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Old 12th September 2007, 05:26 PM   #1
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Default up-to-date El Cheapo schematic

When I began to cost out the SimpleSE, I quickly reached by $200 upper limit. My wife said that over that price would be unjustifiable for an amp for my office, especially as we're saving to build a new house.

This has led to a couple of options: buy one of the kits from S5 Electronics OR look for a cheap push-pull design.

El Cheapo is supposed to be very good and can be built cheaply.

I have tried to link to pages on Decware, but without success.

Are there any up-to-date schematics available?

Eli, I know that you read this newsgroup. If you have PDF's of the schematic, I'd love a copy if you're willing to share.

Charlie
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Old 12th September 2007, 07:00 PM   #2
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Decware has a new BBS, so the old urls have changed.


The new Tube Lovers' Forum main page is here:

http://www.decware.com/cgi-bin/yabb2...pl?board=Tubes



And the "Bargain Basement" (El Cheapo) thread has the latest schematic on page 8 (even though there are many more pages, that diagram was updated and replaced). You'll find it if you scroll down from here:

http://www.decware.com/cgi-bin/yabb2...1126228937/240

A direct link to the schematic is here:

http://homepage.mac.com/planet10/for...3jun06-map.gif

NOTE: Watch the polarity direction in a couple of the 'lytic caps in the CCS and negative supply!



Some real voltage point measurements from my own build are here. These are per the schematic, without the added booster trafo for added B+. Others verified these as typical (scroll to just under halfway) :

http://www.decware.com/cgi-bin/yabb2...1126228937/540



If you want to boost the B+ a little (yes, it could use a boost, but it's not all that crucial to the sound), the diagram is here (any hefty 12-14V trafo will do). Click on the thumbnail image part way down the page:

http://www.decware.com/cgi-bin/yabb2...1126228937/450

Scott M and I were the first to build this project from the schematic, and I still have to build the case (Scott's case looks very nice). Even in breadboard form, the sound is good. This was an excellent choice for my first tube amp build -- and it's nearly a from-scratch experience. (It's not a kit. All the small components are available from Jim McShane, and the trafos and such can be ordered from online electronics vendors.) Jim's page for the El Cheapo is here:

http://pages.prodigy.net/jimmcshane/elcheapo.htm


For anyone else interested (especially newbies!): Click the "print" button that sits in the messages area on the top or bottom of any page in the Decware Tube Lovers Bargain Basement thread. This will give you one LONG document you can print out. I three-hole-punched the printed document, plopped it in a binder, grabbed my favorite beverage and sat back to read while listening to music. What a learning experience, to read through this whole thing! It was well worth the time, and it convinced me to build this project.

Hope this helps!

--Jeff
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Old 12th September 2007, 07:47 PM   #3
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could you detail a tiny bit more why you chose the specific CCS you did for the LTP? what is the B+ voltage and how much current does this CCS supply? I'm looking at putting a 6V6 amp together and would love to see your implementation.
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Old 12th September 2007, 09:37 PM   #4
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The goal is 310 - 315 VDC or so for B+. Without the 12V booster trafo, I get 304 to 307 VDC, depending on time of day and/or mains loads in my city. Adding a 12 - 14 V booster trafo pulls it up. See the link above for typical voltages per the direct schematic build.

I'm also toying with a tube rectifier using the PA447 330 - 0 - 330 VAC, and can get there easily with a cLC topology and a 5AR4. It's harder with a 5U4, but close. The solid state diode rectifier as spec'd in the schematic sounds GREAT as it is.

The CCS is set for 6 - 7 mA per channel, or 3 - 3.5 mA per side of each 12AT7. A few statements about why choice for the particular CCS circuit layout are early in the thread at Decware, but not in great detail. I think just about any CCS layout that supplies the proper current would be fine.

Eli or Jim can add more about why they chose the CCS layout.

--Jeff
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Old 12th September 2007, 10:01 PM   #5
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Jeff,

I have made a quick cost comparison with the S5 electronics kit. The difference in price (excluding chassis) is only around $50.00 ($230 for El Cheapo and $186 for the S5 Elec.).

My assumption is that El Cheapo puts out about 8W per channel?

For building, are terminal strips the best/easiest?

OK, I'll print out the thread and browse through it.

