Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: labb on July 19, 2013, 01:03:11 pm
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Finally have everything on order for a 5F6-A build and waiting on them to arrive..Going to build it in a 16 x 8 x 2 chassis which is kinda tight. Any advice, words of encouargement, warning, help, would be greatly appreciated.
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go for it. Have you thought of doing a 5D6 design? a few less parts.
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This is how I would personally build it. It may or may not be a good choice for you. I am presuming you will use it for guitar.
I'd separate the cathode resistors and caps on the preamp tube. And I'd lose the 220uf which I think will give you a muddier tone than 10uf or 2.2uf would.
I'd change the .02 coupling cap to .01 on the lower channel.
I'd definitely use an "enhance cap" on the plate of the LTPI entry resistor (this adds smoothness to my amps & I use it on every amp I have)
I'd lower the .1 coupling caps post LTPI to .047 or even .033.
And I would check for cap foil orientation to have a quieter amp:
http://www.el34world.com/Forum/index.php?topic=11427.0 (http://www.el34world.com/Forum/index.php?topic=11427.0)
There is an editable ExpressSCH schematic here: http://www.el34world.com/Forum/index.php?topic=571.0 (http://www.el34world.com/Forum/index.php?topic=571.0)
With respect, Tubenit
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Thanks for the replies and the mod schematic. Will probably do all of the mods. Looking at the original schematic I'm not sure what Mr. Leo was on about with this amp. The only difference I see in the two channels is the bright cap on the bright channel. Could just as easily put it on a switch and had a single channel amp. I am going to use a 300-0-300 250 ma. PT and use a diode rectifier. I want to keep B+ below 450 vdc. so that I can use 450 volt caps. I am going to use a Bandmaster OT With an input impedance of 4K and outputs of 4,8 and 16 ohms. Probably am giving up some tone with the PT and OT choices. We shall see. Am going to use a single dual gang pot for the vol. pots. Other that it being a head and not a combo, that is the changes I have planned for now.
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Tubenit's suggestions notwithstanding I think I would build it dead stock, play the crap out of it and then experiment with some of those changes.
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consider using a cap-can for the filter caps, it frees up a lot of space, and if you wire the resistors between the (+) leads, it saves real estate on an eyelet/turret board. You can get a 40-20-20-20 JJ clamp mount cap-can for $20. plus it is rated at 500V. you can get a CE for $50 rated at 525V.
also, save space in the chassis by building the amp to use a GZ34 with an octal socket and use a plug in SS rectifier (either off-the shelf, or make your own for less$$). plus, you can always plug in a GZ34.
I would not lower the B+ on your build for the difference in cost of some higher voltage rated caps. Add up the cost of all the parts, and look at the small difference in savings by using 450V caps (if any! that JJ cap is CHEAP). lowering B+ that much will give you a completely different amp. If hearing a real tweed bassman is what enticed you into this build, I wouldn't add in mods to make it something else. a coupling cap here or there is one thing, lowering B+ on the big tubes changes everything.