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up-to-date El Cheapo schematic
up-to-date El Cheapo schematic
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Old 13th September 2007, 12:50 AM   #11
planet10 is offline planet10  Canada
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up-to-date El Cheapo schematic
Quote:
Originally posted by Eli Duttman
FWIW, those individuals who've built an "El Cheapo" have been pleased.
Very pleased.

dave
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Old 13th September 2007, 12:58 AM   #12
cbutterworth is offline cbutterworth  United States
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What a dilemma!

In a way, I'd like to build it myself from scratch rather than from a PCB. I haven't decided yet, but really need to read through El Cheapo's thread for enclosure options and p-to-p wiring choices, etc.

Charlie
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Old 13th September 2007, 01:07 AM   #13
Jeff Yourison is offline Jeff Yourison  United States
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Charlie,

I've never heard the S-5, but I've heard good reports. It often gets modded, which makes me wonder about the kit as sold. The El Cheapo is a top-quality design using tubes and iron that are moderately priced. I would call it "optimized" in a way that balances cost, stability and sound quality. Jim's parts (caps, resistors, tubes, etc.) are not cheaply made, but rather are of very good quality without being "boutique." They are of a quality that suits the rest of the amp and then some.

Use good output and power transformers. I first used the Triode Electronics output trafo (the part in the schematic) and then got the z565. There was an immediate improvement in detail throughout the sound spectrum and in bass clarity and definition.

My concern about the S-5 is that you may be missing some of the quality that those tubes and that design could otherwise produce, due to the smallish OPTs and power supply. The El Cheapo and other similar designs using adequate power and output transformers may cost more, but the result is worth it if you can afford it.

Terminal strips are fine for the El Cheapo build, except for the CCS, which is more easily managed using perfboard or a homemade pc board. I used this RadioShack pcb:

http://www.radioshack.com/product/in...ductId=2102845

Take the schematic and divide it left-to-right into sections. You'll see how four- and five-terminal strips easily group the connections for point to point. A turret board or two would also work well.

I used shielded mic cable to run the inputs to the VC pot and then to the grids. I grounded the shield on one end only, at the signal ground. I also used a star ground (or rather a backbone bus to a star) and the amp is hum free.

Regarding the B+ requirement, in actual use ("on the bench" as Eli would put it), I couldn't get more than 210-212 VDC on the 'AT7s without hitting the max on the plates of the 12AQ5 output tubes. I haven't tried any alteration of Rp on the 'AT7s to compensate or rebalance the voltages.

--Jeff
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Old 19th July 2009, 03:08 PM   #14
jmillerdoc is offline jmillerdoc  United States
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Default El Cheapo assistance

Hi,
I am thinking of trying this amp out. I have tried to find the threads on Decware but am unable. I was wondering if I could get some pointers here. I have built the S5 K502 as my first amp ever and wanted to build one from scratch now. I was wondering what the specs for the OPTs were for this amp. Also the "LPT",
what is this? where is this connection made on the scematic?
Thanks,
Jeff
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Old 19th July 2009, 05:09 PM   #15
planet10 is offline planet10  Canada
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up-to-date El Cheapo schematic
OPTs for a push-pull pair of 6V6/EL84 are required. Something like 8-12k reflected impedance. If you can find a vinatge amp to use as a donor (we used a Scott LK48, and i have iron from Dyna SCA35 in the wings) you should be able to save some money.

LTP = Long Tail Pair and is the configuration of the 12AT7/ECC81 on the front end. The CCS forces it into "perfect" symmetry.

dave
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Old 19th July 2009, 05:19 PM   #16
planet10 is offline planet10  Canada
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up-to-date El Cheapo schematic
Default Re: El Cheapo assistance

Quote:
Originally posted by jmillerdoc
I am thinking of trying this amp out. I have tried to find the threads on Decware but am unable.
That forum seems to be a moving target. It should be here http://www.audiophiletalk.com/cgi-bi...pl?board=Tubes but i was unable to find it. Eli?

I'll repost the schematic here (i know where it is, as i drew it and am hosting it)

Click the image to open in full size.

Note that you don't need to be a slave to this map, there are lots of opportunities to change things to accomodate parts on hand to keep in the spirit of its name.

dave
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Old 19th July 2009, 06:05 PM   #17
drj759 is offline drj759  United States
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The El Cheapo thread is in the diy tube section:

Audiophiletalk D.I.Y. DIY Tube Gear Bargain Basement

El Cheapo Thread
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Old 12th March 2015, 06:24 PM   #18
tomlang is offline tomlang  United States
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Default El Cheapo LTSpice Model

I couldn't find the "original" thread for El Cheapo but found this one so hope OK, if not let me know where to post.

The LTSpice of this amp is posted below. Also a jpg with the DC voltages as calculated by LTSpice. Let me know if you need the Libraries to run this yourself.

And please comment on this, thanks!
Attached Images
File Type: jpg el cheapo.jpg (182.1 KB, 739 views)
Attached Files
File Type: asc 6bq5 12at7 duttman design.asc (7.2 KB, 59 views)
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Old 13th March 2015, 01:38 AM   #19
Eli Duttman is offline Eli Duttman  United States
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I've uploaded the "latest" good graphic. It does need updating. Is anybody willing to try? Frankly, my drawing skills are POOR.

The needs of the 12AT7 splitter/driver rule the roost. A 'T7 section sounds good with 200 to 220 V. on the plate and an IB of 3 mA. Therefore, the B+ rail should be about 355 V. By itself, a N-77U isolation trafo does not get the B+ rail "tall" enough. Boosting the B+ is necessary. The currently recommended power "iron" set is: a Triad N-77U as main B+, a Triad VPS24-1800 (2X "12" V.) as B+ boost and "12" V. heater power, an Allied 6K27VF as B- and "6" V. heater power, and a Triad C-24X as B+ filter choke.
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File Type: gif EC big.gif (38.8 KB, 682 views)
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Old 13th March 2015, 03:16 PM   #20
tomlang is offline tomlang  United States
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350v supply gives a nice 200v on the 12AT7 plates. Refer to the table below. Note that the 6BQ5 requires less drive to clip.

In the Spirit of DIY, please comment on the two circuit changes, 1. using only a single DN2540 and the other a LM334 with no -155v supply. These latter two utilize fixed bias at about 35mA per output tube.

Results are tabulated. If anyone wants the LTSpice files, I will send.
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File Type: jpg el cheapo table.JPG (88.9 KB, 624 views)
File Type: jpg 6Bq5 12at7 single dn2540.jpg (196.3 KB, 614 views)
File Type: jpg 6Bq5 12at7 LM334.jpg (183.5 KB, 197 views)
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