recommendations for a tube amp for small speakers?

[chobint]

Hey guys, I'm trying to build a tube amp for my gramps. It will probably be driving a single built-in full-range speaker. I was originally looking at using a millet SS, but I'm afraid it won't be loud enough for an old man standing 5-25ft away. I'm thinking it should probably be 1/2-5W to drive a reasonably efficient speaker. Any suggestions that might still fit a starving student budget?

[Malanga]

I guess it would depend on how efficient a speaker your talking about. The Darling SET comes to mind:"Darling" SE 1626 Amps

This puts out a whopping 800 miliwatts! I build one and I love it. Another options is the miniblock tube amp designed by the late Fred Nachbaur:

Fred Nachbaur's Vacuum Tube Projects

There is a SET version which produces about 1.1 watt, and a push-pull version at 3 watts.

None of these should run you over a hundred bucks if you shop around. I believe I spent about 90 dollars on the Darling amp, and maybe 80 bucks on the miniblock SET.

[kuroguy]

check ebay, craig's list, etc for a used Sony TC-521 reel to reel takedeck. it has almost everything needed to build a 6au6/6aq5 amp. I've seen that deck go for $25 used (for parts). All you need to add is a chassis, caps, resistors, etc. Use the schematic at http://www.tubesrit.com/audio/albums...-6au6-6aq5.pdf . Nice sounding amp and up to 4 watts.

I saw a TC-530 on ebay for $50 (shipped) the other day. I couldn't find a schematic of that one, but its age suggests it has a similar schematic. You could definately get that amp built for under $100 and under $75 if you try hard.

[chobint]

Thanks for the suggestions, I'll have to take a closer look at the schematics later tonight.

The most efficient and well priced full range I've found is this pioneer 8" from parts express @ 94 db/W. Altho 8" is a bit larger than I had hoped to use.

Using this calc, .8W into 94 db/W speaker can deliver 75 db at 25 feet away, which is supposedly as loud as a vaccuum in the same room, which seems sufficient.
Peak SPL Calculator

I also saw this amp design

EDIT: that miniblock SET is looking pretty enticing atm

[cotdt]

don't use SET amps to power small speakers as they are really inefficient. That Pioneer 8" you linked works good though. Aim for 98 dB (@1 m) SPL for general music use. Remember that manufacterers usually overrate their efficiency by 2-3 dB.

[chobint]

soo....don't use single ended to drive speakers? Doesn't 1 Watt = 1 Watt regardless of amp topology?

[olblueyez]

Integrated Single Ended Tube Stereo Amplifier 6L6 Amp - eBay (item 180305738340 end time Nov-15-08 14:18:59 PST)

DYNACO SCA-35 Integrated Tube Amp/Amplifier--Stunning!! - eBay (item 110309846293 end time Nov-17-08 08:15:00 PST)

(free shipping) HI-FI 6p3p Stereo Tube Integrated Amp - eBay (item 200274061387 end time Nov-13-08 18:00:00 PST)

[yashicaman]

If you are really good at making stuff, you could just get the schematics of a SET amp and build it. If I were clever enough, I'd probably build all sorts of stuff, but I'm not, so I buy my stuff. Rats. Anyway, you should be able to find all sorts of plans and give it a shot. Good luck.

[cotdt]

Originally Posted by chobint

soo....don't use single ended to drive speakers? Doesn't 1 Watt = 1 Watt regardless of amp topology?

Yes 1W is 1W but SET amps deliver only a few of them at most, and the amps are expensive. Any speaker less than 92 dB (1W/1m) efficiency forget it.

On the diyaudio.com forums, there is a 12W EL84 design called the Baby Huey. While it's not a SET amp it sounds just like one, but it's much cheaper to build than a 300B tube amp. The Baby Huey is an extremely clever and good-sounding design. I love the glassy highs of the EL84, it's simply magical.

I've also used the EL84 in SET mode as a headphone amp, but it can also be used as a 1.5W speaker amp. PM me if you want the schematics.

[Uncle Erik]

There are lots of options here. Have you looked at Bruce Rozenblit's books? You can find them at Transcendent Audio - there are several options and he sells kits, too. Another option is the Angela 91 and you might want to consider the Bottlehead kits, too.

Oh, and there's the Dynaco ST70 reproductions now available. Also, you might want to consider one of the older Conrad-Johnson amps. Those are surprisingly affordable these days and collectors haven't (yet) driven up the prices.

[cfcubed]

Here's some DIY related links you could peruse:

The Musical Machine

K.G. tube amp info

And if you end up wanting to purchase one the Glow Amp One would be one to consider

But as others say really matters what you intend to drive & how loud you want to drive them... There is alot of info & opinions on full range drivers around (e.g.Frugal-Horn site)& 8" full-rangers seem large to me.
Personally I'm enjoying a tube pre & DIY FW F2 driving Hornshoppe horns.

Good luck.

[Malanga]

I still think the miniblock is your best option if you are on a starving student budget. I hooked mine up to a Cerwin Vega I once had which had an efficiency of about 90db, and although it did not shake the windows, I thought the volume was decent for one watt. If you are concerned with more power then build the Push pull version for 3 watts of power. Whats nice about the miniblocks is that the parts are common and cheap with the exception of the output transformer. The author suggested using the Electrolytic capacitors salvaged from old computer power supplies, and for the power transformers you can get some cheap ones on clearance at Parts Express, although they may be out of stock at the moment. I believe I bought mine from All Electronics for about 4 bucks each. I have heard some good things about the output transformers from Edcor. This one in particular is under $18.00 and I have read reviews which makes it equal to the general purpose ones from Hammond costing twice as much.EDCOR Electronics Corporation - Audio Transformer & Equipment Manufacture

For the chassis I used a nice looking cigar box which you can get for free or next to nothing at any cigar shop.

So the iron will cost you under 30 bucks, the components maybe 20-25 bucks, maybe five bucks for a 13em7 NOS tube and some elbow grease will get you a working miniblock for about 60 bucks. Hows that for a starving student budget?

[pabbi1]

Or, look at Pete Millett's DIY Audio pages - as a DIY, all you seek is there. Mighty Midget is calling to you.

[chobint]

Many excellent suggestions, unfortunately as Malanga pointed out many of those exceed my target "starving student" budget. As I mentioned the amp for my 80+yr old Gramps, so it is more of a novelty/nostalgic venture than the typical audiophile persuit. I think the miniblok SET or Push-pull version is a strong contender atm. Pete's mighty midget's innards look much simpler than it's outward appearnce would suggest...I'll have to try to put a BOM together tonight and see if I can keep it under budget.
EDIT: And to give "starving student" a more concrete definition, I was hoping to come in under a $100 perhaps $150 for something schweet like the midget.

[luvdunhill]

Originally Posted by pabbi1

Or, look at Pete Millett's DIY Audio pages - as a DIY, all you seek is there. Mighty Midget is calling to you.

another vote for the Mighty Midget. Just track down the appropriate issue of audioXpress (this one also has the First Watt F5 that you can drool over) and build away. Nice and cheap build that will sound amazing.