Filament current for 4-xxx tubes?

[WB3JOK]

I was browsing Eimac data sheets for possibilities of upgrading my homebrew RF deck (such as substituting 4-250's for the 4-125's).

The two filament transformers are 5 volt, 14 amp and each 4-125A draws between 6 and 7 amps.

But according to the data sheet, one 4-250A filament supposedly draws the same 14 amps that the 4-400 does? Why 

So unless I wanted to replace the fil xfmrs too, the only thing I could do to increase available plate dissipation would be two 4-400's instead of the four 4-125A's... not cost effective...

Is that data sheet in error or does the 4-250A really have that beefy a filament?

[n2bc]

Beefy!

[KM1H]

The 4-400A is identical in all respects except maximum smoke and it has a bunch of fins on the anode and requires air.

Carl

[WB3JOK]

don't they all require air, though?

[KM1H]

http://scottbecker.net/tube/sheets/088/4/4-250A.pdf

Lots of ham articles use no cooling in the 2500V area but Id still suggest a small fan to meet minimum specs. Certainly needed at 3600V with lots of Ip.

Carl

[WQ9E]

At the price of transmitting tubes today I wouldn't skimp on the cooling. 

[The Slab Bacon]

Basically the only difference between 250s and 400s is the fins on the plates (and the rated plate dissipation) (and they're a little neater lookin)

I dont know about NIB ones, but you definately find 400 "pulls" at festers for somewhere in the $10-20 range. New ones bring considerably more down here.

I have also found 4-1000 pulls in the same price range as well. Now that's a tube!!

I have put an amprobe on the filament lead for my 4-1000A. The rated filament draw is supposed to be 21A, I was actually seeing more like 16A after it was lit. The 14A rating on the 250s and 400s may actually be the initial inrush to get it started, actual running draw may be considerably less. Put an amprobe on one of your 125s and see. You might just be able to get away with it.

                                                   the Slab Bacon

[ke7trp]

4-400s are going for about $80 to $100 a tube used now.  If anyone has new ones, I see them for about $200 to $300 a tube.  I got 4 spare 4-400s here.  My GK500 uses one, My T3 uses one and my Big transmitter uses 2.  The real trouble with the 4-400 is that not one of them seems to have exactly the same output as another. Even new out of the box seem a bit different.   

I see more power gain out of the 4-400 then I do the 250.  I have swapped them back and forth. It might be the transmitter itself preffers the 4-400. 

The 4-1000 is going way up price now.  Remember its 2010. NOT 1979 when you last saw 4-1000s at ham fests.  I see them go for hundreds used in the pull range.  New well over $750.   

The 4-400 is a stout tube though.  Its flat out incredible that one of them produces 500 watts Am at 100% mod in the T3.  Thats alot of power for one little tube. I have run 2 of them at 1200 AM.  They do it easy.

C

[KM1H]

I suspect there are geographical differences that determine prices. In the Northeast its been downhill for hi tech since 9/11 which translates to lots of hams in the hurts. The tube merchants decend in force at Nearfest and other decent fests and are often out of there with their buys before the great unwashed have sobered up or even arrived. Ive spoken to many sellers who are there only to get enough money to survive another month or to supplement whatever degrading job they now have. They will often take any lowball offer and there appears to be a constant supply of NIB JAN glass Eimacs in the under the 4-1000A category which have all but disappeared.

You see the final results on Ebay and elsewhere where other areas are willing to pay big bucks since all they have is BCB pulls sources or the closed bases NIB mil surplus has already been scoffed up my the fleamerchants. One tells me that Nearfest is his best by far source of tubes either directly or later purchases. This is in 2009 and not 1979 when BC stuff was everywhere and mil surplus scarce.

Carl
KM1H

[ke7trp]

You guys are flat out lucky Carl.

Clark