low SB-102 xmit audio

[Bob Burns]

Hi Sandy
 
1. There have been several documented instances on this forum of the  
balanced modulator balance pot failing on both the SB101 and 102 - not a very  
good quality item.
 
2. I noted on my SB101 that the screen voltage of the pentode mic preamp  
was significantly higher than the anode voltage and the gain seemed low so I  
changed the screen resistor to 1Meg and the anode resistor to 220K to 
correct  the voltages - changing the valve made little difference. This also 
appeared to  increase both the gain and dynamic range. Not suggesting that you 
make these  changes but you might like to check the voltages on that valve.
 
3. Can you measure the input level into the mic socket that is required to  
got the correct output or if that is not possible what output you do get 
for a  known input level. At the same time can you measure the AF level at the 
preamp  anode and that going into the balanced modulator for a given output 
on say  3.5MHz. I can compare those to my SB101.
 
4. Can you measure the RF level at the input of the balanced  modulator?
 
5. Check that the ALC is working correctly on SSB and not holding down the  
gain of the IF amplifier on Tx.
 
6. Check all carbon composition resistors for value with the SB102 switched 
 off and cold and the PSU disconnected. After all these years they will 
probably  be 30% or more high in value.
 
I have a completely refurbished SB101 that I can use for comparative  
measurements and there are several other forum members who can do the  same.
 
I have not seen your earlier posts because 'something' was stopping my  
Yahoo forum emails from arriving in my AOL inbox for about a month and this was 
 only corrected yesterday after I stirred things up somewhat. I lost 165 
emails  during that period according to Yahoo.
 
73

Bob 

G3OOU
G-QRP  6907
_www.g3oou.co.uk_ (http://www.g3oou.co.uk/) 

-----------------------------------------------------------
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