1/4 A slow blow for HT fuse?

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pula58
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1/4 A slow blow for HT fuse?

Post by pula58 »

I am building a Fender AB763 type of circuit (two 6L6, 4 triodes).

I want to ad an HT fuse to protect the output tranny. Is 1/4A sufficient (slow blow), or do I need 1/2A (slow blow)?
tubeswell
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Re: 1/4 A slow blow for HT fuse?

Post by tubeswell »

I'd use a 500mA T fuse for 2 x 6L6s
pula58
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Re: 1/4 A slow blow for HT fuse?

Post by pula58 »

o.k...here I go exposing my ignorance.

What is a "T" fuse. Is that fast or slow,or something else.
Cliff Schecht
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Re: 1/4 A slow blow for HT fuse?

Post by Cliff Schecht »

Slow blow I think. I know that fast blow fuses last all of 2 seconds in the HT position. 500mA SB is the guy for most push pull pairs.
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tubeswell
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Re: 1/4 A slow blow for HT fuse?

Post by tubeswell »

Sorry "T" in this instance is an abbreviation for 'time fuse' - i.e.: a slo-blo fuse (even tho' 'time' can be fast or slow depending on how fast you are going)
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rp
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Re: 1/4 A slow blow for HT fuse?

Post by rp »

From my reading around the web, I gathered that an SB on the B+ will be too slow to do any good - ie save the output section. I use FB and with the tube rec amps they hold up well. Occasionally one will will pop using the stanby but it's been rare. FB with SS rec doesn't stand a chance. Please correct if I'm wrong.
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David Root
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Re: 1/4 A slow blow for HT fuse?

Post by David Root »

IIRC the standard for 50W Marshalls has always been 500mA fast blow. Personally I would be loath to use a slow blow fuse on the HT, with or without SS rectifier, in any design.

Lately I have only used a fuse in the power section on the CT of an old vintage OT I do not want to lose. 200mA fast blow. This in a 50W amp. I also used a 500mA slow blow on the CT of the PT too, as it was also vintage iron. These are inline fuses inside the chassis, I also use a 2.5A slow blow on the PT primary.
flood
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Re: 1/4 A slow blow for HT fuse?

Post by flood »

I've used 200mA SB in the secondary CT-to-ground of my 18W design. I'm pretty sure this is not the right way to do it, but definitely took it off a schematic as i knew very little about building amps back then.

i'm omitting the fuse on the secondary entirely in my soldano atomic 16 build though.
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Dingleberry
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Re: 1/4 A slow blow for HT fuse?

Post by Dingleberry »

I have been taught by my amp mentor that T stands for Time Delay.
I have been using T for MAINS fuse and fast for HT fuse.

-T
tubeswell
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Re: 1/4 A slow blow for HT fuse?

Post by tubeswell »

Dingleberry wrote:I have been taught by my amp mentor that T stands for Time Delay.
I have been using T for MAINS fuse and fast for HT fuse.

-T
Yeah same diff
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