What tubes for a OTL tube amp?

[atmasphere]

An RC filter is fine. You can certainly regulate if you want to, but the performance of the CCS is high enough that you'll find the performance of the voltage amplifier to be impervious to AC line voltage variation.

 

[alexanderfa]

Thanks Ralph, I really appreciate for sharing and helping

 

[audiowize]

Hello friend, 6AS7G in truth it is much better because it has a heat sink on top of its structure, attached to the G1, this allows the stage in class A2 or AB2 to work, which generates grid current and nor 6080 neither 6AS7GA do not have.

This is not exactly true. I just pulled a sample of 15 6080/6AS7GA tubes out of a box and:


10 have the big G1 heatsink on top. 5 of those are 6080s, 5 are 6AS7GAs.
5 have the small folded box shaped G1 heatsink. 4 of those are 6AS7GAs and 1 is a 6080.

 

[dady]

OK then I am wrong....
I have more than 30 6080 and 20 GA and none has the structure of the Russian 6H13 that are recommended in the Atma amp.
And what you recommend to the college Alexandarfa?

 

[calico88]

bit out of topic,
which Triode Tube is lower operating voltage and lower plate resistance than 6as7 ?

 

[savu]

bit out of topic,
which Triode Tube is lower operating voltage and lower plate resistance than 6as7 ?

6C33C is a very good candidate for low plate resistance and low voltage operation

 

[calico88]

Noted,
What about mini tube ? Smaller in size tube that low rp b+ ?

 

[savu]

Noted,
What about mini tube ? Smaller in size tube that low rp b+ ?

6C19P comes in a 9 pin socket

https://frank.pocnet.net/sheets/113/6/6S19P.pdf

 

[calico88]

Thank you,
that 6C19P design for regulator, I wonder if there is any audio miniature tube ?

 

[Lingwendil]

Thank you,
that 6C19P design for regulator, I wonder if there is any audio miniature tube ?

They work great for audio, similar to half of a 6AS7/6080.

 

[kodabmx]

Miniature audio tube? 12B4 comes to mind but it's not very large...

 

[audiowize]

Thank you,
that 6C19P design for regulator, I wonder if there is any audio miniature tube ?

The 6080/6AS7/6C33 are designed for regulator duty also. That's part of why they work so well in an OTL amp.

 

[Disco-Pete]

Can you guys help me with 6HB5? What tester out there will give a meaningful result? From what I see available they don't provide the voltage required to accurately test these. TIA

 

[calico88]

12B4 Rp is 1030 ohms, I'm looking about 50 ohms.
looks like my option is 6C19P, but I can not find the detail datasheet, that shows Rp curve.

 

[tubetvr]

IMHO 6c19 is not an ideal choice for an OTL.
6C19 400 ohm, 6C41C 150 ohm, 6C33C 80 ohm, (at 550mA, it is lower at higher current). There are more obscure tubes with lower resistance but they are not widely available.

 

[dady]

ED8000 and EC360 triodes.

 

[nautibuoy]

Here's an interesting take on an OTL amp;

Inverted Tube Operation

I've build several SE-OTL amps that have all sounded excellent, including;

• the original Transcendent SE-OTL kit that used 6H30pi tubes

• Transcendent Minibeast kit with EL509 tubes

• The Transcendent 300B SE-OTL, now much modified with a revised output configuration and Voltage Controlled Current Source DC filament supplies

• I'm working on a new project that will use a single output tube, either a 6C33C or 13E1.

Apart from the Minibeast, which puts out a mammoth 4WPC, these are all flea-power amps (around 1.5W) to suit my speaker choice so will only have a narrow interest. The 300B is the best sounding IMO - will be interesting to see how the new project compares.

 

[kodabmx]

12B4 Rp is 1030 ohms, I'm looking about 50 ohms.
looks like my option is 6C19P, but I can not find the detail datasheet, that shows Rp curve.

Ah... Good to know. Rp of 1000 is "low" compared to the 7700 or so of a 6SN7, right?

I considered an OTL but after reading this article from Patrick Turner, I decided matching transformers made MUCH more sense in my case.

OTL-amps-pros-cons

 

[dady]

After read again this article I deny this kind of amplifier. To many solutions for avoid transformers. After reading this article again, I deny this type of amp. To many solutions to avoid transformers. I may have become obsessed with the issue of avoiding a transformer on the way out. Then I discovered that the most important part of a HiFi chain are the transducers, the choice of crossover frequencies. This is key and gives the different tone of each system. I think if an amplifier respects the load impedance by adapting it to its damping, anyone can sound good. I had an OTL with 10 6AS7G per channel, I could never tune in without a fuse blowing, it was terribly hot and I spent more time in my workshop than in my living room. I kept introspecting the idea, many nights I went to sleep trying to improve the idea, I bought a software to calculate the optimal polarization and the minimum distortion. And an important issue, taken from that paper that the colleague published, the output of an OTL in the case of the Circlotron, is a cathodic follower, that is, I do not even have a triode transfer curve and I can use any power mosfet in that place either in circlotron or complementary. Respecting that the front end part is valvular or with triodes, even using a driver transformer. The idea of ​​the OTL is romantic, it is a retrograde search for an ideal for which, a lot of power is consumed and something profitable is not obtained, except by using 40 valves per channel and in parallel.

 

[savu]

@dady

I have designed and built a fully differential OTL based circlotron topology with 4x6C33C driven by individual cathode followers and I have never encountered any problems with it.
I use separate supplies for the input differential cascode, driver stage and power stage. Being fully differential it has two identical oposing GNFB loops at about 25dB. I must admit it sounds better without GNFB because it has more headroom.
I use it with my QUAD ESL 63 speakers
Silviu