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Old 27th February 2012, 12:51 AM   #11
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Originally Posted by overtheairbroadcast View Post

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

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.
I think I get it now I'll sift through all the stuff I've printed and book marked, and then start narrowing down amplifier project one...

I also have lot's of TV and Ham tubes so maybe I can mess there sometime too. Have a pair of 807s that would be fun
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Old 27th February 2012, 01:15 AM   #12
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Originally Posted by kevinkr View Post
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..
Thanks Kevin.

The B&Ws only have an 88db sensitivity, and need a 100w solid state amp to make them work well, so maybe not the best candidate for a tube project. I was just trying to reserve budget

I certainly follow your reading advice, and look at PP designs more closely.
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Old 27th February 2012, 01:54 AM   #13
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Originally Posted by Nodric View Post
Thanks Kevin.

The B&Ws only have an 88db sensitivity, and need a 100w solid state amp to make them work well, so maybe not the best candidate for a tube project. I was just trying to reserve budget

I certainly follow your reading advice, and look at PP designs more closely.

The B&Ws need power and good damping factor, in order to "dance". FWIW, I think I see a reasonable path to system synergy. A project of acquisition and complete overhaul of a Harmon/Kardon Citation II, ala Jim McShane, will give you 60 WPC continuous and upwards of 130 WPC instantaneous, along with a good damping factor. That will do very nicely for the DM6s. As the owner of a "Duece", I can tell you the chocolate behemoth betters most SS amps at playing bass.

The higher than usual I/P impedance of a Cit. 2 makes a passive control center quite feasible. Whether you go that route or a buffered volume control with source switching is a matter of personal preference.

There are lots of good phono preamp designs to choose from. The tweaked RCA schematic I've uploaded is about as easy as they come in the building dept. and a highly satisfactory PSU for the circuitry can be built around an inexpensive Allied brand power trafo.
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Old 27th February 2012, 04:39 AM   #14
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Hi Nodric
Love the 'scope clock.
Any link to construction details?
Cheers
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Old 27th February 2012, 01:17 PM   #15
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Nodric: What's your budget for this project? Do you have any iron? Do you have more than a pair of any output tube candidates?
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Old 27th February 2012, 03:07 PM   #16
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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
The 6550's in an SSE will make about 8 WPC in triode mode, or about 14 WPC. With 88db speakers it will be loud enough for small room listening, but will not shake the house. It's a good project if you want to build a tube amp, and plan to build a bigger one some day. Either way save the 6550's.

The 6386 tubes have no use in a tube audio amp. They however are rare and are the control VCA in an old audio compressor (Fairchild?) that is worshipped by the vintage tape recording crowd. Sell them on Ebay ($50+ each). The 8417's are a good audio tube for 50+ WPC, but also rare and quite fragile (very close grid to cathode spacing) and subject to early failures. I would sell them to someone who needs them for an old amp.

Big powered tube amps are not cheap, due to the cost of transformers. Use the money from the sale of these tubes to fund the cost of transformers. Several of us here have figured out how to make 100+ WPC for the lowest possible cost. This thread details a 18WPC amp developed by Pete Millett, and modified by me for much more power. TV tubes are used to get big power for minimal $$$$. Read the whole thread if you have a whole lot of time:

Posted new P-P power amp design

There will be some more higher powered tube amps coming in the future, but nothing is ready just yet.
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Old 27th February 2012, 06:05 PM   #17
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Originally Posted by tubelab.com View Post
Big powered tube amps are not cheap, due to the cost of transformers. Use the money from the sale of these tubes to fund the cost of transformers. Several of us here have figured out how to make 100+ WPC for the lowest possible cost. This thread details a 18WPC amp developed by Pete Millett, and modified by me for much more power. TV tubes are used to get big power for minimal $$$$. Read the whole thread if you have a whole lot of time:

Posted new P-P power amp design

There will be some more higher powered tube amps coming in the future, but nothing is ready just yet.
Mr., Tubelab,

That was the amp I was talking about (red board and all). With your mentioning modifications to it, you have really re-sparked that interest in the pmillet TV sweep tube amp and given me a lot of reading to do too to check out your modifications (101 pages worth). Awesome.
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Old 27th February 2012, 08:25 PM   #18
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Originally Posted by Bibliophile View Post
Hi Nodric
Love the 'scope clock.
Any link to construction details?
Cheers
How's your German

The circuit was designed by a great guy called Bernhard Thiem. This is his site where you can get the PCB and small components Thiem-Work He speaks fluent English but his site is all German.

