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Old 26th February 2012, 11:07 PM   #1
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Default Start to Salivate - My Tube Amp Candidates - Your thoughts welcome

Hi all,

New member/first post, so be gentle! Also I am no expert, just someone who has played with electronics over the years, and can solder to a good standard

Having just completed my Scope Clock See Photos Here I am ready to start on my 'first' amplifier project, and am blessed with having acquired 1200+ tubes (All NOS), along with a nice Tektronix scope, HP audio sig gen, and lot's of other nice test gear and discrete components, including 300+ capacitors that all test perfectly (including leakage thanks to the Heathkit cap tester I also got).

Having sorted and tested my major numbers I have the following candidates for pre-amp and power amp. All tubes match within acceptable measurements, so I'm very lucky!

2 x Tungsol 6550 Grey 3 hole Plates Top and Side getters (only option is SE as I don't have any more and they are sooo rare)
2 x RCA Red Base 5692 (Read that they are sonically stunning?)
3 x RCA Brown Base 5692 (Could I combine these well with the red base examples?)
2 x GE 7027a
5 x GE 8417
1 x RCA 8417
2 x GE 5 Star 6386 Matched Pair (Ultra Rare I read?)
1 x GE 6386 (not 5 star)
1 x GE EL34/6CA7 (wish I had a pair)
5 x GE 5751
1 x United Electron 5751
1 x RCA 5751WA
1 x GE 12AX7 (wish I had more)
3 x GE 12AY7
2 x United Electron 12AY7
7 x GE/RCA 12AV7

I do have many more 12xxx tubes so if I missed any good ones let me know. I also have an array of rectifier tubes (5U4GB/5R4 amongst them), and so if anyone wants to recommend the bests ones to use I'd also be grateful. Main listening is radio, and vinyl (Thorens TD160 with an SME 3009 MKII Improved coupled to a Shure V-15 Type III). Current amp is a Quad 405-2, Quad 34 pre, FM4 tuner coupled to a pair of B&W DM6s. I'd like to continue with the DM6s if they will match well to tubes.

I'd love some feedback on which to choose for which application, although I assume only the 6386s and 12Axxs are only good for pre-amping? I also lean heavily to single ended as this seems to be the 'audiophiles' favorite, although I suspect that comment will generate much debate

Once I have the right tubes chosen, I'll move onto which trannies to use, and then the 'spare tubes' might be offered (really cheap) to a good home, or someone who gives me great advice and help on the way

TIA

N
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Old 27th February 2012, 12:01 AM   #2
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Welcome on bord !
First, you're a bit on the wrong track. Having a stash of tubes is nice but this guarantees nothing. You can build a perfect amplifier with nearly every kind of tube. Intelligent circuit design makes this possible. On the other hand, there are EL34 which sound awful.
Why not don't you start with some theory about valve operation and circuit design. Don't get me wrong, I won't badmouth your first post but if a 6386 tube is a five-star one or not really is the most unimportant thing when you want to get started in building a tube amp. (When you light the amp up the first time and the tube blows with a nice 'bang' you will have wished it wasn't a five-star !!! )
There are thousands of designs out there with those mainstream and standard tubes you mentioned. Sound is subjective so maybe you like the sound of a starvation mode operated 12AX7 whereas I prefer a 12HG7 with lots of current.
What I want to say is, put the tubes aside, they won't ran away (or get gassy....that takes lots of years) and get familiar with the tube business. Read here in the board, build some small test circuits and amplifiers etc. When you start with the big project at once, your next posts will be titled: "why does my amp oscillate/hum ?", "what's that blue glow ?", "Can I swap a 6L6 with EL34" etc.
You will have much more fun learning and applying everything step by step.
And...this one is important. Never let the so called "audiophiles" try to give you silly ideas. Make your own decisions, ask when you're not sure and try it out.
I hope you don't misconceive my post but experience tells you how not to get started with something new.

PS: Be sure to have some spare tubes for the scope clock. These things eat them up really quickly.
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Old 27th February 2012, 12:14 AM   #3
kevinkr is offline kevinkr  United States
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What Manta said..

One potential choice if you are chomping at the bit would be Tubelab's simple SE using the 6550s in UL or triode mode, but I would first do a whole lot of reading and studying up as suggested by Manta.
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Old 27th February 2012, 12:15 AM   #4
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Amps and speakers have to be viewed as parts of a whole. What sort of speakers do you already own or plan on acquiring? What are you using for signal sources?

Some of the NOS power tubes you have are valuable and it may make sense to sell them, thereby funding "iron", etc. purchases.

A possible use for the 5692s, which are "glorified" 6SN7s, is in a Williamson topology PP power amp. Really good O/P "iron" is essential, when constructing a Williamson. Otherwise, phase shifts can eat you alive.
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Old 27th February 2012, 12:32 AM   #5
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Originally Posted by kevinkr View Post
What Manta said..

