The kicker here is the high plate resistance (Rp), requiring the < 7K transformer. Most of the good affordable multiple tap transformers, like the Lundahl or James run about 3K to 6.5k. The higher K transformers tend to be for the high power triodes like the 845, so get expensive.

If the designers feel that 6.5K will do. The James transformers at about $150- $200 a pair are a fine choice and will be right at home in any number of future amps. I have a pair in my DRD amps.

If 6.5K is to low, or over budget, take a long look at the Hammond 125 series. At $20-$35 each, they are not the last word in thunders bass, or shimmering highs but are pretty pretty damn good for the money. Have a look at Angela. http://www.angela.com/catalog.html
Keep in mind that I would not expect more than a 1-1.5W with this tube. So thunder is probably not in the program.

I don’t want to dissuade you from your project but have you considered the 2A3, at about $30…John

So for the 6ah4 the little Hammond’s might be the way to go. Another possibility, if you have a set of P-P transformers handy from say a EL84 or 6V6 amp, these run about 6-8K. Yea I know a P-P trans is not designed to run single ended and you will saturate the core, at least somewhat. But at very low power it works.

As for the Aikido, I have not done anything new with it. It works POS power supply and all and I have lately been spending my time on my 300B amp, when it is cool enough to run it (92 here in Valley Forge today). there is more over at G.B…John

When we talk of common DHT for SET amps we, (I) mean 45, 2A3, & 330b.

I love the 45. My 45 DRD is probably the most "refined" amp I have but with my 96db speakers, they are more than sometimes, not enough. Even at very moderate volumes.

OK, flashback time. A few years back, when I thought to try the SET thing, I, as I suggested above tried it by inflicting it on my long suffering ST-70. I wired one EL34 across both sides of the output trans and let her rip. I liked it enough to pursue the idea. I had less efficient speakers back then and was used to 20-50W of P-P tubes and 250W of SS. So the 300b seemed like the only choice.

The 300b has the most output power, they say 8W into a 3.5k load. I use a 5.6k load for about 4~5W and it’s still plenty.
But the 300b is a hard tube to drive. So (in my opinion) it’s sound ,is more dependent on the input stage. I have tried .
FI, OK but soft.
SSRP, just couldn’t get it to work for me.
WE-91(6sj7) not bad at all, may well be many people’s cup of tea. If I had the money I’d try 310’s.
DRD,I was still on the 45 honeymoon, so not a fair trial, must get back to that.
And now the choke loaded D3a. This is working for me so far. What I am looking for may not be the "best". What I Want is a sense of life or emotion. Not something pure but clinical like a gain clone. (though I will not part with mine)

Some reviewer once said something like "the 300b sounds great but you always know you’re getting a show"

I was playing some James Cotton a wile ago and I was at the show.

On to the 2A3.

2.5 Watts.

If this is enough power for your speakers. It’s pretty much a ‘no brainer’ They are not too expensive and easier to drive. There are so many kinds out there both, new and old you can tune the sound a little

If you have high efficiency speakers, that’s what I’d do. If you have a 3-5K transformer you can try something else later…John

The D3a is working well for me, I am still trying this and that. I am about due for an update over at GB, so I wont go into detail. To be honest this setup may be guilty of being a little bit larger than life. I will take them to the Bottlehead meet and see what everyone thinks.
I will have to revisit the DRD. What is now the DRD45 uses the James outputs and a really trick universal power transformer. But that is a project for a bit later on.

One thing I want to point out is this amp (the non DRD) has used the same power supply, 300b’s, and output transformers (Lundahl 1623) and by changing only the driver/input stage has turned it into 4 or 5 completely different amps. If I had started with the SSRP I may have given up on the 300b. Yet this works well for others.

I am curious as to who the 6ah4 will sound. Do you have a link to the schematic?

Happy Independence day…John

• http://www2u.biglobe.ne.jp/~tossie/6AH4-.html

If it doesn’t work out, consider the 6bm8 STC amp, from the same site and others. It would use the same power supply and chassis.

I built one and it is a great sounding little amp. My friend Dave prefers it to my other amps. hasn’t heard the new 300b yet…John