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Old 7th November 2003, 04:56 AM   #1
navin is offline navin  India
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Default Newbie, Tubeee

I will be visiting singapore (from bombay) in the near future.

I am looking to build my 1st tube amp.

I am looking for good simple circuit that can will be used to drive a speaker using either a Jordan JX92 + SEAS W15CY001, Jordan JX92 + Scan Speak 15W8530, or, if I can get one, a Fostex FE103 mated to a Seas W12CY001. The JX92+SEAS W15 seems the most likely option.

since the speaker impedance will drop to about 4 ohms i wonder if it advisable to even consider using tubes.

any ideas? recomendations? do all tube amps require output transformers?
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Old 7th November 2003, 06:54 AM   #2
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Default Re: Newbie, Tubeee

Quote:
Originally posted by navin
I will be visiting singapore (from bombay) in the near future.
Can't help with resources in Singapore, but I'm sure others can

Quote:
I am looking to build my 1st tube amp.

I am looking for good simple circuit that can will be used to drive a speaker using either a Jordan JX92 + SEAS W15CY001, Jordan JX92 + Scan Speak 15W8530, or, if I can get one, a Fostex FE103 mated to a Seas W12CY001. The JX92+SEAS W15 seems the most likely option.

since the speaker impedance will drop to about 4 ohms i wonder if it advisable to even consider using tubes.
I don't see why it's not.

Quote:
any ideas? recomendations?
Sure heaps. What's your budget, what parts can you source there, how much power, how loud do you want it to go etc all need to be answered to give useful advice.

Quote:
do all tube amps require output transformers?
No, but an OTL will have more difficulty with low Z loads, will likely be more expensive and is not something I would suggest for a beginner.

My first though in leiu of any further info is something like Gabe's Magnavox EL84/6BQ5 PP amp. Good for 15W. I also have a neat Lowther 25W EL34 based amp that could be cloned, and there are numerous Dyna, Eico etc models that could be copied.
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Old 7th November 2003, 08:32 AM   #3
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25W should be enough. I dont need to blow my brains out but I would like to have enough to feel the pace of the music. i like goosebumps. :-)

I think we can get most stuff here but the valves so I was looking at getting the valves from sing. However I can only do that if I know what valves I should get. my budget is about US$200 for a set of valves. Is this too little?

I figure US$200 for the vales another $300 for the rest of the box incl. the trannies and for $500 I get a decent tube amp.

i an find good R core or torodial trannies here. what else will I need other than a chassis, some passive componenets, trannies and the valves? See I warned you I was a newbie. :-)

BTW thanks, Brett, for your very positive response. If I get this done I will dedicate the amp to u. I'll call the Brett Power (instead of brute Power).
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Old 7th November 2003, 11:34 AM   #4
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Quote:
Originally posted by navin
25W should be enough. I dont need to blow my brains out but I would like to have enough to feel the pace of the music. i like goosebumps. :-)
Cool. 25W or so is easy for a nice class AB PP tube amp.

Quote:
I think we can get most stuff here but the valves so I was looking at getting the valves from sing. However I can only do that if I know what valves I should get. my budget is about US$200 for a set of valves. Is this too little?
Depending on what design you decide on, it should be enough to get you a quality functioning amp. Later you can experiment with tube rolling, if you want. The reason I suggested an EL34 amp is twofold; the tubes are available, good (Svetlana & JJ) sounding, and at about $US80 a quad, not too expensive.

Quote:
I figure US$200 for the vales another $300 for the rest of the box incl. the trannies and for $500 I get a decent tube amp.
$US200 will be fine for the tubes.

You'll need a pair of output transformers, a power transformer and perhaps a choke in the power supply. What is available and what they'll cost in S'pore I don't know

Quote:
i an find good R core or torodial trannies here. what else will I need other than a chassis, some passive componenets, trannies and the valves? See I warned you I was a newbie. :-)
You'll need tube sockets, resistors, capacitors, chassis, wire, terminal strips, nuts&bolts, signal sockets and a power cord.

Whilst I was thinking about this, I remembered a kit amp called the Ella from Brian at DIYHiFi Supply in HK. The amp has a good reputation for sound quality and parts. For $US500 you get a kit of everything, instructions and a support forum for any construction specific help and, later, modifications. A kit is actually a waaaaay better idea for a first timer than a scratch build; the chances of success are much better and a ton of issues such as layout and earthing have already been solved. This is by far my preferred suggestion for you to try, though if you want to scratch build, I'll help all I can.

You've mentioned shipping and taxes to India as being an issue, so perhaps you could have it despatched to S'pore and take it home as hand luggage. Brian is an excellent person to deal with.

