SB-102 mic level

[Glen Zook]

Check the resistors from the 6146 cathodes to ground.  There are 3 resistors for each tube and these should read right at 10 ohms each.  These resistors form the meter shunt for the "plate" reading (actually reads cathode current).  

The resistors very often change from the original value and then the "plate" meter will not read correctly.  Replace the 1/2 watt resistors with 1% or 5% 1 watt resistors (new resistors are much smaller than the originals).  These are really cheap from Mouser (http://www.mouser.com ).  The 6 resistors in parallel form an effective 1.6667 ohm resistor.

Glen, K9STH

Website:  http://k9sth.com


--- On Wed, 2/25/09, Emil Dular <wd4scz at AOL.COM> wrote:

I have been running some 80 meter phone lately and the amount of mic gain needed to peak the ALC has slowly gone up. 80 always did take more than the higher bands. I swapped microphones from an HM-12, to EV-638 to a D-104 and negligble difference. Swapped out the 6EA8 at V1 for a 6CQ8 which was always the old trick for low mic drive and no difference.
 
In tune, you can turn mic level to about 3 o'clock and the plate current will top out at 210 ma. 
 
Anyone else been down this road that has a list of suspects or likely places to start troubleshooting?


      

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