Sb-220 power output at about half..

[John]

THANKS A BILLION GUYS!
I have tried to take everyone's thoughts and put them with what I have tried
or am able to try. At this point I believe the one tube is not conducting as
many have said. Even though it works fine in another amp. I have ordered 2
two 2 watt Allen Bradley 33 ohm carbon composition resistors and I am going
to redo the parasitic chokes. After much good advice from you guys I
inspected everything very close and the 33 ohm resister on one of the chokes
has been really hot. After reading my own statements about when and what was
taking place when the power left me. I have in my head the while putting the
outer cover back on, I must have rattled the cage just enough to crack that
resistor which likely got to hot when the last tube failed which was in that
same stop where the burnt looking resistor is at. I cannot see a crack in
it, but it makes sense to me at this point. There is this and also other
things some of you have suggested that I have not fully explored and I WILL
BE SURE and let everyone know what the final fix is. 

PS> PAUL is correct in that this amp had no problem doing 11 to 14
PS> hundred watts out with 3-400 tubes before this failure. Thanks so 
PS> much for everyone help.. Stay tuned for the rest of the story (-:..

KE5NZY
John Godfrey

-----Original Message-----
From: Heathkit Owners and Collectors List [mailto:HEATH at LISTSERV.TEMPE.GOV]
On Behalf Of Paul Blumhardt
Sent: Tuesday, May 29, 2007 5:28 AM

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

-----Original Message-----
From: Heathkit Owners and Collectors List [mailto:HEATH at LISTSERV.TEMPE.GOV]
On Behalf Of R Johnson
Sent: Monday, May 28, 2007 9:00 PM

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 outputjust>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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