Ok, well that gives us some info on what you are looking to do.
I would suggest a 3 stage design instead of 2 stage. I am driving a 211 with an SRPP 6SN7GT coupled to a 6BX7GT w/interstage transformer, getting 25 watts RMS out/8 ohm. Power supply is 1kVDC.
Why not read through the current thread "All DHT amps" - lots of useful information for you and circuits of many types. I would ABSOLUTELY build an all-DHT amp here. I have to disagree with 3 stages - I tried that in an AB test against 2 stages with a 1:4 step-up on the input. The 2 stage version wiped the floor with the 3 stages, It was so obvious it only needed a couple of tracks to make a definite decision. In fact about 1 minute was enough. I've been using input stages 10Y, 46 and 2P29L in triode. All three in filament bias with resistor anode load and Rod Coleman V9 regs, and all sounded good. 46 my favourite, 10Y favoured by a friend who has borrowed both in his system. He's also committed to DHTs now. I'm currently using a Hammond 1140-LN-C which I like - very solidly built and 80% nickel core with permalloy case. Broadcast quality. It's a bargain right now. I paid £90 a pair. Recommended. This should give you what you need. You could also use 112A or 26.
Since I've gone all-DHT the sound has gone up a whole level, and it's not subtle. I'm 100% committed - no more indirectly heated tubes. I feel that strongly about it. I've never had such a good sounding system in 15 years of building amps.
You might take a look at Ale Moglia's 300B amp with 47 input and Lundahl LL7903 SUT. On Bartola Valves site. I use resistor loads which I like for their natural tonality, he uses active loads. I prefer the 2a3, but many use the 300B for more power. For a big output tube you could use a plate choke on the input DHT to give you more drive.
Since I've gone all-DHT the sound has gone up a whole level, and it's not subtle. I'm 100% committed - no more indirectly heated tubes. I feel that strongly about it. I've never had such a good sounding system in 15 years of building amps.
You might take a look at Ale Moglia's 300B amp with 47 input and Lundahl LL7903 SUT. On Bartola Valves site. I use resistor loads which I like for their natural tonality, he uses active loads. I prefer the 2a3, but many use the 300B for more power. For a big output tube you could use a plate choke on the input DHT to give you more drive.
Motor - what level are you looking at for a build? Simple, medium or complex? There are a lot of factors to consider before you start building. It's important to have some goals to follow as your build progresses.
yes, the 10y is certainly considered, as is the 811 and 801. Even looking at the EML drive tube series : 20a, 30, 12a..But can they compete with the "vintage" thoriated triodes? I already have 2 three stage amps(1 is even being parted out as we speak) , now its time to try a 2 stage design. As much as possible i want it interstage/input coupled through transformers not tubes. And... a power supply section to match. Much thanks for the info Andy!
I think you always strive for simplicity? But, for big triodes there's always an amount of complexity involved
When looking at your postings on this forum so far, I see lots of planning, which is of course is great, and at least for me, part of the enjoyment of this hobby.
Did one or more of your plans materialize? If so, could you show us one of your builds?
Did one or more of your plans materialize? If so, could you show us one of your builds?
20A is great VAS tube.
It's gain enough for 150Vpp (at marvellous low distortion) -BTW for 211 180Vpp need at least 1:2 SUT-, the Ra not so low, but enough to drive easy driving power tubes.
211 isn't such type, for proper operation (and higher power than about 8W at A1) need CF or SF.
It's a nice tube the REN904. I have a few, plus more of its equivalents like AG495, K1694, E428, A4110. These are all really good sounding triodes with a mu of around 30 - excellent driver tubes. Very few people use these old radio tubes or even know about them. They're a European tube - very few made it over to the USA, but they're prized in Europe.
I really like REN904, as an input tube, an indirect heat triode tube which is mu medium an alternative solution for DHT.
I apply it to my 300B SET Amp. with REN904+B403+IT+300B, have nice Sound.
NOTE: CORRECTION IN PREVIOUS POST, REN904+45+211.
