questions on Mikael Abdellah circuit optimized for EL34 triode operation

[ambience exists]

I am thinking of building this amp but using the EL34.

http://diyaudioprojects.com/Schemati...-Amplifier.htm

I am attracted to the simple topology yet being a bit green I still have a few questions:

1. Is there a way to optimize this circuit for the EL34? Would it need a change in the cathode resistor?

2. Could I use the lower cost Hammond OPT's (125 SE I beleive) and how would I connect them to an EL34 for triode operation?

3. Which Hammond 200 series Power Trans would be the best for this circuit using the power supply circuit shown in Alex's build:

http://diyaudioprojects.com/Tubes/KT88/

[ambience exists]

If anyone knows of a different but still good sounding EL34 SE circuit in triode configuration, I would be open to that as well!

[ambience exists]

Also considering Edcor transformers as an affordable alternative to Hammond- any thoughts on the XSE or the GXSE for this circuit?

[Andrewbee]

el34SE

I have not heard it but it looks okay to me.

[ambience exists]

Looks like a well designed circuit- has pretty much a detailed explanation of all the parts I would need. However, the schematic is a bit fuzzy so some of the values and more importantly- the way the output tube is wired- is hard to understand. Could someone help me decipher this?

http://angela.com/stereosingle-ended...amplifier.aspx

-Also, what the hell is up with the lug numbers on the driver tube? It looks like it uses two 6SL7's? Can someone better explain this circuit?

-This next question may seem really newbie but if a circuit calls for 100uf 25v but you can only find 100uf 50v, will that still be OK?

[Andrewbee]

While the schematic is not the clearest I can read it fine. Try zooming in using your browser.

For Triode operation you simply wire a 100 ohm 1/2Watt Carbon Composition resistor between pins 3 and 4 as per the schematic.

Driver tube numbers have one by itself and another in brackets E.g. 1 (1).

The reason is because the driver tube which is a 6SL7 is a dual triode, IOW two triode tubes in the same bottle so pin 3 would denote the cathode of lets say triode number one and (3) is the cathode of triode number 2. The Anode and Grid both have the same pin system and the filaments are shared by both triodes.

A 100uF@50V will always be safe to substitute for a 100uF@25V. IOW a higher voltage capacitor is safe but going the other way is trouble.

Before you go any further with any build I suggest you read up some more on Vacuum tube circuits or get someone who is familiar with them to help you.

Morgan Jones has a good book on the subject.

[ambience exists]

I understand that the 6SL7 is a dual triode, I just don't get how it is wired in this circuit... is the second triode in the tube wired at all? For example, are both pins 3 AND 6 connected to one cathode resistor? If I knew this I could build this circuit...


Also... Does anyone see a problem with running some old Tung-Sol 5881's in this circuit? Or 6l6's?

[sorenj07]

I recommend the Edcor GXSE transformers. They're pretty beefy, especially if the amp is only going to put out around 5W maximum. I recommend using around 4K or 5K on the primary. For 4K, I have their 8K:16 transformer with 8-ohm speakers, and loved it.

[ambience exists]

I am leaning towards the Edcors...

Is there anyone out there with knowledge of this amp or a circuit similar?

[Andrewbee]

I understand that the 6SL7 is a dual triode, I just don't get how it is wired in this circuit... is the second triode in the tube wired at all? For example, are both pins 3 AND 6 connected to one cathode resistor? If I knew this I could build this circuit...

One driver tube is used. One triode half for one channel and the other triode half for the other channel. Each triode half uses its own cathode resistor, (pin 3 has one and pin 6 has one) a 1K, so a stereo amp uses 3 tubes total, one input tube and two output tubes.