Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: catnine on December 27, 2012, 10:48:03 pm
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I screwed around with paint and fender schem's to get this down. The only thing I forgot was to add the 470 ohm 3 watt screen resisters it was too much trouble , paint is difficult enough but rh 470 ohm screen resisters are on the power tube sockets .
(http://i286.photobucket.com/albums/ll112/blues90/harvard_5f10_schem6g2.gif)
I am pretty sure the bias pot setup is right or at least how I set mine up , it does work great.. Also the out put jacks . The one the 8 ohm speaker is connected to does have the shorting jack and I didn't add that in the schem . the 4 ohm jack is not a shorting jack . Since I used 2 jacks one for the 4 ohm load and one for the 8 ohm load instead of one jack and a switch then in order to use the 4 ohm jack I have to plug a dummy 1/4" plug into the 8 ohm jack so the 4 ohm is not shorted to ground . I didn't have room for a switch. I haven't used the 4 ohm jack in a long time so it is wired but sits there. It's not like an external speaker jack . Since there are 4 and 8 ohm secondaries on this OT I saw no other way to do this without a selector switch and one jack or a mini toggle spdt to break the ground to the one or the other shorting jack if I used two shorting jacks .
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Looks like you finally got everything worked out. I re-did your schematic in JSchem dhost.info/jschem/ (http://dhost.info/jschem/), which you should definitely get and start using it. For the speaker jacks, I think you should change the shorting jack for the 8ohm to a non-shorting type, so you can just plug in whichever one depending on the speaker that you are using. I think you know this, but do not operate the amp without a speaker plugged in.
JSchem: https://dl.dropbox.com/u/1326040/Catnine%206G2_5E3%20v.1.sch (https://dl.dropbox.com/u/1326040/Catnine%206G2_5E3%20v.1.sch)
PDF Version: https://dl.dropbox.com/u/1326040/Catnine%206G2_5E3%20v.1.pdf (https://dl.dropbox.com/u/1326040/Catnine%206G2_5E3%20v.1.pdf)
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470 ohms are a must if you want to save your tubes. Or you can use a single 1 K ohms from the B+ 387 V to feed both grids.
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470 ohms are a must if you want to save your tubes. Or you can use a single 1 K ohms from the B+ 387 V to feed both grids.
I do have the 470 ohm screen resisters on this amp , I just didn't put them on the schematic.
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Looks like you finally got everything worked out. I re-did your schematic in JSchem dhost.info/jschem/ (http://dhost.info/jschem/), which you should definitely get and start using it. For the speaker jacks, I think you should change the shorting jack for the 8ohm to a non-shorting type, so you can just plug in whichever one depending on the speaker that you are using. I think you know this, but do not operate the amp without a speaker plugged in.
JSchem: https://dl.dropbox.com/u/1326040/Catnine%206G2_5E3%20v.1.sch (https://dl.dropbox.com/u/1326040/Catnine%206G2_5E3%20v.1.sch)
PDF Version: https://dl.dropbox.com/u/1326040/Catnine%206G2_5E3%20v.1.pdf (https://dl.dropbox.com/u/1326040/Catnine%206G2_5E3%20v.1.pdf)
Thank you jazbo8 for doing the schematic . looks perfect . Since the output jacks have insulation bushings I can just clip the ground lead off the shorting jack solder tab. I just left it that way since most often that's the only jack I use and the only time I unplug the speaker is when I have the chassis out and check things so then I use a cable to the cab speaker . just a bit of added security in case I get distracted and forget.
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470 ohms are a must if you want to save your tubes. Or you can use a single 1 K ohms from the B+ 387 V to feed both grids.
I do have the 470 ohm screen resisters on this amp , I just didn't put them on the schematic.
Oh Sorry ! You do a nice job as I read