45/100 Style Build

[thousandshirts]

New web page address - new photos - updated March 14/09

http://members.shaw.ca/wrbrooke/45-100.htm

[thousandshirts]

While we're here, I'm wondering what the advantages/disadvantages of putting the two center taps of the power transformer (both HT and heaters) on the same fuse to ground. In the last photo, on the transformer, you can see I've used a green wire with a yellow stripe on it to connect two of the PT lugs together, and then to ground via the flush mount fuse mounted just below the PT in the picture. The top side is the 375-CT-375 side (blue with white stripe is the common lug), the bottom side is 3.15-CT-3.15 (heaters), and the two CT's are green w/yellow stripe. It works beautifully as is, and works beautifully with the two separated (and running the heater center tap directly to ground without fuse, but fusing the HT CT). Having the heaters fused is nice. Maybe I'd use more fuses over the years, by a small amount? I know my ass is covered so far as protecting the transformers are concerned. I can deal with the odd tube replacement. But technically speaking -- is there a best way to do this? Put that fuse someplace else entirely (there is a separate Mains fuse, the layout is near the bottom of my website)? Hmm. Thanks in advance.

[Tubetwang]

Thanks for sharing!

Major Twang

[tubetek]

Howdy Thousandshirts-
Unless I misunderstand, a fuse big enough to protect the filaments (several amps) wouldn't protect the B+ (perhaps 500mA) You may be mislead into a false sense of protection (and I may be short on coffee this AM!!)
Tom
EDIT> Oh, BEAUTIFUL WORK!!!

[jelle]

Sweet job!

[Luthierwnc]

Nice job.

Usually you see the HV protected with a series 1/2 amp fuse and the filaments just work off the main fuse. Most people don't use the heater center tap anyway -- typically they reference ground with either a pot of a couple of 100R resistors. Although, if it doesn't hum, it works. Skip

[Allynmey]

Beautiful Job!!!!!!!!!!!

[Jana]

Yes indeed, nice work!

As for the fuse, there wouldn't be much current, if any, from the CT of the heaters and a fuse in this location for the heaters wouldn't really be "fusing" the heater supply, only its reference to ground. A fuse with wattage rating for the HT, typically 1/2 amp would be fine. Here is what would happen though if the HT blows the fuse for one reason or another: the supply for the HT is cut and the tubes lose all their high voltage, which is the desired effect. The heaters, however, will still have their 6.3vac going to them, they just won't have a reference to ground anymore. Is this what you want?

[thousandshirts]

Thanks for sharing!

Major Twang

Glad you had a look, Major Twang!

Sweet job!

Thanks Jelle!

Beautiful Job!!!!!!!!!!!

Thanks Allyn!

Nice job.

Usually you see the HV protected with a series 1/2 amp fuse and the filaments just work off the main fuse. Most people don't use the heater center tap anyway -- typically they reference ground with either a pot of a couple of 100R resistors. Although, if it doesn't hum, it works. Skip

Thanks Skip. Right, giving a heater ground reference is part of the attempt to keep things quiet. And if the HV goes, blowing the fuse, the amp will be very quiet anyhow, so the heater hum will be a non issue. Got it!

Yes indeed, nice work!

As for the fuse, there wouldn't be much current, if any, from the CT of the heaters and a fuse in this location for the heaters wouldn't really be "fusing" the heater supply, only its reference to ground. A fuse with wattage rating for the HT, typically 1/2 amp would be fine. Here is what would happen though if the HT blows the fuse for one reason or another: the supply for the HT is cut and the tubes lose all their high voltage, which is the desired effect. The heaters, however, will still have their 6.3vac going to them, they just won't have a reference to ground anymore. Is this what you want?

Right! Thank you very much for your explanation, Jana. This is exactly what what I was hoping to get sure on. I'm going to leave it as is and play on.

[benoit]

Ha.. as I said over on tapeop (as vorian), looks great!

[thousandshirts]

Ha.. as I said over on tapeop (as vorian), looks great!

Ah-ha! Thank you -- again! That is a great forum. But, so is this!