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b+ fuses

40.137.146.136
Posted on February 25, 2017 at 03:27:03
altecboy
Audiophile

Posts: 404
Location: Northern NJ
Joined: May 29, 2004
 I want to fuse the b+ in my set amps to protect the xmers against output tube failure. 200 mA power transformer. 10 watt opt's. What fuses do you use?

 

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RE: b+ fuses, posted on February 25, 2017 at 06:29:03
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 That will mess-up the sound on ALTECs, on a continuous basis. How often is it, that outputs fail?

What is your operating point and tube type?? I run my outputs at high VDC P-K and low current, such that it is dissipating only about 55 to 62 percent of rated maximum dissipation. I use good output tubes...NOT Chinese made crap which is false economy.

I am sure some engineer will give you a fuse type, but is that a smart thing to do, sonically ?? I think not. Re-think that whole topic !!

Jeff Medwin

 

RE: b+ fuses, posted on February 25, 2017 at 07:52:32
FenderLover
 I kinda agree with Jeff here. A fuse should not be used as a safety net for a poorly implemented design. Staying well within the operating parameters of the component parts, good layout, using quality parts, making sure to avoid instabilities, and utilizing a sound idle bias scheme should yield a long lasting stable unit. Of course, much depends on the reliability of those tubes.

This is just my opinion. But, IME... some of the longest lasting amps have simple layouts. And a single fuse on the outlet side of the PT.

 

RE: b+ fuses, posted on February 25, 2017 at 08:31:05
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Hi FL, what do you mean by "And a single fuse on the outlet side of the PT. "?

 

RE: b+ fuses, posted on February 25, 2017 at 09:18:28
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 I THINK he meant to say " A single fuse on the Primary side of the Power transformer ".

Jeff Medwin

 

RE: b+ fuses, posted on February 25, 2017 at 10:08:03
altecboy
Audiophile

Posts: 404
Location: Northern NJ
Joined: May 29, 2004
 In previous designs, I have used 1/4 watt resistors after the cathodes. These will open under tube failure conditions. Those were push pull designs.

One electron, the mfr of the SE opt's that I am using for the current design recommends fusing the b+ to protect his opt's.

Of course the PT's primary in my design is fused.

These days I'm not such a devotee of magic wires and cables. Later, after I get this amp up and running well, I can maybe roll caps, wires and tubes. Initially, I'd like to keep everything safe and secure. Hence the fuse inquiry.

thank you for the replies.
Altecboy

 

maybe?, posted on February 25, 2017 at 11:06:57
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 ARE YOU SURE!

 

RE: maybe?, posted on February 25, 2017 at 17:26:43
FenderLover
 Outlet = wall outlet or primary side.

 

RE: b+ fuses, posted on February 26, 2017 at 15:35:48
6bq5
Audiophile

Posts: 4391
Location: SF Bay
Joined: August 16, 2001
 Given the vagaries of tubes- condition and build quality I like the idea of B+ fuse - but then I own two Music Reference amps - both of which have B+ fuses-
the fuses are between the bias supply(x-former) and the tube (s)-
for the RM-9, 1 A fast blow...
I'd rather replace a fuse than speaker
Happy Listening

 

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