I have several very good 4-400 A tubes and have replaced a pair of bad 3-500Z tubes with a pair of 4-400A tubes in a Heath SB 220 amp. I have noticed much lower resting current being drawn when keyed
Thats a perfectly normal result as the 4-400's have less gain in GG. Im assuming the grids are also now directly grounded. Reduce the bias a bit and shoot for about 200ma idle for decent IMD. Replace
One possible issue with the 4-400A is that it has a metal shield around the glass seals on the base. The cross flow cooling used in some amplifiers does not work well and an additional fan may be nee
The SB-220 cools the filament pins. Carl KM1H _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps
Pin cooling worked just fine on the Johnson KW using a little fan similar to the SB-200. No chimneys either, just a big fan blowing air on the glass.. They did it again in the Invader 2000 and again
Well, it does blow some air on the socket but not up thru the socket to the seals. In some 4-400A tubes the pins are connected by smaller conductors from the socket and do not themselves conduct a lo
1500T is the only one I am missing in my collection. I think if you really push the 4-400A to its dissipation limits it could be a problem. Back then the max power output at best in a continuous mode
Since the 4-400A's run about 200W less output with 100W drive in a SB-220 they are far from being pushed. The TBolt and Invader were also 2000W PEP SSB and 1000W input CW amps. Many ran them on CW in
I have several very good 4-400 A tubes and have replaced a pair of bad 3-500Z tubes with a pair of 4-400A tubes in a Heath SB 220 amp. I have noticed much lower resting current being drawn when keyed
4-400s will work in an SB 200 , but you cant slide it back in its case. ( tube checker only !!! HV EXPOSED !! ) Don W4DNR _______________________________________________ Amps mailing list Amps@contes
A 4-400 works fine if you use a heat radiator that doesnt extend above the anode cap. Buy them from Ameritron. Carl KM1H _______________________________________________ Amps mailing list Amps@contest
How are you going to use an SB-200 as a "tube checker"? The 572B tubes used in the SB-200 are 4-pin "medium" and the 4-400A and 3-500Z tubes use a 5-pin "large"! Then there is problem of the filame
Fingers slipped... meant SB-220 instead of SB-200. ( but you alreay knew that ... right ?? ) Don W4DNR _______________________________________________ Amps mailing list Amps@contesting.com http://lis