| 6EM7 amp PSU question [message #11273] |
Sat, 21 January 2006 23:14  |
Shane
Messages: 1117
Registered: May 2009
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Illuminati (3rd Degree) |
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Ok, I'm going to start getting everything together over the next couple of months to make a 6EM7 SE amp. I've got 6EM7 and 13EM7 tubes a plenty. I've looked at lots of schematics and decided I'd like to run the B+ at around 220V. I've seen these tubes ran everywhere from 175V to 325V. 220V seems to be a good middle range for about 1 watt. I've been playing with PSUD2 and came up with the following PSU. It is just for one side, as the channels would seperate after the first 10uF cap after the rectifier. I basically copied this from Gary Kaufman's design with a slightly lower power trafo and added a RC filter at the end (1.8k on the resistor). Total mA needed for both tubes would be around 104mA. Trafo is the Hammond 370FX, but I don't have any other specs than the voltage/amps so I guessed on the source impedance. If anyone has any other suggestions or can point out what I'm doing wrong I'd appreciate it.
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| Re: 6EM7 amp PSU question [message #11274 is a reply to message #11273] |
Sun, 22 January 2006 04:18  |
Damir
Messages: 1005
Registered: May 2009
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Illuminati (2nd Degree) |
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See this variant - choke input filter (10H/100 Ohms/200mA) with "tuning" C1=1,5µF/600V (MKP, MKT...), then C2=220µF/450V electrolitic.
Bypass C2 with "bleeder" resistor, Rb=27kOhms/5W (it draws 8mA).
Then split for two channels - L2/C3 + R1/C4 for the L channel, and identical LC+RC filter for the R ch.
You`d get about 213V for the output stage, and 207V for the driver.
Of course, Rtr is a guess, and maybe you`d need to adjust the value of C1. Caps C3 and C4 can be "motor run", or MKP/MKT, 400Vdc ratings.
BTW - if you choose to build it, you can post on "Group Build" (Tube DIY) forum...
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| Re: 6EM7 amp PSU question [message #11275 is a reply to message #11274] |
Sun, 22 January 2006 11:29 |
Shane
Messages: 1117
Registered: May 2009
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Illuminati (3rd Degree) |
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I tried a very similar PS design with two chokes, but I never could get the ringing on the initial voltage rise completely gone. Thanks a heap.
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| Re: Damir--help! [message #11277 is a reply to message #11276] |
Sun, 22 January 2006 16:07 |
PakProtector
Messages: 935
Registered: May 2009
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Illuminati (2nd Degree) |
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Hey-Hey!!!,
Don't worry about the warning, it's an artifact of the electrical FEA. It wouldn't happen in real life, the CCS would just saturate at low voltages.Also, the overshoot is a result of turning the system 'ON' with the tubes heated up( it's valid for SS and Hg-vapour models ). With a slowly heating cathode, there is none of that sort of overshoot with L-C filters.
cheers,
Douglas
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| Re: Damir--help! [message #11278 is a reply to message #11276] |
Mon, 23 January 2006 00:05 |
Damir
Messages: 1005
Registered: May 2009
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Illuminati (2nd Degree) |
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You can "stack" many RC and LC filters in series, but in this program you can`t build "splitting" PS. In other words, after the L1/C2 filter, we have a "split", one ch shown (L2/C3 + R1/C4), and other ch is the same (parallel), but "expressed" only like current tap, 60mA.
It`s about 50mA for output tube, 2mA for the driver, and 8mA for the "bleeder" R=27k, not shown - but recommendable bypass of C2.
Shown ch "pulls" 50+2 mA.
"Voltage below zero error" - probably you made a mistake, see my picture and try it again... 
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| Thanks ! [message #11280 is a reply to message #11277] |
Tue, 24 January 2006 18:53 |
Shane
Messages: 1117
Registered: May 2009
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Illuminati (3rd Degree) |
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I put the values in 3 times before I got it to work! Never changed a thing between any of them. Weird.
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| Re: Thanks- question about D1 current [message #11283 is a reply to message #11282] |
Mon, 30 January 2006 06:43 |
Damir
Messages: 1005
Registered: May 2009
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Illuminati (2nd Degree) |
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Basically, C-input PS has a disadvantage that charging current "on the capacitor" is in the form of sharp peaks, with peak value many times the load current. This current flows through D1 & T1, you can see it graphically if you look on the little time segment, for example see the link. Choke input filter has much better "behaviour", it "draws" more or less constant current.
Our example (small, 1,5µF cap input) is something in between, "almost" L-input, with small charging current peaks.
To be on the safe side, and have some "room" for experiments - use the 275-0-275V PT with 160mArms current capacity. For "pure" L-input Itr~Iload.
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| Re: Thanks ! [message #11284 is a reply to message #11280] |
Mon, 06 February 2006 18:15 |
PakProtector
Messages: 935
Registered: May 2009
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Illuminati (2nd Degree) |
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You'll love this one then...I tried some very small input cap Pi( or CLC ) filters. Started small and worked my way up. I got some errors realted to allowable time step size which went away and re-appeared as I increased the size of the cap. Good old finite-element numeric methods and all the stability problems which can crop up if the proper math and approximations aren't used. For a system composed of masses and springs and forcing functions, the results are pretty close to what real stuff does in the continious world.
cheers,
Douglas
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