[Boatanchors] SB-220 in AM service

[jeremy-ca]

There are many 2 x 3-500Z linears being used on AM, especially within the 
past few years as AM interest has really taken off.

Ive used a NCL-2000 in the past and it works fine at 400W out as well as 
looks good on a monitor.

My primary station linear these days is a LK-500ZC (also with the PD xfmr) 
that Ive had since new and with original tubes. Ive used it with the TS-940 
on AM and have recently been playing around with a DX-35 driver with audio 
mods. The controlled carrier gives the signal superb punch according to 
reports.

All my AM is tuned with a home brew modulation monitor made up from an 
antique DuMont 5" scope.

When I want to get serious I go to another section of the basement and fire 
off the Viking I and PP 250TH's with 810 modulators and a modified Bogen amp 
as the driver. That currently lives on 20M as I dont like changing coils. A 
new bandswitching amp is under construction.

BTW, Ive always considered the L4B to have been designed by two companies. 
Superb RF deck and a PS about as wimpy as the SB-220 and less cooling. Ive 
built many for 6M with HD supplies and they loaf at 1500W on CW/SSB.

Carl
KM1H


----- Original Message ----- 
From: "rbethman" <rbethman at comcast.net>
To: "Boatanchors Mail List" <boatanchors at mailman.qth.net>
Cc: <ke7kk at earthlink.net>
Sent: Wednesday, March 12, 2008 7:15 PM
Subject: Re: [Boatanchors] SB-220 in AM service


> Looks like we are finding the SAME results!
>
> The only thing different in the LK-500ZB would be the PW Dahl XFMR in the 
> power supply.  I've NEVER smelled anything from the power supply.
>
> GO FOR IT!
>
> Bob - N0DGN
>
> Jim Wiley wrote:
>> I use an old Drake L-4B in AM service, and have used it for more than 20 
>> years, with no failures - and the same set of tubes.  I usually set it 
>> for about 350 watts unmodulated  carrier output (the max allowable is 375 
>> watts, which which with modulation equals 1500 watts PEP).  I tend to be 
>> long winded, but the L-4B is a continuous duty rated amp, and was built 
>> properly.  It has a pair of 3-500Z tubes, a squirrel cage blower, 
>> chimneys on the tubes, tube sockets in a pressurized plenum, plus a 
>> separate power supply that can really take some guff.
>> The SB-220 should be OK at  250 watts  or so out, as long as you limit 
>> continuous talk time to 10 minutes or less , with no more than a 50% 
>> overall duty cycle. Keep your eye (or nose?) on the transformer - if it 
>> starts to smell hot, back off on the talk time.  For a test, I ran the 
>> L-4B on 20 meters at 1000 watts output  for a hour into a dummy load - 
>> other than the power supply starting to smell a bit warm,  and the tubes 
>> getting sort of orange, no problems.
>>
>>
>> Before the rules for AM changed, I used to run it at about 400 watts 
>> carrier output, mostly on 10 meters AM, also with no problems.  However, 
>> I did manage to unsolder the connections inside an external low-pass 
>> filter doing that.
>> Good luck.  Maybe I will hear you on  the band once I get my 10-meter 
>> antenna back up.
>>
>> - Jim, KL7CC
>
> -- 
> Bob Bethman/NØDGN/BC-610/Northern Radio SP-600 Manassas, VA - MultiBand 
> Dipoles
>
> _______________________________________________
>