Quote:
BTW thanks, Brett, for your very positive response. If I get this done I will dedicate the amp to u. I'll call the Brett Power (instead of brute Power).
Aw shucks. Thanks but it's not neccessary.
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Old 7th November 2003, 12:30 PM   #5
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first off the price of the el34 svets matched quad in well-audio is around Singdollars 88. They also stock tamura which is higher end. While Martins stock lundalh and eh,sovtek maybe svets too.
i built the ella before from diyhifi . Sounded too good for its prices. If you have problems bring into india. A audio shop in Malaysia carries them too(more expensive you have to mail for quote octave-electronics) then you could hand carry them back to India. The components used in ELLA were the JAN china stuff resistors, solens and wimas. Output trans was bifilar and overated also. power was toroids big and meatier
EL34 might be cheap but do not underestimate them, sounds better than kt88 or 6550 to me when not considering power. they are cheaper due to mass manufacturing as a very common guitar tube hence the economics of scale is implied.
Hope this helps
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Old 7th November 2003, 12:43 PM   #6
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Depends a little on your ability. This is not a very original idea but why not a kit? Sourcing and doing everything from scratch makes it quite a bit harder. If you are an EE or something no problem. Have you soldered lately?

There will more than enough on your plate if you are a real newbie. It seems you are asking very basic questions so I assume you are new to it. A kit solves a lot of problems and lets you focus on the basics your first time around. I would not want to face all the layout issues on my first project. (all of these parts reach out and effect each other throught electric and magnetic fields (electric coupling)). Just organizing the components on a chassis in an efficient manner is a trick that takes some real experience. The gap between a schematic and an amp will become apparant to you as soon as you place the first transformer on the chassis.

The Ella is a good one so I second Brett's recommendation..

http://www.diyhifisupply.com/diy_kits/the_ella.html

There is such a thing as being to ambitious. Some of the folks around here are very good and have been doing it for years and forget the difficulties. I'm kind of new to it so they are still fresh in my mind.

Cheers
Craig Ryder
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Old 7th November 2003, 03:26 PM   #7
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> since the speaker impedance will drop to about 4 ohms i wonder if it advisable to even consider using tubes.

Transformer-coupled tubes can drive any impedance. You just have to find a transformer. 4Ω is a very common tap. Tubes usually tolerate varying impedance just fine too.

> if I can get one, a Fostex FE103

This is a wonderful classic driver. Don't ask it to work hard below 200Hz, and above 6KHz you need to sit just a small amount off-axis, it won't spray 15KHz all around the room like a 1-inch driver. Not the world's smoothest, but very musical. 7 watts is usually enough to make it sing nicely. The early ones (I've been using them since 1969) would melt with 3 watts of test-tone. Believe it or not, Radio Shack sold the FE-103 under their own part number for decades, and I found my first pair under FE-103 markings in a cheap stereo record player that sounded really good. But alas-- Radio Shack no longer lists that driver.
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Old 8th November 2003, 07:21 AM   #8
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Quote:
Originally posted by PRR
This is a wonderful classic driver. Don't ask it to work hard below 200Hz, and above 6KHz you need to sit just a small amount off-axis, it won't spray 15KHz all around the room like a 1-inch driver. Not the world's smoothest, but very musical. 7 watts is usually enough to make it sing nicely. The early ones (I've been using them since 1969) would melt with 3 watts of test-tone. Believe it or not, Radio Shack sold the FE-103 under their own part number for decades, and I found my first pair under FE-103 markings in a cheap stereo record player that sounded really good. But alas-- Radio Shack no longer lists that driver.
I'll 2nd that... i'm using the RS version (40-1197 and i have a stock of them ) and the vintage Foster alnico ones of which i've managed to scavenge quite a few. The RS driver is not really as good as the Fostex FE103, but was a fraction of the price, and the alnico is better yet. The 40-1197 resonds well to tweaking.

Click the image to open in full size.

dave
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Old 8th November 2003, 05:38 PM   #9
navin is offline navin  India
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dave, where did you come from? are teh Fe103s readily available?
what other full range alternates would you recomend (TB and jordan notwithstanding).

as far as a tube amp is concerned i will travelling with my wife and kid (19 months) so I will be limted to what i can carry (weight and volume) hence i dont think i would be able to carry a tranny or stuff like that. I was hoping to get just the tubes from sing and source the rest locally.

I have reasonable experience with a soldering gun and electronics. although i have not used it recently somewhere in my past i did do a lot of this stuff and have a EE background.

if u guys could recomend a good tube ckt/layout i feel i could manage to source the rest locally buy the tubes from sing and come away with a nice amp and not have to pay heavy customs duties and incur other importing hassles.
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Old 9th November 2003, 12:29 AM   #10
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[QUOTE]Originally posted by navin
where did you come from?

I came from Alberta, but i don't think that is what you are meaning

Quote:
are teh Fe103s readily available?
what other full range alternates would you recomend (TB and jordan notwithstanding).
FE103 should be readily available... FE103A are much much harder to come by. You need to find something from the early 60s that shipped with them -- Admirals Tunnel Reflex, some obscure Canadian speaker, and i am told, some Sony portable reel-to-reels shipped with these. From the sketchy evidence i have this was a hotly contested market niche and similar drivers were also built by Coral & Panasonic. There is a little Monarch speaker that comes with 2 16 ohm Corals that might be more common in the far east, and i found a set of Pioneer labeled Corals with a slightly smaller magnet.

As to other brands, the ones mentioned are standouts. I've got a set of Korean made SOM 65s i'm playing with which have potential but they are 6.5" and open baffle material.

dave
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