The sunn Forum
Sunn Musical Equipment => DIY => Topic started by: arskas on November 04, 2010, 11:56:04 am
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I'm building an amp based on the 200S schematic diagram. I'm not attempting to make a perfect clone. I'm just trying to make a good simple amp. For example I'm using Hammond transformers because they are easily available here.
The cab will fit nicely on top of my Aurinko)))-speaker.
8-)
(http://lh3.ggpht.com/_iDSKxIyzbBY/TNL1K2fhmsI/AAAAAAAACw0/T9M82eB_2Hs/kuva1.jpg)
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I see you've gone the red knob route :)
There is a mistake on the schematic at the volume control. None of the amps I have are wired that way. I posted a corrected 190B schematic in a thread about building a 200S clone started by EdBass. I think the title was "What do you think?". What Hammond transformers did you use?
Edit, Here's the thread: http://sunnforum.ampage.org/sdp/index.php/topic,4961.0.html
Look on page 3.
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Thanks for the tip! The OT is 1650RA and PT is 378X. Choke is 193H.
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there it is now:
(http://lh5.ggpht.com/_iDSKxIyzbBY/TNlk6cZe5JI/AAAAAAAACxY/9QLP0ANda-M/s640/09112010896%5B1%5D.jpg)
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Well, the amp is now ready and I have done some testing with it. It's eating a lot of main fuses when I switch on the standby.
Amp works fine when I do a cold start with stdby on. All voltages look ok. A 3.15Aslow blow holds the stdby-switching but that is about three times too large at 230VAC(!). There is an arch inside the JJ gz34 when I switch on with the 3.15A fuse.
I have read bad things about the jj tube. Could it be that I have a bad tube?
I have slightly modified the power supply filtering. I have two sets of 100uF/350V in series and a cap can 32+32uF/500V. The choke is 5H 65ohm 600V. Can the power supply overload the rectifier?
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Take all the tubes out and replace the fuse, then turn the amp on. If you blow a fuse in that situation, then you have something incorrect with your wiring or a bad component. If you don't blow a fuse in that situation, then stick in just the GZ34 and repeat. If you blow a fuse in that sitation then the GZ34 could be bad. If it is ok, then sticking in the power tubes and lowing a fuse could indicate a bad power tube, incorrect bias, etc. Most likely though, you will discover that you have a wiring problem or the rectifier is the problem. I never fire up an amp for the first time with a new build or a repair with the tubes in.....and always do the first power through a current limiter, just in case there are problems, and also to save the cost of blowing a bunch of fuses too....
greg
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If you correctly wired the two 100 uf caps in series, then you have a 50uf cap essentially, and the GZA34 should be ok with that, because it's max is 60uf, but you don't know with today's low quality GZ34's.
Greg
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Thanks Greg. The wiring is ok because the amp works when I don't touch the standby-switch. I have been reading this: http://www.freewebs.co.uk/valvewizard/fullwave.html (http://www.freewebs.co.uk/valvewizard/fullwave.html) and it looks like I need to add limiting resistors to the rectifier circuit. I'll wait and see how the amp will work then.
I have considered a ss-rectifier but I think I would need to replace filter caps to hold the higher voltage.
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If the amp is in standby, then the B+ is not going through the circuit past the standby switch, so your wiring may still be suspect. If the problem occurs as soon as the standby is moved to the operate position, then you have to look at what occurs when that happens. Suddenly a surge of high voltage goes through your circuitry, and because the tubes are in the amp along with the rectifier, then there is a large current draw too that your power supply and caps have to supply to the circuitry. If you have a defective power tube, rectifier tube or incorrect wiring, then you will have a problem with the fuse blowing when the current draw for that part of the circuit is exceeded. Testing without the tubes will verify if you have a wiring problem or not. If it works without tubes, then try the rectifier and see if it works that way. If it doesn't then having a solid state module that you can try will show if your rectifier tube is a problem or not. Regardless, the first time an amp is fired up, it should be on a current limiter and should be run without tubes to verify that there is not a problem. This way you don't blow through a ton of fuses to try to find the problem. Once you've verified that it works without tubes, then you know your circuitry is correct and you can proceed step by step to find the problem as I mentioned. A solid state rectifier would work fine with your amp the way it is now. Adding limiting resistors might help, but it is not your problem. Try the tests.....
Greg
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I put in a ss-rectifier today and replaced the 15k resistor (in power supply) with a 25k to drop the voltages a little. Amp works nicely now but
it feels a little weak. Somehow I expected a little more punch. A bias check must be done next I think...
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Once you get the output stage biased, check the voltage on pin 3 of the 6AN8. It needs to be 80-100V. If it's too far off, drive to one of the output tubes will be weak. A 200S won't have a great deal of overdrive, but it should be loud an clean with the right speakers. The 1650RA is not really the right choice, the original Dynaco transformers had a primary of 4200 IIRC. The 1650RA needs a B+ of around 600V to make 100W so you still should be close to a factory 200S.
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Well, I put the 15k back to the power supply, increased first cap value to 50uF(100uF+100uF) ...and there was all the power I was looking for :-D
Look like all the voltages are good now.. Thanks for help.
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Just thought I'd share this photo here.
(http://lh3.ggpht.com/_iDSKxIyzbBY/TQfehI8viKI/AAAAAAAAC0M/EESRPEWiCl8/s576/08122010929.jpg)
I finally got the name plate for this one. ...I've been totally happy with the amp now.
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Cool amp arskas!!
Greg, what do you use for a "current limiter"?
Johnny G.
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Johnny,
I made myself a box that has a 5 amp variac in it, along with a voltage meter and a current meter so I can measure what is happening, and the variac and a light bulb are in series with the amp under test if plugged into one plug, or just the variac if the amp is plugged into the other plug. I use a 100 watt incadescant light bulb for it and it works very well. The light bulb limits how much current the amp can draw, and really only lights up initially when the amp is turned on (since there will be a current surge from the caps charging up) or if there is a problem with the amp under test. If there is a problem, then the bulb runs much brighter than it should and it also limits how much current can be drawn so you have time to shut the amp off before a fuse would blow as compared to normal conditions. I use it any time I work on an amp.
Greg
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Hi all. I just thought I'd write a bit on some of my old threads. Both speaker cabs and one amp are in good use still. I've had a few blackouts with the amp because of bad contacts and soldering faults. And I think parts layout could have been much more clever. The amp cabinet dropped all of its tolex. My fault. I used glue direct on wood and it never stuck on really good. When I built the speakers I used some clear coating spray on wood and glue on top of that. I Didn't do that with the amp cab. Silly Me. :-D
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Here's another status update of life with a sunn clone amp.
After two and a half years of use (hours?...don't know) one of my electro harmonix kt88 failed. It doesn't heat up. Only a tiny orange glow is visible in the tube guts. A nice blue arc sparkles inside the tube when I lift standby. There may have been some kind of power surge that caused the breakup. Or maybe the tubes got cold startup once too often. I'll fit some JJ's in and continue..
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Beautiful work, I looked through your link in your signature with your 200s build. Very cool stuff!
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I really needed a short scale gibson to complete my bass rig.
(https://lh3.googleusercontent.com/-BJy_ZVRkSjY/UjlF6qFYzeI/AAAAAAAAEE0/Bq4JlIKHpOo/w595-h793-no/IMG_1241.JPG)