3A5 thoughts

[Ryssen]

Have anyone built anything with these,how is the sound?
Thought of maybee use them as an outputstage after a DAC (CS4398)
But I wonder if they are worthy..

[revintage]

Hey Ryssen,
Don't think it's worth adding a tube at all. Differential output is 2,4Vrms. Just add a balanced to SE 2:1 transformer, Lundahl off course, and you're done. Still you have over 1V signal level and acceptably low Zout.

andyjevans have tried the 3A5 as a preamp and reported it sounding good. Probably the halves should be parallelled(like in a 2A3) and fed to a 4:1 transformer.

[Ryssen]

Don't think it's worth adding a tube at all.

Thats what I thought..

Just add a balanced to SE 2:1 transformer, Lundahl off course, and you´re done.

How much current should the trafo withstand?

[revintage]

As the input is balanced there is no DC-current flowing. A LL1676 would probably be a good choice.

[iko]

Originally Posted by revintage

Hey Ryssen,
Don´t think it´s worth adding a tube at all. Differential output is 2,4Vrms. Just add a balanced to SE 2:1 transformer, Lundahl off course, and you´re done. Still you have over 1V signal level and acceptably low Zout.

andyjevans have tried the 3A5 as a preamp and reported it sounding good. Probably the halves should be parallelled(like in a 2A3) and fed to a 4:1 transformer.

I recall a little while ago some people pointed out the paralleling as not a good idea in a thread over at audioasylum/tubediy. Might be better off just using each half for a channel. In the end, you trying both setups will be the best answer.

[revintage]

ikoflexer,
Know how a 2A3, 6B4G or 300B is built? Also with 3A5´s common-cathode, one for each channel probably isn´t the best idea.

[iko]

Proof by similarity sometimes works, sometimes doesn't. That I know.

[andyjevans]

Hi,

I personally like DHT small triodes as DAC outputs. Cheap version if you have a balanced DAC is something like 3a5 or 1J6 into a Hammond 124b. 3-1 stepdown. Doesn't give you much more than unity gain with a stepdown, though. If you need gain I'd go with the 2C22 - one of the few indirectly heated tubes I'd think of using.

But let's go for some quality here! Use the 26. Cheap and plentiful and close to the best you'll get. Arguably the 10y is better and the 01A is as good in lighter more airy way, but the 26 is just one of the absolute great all-time tubes. WAY better than any 6SN7, for instance. The 26 is a Hall of Fame tube. So learn to use it and you won't regret it. For filament just use a big cap (15,000 or similar) and a LM1084 configured as current source, with a 1.25 ohm 5 watt (or more, like 12W is good) resistor between gate and output, and positive taken from the gate. And a decent heatsink like 2 to 3 ins square at least. And a 6v secondary transformer. Nothing more fancy than that and you're good to go.

To make the 26 sing, use an active plate load, like two IXYS 10M45 in cascode. Search the forum for designs, but basically you want 1k gate resistors right on the LM1084 chip. Start the sense resistor around 1K and go down until you're right. I've been trying red LEDs in the cathode of small tubes - 1.7v so you may need a few! The above is assuming single ended. For balance I guess use a CCS in the cathodes. Then you can use a transformer, parafeed a transformer or use cap out. Dave Davenport has a nice parafeed balanced line stage design on the K&K website. Tells you all you need to know really.

good luck

andy