Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: scstill on October 29, 2020, 03:58:22 pm
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Will I have any issues with tubes operating close to the speaker magnet?
In my newest build (Robinette's "Deluxe Mini" in a Silvertone Radio cab) my desired layout has the tubes close to the magnet. Tubes (R to L) are: 6ca4, 12au7, 12ay7. The rectifier tube (6ca4) is physically pulled by the magnet so I wonder if that might affect its operation. I used a wedge of cardboard to keep it upright for the pic, but of coarse it will have a socket in real life.
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I would line all four tubes across the rear of the chassis. Just put them closer together. You got plenty of room.
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three tubes...
I was trying to get the rectifier close to the PT for shorter wire runs
I suppose it would not be a big deal with couple of extra inches.
BTW - the original design had solid state bridge rectifier which wuld be easier to fit, but
I am opting for tube rectifier just because I like tubes.
Would there be any noticeable sound difference between the two options?
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Sorry. Can't count today. :icon_biggrin:
I don't think a tube recto will give you enough B+. Probably gonna have to use a bridge. If you post a clear pic of the label on the PT we can tell you for certain.
It's possible to use a hybrid tube/ss recto if that appeals to you.
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Looks like 240V 55mA?
Then silicon will give near 340VDC which is high-ish for a 12AU7. And it's not like we need supercharged performance from a 12AU7.
EDIT: ah, you mean a 2-diode (tube) rectifier won't work on the one 240V winding; it wants a CT. Since we are not pulling 55mA with a 12AU7 we "could" do half-wave tube; but that sucks. Bridge and auxiliary resistors does seem a best path.
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Google Robinette's "Deluxe Mini" returns a LOT of hits for cheesecake and cupcakes. WTF??
After too much time hunting a link you cudda gave us, I think you mean "Deluxe Micro". (May be the same to you, but not to Google's pea-brain?).
https://robrobinette.com/Deluxe_Micro.htm
And yes, it runs near 400V DC, but a late note suggests changes "cooler running " to reduce tube stress.
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yes its 480 ct at 50ma, figure to get 320vdc after 6ac4, maybe should add dropper to get down to 250??
Is odd that the robinette design with EZ81 adds silicon diodes to the tube. Says for backup which I don't understand (pic below). https://robrobinette.com/Deluxe_Micro.htm
What about your thoughts on tone and sag difference with the tube vs silicon?
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sorry about the cupcakes
yes indeed its micro
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yes its 480 ct at 50ma
Are you sure? Have you actually measured 480V?
I interpret what I see on the label as 240V center tapped, IOW, 120V-0-120V.
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I was careful when I sourced it to get the right voltage
Just measured and get unloaded 262vac line to CT with 118vac in
plus the base says it. BTW - PT base is gone in the build.
Secondary advantage is that its silver.
Going into a Silvertone cabinet so everything needs to be silver - right?
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Going into a Silvertone cabinet so everything needs to be silver - right?
A real silvertone would use tin, not silver. :icon_biggrin: