Sb-220 power output at about half..

[John]

I replaced the parasitic chokes, tightened all the paths of the output tank.
Removed the chokes and capacitors from grid and made a solid short ground
from all the pins other than the heaters of course. Cleaned the band switch
and powered the amp back up. I am now getting 975 watts out with 100 watt
drive on 10 meters. I can live with this especially with the 3-400z tubes.
Thanks for all you guys help, I was just lost for ideas and you have all
been a great help. If I can ever help I will do my best to return the favor.

John Godfrey--- KE5NZY
Subject: Re: Sb-220 power output at about half..

Bob
We haven't heard back from John lately as to if he's solved his problem or
not, but if you reread his original posting, his 3-400's tested fine in
another amp.
I can categorically state that 3-400's (in good condition of course) will
put out at least 1200 watts on 80,40,20 meters in an SB-220 with 100 watts
drive. My amp would do 1kw out on 15 and about 900 watts on 10 meters with
the 3-400s.
The considered opinion of those who responded to this post was that it
appears that John has a tube that isn't conducting for one reason or
another.
Paul K5RT

On Behalf Of R Johnson
Sent: Monday, May 28, 2007 9:00 PM
Subject: Re: Sb-220 power output at about half..

John:
I assume that the 3-400 tubes you refer to are really 3-500's !!!
All the SB-220'S I've used, repaired, or owned used a pair of 3-500's !!!
If not a TYPO and you really 3-400's in the amp, that's the problem.
A 3-400 has about half the Mu (Gain) of a 3-500 which may be your problem.
If it was a TYPO then you still have a problem, if not you need to spend the
$$$ for a set of 3-500's !!!
Hope I'm not the "bearer of bad tidings".
73 es GL
Bob, K1VU


At 06:33 PM 5/24/2007, John Godfrey wrote:
>I do hope you guys can help me. I have been in the process of restoring
>a heath kit SB-220. I replaced all the filter caps - diodes in the 
>doubler etc. all with new parts including a new air variable for the 
>plate tuning. All was well and output was plenty acceptable on all 
>bands. Then output just went to zero after a power-on condition. Meaning it
was fine when
>turned off. Then after much investigation I found that the little 
>bolt/nut that holds the output tuning 10/15 meter coil to the plate 
>tuning capacitor was loose. After tightening and re-power up and tune. 
>I just get half the output as before. Both tube filaments light bright and
voltage to the pins on
>the filaments is 4.9 volts ac on my meter. Cleaned the sockets and pins 
>in case of any resistance but like I said voltage seems to be correct. 
>Zener diode seems to deliver exactly 5 volts DC through the center tap 
>of the filament transformer to the tubes at transmit and the 117 volts 
>dc at receive mode. Tubes do produce gain. With 40 watts in you get 
>about 150 out. 100 watts in gives 400 watts out. Again about half what 
>I was getting. Both tubes EIMAC 3-400z l believe them to be full output 
>because I tested them in another amp. Tested the high voltage on SSB 
>mode and I have about 3010 volts DC. Input SWR is acceptable and I am 
>driving it with tubes as well instead of transistors

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