7/6CG7 group for the 12AU7. Make certain sufficient heater current is available.

Paralleled sections present their own issues. Frequently, some tweaking is needed to prevent current hogging.

 

[lquintas]

Thank you again, Eli. I'll try so.

 

[VictoriaGuy]

Reviving the thread ...
I just built the recommended circuit:
1.000.000 de Circuitos Eletrônicos Audio: SRPP 12AU7 / EL34 SE

using 6SN7 tubes in the preamp section(s).

My first impression is that it is pretty 'quiet'...this is using my 'workshop speakers' (today Wharfedale W60Ds) and feeding a CD player signal.

Am I missing something? I know from the guitar amp world that 5 watts can be pretty loud...do I need to use more sensitive speakers, or is something wrong. I'm not trying to break the lease here, BTW....
I'll get some more voltage measurements tomorrow and post them here, but the bias voltages seem to be in the right 'ballpark'...

Well, it doesn't hum anyway!!



Thanks
John

 

[lquintas]

Well, finally I haven’t built the SRPP circuit because I have not been able to find a smart power transformer 230/230 for it (this amp is a present for my daughter), so I built Angela’s circuit with the paralleled 6SL7. It works very well. Unfortunately I can't help you.

 

[mastodon]

You could have used a 6.3V transformer for the heaters with some extra capacity, and connect another 6.3V transformer back-to-back to it to obtain 230V. Of course, you'd have had (at least) two transformers, but it's a workable solution in most cases.

 

[Troncones]

All of the example schematic use the EL34 in triode mode. Is there a prolblem with using this tube in pentode mode?

 

[VictoriaGuy]

About the 'not very loud' comment I made -
I moved the amp upstairs and hooked it up to higher-efficiency speakers- AudioNirvana 10" (supposedly 95dB/W?).
There's plenty of power/loudness with those speakers.
Volume control is at about 3 o'clock for 'loud' (not ear-shattering, but you wouldn't want to carry on a conversation either) listening.
I put a triode/pentode switch into my build and the volume control is at about the 11 o'clock position for the same loud listening.
So, you want to keep speaker efficiency in mind when building something like this amp.
BTW, it sounds very good, even with very ordinary tubes.

More details to follow, once I get some pics organized.

John