SB-201/200 no output on any band

[RAY FRIESS]

One of the most common problems is the antenna relay.  Check the contacts on that and clean them.
A friend of mine had an sb-200 that showed no output.  He went through all the same rigamarole you did
and still nothing.   When he finally check the antenna relay, he found a bad contact on it.  Not making
contact when it closed.  He replaced the relay and everything was fine.
 
I had a similar problem in mine.  I was not receiving anything on my receiver when it the receive mode.
I cleaned the antenna relay contacts in the amplifier and everything came to life.



> Date: Sat, 18 Oct 2008 18:59:59 -0700> From: kgordon2006 at VERIZON.NET> Subject: Re: SB-201/200 no output on any band> To: HEATH at LISTS.TEMPE.GOV> > On 18 Oct 2008 at 17:40, Tom Chesek wrote:> > > I have an SB-201 which was converted to an SB-200 equivalent with a> > complete bandswitch swapout. I cannot tell you if it ever worked after> > the swap. This amp has the Harbach power supply mod and antenna relay> > including the resistor change that comes with the relay kit. The tubes> > are a pair of Cetrons which are soft but verified as working in my> > other SB-200 amp. Using the Taylor tubes from my SB-200 make no> > difference at all. There is no output on any band. I've cleaned the> > bandswitch with Deoxit, verified that the wafers are aligned with each> > other corectly, and verified that each contact has good wiping action.> > I have verified the -2vdc bias by measuring with a DVM and get a> > reading of -1.78vdc. The filament voltage measured at the tube side of> > the bifilar choke measures 6.72vac. The HV reads just under 2400vdc on> > the built in meter. The idling plate current reads about 98ma. PC1 &> > PC2 both have NOS carbon resistors. R21 and R22 are new also.> > > > I've tried drive on each band from 30 watts to 100 watts with no> > output measured on the amps' meter or on the watt meter inline to the> > 50 ohm antenna load. If I drive it with higher power, such as 100> > watts, the tubes will start to "cherry up" in color if I keep the key> > down for 30 seconds or so. It almost appears to me that no rf is> > passing beyond C24 but I have swapped that cap with the one in my> > working SB-200. All screws have been tightened to be sure the ground> > paths are intact. > > > > Nothing is going up in smoke so where is my output? This is driving me> > nuts!> > > > 73 and Tnx,> > > > Tom K3TVC> > > > ps: for what it is worth I know that at one point this amp was> > modified for 11 meter use and then changed to the current SB-200> > configuration.> > Hmmmm....most odd.> > OK. Let's start at square one:> > 1) Assuming that your meter circuits are OK, when you drive it and the > tubes start to "cherry up", what does your plate current read?> > 2) Under the same conditions (drive), what does your grid current > read?> > 3) Under those conditions, what does your +HV read?> > 4) Have you verified the center frequencies of the input tuned circuits > with a grid-dip meter or some other means? Or you could check the > SWR between the driver and the amp. If it is above 2:1, there may be a > problem.> > 5) Have you checked RFC-3 1.1 mH (under the chassis) to see if the > jerk who modified it for 11 meters burnt it shorted? That RFC is to > prevent +HV from appearing on the antenna if C-24 shorts out. You > might try lifting the ground end to see if you have output then.> > 6) Have you CAREFULLY checked the plate coil L-6 and L-7 for > purposely shorted turns? Under the coils, perhaps?> > (Actually, the inductance of RFCs 1, 2, and 3 are really too low for > proper RF filtering at 80 and even 40 meters, and for maximum output > on those band, really need to be replaced with RFCs of higher > inductance.)> > 7) Have capacitors C-14 and C-15 been changed from their original > value of 200 pfd? (BTW, this value is pretty critical: it makes the grid > circuit series-resonant to ground, tuning the inductance of the grid and > connecting wires. Collins' 30L1 uses a similar method to properly > ground the grids. If you want to change this for what you think is a > more "reasonably high" value, you have to do some OTHER things to > make that work properly).> > 8) Are you sure that RFC-1 is OK? If that was burnt shorted, your RF > could be dumped into the power supply, but there would probably be > other noticeable (!) effects.> > 9) Is C-28 your dual-section 437 pfd/section output tuning capacitor > shorted? Have you checked to make sure it really IS 437 pfd/section?> > Let us know what you find out after following as many of these > suggestions as you feel worthwhile.> > BTW, for those interested, this site is possibly the best I have found for > SB-200 mods.> > http://www.xs4all.nl/~pa0fri/Lineairs/SB200/sb200eng.htm> > Ken Gordon W7EKB> > -----------------------------------------------------------> Products bought, sold or traded here is the responsibility of the> parties involved. This list and the City of Tempe are not responsible> for losses or misrepresentations of any kind. Buyer beware!> > -----------------------------------------------------------> This list is a public service of the City of Tempe, Arizona> -----------------------------------------------------------> > Subscription control - http://www.tempe.gov/lists/control.aspx?list=HEATH> To post - HEATH at LISTS.TEMPE.GOV> Archives - http://lists.tempe.gov/archives/HEATH.html
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