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RH Universal the power tube rollers amp

72.235.7.37
Posted on March 15, 2015 at 15:40:45
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010



I just completed my RH universal amp with the 6sl7 driver tube a few days back and the versatility and flexibility is very exciting. I am having a great time trying all my 6L6 based beam power tube types. With a simple swap of the tube rectifier I am able to adjust the B+ from 300vdc to 380 vdc. The B+ voltage chosen corresponds to the tube type. This is actually my second RH universal amp but able to deliver more power with 15 watt Transcendar OPT and a Triad PT. I implemented a 2 chassis design to more easily accommodate all the transformers and PIO and film caps.
Getting back to the tube rolling. So far, I have used in the same amp, in no particular order, Tungsol 5881, RCA 6L6GB, 7581a Phillips, Mullard KT66, Mullard EL37, VTL KT90, Tungsol 6550. Once I track down my Mullard KT88 I will try those as well. Depending on the b+ output desired I am using RCA 5R4GYA, Raytheon VT244, Mullard GZ37 and GZ34.
Currently, my favorite power tube is the Mullard EL37 used with the 5r4. It has slightly less power but this combo has excellent bass, detail, and a very clean precise sound. All the output tubes have their own character to their sound which makes for a plethora of listening possibilities. (I can't believe I used "plethora" in a sentence.) Anyway, many thanks to Al Kitic for providing the schematic and guidance for helping to make the amp a reality. And also to all the other inmates whose suggestions/hints/tips and encouragement also helped to finish the project. Cheers, Dak
PS I will try to post some pics soon.

 

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RE: RH Universal the power tube rollers amp, posted on March 15, 2015 at 16:18:22
GSH
 Add to that same family: 807, 5933 (807W), 7027A, 6L6G, 6BG6G, 6BG6GA, 6384, EL156, 350A, 350B, 7868, 6146, etc...

 

RE: RH Universal the power tube rollers amp, posted on March 15, 2015 at 16:34:13
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 The tube needs the same pin out as a 6l6 type to be operational in my amp. I suppose if you were truly industrious you could wire various tube sockets properly to accommodate all of the tubes that you listed. Dak

 

RE: RH Universal the power tube rollers amp, posted on March 16, 2015 at 05:01:34
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Or just buy or make a few adapters that will fit the sockets you are using.......

 

RE: RH Universal the power tube rollers amp, posted on March 16, 2015 at 11:01:19
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Right. I just bought a pair of 6384 to 6l6 adapters from Taiwan. Now I will be finally able to listen to those tubes. Impressive as their looks I find that the sound from purpose built "military" tubes are so neutral to be almost boring. We will see about the 6384. cheers, Dak

 

RE: RH Universal the power tube rollers amp, posted on March 20, 2015 at 01:25:26
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
 Finally someone posts about the fun and joy of listening to music and effortlessly trying and evaluating different output tubes :)

Indeed EL34 and 7027 are additional candidates, but they are going to require an additional switch, as implemented on my amp. The EL34 requires g3 to be connected either to cathode or ground (the usual solution is cathode), but if you are going to use 7027 and 7027A, you need to be able to disconnect pin 1 from pin 8, as these tubes have a second g1 connection to pin 1. Interestingly enough, if set for 7027 (disconnected) and used with EL34, the latter are going to operate in tetrode mode (g3 disconnected) which comes down to demonstrating the essence of the "Hazen mod"...

807 is perfectly usable if you make (or buy) an adapter UX5 to octal plus anode top cap.

EL38 is another suggestion, plug-in replacement for those expensive EL34, if you add a small too cap and a piece of wire to connect somehow to pin 3 (anode connection left unconnected on the base of EL38).

******

http://rh-amps.blogspot.com/

 

RE: RH Universal the power tube rollers amp, posted on March 26, 2015 at 00:49:06
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
 Have you tried other output tubes?

One plug-in suggestion is obviously 8417.

Any impressions on differences emerging between tube types?

Have you tried 6SN7 instead of 6SL7?

