My X10 has begun

[tweedeluxe]

Keeping this simple regarding the 1k 5W wattage rating. taking 12W as max dissipation and 330 volts on the plate:

12w/330v = 36mA draw
screen = 10mA
3x12ax7 = 5mA

This is 51mA

0.051 * 0.051 * 1000ohms = 2.6W so the 5W being double should be okay. I assume it is if Xits used them but just want to understand this. At 90% dissipation, its even less.

add ~50% to avg HT current draw to account for ripple current. so assuming 75mA total current = 5.625W per resistor. No wonder they're discolored in the xits gut shots.

[Gaz]

Hate to be a hater, but it wouldn't surprise me if the Xits guy is more of "designer" with a great ear, and less of an engineer. Hey, if that's true, I'm in the same boat anyway Perhaps it was just the VVR, but it's an interesting, and perhaps overlooked point made by FunkyE9th: What are those damed things for, besides a primitive voltage drop?

[tweedeluxe]

they most certainly cause voltage sag, but it is interesting that they are so large. maybe the load current doesn't actually vary that much so 1k was the smallest value that caused noticeable sag in the response. the amps sounds pretty "loose" to me in the clips - reminds me a lot of a 5E3 actually.

[pamaz67]

FunkyE9th is right on the transient, but it appears that the whole story ends in 250 milliseconds, that for a COLD wire resistor I suppose are fine. I mean . its' dissipating 10 w for 0,25 sec and is a 5 w rated resistor.
It's not something that will destroy the all thing in a while.

[surfsup]

I already ordered 1k 5W and a pair of 1k 6.5W resistors as replacements. I'll get it working with those first then decide later on my next order whether to change it up to something like this...

Due to the length constraints of 1.15 inches, I can't find any 7W or 10W resistors that would fit between those turrets, so maybe put a 680R 5W where the 1k 5W was, and put another 500R 5W between the first two filter caps (labeled "new R" on the voltage xls). That plus a 3k3 supplying the PI would put me at the same voltages with lowered wattage ratings (in orange):

[img:450:304]http://chicagocadcam.com/ChrisHahn/xen10/voltages2.jpg[/img]

[Lonely Raven]

Surf, don't let size hold you back...you can always have the leads bend back on themselves and float the resistors over the board. I'm sure you have plenty of room considering how tall those Solens are.

[FunkyE9th]

If you really want to stick with 1K, another option is to piggy back 2 5W 2K resistor in parallel. You get the equivalent of a 1K 10W resistor.


Edited to add...
Just wanted to say that the simulation I provided was not meant simulate the Xits amps PS. The main point I was trying to make was that the 1K resistors will see a different current than the tubes. Plus the simulation only shows about a 27mA current draw on the load. I'm guessing your idle current will be more.

[surfsup]

Once i have it running and can measure, i might go w the 1k 6.5watters i dunno. If i add the extra resistor, what would that do to my filtering?

Surf, don't let size hold you back...

Heynow, what r we talking about?

Bigger means they wont fit n wont look as nice!

[rhinson]

[quote="FunkyE9th]I am really wondering what those 1K's are for. It's too big for current limiting purposes or for simulating sag. So maybe it's for dropping the voltage because of the high HT. If it's there for dropping, there are better ways to drop it especially since you are using a VVR.[/quote]

that's exactly what they're there for and you're right, there are better ways----like getting the power trannie you want to start with. but we saw in some other pics of another amp (the ef86 amp) that had a 6ca4 rect tube---so he's using a merc repro ac15 power trannie and these have a pretty high hv sec even with the 6ca4 drop. it would be best to have one designed like you need it, but looks like thus far he's decided to do a work around and keep the trannie and use it with other amps perhaps. rh

[Lonely Raven]

The guy who designed the Xits amps has his chassis custom machined, and uses an unusual "tolex", and has tweaked the snot out of these amps.

I find it hard to believe he didn't use *exactly* the transformers he wanted, and very likely had them custom wound.

[shane]

Those 1K 5W worry me, after all they will also carry the ripple current which can be 3 times the dc current draw you'd have to factor that in.

I would imagine they provide quite a bit of sag too!

Cheers
Shane

[rawnster]

surfsup, when are you going to get this amp finished? Talk about milking it! Just giving you bad time. Should be able to knock this little circuit out in a couple of weekends.

[Masco]

Once i have it running and can measure, i might go w the 1k 6.5watters i dunno. If i add the extra resistor, what would that do to my filtering?

Surf, don't let size hold you back...

Heynow, what r we talking about?

Bigger means they wont fit n wont look as nice!

Use 2x 82R/5W like the Vox AC-15CC. This will bring you to specs.
Your B+ will be hotter, but w/ the VVR installed things should work out ok.

[surfsup]

I'm expecting the mouser order to show up tomorrow. I'll wire in the 1k5W first, then once its all up and running okay, I'll pull em and put in the 1k 6.5watters. This way I don't burn up the 6.5W Rs if the VVR wasn't the problem before.

[angelodp]

Still have time to build that bulb limiter.

A