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[Amps] Replacing padder caps on an Alpha 77DX/SX

Subject: [Amps] Replacing padder caps on an Alpha 77DX/SX
From: "Gary Smith" <>
Date: Sun, 17 Mar 2019 16:31:27 -0400
List-post: <>

I have been having drifting issues on 160 
only, not 80M or above, with my late model 
SX. I was thinking the 160 toroid 
transformers were overheating but the tape 
is not brown and I've been assured the bit 
of bubbling at the ends is from normal 
warming, not excessive heating.

160M & 80M transformers L7 & L5 

Upper band transformer L6

I tested the plate caps with my LCR and 
all tested as WNL. I cannot do a leak down 
test with this LCR meter.

As there's no sign of overheating I can 
find anywhere and I haven't been beating 
on the amp, I'm assuming the drift is from 
the 160M padder caps breaking down over 
the years and they should be replaced.

Alpha could have made them easier to 
access, they're right underneath the band 
switch, screwed to the front RF panel and 
the front panel of the RF deck is not 
removable (this would have made access a 
cinch). The only access to the front area 
of the deck is from above and from the 
left side. 

I did not remove the side panel at this 
time, I'll do that when I order & get the 
padders. Here's the view of the padders 
from above. 

100pF band position A

1000pF band position B

I understand the early models had one 500 
pF padder and later models like this one 
have two 1000 pF padders in parallel.

The two paralleled 1000pF caps for 
band-switch position B are easily 
accessible from the side, the two 
paralleled 100 padders for Band-switch A 
are located deep where I can't get a 
screwdriver in to undo them.

For anyone who has replaced these on one 
of these amps, have you any suggestions of 
how to best get to the 100 pF caps and 
remove/replace them with a minimum of 

Also, I'll probably get the HT58 padders 
from RF Parts, any other worthy places I 
might also check into?

Thanks & 73,

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