Hello
I have a problem with my Ameritron AL-811H, 8 months old. Using 4 pcs
original no-name 811As.
I turned it on tuesday evening and it blew fuse. It was my first time using
it after last weekend's contesting. Still worked nicely on sunday and not
pushing amp too hard. Very nice and relatively cheap amp.
I opened the case of the amp to see anything suspicious. Everything looked
ok. I changed new fuse to amp and turned it on again (safety switch pressed
on).
I saw a flash inside of one of the 811As (tube back right). It arced. I
took tube off and changed new fuse. Now amp had only three pcs of 811As
inside. I turned it on again. New flash inside next tube (tube front right).
Today I took all four tubes out. New fuses again. Turned the amp on. Stays
on, meter lights on, HV normal approximately 1750 V.
I checked grid resistors. Three are 51 ohms, one is broken. Broken resistor
is for right front tube (second arced). Next I put two tubes to the left
side sockets. Tubes which haven't arced. Turned the amp on, stays on, HV
normal 1750 V and if I key the relay grid current shows about 15 mA amd
plate current meter maybe 25-50 mA. Looks normal.
Local supplier will send me some resistors and new set of tubes. Resistors
seems to be well placed for easy change. Instead capacitors which are in
parallel with these grid resistors are close to sockets and not reachable.
One thing which I noticed already first time when I opened the amp was that
there was some very small pieces of metal "clips" (clamps ? / fastener ?)
in the bottom of the case. First clip was cut into two pieces. Later I found
another clip, also cut into two pieces. This clip is black, about 2 mm wide
(about 1/10 inch), maybe 15 mm long (abt 1/2 inches) thin plate, bent to
half-circle, maybe a spring, like a horseshoe shaped. First I didn't have
any idea where those came from, specially because first pair was close to
front panel but yesterday I found that there is similar clips left in the
bottom of tube sockets, close to grid capacitors, maybe holding something in
the sockets. Very hard to see those clearly without dismantling most of the
amplifier parts... Should I worry about these ? No any other more radical
things hanging loose there as far as I am able to see. And I have already
tried amp with two tubes. Anyone else loosing horseshoe shaped clips from
sockets and still running fine ? I guess at least first broken clip has
been lying in the bottom of the amp-case from delivery or very long time,
because it was 10 inches from sockets (close to front panel, inside) and I
haven't moved amp lately.
I am planning to change all the four grid resistors (R19-R22) and place new
matched set of tubes.
What do you think ? Should I check something else ? And how about those
horseshoe clips ?
Any suggestions would be greatly appreciated.
Thanks in advance
Ari oh6mw
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