******

http://rh-amps.blogspot.com/

 

RE: RH Universal the power tube rollers amp, posted on March 26, 2015 at 10:34:48
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Hi Al, I have no 8417 tubes so I can not try that one. Also I did not put in a switch to make the anode to anode feedback adjustable between 100 and 200k. I will do that in the future and report on the 6sn7. I bought some high quality toggle switches so I can install them.
About output tubes, So far, the EL37 is the best sounding tube and I also tried some USA made KT88 made by Richardson electronics which sound very much like the EL37 but with more power. In the photos I am using some Mullard KT66 which are very smooth sounding. I bought some adapters and tried the 6384 guided missle tube. But I can tell that the adapters affected the sound as it made the music somewhat diffuse. I also used some vintage tung sol 6550 with dark grey, no holes plates. They sound very good similar to the kt66. The flexibility of this amp is amazing. it is like I have 6 amps or more!
On a different note, I was wondering if you would like to guide me in building a parallel single ended amp that would accommodate KT88, KT90 and even KT120 tubes for maybe 35 watts per channel. Maybe with fixed bias? I have already made a power supply on a separate chassis that can output 400ma of B+ (I am not sure what the loaded voltage will be, but the unloaded voltage is over 400v) with a -60 volt bias supply. An amp like that would enable me to use my Magnepan speakers. I believe I have all the transformers that I need to make such an amp. Thank you so much for all your help and support, cheers, Dak

 

RE: RH Universal the power tube rollers amp, posted on March 26, 2015 at 22:39:38
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Hey Al, I just finished making the additions of the 2 toggle switches to make the anode to anode FB adjustable between 100k and 200k ohms. Right now I am listening to the amp with the 6sn7 , actually , RCA red base 5692, with Tung Sol black plate 6550 and the sound is great. I am listening to War Greatest Hits, and the percussion is awesome. That group is one of my favorites for percussion with lots of well recorded funky jazzy type rock music classics such as "Low rider" and "Cisco Kid". I love to hear one of my favorite lps on new equipment and hear instruments in the track that were previously buried and now have a chance to share the stage with the other instruments. To me if an amp can not realistically recreate all the elements of the percussionist then the whole foundation of the music is compromised. take care and best regards, Dak
So as far as using the 6SN7 I would definitely recommend it. 2 thumbs up!

 

RE: RH Universal the power tube rollers amp, posted on April 2, 2015 at 00:21:33
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
 The next step could be building an adapter that would allow you to plug in noval ECC81, 83, and 82 tubes as drivers.

I guess you can try either buying one, or building your own.

******

http://rh-amps.blogspot.com/

 

RE: Al K. your help is needed, posted on April 4, 2015 at 18:36:18
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Hi Alex, I think my next step will be to build a higher power Universal Amp. I would like to use my Audio Note SE OPT designed for paralleled 6550 tubes. Would you care to help me with pursuing this endeavor? Cheers, Dak

 

RE: Al K. your help is needed, posted on April 5, 2015 at 01:07:43
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
 Hi DAK,

Of course, and it is going to be easier than you think.
Start thinking monoblocks ;) and it should already be dawn for you.
Just keep in touch via e-mail.

BTW, if you are looking for more power, possibly the RH813 is the real answer: I am not calling it "flagship" for nothing.

I am currently working on a different flagship, even more impressive, that's going to raise even more eyebrows - but my job is currently consuming me completely, thus while everything is already designed, I lack the time to build it.
******

http://rh-amps.blogspot.com/

 

RE: Al K. your help is needed, posted on April 5, 2015 at 10:48:23
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 OK, I think I know what you are hinting at. Are you saying to instead of joining the outputs of the individual 6550 tube from each tube going to a single output transformer to both tubes going to the Audio Note OPT?
What about the driver tube or tubes? How would it be designed? Don't I need twice as much current from the driver tube to power 2 output tubes? best regards, Dak

 

RE: RH Universal the power tube rollers amp, posted on April 5, 2015 at 13:40:33
hifipaul
Audiophile

Posts: 735
Location: NY
Joined: December 22, 2008
Good work. Keep the solder flowing.

Used 8417s are only $25 or so, they are worthwhile to try.

 

RE: Al K. your help is needed, posted on April 5, 2015 at 21:27:03
lugnut1
Audiophile

Posts: 132
Location: Austin,TX
Joined: September 24, 2011
 Can you sub an 811A for the 813?

 

RE: Al K. your help is needed, posted on April 6, 2015 at 23:39:54
Alex Kitic
Audiophile

Posts: 182
Location: Serbia
Joined: June 25, 2014
 The 811A is a high mu power triode, and requires to be driven in class A2 (AB2 for push-pull).

The 813 is a beam tetrode and quite easy to drive in "pentode" mode. And, it's anode dissipation rating is much higher than the 811A's.

Thus you cannot sub the 813 with 811A. But you can build the RH813 with GK71 tubes, if you observe the maximum g2 voltage the latter can handle.

Lower g2 means "flatter" curves and less output power, and as an additional aside, the GK71 has a non-standard top cap which makes it more difficult to safely accomodate in a home environment.

On the other hand, GK71 requires less heaters current and can be found relatively cheap (cheaper than GM70).
******

http://rh-amps.blogspot.com/

 

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