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DIY in an RCA Cabinet


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This thread got weird quick....

 

Probably not going to do a SETH. I've seen it. Power supply will be beefier than the JFL. Input will be alot different as well.. I was also looking at Feral Eye but likely won't do that either. I have lots of parts on hands and will likely use what we have available.

 

 

 

 

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I prefer simple circuit topologies or topologies that satisfy the requirement, but no more than that. I know that sounds odd, but a lot of times, circuits are more complicated than they need to be. For a PP 2A3 I would go with a simple circuit such as a 6SL7 input coupled to a low gain triode "long-tailed" phase splitter coupled to the 2A3's. 

 

After tweaks and fine tuning, you can add a CCS to the long-tailed pair if you want to balance the drive signal (if needed or desired). 

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6 hours ago, Curious_George said:

I prefer simple circuit topologies or topologies that satisfy the requirement, but no more than that. I know that sounds odd, but a lot of times, circuits are more complicated than they need to be. For a PP 2A3 I would go with a simple circuit such as a 6SL7 input coupled to a low gain triode "long-tailed" phase splitter coupled to the 2A3's. 

 

After tweaks and fine tuning, you can add a CCS to the long-tailed pair if you want to balance the drive signal (if needed or desired). 

 

You guessed it..  Actually I have some 6SL7s in military boxes or VT229's. They don't appear to ever have been opened. 

 

 

 

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I have a few 6SL7WGT's and they appear to be NOS, but in circuit, they have high distortion. My favorite 6SL7GT is the GE "silver looking" plate. They seem to be consistent (tube to tube) and have low distortion readings in my single-ended circuits. They are quiet too and not microphonic. The 6SL7WGT's are strictly for back-up. 

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On 9/21/2021 at 12:31 PM, Curious_George said:

 

 

I saw your comment in another thread about 2A3 amp. What 2a3s are you using?

I have a bunch of 2a3s like vintage biplate RCA 2a3 and modern single plate sovtek, eh, and even a fake mullard... I didn't even notice they were monoplates. The EH are pretty nice porcelain base and gold pins. Now I gotta compare...

 

 

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For the price, I like the Sovtek 2A3. I have 3 pair of them and they are very consistent (measurement wise) and sound very good to me. It is a single plate and according to some other people who have used them, they have a higher power dissipation than your standard 2A3, but I have not tested or run them that hot. In use, they measure and perform like a "standard" 2A3 as far as bias, plate voltage, etc. Even though the price has crept up on the Sovtek 2A3, it is still the best tube in its class in my opinion.

 

Except for 211 and 845 tubes, I prefer to not use Chinese tubes. I have not had good luck with them. 

 

 

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On 9/23/2021 at 9:44 AM, Curious_George said:

For the price, I like the Sovtek 2A3. I have 3 pair of them and they are very consistent (measurement wise) and sound very good to me. It is a single plate and according to some other people who have used them, they have a higher power dissipation than your standard 2A3, but I have not tested or run them that hot. In use, they measure and perform like a "standard" 2A3 as far as bias, plate voltage, etc. Even though the price has crept up on the Sovtek 2A3, it is still the best tube in its class in my opinion.

 

Except for 211 and 845 tubes, I prefer to not use Chinese tubes. I have not had good luck with them. 

 

 

 

Interesting I'll have to try those sovtek and EH 2a3s.

 

A friend left a dozen RCA or GE 211 tubes at my house but we haven't done anything with them... 

 

 

 

 

 

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I bought 4 NOS GE 211 / VT-4C's back in 2005 or so. They each have developed issues, quite surprisingly. I have not messed with them lately, but it could have been a dirty tube socket. However, my Chinese 211's keep going and going. current is stable and no noise or other issues. Granted, I don't use the amps as much as I probably should, but now that fall / winter is here, I think I'll use them more to add a little extra heat in the basement / mancave. 

 

 

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16 minutes ago, Curious_George said:

I bought 4 NOS GE 211 / VT-4C's back in 2005 or so. They each have developed issues, quite surprisingly. I have not messed with them lately, but it could have been a dirty tube socket. However, my Chinese 211's keep going and going. current is stable and no noise or other issues. Granted, I don't use the amps as much as I probably should, but now that fall / winter is here, I think I'll use them more to add a little extra heat in the basement / mancave. 

 

 

 

What do you think about 211 vs 2a3 ?

 

 

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Now there is a question... In terms of sound quality / differences, the 211 has more micro-details to my ears. The dynamics and headroom that the high voltage affords has a dramatic affect on the sound, especially when you use a high impedance output transformer >10k. My output transformers are 16k into 8 ohm, so the load line is more horizontal reducing distortion, but increasing drive requirements. 

 

I like both the 211 and 2A3, but they do give a different presentation. 

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1 hour ago, Curious_George said:

Now there is a question... In terms of sound quality / differences, the 211 has more micro-details to my ears. The dynamics and headroom that the high voltage affords has a dramatic affect on the sound, especially when you use a high impedance output transformer >10k. My output transformers are 16k into 8 ohm, so the load line is more horizontal reducing distortion, but increasing drive requirements. 

 

I like both the 211 and 2A3, but they do give a different presentation. 

 

I know some that claim a 211 never sounds as good a s a proper 2a3 amplifier. With 107db1w speakers I got headroom with all of it in my room.

 

 

 

 

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For a DHT tube, it is hard to beat the 2A3. It's circuit can be simple and the voltage and drive requirements are easy to implement.

 

The 211 and 845's require much more effort and cost to build a good amp, which is why I suspect more DIYers don't try them not to mention the high voltage (over 1kV) needed to make them work where the plate curves are most linear. 

 

I've been tossing around the idea of a simple 211 or 845 amp for the beginner just so more people try the big transmitting tubes. If I do, it will be the 845 because you can use a much lower impedance output transformer than a 211. 

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