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up-to-date El Cheapo schematic
up-to-date El Cheapo schematic
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Old 11th November 2017, 04:55 AM   #41
crazyfrog is offline crazyfrog  Canada
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up-to-date El Cheapo schematic
Default possible MOSFETS

Hi. Having in mind 6P14P-ev (or 7189a) as output tubes under 400v on anode, 300V G2 and bias around -14V, I checked here and there and found two possible candidates for source follower in the case Vds could go near 450V with low Crss (few pF) and "good" Gfs (say around 100 and more) at low current (10mA).

AOT1N60 http://aosmd.com/pdfs/datasheet/AOT1N60.pdf

and IXTU 01N100 http://www.mouser.com/ds/2/205/98812-1110144.pdf

Comments are welcome

Pierre
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Old 27th December 2017, 06:01 AM   #42
ycroosh is offline ycroosh
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Default Question about the power supply

Hi,
I'm about to start building the El Cheapo and have a few questions. I hope it's OK to ask in this thread, since it seems to be topical.
I have some components that I purchased with the intention of building another 6v6 amp, so I have a 550VAC CT 250ma transformer (Hammond 270HX), two 200ma 1.5H chokes and one 200ma 5H choke. Rather than buying the parts specified for this design I would like to use the ones I have. Playing with "PSU Designer II" I came up with a design that gives me 330 VDC at 6v6's plate and 220 VDC at 12AT7's plate (crude schematic below).

Ali stated in one of the posts in this thread that T7 likes 220-220 VDC and B+ needs to be 355. I've spent last two days reading every possible post about "El Cheapo" but can't figure out if the negative supply is needed, and what is the value. In one of the earlier posts someone stated that it's 35V. Is it +35V, so 0+35v+"B+" add up to 355VDC, or is ii -35/0/+355? Also, do I need to use B+ for both stages or can I use a more traditional approach of separate supplies for the 6v6 and 12at7?


I would really appreciate any info.
Thank you in advance
Yuriy


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Old 27th December 2017, 07:26 AM   #43
Eli Duttman is offline Eli Duttman  United States
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Location: Monroe Township, NJ
The rectifier winding of Hammond's 270HX is 225-0-225. Ignoring the inevitable losses, the B+ rail will be 318.2 V. and that's way too "short". Your simulation is for 275-0-275. You would have to acquire a 120 VAC to 2X 50 VAC boost trafo of sufficient VA capability and a good HIPOT rating between both the primary/secondaries and the 2X secondaries.

The reservoir position in the B+ supply of "El Cheapo" is a 220 μF. 'lytic bypassed by a 4.7 μF. metalized polypropylene part, not a wimpy 47 μF. Energy storage matters.

Pseudo dual mono is employed for 'T7 B+, for improved channel separation in an economical matter.

B- means exactly what it says, a separate negative supply. A 35 V. rail should be adequate.

You show 1N4007 diodes, which are hideously noisy. Never use a 1Nnnnn part in a HIFI build. Instead, use the corresponding UFnnnn part,
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Old 27th December 2017, 08:43 AM   #44
ycroosh is offline ycroosh
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Eli,
Thank you much for response. I'm very much a beginner, and this is my first foray into scratch building (i've restored several old radios and R2Rs, but that obviously doesn't require great electronics knowledge).
I did the simulation as a quick check if I could get the voltages. That said, as far as I can tell 270HX is 550 CT, so that is 275 per side; 225x2 = 450. Next question, then: assuming that I follow the spirit of your PS design and use the parts that your design uses, can I make the transformer work? If yes, can I use the 5V winding with voltage doublers to get my B-. I can't do the math right now - it's 1AM in my part of the world and my brain is shot...

Thank you again for the response.
Yuriy
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Old 27th December 2017, 09:30 AM   #45
Eli Duttman is offline Eli Duttman  United States
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My bad, the 270HX is 275-0-275. You are good to go.

You can voltage multiply the 5 VAC winding to get the B- rail. Use Schottky diodes, as that will maximize the O/P of each stage. Approx. 6 V. are available per stage. So, 8 stages will surely be enough and 6 stages probably good enough. The half wave parallel setup provided is quite satisfactory, in this low current situation. Reverse the polarity of the diodes, as the schematic fragment is for a positive rail.
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File Type: jpg Half Wave Parallel Multiplier.JPG (77.4 KB, 304 views)
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Old 29th December 2017, 05:27 AM   #46
ycroosh is offline ycroosh
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Quote:
Originally Posted by Eli Duttman View Post
My bad, the 270HX is 275-0-275. You are good to go.

You can voltage multiply the 5 VAC winding to get the B- rail. Use Schottky diodes, as that will maximize the O/P of each stage. Approx. 6 V. are available per stage. So, 8 stages will surely be enough and 6 stages probably good enough. The half wave parallel setup provided is quite satisfactory, in this low current situation. Reverse the polarity of the diodes, as the schematic fragment is for a positive rail.
Eli,
Thank you, this is very helpful.
Another question: since I have a center tapped transformer, is there any benefit of running each channel completely off a separate side of the winding? I.e. take your ideal of "pseudo duo mono" all the way to the transformer.
Regards
Yuriy
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Old 29th December 2017, 11:42 AM   #47
Eli Duttman is offline Eli Duttman  United States
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IMO, the expense and bother of separate PSUs back to the power trafo is not warranted. Right now, the B+ PSU is full wave center tapped, using 2 diodes. Separation requires 8 diodes, in 2 bridges, and replication of caps., chokes, etc.

Blocking small signal interaction between the channels is quite beneficial, without incurring much complexity or cost. "El Cheapo" is about obtaining performance beyond what is to be expected from the monetary outlay.
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Old 23rd July 2018, 09:01 PM   #48
bbuz is offline bbuz  United States
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Default EL Cheapo parts/ build kit

Hope this is ok to tag on this, but I have a full complement of new transformers and vintage tubes for an EL Cheapo amp build which I never used.

Moving and have to slim down. So, if interested, please PM me.

Thanks!
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