my CELLINI triode amp

[Bigun]

I've been building SS amps for about a year [designing TGM3 - output Triples], but a friend of mine who is an ardent tube fan couldn't suffer my blundering about with transistors any longer. This past couple of weeks I've been receiving bits and pieces as a gift. A chasis, some glass bulb shaped objects, a couple of strange looking objects which I'm told are paper-in-oil capacitors made in Russia before I was born and some Hammond iron.

So now I will try to learn about tubes (or valves as they call them where I come from)

I'm seeking a bit of encouragement and advice from the Forum as I go.

The schematic for which these parts are for is based on an old design known as Lilliput so it may be familiar to some of you.

[kavermei]

Hi, welcome to tubes, I have some thoughts...

- 6as7 often has poorly matched sections, so it is not the best choice for an amp without feedback... Also there are tubes with nicer curves around (the 6as7 was never designed for audio use.) It does have great looks, though.

- This amp will not have very much gain. Depending on your source, you may need to use 6sl7 instead of 6sn7 to get sufficient drive to the output tube.

- You have almost no current margin on your 155C choke. I don't know how close it is specced so you'll probably get away with it, but it would be bad news if it went into saturation during signal peaks.

- Remove LED1 and LED2, they don't serve much purpose and they'll cause nasty switching noise.

Kenneth

[Stixx]

6as7 often has poorly matched sections, so it is not the best choice for an amp without feedback... Also there are tubes with nicer curves around (the 6as7 was never designed for audio use.) It does have great looks, though.

True, still the original Lilliput was built many times and is still being sold as a kit in Italy (audiokit.it)... maybe for its looks ...

The original Lilliput also uses the 6922/ECC88 as input tube that has more gain.

While those ESE125 are quite inexpensive they don't offer much in the bass department which the 6AS7G are capable of, so I'd think about better OPT's (1.4K:6 ohm was the original from Megahertz).

Good luck!

[Cassiel]

Originally Posted by kavermei

Hi, welcome to tubes, I have some thoughts...

- 6as7 often has poorly matched sections, so it is not the best choice for an amp without feedback... Also there are tubes with nicer curves around (the 6as7 was never designed for audio use.) It does have great looks, though.


Kenneth

The looks is the only thing I like about the 6as7. Don't waste your time with that tube, el84 and 6v6 are much much better. I did build the Lilliput and I was never happy with it. Tube is cheap but the power supply and the OT makes it expensive. It needs big caps and a big OT. Hard to drive also, hum likely a problem... I hate that tube :-).

It might be OK in PP but not for a SE amp.

[Bigun]

Thanks guys, it's good to have company.

Well, the bits I have are provided as gifts from a friends junk box so it provides the easiest path for a first build - i.e. it's free. The looks might be important for the WAF yet...

How do you think I could build it / design it so that it would be relatively easy to upgrade the performance ? Would I be able to drop in a different tube and tweak the bias ?

The 155C, if I understand the concern correctly, it is that it's rated for 8mA and I'm already expecting a bias current of 6mA through it leaving only 1-2mA headroom for signal swings ? Doesn't C2 keep the signal out of the choke ?

[Wavebourn]

Welcome Bigun, and congratulations with widening of your horizon!

Try 6V6 or EL84, as suggested!

Also, a single EL82 (or Russian 6F3P) is a good start! It contains both preamp triode and an output pentode.

[Bigun]

Hi Wavebourn, thanks for welcoming on board !

Well, 6V6 and EL84 are Pentodes, which is different right ? It's like taking a BJT amp and changing to MOSFETs (for a SS guy).

Is it not possible to build this amplifier with Triodes ?

[planet10]

With those OPTs EL84 or 6V6 will make a better amp and a less problematic build... if you need some EL84 to push you over the edge, i could offer some for the cost of post.

dave

[Cassiel]

Originally Posted by Bigun

Hi Wavebourn, thanks for welcoming on board !

Well, 6V6 and EL84 are Pentodes, which is different right ? It's like taking a BJT amp and changing to MOSFETs (for a SS guy).

Is it not possible to build this amplifier with Triodes ?

To triode wire a pentode is easy, it only takes one 330 Ohms resistor from the plate to the screen. Planet 10 is right, less problematic and better sounding.

[Wavebourn]

Originally Posted by Bigun

Is it not possible to build this amplifier with Triodes ?

Nothing is more valuable than an experience!

You may use tubes you friend gave you then go forward and do something different to compare!