If you want the CRT Tube, and the post acceleration board (for the HT Anode) then you can get those from Jan Zuerst also in Germany. His site is in English and he also speaks fluent English if you email him. Ask Jan First ; electron tubes and more He also supplies the toroidal transformer for the kit, but you can also get that elsewhere.

Be aware that my CRT is at +1500 VDC at the anode cap, and a PD of 2400 VDC between negative and positive, so it's going to make you dead if you're not very careful and respectful of the power supply. Make sure you have a HV Probe before attempting this build.

The case was made from Walnut (American not UK Walnut) and I was able to use my father in laws milling machine machine to cut the slots for the glass, but a router would work. The brass panel was made by hand and the pots, switches and fuse holders came from Digikey in the US. The glass was cut and polished by a local company for me.

It really is the most pleasing thing to have built.

Total cost was about $500 when everything was factored in, and 100hrs of my time. The case took much longer than the electronics!
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Old 27th February 2012, 08:47 PM   #19
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Originally Posted by boywonder View Post
Nodric: What's your budget for this project? Do you have any iron? Do you have more than a pair of any output tube candidates?
I can stretch to about $1000 for the iron and discrete components. I can get the chassis CNC cut and chromed for cost through a friend in the family

I am looking at a pair of Hashimoto HC-507u that run about $480 for a pair, so that leaves me some room for a good PT and some Chokes.

The tubes I listed are the ones I have. I do also have a pair of 807s, which I know some have used in high power amps, but I was concerned about the quality of these, and the very high voltage I'd need to use them, plus ugly anode caps

I have a pair of 6AS7G tubes, but I think I'd need four in PP mode if I wanted to try these as I'm not sure if they'll work in SE. I also read they are used in OTL amps, but they seem over complex, unless for a headphone amp, which then seems to be huge tube for just cans use.

I also have a pair of 6011 mercury Tetrode Thyratrons, but I'm sure they're not much use for amps, but would look pretty all glowing in the dark

Arrrgggghhhh, too many options!
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Old 27th February 2012, 08:55 PM   #20
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Originally Posted by tubelab.com View Post
The 6550's in an SSE will make about 8 WPC in triode mode, or about 14 WPC. With 88db speakers it will be loud enough for small room listening, but will not shake the house. It's a good project if you want to build a tube amp, and plan to build a bigger one some day. Either way save the 6550's.
Yes I intend to hang onto the 6550s.

Quote:
Originally Posted by tubelab.com View Post
The 6386 tubes have no use in a tube audio amp. They however are rare and are the control VCA in an old audio compressor (Fairchild?) that is worshipped by the vintage tape recording crowd. Sell them on Ebay ($50+ each). The 8417's are a good audio tube for 50+ WPC, but also rare and quite fragile (very close grid to cathode spacing) and subject to early failures. I would sell them to someone who needs them for an old amp.
The 6386s will be on evil bay later this week Thanks for the heads up!

I have five of the 8417s and they are good candidates, but your advice about their life concerns me if I need replacements in 10 years time.

Starting to narrow down the field.

Can I use the 5692s in PP class A?

Quote:
Originally Posted by tubelab.com View Post
Big powered tube amps are not cheap, due to the cost of transformers. Use the money from the sale of these tubes to fund the cost of transformers. Several of us here have figured out how to make 100+ WPC for the lowest possible cost. This thread details a 18WPC amp developed by Pete Millett, and modified by me for much more power. TV tubes are used to get big power for minimal $$$$. Read the whole thread if you have a whole lot of time:

Posted new P-P power amp design

There will be some more higher powered tube amps coming in the future, but nothing is ready just yet.
I have some of the tubes mentioned in that thread, so I'm going to have a big cup to tea later and wade through it for education.

Last edited by Nodric; 27th February 2012 at 08:58 PM.
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