[TenTec] Hercules II problem

[JohnCrux]

Desperation time.

I repaired my 9420 PSU and reset the four 25 amp rails at  exactly14 v under 
load. I repaired and re-aligned the Omni-V. 
Then I re-assembled the entire station, including the auto-atu. All 
inter-connecting/control cables are original TT.  My added 120 amp commercial 
ground bus wire connections linking everything are rock solid as are the coax 
connections. 

For a few days there was no problem getting 500 watts from the Hercules II on 
any band 10-80m (not tested 160; no antenna at present.) 

That held good for a week or so.  Then a very old problem came back to haunt 
me. The Herc trips out ("fault") at around 150 watts out on 10m and at around 
250 watts out on 12m. Switch off and back on, and all other bands work as 
before. The SWR  remains as before on all meters ( Herc, ATU and external 
SWR/power bridge. It is 1:1 or very close. 

But it does not always trip. Today after having it trip at 150 watts on 10m, a 
little while later it ran perfectly OK on 12m at 400 watts out.  I have also 
had 10m return to normal output from time to time. 
It is unpredictable, except that if it trips on 10 then will probably do so on 
12m. 

OK; I already swapped the 10/12m low pass filter in the Herc. The Omni-V is 
working fine on all bands including 10/12m and gives normal output.

My best guess is that this is maybe a mechanical problem with one or more 
bandswitch relays. The front panel bandswitch is normally set to "auto", but 
even if I manually select 10/12m, it makes no difference, so the switch is 
probably OK.

The Herc manual indicates that it is not just a matter of the relays switching 
in that LPF for 10/12m. Other relay contacts appear to be used to disable 
(short ?) other band filters, perhaps to avoid stray resonances in the unused 
circuits. 

Anyone seen this problem (including my friends at TT service, please !) and is 
there a solution ? If only I could pop the covers off the relays to check the 
contacts .....   Surely someone has seen this ????
Yes, I know it is no longer made, but the Herc is a super amplifier and I have 
made many QSOs with it.  Just need to get 10/12m back in service reliably.
73   John   G3JAG