One potential choice if you are chomping at the bit would be Tubelab's simple SE using the 6550s in UL or triode mode, but I would first do a whole lot of reading and studying up as suggested by Manta.
Hey guys thanks for the advice, but maybe I should clarify. I have 30 years of playing with electronics, and was building tube stuff as a teenager back in the 70s, and do have a nice lab at home. I've also worked in related industries for most of my career. I am familiar with safety and testing procedures, and have worked with high voltages for a long time. I used to work on microwave equipment as a job, so I tend to keep my fingers away from the dangerous stuff

However, I have not yet invested time (and money) in a high end amp so far, but that does not mean I've not read the forums/articles quite extensively. I just find myself getting lots of conflicting information, which I guess is the nature of the beast (sound being 'very' subjective).

I have many text books dating back to the 40s, and I do understand a great deal of the theory, but I am not as knowledgeable as many of those who can write schematics and work out NFB, or Bias on the back of their hand, or better still in their heads, so I wanted to seek out some constructive advice on a good combination of tubes from those I've been lucky to acquire. I have access to a 539b so was able to verify the condition and quality of the tubes, all unused before I tested them.

If your advice is to simply read more posts, and then go build a simple amp and slowly graduate to big boy stuff then off I'll trot. I think I am capable of more, and may just have to take pot luck with the various schematics out there, and then read/tune/adjust if the sound does not meet my expectations.

For instance I've seen a nice amp project using the 5692 as a driver for pair of 8417s in SE mode.

I'll keep reading
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Old 27th February 2012, 12:38 AM   #6
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Originally Posted by Eli Duttman View Post
Amps and speakers have to be viewed as parts of a whole. What sort of speakers do you already own or plan on acquiring? What are you using for signal sources?

Some of the NOS power tubes you have are valuable and it may make sense to sell them, thereby funding "iron", etc. purchases.

A possible use for the 5692s, which are "glorified" 6SN7s, is in a Williamson topology PP power amp. Really good O/P "iron" is essential, when constructing a Williamson. Otherwise, phase shifts can eat you alive.
My current gear is:

Thorens TD160/SME 3009 MKII Improved/ Sure V15 Type III
Quad 405-2/Quad34/FM4
B&W DM6 Penguins

My first thoughts are to replace the Quad elements with the future tube gear.

My primary listening is Radio and Vinyl (Prog Rock/Vocal/Keyboards).

And yes, my plan once I've selected the right sets of tubes for me, is to sell the rest to pay for the O/P and Choke Iron etc. This is partly why I want to narrow down my best options, before I sell the wrong tubes
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Old 27th February 2012, 12:39 AM   #7
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Hi Nodric,
Perhaps in your case it is just down to thinking about the sort of system you want to put together - sounds like you're well equipped for the technical end of things, it's just a question of integration, choosing the right speakers, amp design, and sources for what you want to achieve - something I've been working on for a long time.

In any event you will have a lot of fun figuring out what direction to go in and building it out..
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Old 27th February 2012, 12:43 AM   #8
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Never mind my post. I typed too slow and posted even slower... Original post below. I'll add one thing -- Pete Miller's amplifiers seem quite nice and the over the top 300B amp there has got me thinking way down the road when I get that good.


I have read and seen some amplifiers that defy logic in that they should not sound good at all. First they are cheap, use television sweep tubes for output, pentodes for input, mosfets, silicon, and all for about $400 or so. I have just decided that this will be the next likely candidate for project number four for me (I have three so far).

And they sound great. Television sweep tubes! I mean really.

Now I have seen really great tubes in amps that makes you wonder, "what is that horrific noise? "

It boils down to design and the ingredients . Find a good design and spend the money on good components like iron, capacitors, pots, chassis, and all the other things that will make it a great sounding amplifier.

And add in a lot of research and reading. Then construct and test. You'll have fun in the process ; trust me.

Last edited by overtheairbroadcast; 27th February 2012 at 12:52 AM. Reason: I think I type too slow...
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Old 27th February 2012, 12:44 AM   #9
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Originally Posted by kevinkr View Post
Hi Nodric,
Perhaps in your case it is just down to thinking about the sort of system you want to put together - sounds like you're well equipped for the technical end of things, it's just a question of integration, choosing the right speakers, amp design, and sources for what you want to achieve - something I've been working on for a long time.

In any event you will have a lot of fun figuring out what direction to go in and building it out..
I think you maybe right, and that there's no 'magic' answer. I know I love my bass, but it has to be very clean, and I love crisp clear and natural vocals, so I'll focus on what designs seem to have been successful in delivering that for others.

Maybe I'll do a simple RIAA phono stage for my TT and feed that to the 405 and, then take it from there. Maybe I'll keep all the tubes and try several different amp designs, but then I'll have to sell the car to buy the iron
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Old 27th February 2012, 12:45 AM   #10
kevinkr is offline kevinkr  United States
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The 8417 would be prime candidates to sell on, they're worth a lot of money and replacements down the road are not going to be readily available.

From what you've described a fairly large PP amplifier is probably what you need to pursue. I'm running home brew Onkens of >100dB efficiency with 20W GM70 SE amps, and it gets loud, very loud.. What is the efficiency of your B&W speakers?

Definitely check out Morgan Jones latest Valve Amplifiers (edition 4) when it finally shows up at Amazon for some inspiration..
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