[Amps] L4PS Xfmr buzz

[Jim Thomson]

Date: Mon, 15 Feb 2010 09:41:56 -0800
From: Michael Tope <W4EF at dellroy.com>
Subject: [Amps] L-4PS Transformer Buzz

I just installed the Harbach PM-400 in the L-4PS power supply for one of 
my Drake L-7 amps after I popped a rectifier diode in the old bridge:

http://www.harbachelectronics.com/main/page_products_drake_l4l4bl7.html

Electrically, the amp and power supply appear to work perfectly with the 
Harbach board. Plate voltage and RF output are as expected. There is one 
problem, however. Last night about 20 minutes after I fired up the power 
supply I noticed a loud 60 Hz buzz coming from the supply.

## whoa, stop.   did it buzz  b4 u added the harbach mod ??


 Pressing on 
the sides of the cabinet or changing the physical orientation of the 
supply didn't seem to help. When I switch to the low-voltage setting on 
the L-7, the buzz stops. Also if I let the supply cool off the buzz 
stops for a while and then returns after the supply warms up. Looking at 
the supply in the dark, I saw no evidence of sparking. Additionally, the 
amplitude of the buzz seems to be totally unaffected when I go from 
standby to full RF output power.

Any ideas on what might be causing this problem?

## try disconnecting the HV  AC   sec leads [ both of em]  from the 
FWD.. tape em.. then turn the supply back on, then toggle  between
SSB / CW position.   I think Carl is right, the xfmr is trying to tell u
something. 

##  If it still buzz's  with sec disconnected, then at least you have isolated
the harbach mod / FWD  and  8 x caps, etc.  It may be mech vibration,
how loud ..is 'loud'  ??   Are you sure it's not metal work, 2 x bleeders
[ toss the bleeder's, then ur cab will run stone cold, and B+  will NOT
rise at all].. or mounting posts for bleeders , or something below
chassis, either breaker etc ?  

##  this buzzing is one problem I have never heard of in a L4-PS,
and  I have  3 of em .

later.... Jim  VE7RF


Thanks,

Mike W4EF......................