Ralph Amp - Thoughts?

[Thermionic Idler]

I'm debating whether to tackle this design as my first scratch build after a few years of building from kits.

The circuit looks remarkably elegant and simple. Having looked up the data sheets for the 6B4G and the 2A3, I'm thinking a 2A3 could also work in that circuit with little alteration?

People who've built this seem to rate it and there is something that appeals to me about a circuit containing only 2 resistors and 1 capacitor per channel. Can anyone see any downsides / potential issues with it? Too simple?

http://www.meta-gizmo.net/tri/interstage.html

To put this into perspective, my preamp is a Modwright LS100 (300ohm output impedance) and the speakers are Horning Aristoteles (96dB sens. 6.1 ohm impedance).

[rowuk]

I generally approach an amp from the speaker side. In this case they claim 8 Watts with push/pull 6b4Gs.

The only part of the article that bothers me is the BS about contamination being lower with a transformer than a cap and resistor for instance. That would be a tough claim to defend.........

I am sure that it will sound fine. Better than a SE 6B4G? Well now we are back to the speakers that it is hooked up to..........

I switched from Push/Pull to dedicated SE last year (separate amps for each driver and passive crossover built into the amplifier as well as output transformers matched to low/mid/high range use) and solved a bunch of issues. Your situation (room/speaker) is different than mine however.

I'm debating whether to tackle this design as my first scratch build after a few years of building from kits.

The circuit looks remarkably elegant and simple. Having looked up the data sheets for the 6B4G and the 2A3, I'm thinking a 2A3 could also work in that circuit with little alteration?

People who've built this seem to rate it and there is something that appeals to me about a circuit containing only 2 resistors and 1 capacitor per channel. Can anyone see any downsides / potential issues with it? Too simple?

http://www.meta-gizmo.net/tri/interstage.html

To put this into perspective, my preamp is a Modwright LS100 (300ohm output impedance) and the speakers are Horning Aristoteles (96dB sens. 6.1 ohm impedance).

[IslandPink]

That's well worth a try . The LL1635 is one of Lundahl's better-sounding transformers - I used a pair on the Aurora PP amps I had years ago .
2A3's will be fine .
You might want to look at Lynn Olson's circuits for the 'Aurora' and 'Karna' see how the ultra-path cap connection is used on the output stage - would work very well as a minor mod to what you have there .

It's probably better to phase-split earlier and have a PP stage driving through the 1635 to the 2A3's , but you could always try that in the future if it doesn't work out quite as well as you want. PP class A is nice though, and 2A3 or 6B4G is a good way to do it - drives speakers nicely regarding timing abd bass tone .

[Thermionic Idler]

Thanks for the input

Researching this circuit turned up another very interesting one which I may build instead, with 2A3's in place of the 6B4G's. It's apparently inspired by Olsen's work (noted it uses tube voltage regulators) and was designed by Stig Larsen.



There's a thread here from 2002 which documents the build: http://www.diyaudio.com/forums/tubes-va ... genumber=1 and overall it looks pretty promising.

My current thinking is to build it as a stereo amp, obviously making sure the power supply is sufficiently man enough to cover both channels. That will prevent costs spiralling out of control and also make more efficient use of the ECC99 - being a double triode.

[IslandPink]

Very good, haven't read the thread yet, but looks like a nice circuit with a couple of improvements over the first one. Don't go out of your way to get ECC99's though ( in my opinion ) - I found I preferred RCA 5687 or mid-1980's 6N6P , both of which sounded more refined , with better tone, in the upper mids and treble ( in the Aurora circuit that was ) .

[Thermionic Idler]

Thanks --- that's an interesting thought. I think the 5687 and ECC99 are pretty similar electrically aren't they, so they should be interchangeable in that design. Wondering if there's an octal option too...

I sketched out my version on the drawing board this afternoon, when I've copied it down to A4 I'll scan and post it. I've altered the power transformer arrangement a bit - one mains TX to cover HT and the rectifier filaments, and another separate transformer covering the heaters for the 2A3 and input valves.