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cheap but good SET amplifier?
cheap but good SET amplifier?
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Old 25th October 2004, 07:22 PM   #1
needtubes is offline needtubes  United States
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Join Date: May 2003
Default cheap but good SET amplifier?

I've taken a lot of time off from DIYing amps and such... but am currently not happy with my standard receiver for music. I dealt with headphones for a long time, but am tired of that, so I want to get my speakers up and running with new life from a better sounding amp.

I've heard a lot about digital amps- how warm and "tube-like" they are, so I thought I'd build or buy one of them. But, why spend money and time building something that is only going to sound like tubes... Like my father always said, "why buy something that is going to be LIKE something else... just get what you want to start with." So, I figured I'd just do that.

I saw that Bottle head was re-releasing its S.E.X. kit, which would be nice, but $400 is WAY too much for me to spend right now on a 2W amp. I am looking to spend more like $100 or so right now...

My main speakers are Klipsch RF-3's, which are 98dB @1W/1m. I am actually about 1m away, too, so no issues there. I measured the voltage across the speakers under my normal listening conditions and found that they were drawing around 0.1V continuous with 0.3V peaks. Not much... so I can easily get away with a low-powered amp, which is what I'd like. Less than 3W would be plenty, even allowing a little overhead.

I found a couple of amps that look as though they might fit... but would kind of like some comments/pointers that would be useful to know. If possible, I would also like to have the amp adapted for use for headphones whenever I wish, like the S.E.X. kit is. That was a very good point of that amp, but the price killed it for me. I am getting rid of all my other headphone amp stuff, and I'd like one simple SET amp for my speakers that would also work with my headphones (Sennheiser HD580, 300-ohm). How might I adapt most transformer coupled amps to run these?

I found a few amps that looked ok, but if there are anymore I didn't see, please point them out. The ones I saw are:

the Miniblock
half-watt 6EM7 amp
and one here on the forums- Morse's 6BM8 SEP amp. Not SET, but I suppose it might work...

The half-watt I am not sure about. I wouldn't use the power tranny outputs, but I am concerned about it not having enough power.

Any thoughts, comments, or other suggestions are welcome. Thanks all!

EDIT: Forgot to mention... simplicity also highly preferred. I would actually prefer a design using dissimilar triodes as shown in the links.
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Old 25th October 2004, 07:38 PM   #2
Gabevee is offline Gabevee
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Location: Richmond, VA.
Hi There,

This is going to sound hard, but not meant to.

My suggestion? Save your money until you have the $400. Halfway decent iron for an SET amp that'll give you 2 watts per channel will cost $100 alone. That is, about $35 for the power transformer, and between $25 and $35 apiece for the output iron. Decent output tubes, if you want to do triode, go for the 2A3 for about $50 a pair. Otherwise, the 6BQ5/EL84 is decent for SE. They go for about $17 to $24 a pair. Then a decent 12AX7 (some wil shout "NO! NO! The 12AU7!). But we are using one dual triode to drive both output tubes. That will be another 10-30 bucks, depending on whether you want OK sound or very good sound.

So look to spend a total of about $230 for parts you buy yourself... oh, not counting the chassis and hole punching and... time.

Hope this helps.

Gabe CGV Electronics
Home of the CGV-300B amplifier on a budget
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Old 27th October 2004, 12:50 AM   #3
Norris Wilson is offline Norris Wilson  United States
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Join Date: Aug 2004
Default Magnavox SE 8303 console amp!

Hi needtubes,
Here is a link regarding some Magnavox console 6BQ5 amplifiers.
I think that this could be a good place to start, playing and experimentation with various system configuration is half of the fun.
I have heard a few of the PP Magnavox units over the years, and I liked it.
I hope this will help, it should be fairly cheap when you track one down.
Good Luck
Norris Wilson

PS. I like your moniker, for I think I need tubes too.
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Old 5th November 2004, 07:02 AM   #4
Ori is offline Ori  United States
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Join Date: Oct 2004
Location: San Jose
Default How about a single-tube OTL amp?!

At less than 1 watts into 8 ohms, your amp needs only 8V peak-to-peak, so the main issue would be getting the 1A (p-p) of current. You'll need a big tube like a 6336A, so the power tranny will be big, but that's the cheaper of the iron parts...
You will need a power resistor for the plate load and a decent output cap (low voltage, so it's not super expensive!)
If you can settle for 1/2 a watt per side, then run each of the individual triodes one per channel. Notice that the gain is low but just enough for a direct feed from a line-level source like CD player. Your stereo amp may end up being a single tube...
Other regulator tubes like the 6080 and 7233 might be good candidates for the same topology.
Have fun!
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Old 5th November 2004, 07:24 AM   #5
JZatopa is offline JZatopa  United States
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Location: Chicago
check out www.decware.com. They have a kit version of the zen that is about $399. It is an amazing amp.
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Old 5th November 2004, 08:56 PM   #6
mcs is offline mcs  Denmark
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Location: Denmark
Why not just try Fred's Miniblok? The parts are cheap, and the amp is easy to build. You can always buy a bigger/better output transformer later. But even SE amps with small transformers sound fine to me...

Best regards,

Mikkel C. Simonsen
My personal electronics website
Remote control kits website
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Old 5th November 2004, 11:01 PM   #7
planet10 is offline planet10  Canada
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Location: Victoria, BC, NA, Sol III
cheap but good SET amplifier?
Originally posted by Gabevee
Halfway decent iron for an SET amp that'll give you 2 watts per channel will cost $100 alone.
Maybe if you are buying new...

A Decware ZEN clone (which we have dubbed Mulligans -- Bogus ZEN -> Bogey -> Mulligan) can be built using something like these vintage RCA OPTs -- average sell price so far is about $30.


(disclaimer: i have everything to do with this auction, me & my wife are planetsofta)

And i have a ton of similar, but nicer, European iron. A friend recently built an amp inspired by the Dec ZEN but with an ELL80 (2 EL95s in a single envelope). The OPTs were quite small so bass is limited, but everywhere else it sounds quite good (he is very surprised at how good)


excluding the fact that i gave him the donor (out of a Normende console -- OPTs often called Telefunken -- i'm accumulating favours towards kitchen cabinets), he has $30-40 CAD into the whole amp.... and a lot of that was going out and buying a new Hammond chassis instead of heading to Value Village and finding a suitable "round" chassis.

With attention to Frugal-phile(tm) directives a $100 USD triode strapped pentode SE should be very doable.

community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
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