What I like about the S5 is that it is fast and probably sounds OK. This would be just fine for my office and I would not have the stress of trying to figure out wiring from the schematic.

Later, for a second home amp, I could build El Cheapo.

Hmmmmm......I need to think about build speed versus quality.

Charlie
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Old 12th September 2007, 10:35 PM   #6
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I built one of the S-5 kits once while un employed because I couldn't afford to build one of my own designs. Honestly, for the price it's pretty freakin' hard to beat. In fact, I shamefully admit that un-modified, it sounded better than one of my homebrews which cost 4 times as much and was far more complex. There are plenty of cheap and simple upgrades that can be done to it as well.

It was a while ago when I bought the kit that may be different. However there are some things you should know about the S-5 kit.

-The 8W power spec is peak watts, not RMS. But it does clip pretty soft for a push pull amp. I've found this to be plenty for my office with speakers that are only 91dB efficient.
-Silk-screening for the electrolytic's was backwards! It caused me to blow the first set of caps since I assumed the silk-screening was correct without checking.
- The hole thatís meant for tacking a lead to the pot shaft is connected to the input of one of the channels, instead of to audio ground like it's suppose to be.
- Silk-screened on the board says "Sterio" instead of Stereo.
-Order the kit from www.tubesandmore.com. The only way to order from S-5 direct is to e-mail them a credit card number, which seems sketchy to me.
-Unless you buy S-5's, you still have to build an enclosure/chassis which is the biggest PITA of DIY. I'm not sure how much the S-5 chassis is. It is probably worth saving the headache though.

More than likely it has been revised by now. But even as-is they are issues that can easily be worked with.

Overall itís a bang for the buck!
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Old 13th September 2007, 12:30 AM   #7
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Quote:
Originally posted by sorenj07
could you detail a tiny bit more why you chose the specific CCS you did for the LTP? what is the B+ voltage and how much current does this CCS supply? I'm looking at putting a 6V6 amp together and would love to see your implementation.

The CCS used in "El Cheapo" was devised by Bandersnatch. I knew it would provide the high AC impedance needed under the LTP's tail. Any CCS that provides an AC impedance of several MegOhms should work well. Set the CCS for 3 to 3.5 mA./triode.

The needs of the 12AT7 control the B+ rail voltage. The 'T7 sounds GOOD with 200 to 220 V. on the plate and IB = 3 mA. 3 mA. thru 50 KOhms drops 150 V. So, 355 to 360 V. of B+ is "perfect". Less than 2 V. are dropped in the B+ decoupling network.
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Old 13th September 2007, 12:44 AM   #8
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In the variation of el Cheapo Chris & i did up we used the diyA proto CCSs (ie the one out of Morgan Jones ' book). If you are willing to give up a bit of performance you can even substitute an appropriate resistor network (see Poinz's 6V6 PP amp)

If you want to make el Cheapo on the cheap, then finding a suitable donor amp (mostly for the iron) is the way to go. Both the one's we have built so far used Scott donors -- the 2nd one cost less than $100 complete (the 1st one is now a parts donor since the power tranny puked its guts all over everything)

dave
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Old 13th September 2007, 12:47 AM   #9
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Jeb,

I am glad that you think the S-5 kit sounds good. They do a 16W version into 4 ohms (although I think my speakers will be 8 ohms), using 5670 and 6005 tubes, and a 8W version into 8 ohms using the same tubes.

The 8W using 10GV8 also goes into 8 ohms and is a little cheaper than the version using the 5670 and 6005 tubes.

An enclosure would cost around $30.

This approach would allow me to get an amp in my office very quickly, giving me time to plan for El Cheapo or SimpleSe for an at-home amplifier.

I'll make a post about the two kit variations and folks' preferences.

Charlie
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Old 13th September 2007, 12:49 AM   #10
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Charlie,

You might get out for $200. It depends on what's in your "junk box".

IMO, even using the low cost guitar amp O/P trafos, it's fair to say that "El Cheapo" is BETTER than the S5. You easily get the same power O/P in triode mode from "El Cheapo", as the pentode mode S5 delivers. The B+ PSU has considerable reserves of current, as 200+ mA. are available. While "boutique" parts are not called for, all parts specified are of excellent quality.

FWIW, those individuals who've built an "El Cheapo" have been pleased.
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