I'm in the process of renovating an existing 2a3 amp with no room for more complex solutions. My own system uses a 10Y driver with 1:4 step-up on the input, Hammond 1140-LN-C from their broadcast series. That's as good as it gets for me after throwing the kitchen sink at 2a3 drivers. But for the renovation I want to use just a single double triode driver with a mu of 25 or more so the amp can be integrated with no pre needed. My past experiments are as follows:
So once the amp is set up I'll try 6N1P, E80CC and E180CC. Simple circuit, anode and cathode resistors with DC Link bypass.
Anything I've overlooked in 9 pin double triodes?
- 12AT7 wasn't too good
- ECC88/6922 types didn't sound good to me either
- European radio valves like REN904 and TDD4 sounded good but are single tubes with 4V heaters.
- E80CC was interesting
- 6N1P was interesting
- E180CC was the best of the 5965 types, taller valves can sound better indeed.
- 6N6P/ECC99 has no more gain than a 6SN7 which is very good, so both were put aside for a higher mu choice.
So once the amp is set up I'll try 6N1P, E80CC and E180CC. Simple circuit, anode and cathode resistors with DC Link bypass.
Anything I've overlooked in 9 pin double triodes?
No - good idea and I've seriously considered it, together with 6S3P and 6S4P. What puts me off thee types of tube is the possibility of oscillation with high S. We're talking S=18 with 6S4P and 14 with EC86. Not sure what measures need to be taken since I don't use these types of tube. In any case a mu of over 30-40 isn't really needed.
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I have used in a single ended prototype, did not see instabilities on the oscilloscope. But yes, they were designed for RF, not audio, therefore "handle with care"
Maybe try the Russian 6F12P? It's a pentode triode. Triode connect the pentode, direct couple the triode as a cathode follower. The triode has 100 mu and good drive capabilities.
Or, pentode connect the pentode. Then you can play with different screen voltages to dial in the gain.
Or, pentode connect the pentode. Then you can play with different screen voltages to dial in the gain.
I use a 6sl7 tube wired as SRPP with a constant current source. The Sylvania JAN tubes are particularly sweet tubes. I have paired it with a 300B tube parafeed style with the transformer wired as an auto former using a V-cap as the parafeed cap, which is doable since I am only using this amp above 500hz. According to the late Allen Wright, the SRPP needs a constant current load to sound their best.
Well, I got the 2a3 amp working with 6N1P driver and it's rather good - better than I expected. I substituted some 5K Techno OPTs for the 2.5K Hammond ones which were huge and heavy, and I really need more B+ like 350V whereas I have just 300V. The 5K OPTs are fairly small and probably only good for 45mA-50mA. Just guessing since I don't have the specs. So right now it's giving 12W with 50mA current. Needs to be 15W or close to - I can try taking up the current a little. Good parts - Holco resistors and teflon FT-2 coupling caps and DC Link for bypasses and last cap in the PSU. Excellent Hammond iron, big choke.
Sound is kind of "fruity" and dynamic. Quite involving. Detail is OK though not micro-detail. Probably best on jazz and popular music, though classical music is OK too. Voices are good. More dramatic than a 6SN7 but not as neutral and not quite as detailed though it's close. Much to like. I was pleasantly surprised.
Schematic attached.
Sound is kind of "fruity" and dynamic. Quite involving. Detail is OK though not micro-detail. Probably best on jazz and popular music, though classical music is OK too. Voices are good. More dramatic than a 6SN7 but not as neutral and not quite as detailed though it's close. Much to like. I was pleasantly surprised.
Schematic attached.
I really like 6N1P-EV tubes. I first used them years ago when I started building tube amps. My first few amps were Decware Zen SE84C clones. Your schematic shows one half of a 6N1P as the driver for the 2A3. Is the one triode sufficient to fully and properly drive a 2A3?
How about ECC85/6AQ8? I have not tried them yet. They are kind of expensive to buy, but have heard good things about them.
There are just SO many double triodes out there. The goal for this thread is creating some kind of magic with a 300b or indeed 2a3 output stage. No doubt several contenders could do the job. I thought I was home and dry with a E180CC but that morphed into a 6SN7 and now a 6N1P. I'm really liking the 6N1P now I have it working. I didn't expect it to sound this good. I need to do some tube rolling to see if the 60s versions are audibly better than the later production, as people say they are.
The problem with "magic" is that we have to define what it is. For some is a highly subjective thing like how it sounds, for some is about measurements, or a combination of the two.
How would you decide which combination gives you the magic result?
Straightforward for me - I listen to it! I'm a conservatoire trained musician so I've played for many years in orchestras, theatres, clubs and so on with a whole range of classical and jazz instruments and voices which are now forever imprinted on my brain. So I just listen for the tonality of acoustic instruments, and of course clarity so you can hear everything. But it's mostly acoustic tone quality. Something that sounds as real and lifelike as it's possible to achieve with metal, glass, good parts and a bit of design work.
Hey Andy, have you tried battery bias for the input tube? I have found it to be better than a bypassed resistor setup.
Retsel
