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Old January 4th, 2014, 07:57 PM   #1 (permalink)
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5F6a bassman build Help! (first build)

Hi guys

Decided to build myself an amp. The 5F6a bassman. Have looked at a few layouts on the web and just have a few questions if anyone will be nice enough to help me out. Im a carpenter by trade and will be building a super nice cab when its done so will post pics along the way! Ive posted the layout pic im using below.

Are the diodes and cap needed on the rectifier tube? if so what sort of diodes are they?

The 25k bias pot with 22k resistor in series is shown here. Can i directly replace those with a 50k bias pot ans 15k resistor??

The filter caps show 2x22uf and 2x20uf, some layouts show 4x20uf...will there be any difference??
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Old January 4th, 2014, 08:20 PM   #2 (permalink)
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Thanks for reposting here, it will get more attention.
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Old January 4th, 2014, 08:32 PM   #3 (permalink)
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Here is a discussion on the diodes for the 5Y3 socket. The discussion is based on a 5E3 diagram but the content still applies.


Specifically the diodes are 1N4007.
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Old January 5th, 2014, 01:36 PM   #4 (permalink)
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I cannot comment on the diode/cap combination. I have never seen that, but I assume it is a safety measure in case the rectifier tube were to fail. Either bias resistor/pot combination would be fine just as long as you can dial in the proper bias setting. As for the filter caps, this is a good place to assess your goals. There will be no difference between the two options you mentioned. A set of low value filter caps largely contributes to that vintage, slightly mushy character when pushed. Those smaller caps also cannot support quite as much low end, if that is important to you. In my Bassman build, I used 47uF filter caps across the board. Others have reported to using as high as 220uF for the first cap. With higher caps, you will get a little more clarity at higher volumes, tighter bass, and a little more headroom from the power supply
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Old January 6th, 2014, 03:24 AM   #5 (permalink)
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Thanks for your replies! great info about increasing the filter cap value to get a better low end. That's definitely something i will be doing. Along with some very high powered high efficient 10 inch speakers It should have clean volume for days
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Old January 6th, 2014, 04:03 AM   #6 (permalink)
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Hey Floorboards,

The diodes are a fail-safe in case the rectifier tube goes south. As has been said, 1N4007. A fellow at Ampage says abou the caps ...

The cap is not essential. It has been put there to help suppress the switching noise of the added semiconductor diodes. The switch noise will not get through the tube rectifier BUT it will couple back through the transformer to other windings which can cause the switching noise to appear on heater windings or worse still on a winding used for a bias supply.
The bias pot + resistor combinations are abundant, those two seem pretty popular. I would guess that you want your bias pot somewhere 'round the middle, with leeway both directions.

Filter caps can be all kinds of combinations ... certainly can't see much reason to have 2 X 20uF + 2 X 22uf ... all 20uF or all 22uF won't be much different With the GZ34, you can go as high as 60uF and be in spec. You can go higher with solid-state rectification, but don't see the need unless you're a little shy on P.T. voltage. As has been said, more filtering = cleaner and tighter at the top.

Have fun!

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Old January 29th, 2014, 01:58 AM   #7 (permalink)
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Any progress?
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