OK Brian,
Yes well 1/4" should be far enough at under 5KV, but who knows what sort of
spikes happen in there. There might be a cold solder joint at the choke
that is FURRING UP with ozone and once ionization occurs BWAMMO. Look close
at the HV bypass cap and make sure it looks good. Check all wiring around
it.
The HANK 8K has a problem right there! The Bypass was too underrated and
had to be increased V wise.
The small cap on the 25W resistor is only rated at 16V, that's the only
reason I would worry about it.
The Diode there from B- to ground is to hold the B- to ground and I suspect
it WOULDN'T be shorted but blown open.
Your Bias diode and all components in the "Head" are probably OK.
D105? I'm still a little groggy here. Still 2 hours before normal wake up,
all sorts of dips on the phone this AM, this and that. Now can't get back
to sleep. There might be some schematic differences between amps.
OK so.
I agree with Tom the grid meter is acting like a low current version of the
plate meter.
Next:
If you can get yourself some thin Teflon sheet. You could put a square on
either side of that plate choke. HENRY used this sheet for making caps for
heating amps and VHF and UHF stuff. A call (better yet email) to TED might
be able to get you a couple squares of it after telling him your problem.
A nice 2" circle under each end would stop the arc issue and look good too.
Anyway, R108 is the precision resistor that grid current is measured across
in my amps. It is point 51 ohm (.51) and only 2 watts.
That would allow the grid meter to be unshunted. Its pretty small sized
when you've already blown up a 25 Watter! But the fact that the cathode
fuse took the hit I'd doubt the .51 went away... The meter would have taken
a hit too.
FYI:
I had a Hank 4K-Ultra here up until a few months ago. It had a questionable
output relay until I replaced it.
When the relay wouldn't make connection the power output would go to zero,
the plate current would over current and grid would go to zero current.
Fortunately it didn't go the other way. Well when it would over current,
the voltage in the plate metering circuit would go wild and there was a 100
V zener in the PS that was used to provide the ALC reference voltage.
Every time it would click out the zener would BLOW and then the ALC would be
pinned to zero and no drive would go to the amp until removing the ALC
cable.
The ZENER was not in the best place and usually took an hour to replace. I
kept a box full of them. HAHAHA
Once repairing the relay all was right once again.
The Hanks are pretty good amps, they do a few things very wackerized
however. Like stepping down 5000v to make 100v and things like that.
Tom was a little more straight forward when he designed the Ameritron amps.
I have to give him some serious credit there.
Keep me informed as to progress.
BOB DD
PS OH yeah ALC guys. I have been a vocal non-supporter of amp ALC for 30
plus years. Just adjust driver output to max grid current and have at it.
It always seemed to work good.
I ran into some issues with blowing up stuff while using the IC-781 before
somebody out there put a scope on the output and figured out there was an
ALC overshoot in the rigs. The Signal One CX-11 (240 watt ones especially)
would give you almost 500 Watts of drive when it felt like it.
Well....
To correct this overshoot issue now ICOM in the IC-7800 made the ALC
internally in the rig very aggressive. This was limiting my average output
from my amp to about 250 watts when setting the output to max grid current.
Measured BIRD 2500 slug no peak reading on.
By hooking up the ALC line and controlling the max grid current I can swing
the wattmeter to between 500 and 1000 watts. Instead of having 60 watts
only to drive my 8877 I can turn the rig up to 125 and the weaker components
in my voice have more zoom behind them.
That's why the meter appears to swing 250-750 watts higher. Peak reading
only appears to be slightly higher.
SO that's that story.
I think I've mentioned this once before. Was probably on the 7800 reflector
before I told them all to take a hike... They couldn't understand what and
the world I was talking about since it didn't include a PW-1, or a roofing
filter.
-----Original Message-----
From: A.R.S. - W5AMI [mailto:ars.w5ami@gmail.com]
Sent: Wednesday, November 01, 2006 8:21 AM
To: Robert B. Bonner
Subject: Re: [Amps] Henry 3K trouble
Thanks Bob. I will look at those too. I checked the cathode fuse and
it appears to have made it okay. I don't know how fast R106 can
react, but maybe it blew before taking too much out. D105 is actually
tied physically from one lug (as is c105) of R106 to ground. That is
another one on my list to check.
Wish I could move the plate choke on this thing! Top and bottom are
much too close to ground for my comfort. The solder lug at the bottom
where the plate bypass and HV are soldered is probably less than a
1/4" from the chassis!
This short happened once before but only took out R106. Everything
was fine once I replaced it. Shorted in the same spot and as soon as
I turned on the amp. There are now TWO tiny craters, side by side on
the chassis.
Thanks for all the suggestions!
73
Brian
On 11/1/06, Robert B. Bonner <rbonner@qro.com> wrote:
> D107 is 100V 3AMP
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of A.R.S. - W5AMI
> Sent: Wednesday, November 01, 2006 5:51 AM
> To: amps@contesting.com
> Subject: [Amps] Henry 3K trouble
>
> Hello,
>
> I have a Henry 3K Classic (8877) which developed a problem a couple days
> ago.
>
> I'm hoping some long time Henry types (or anyone else) might steer me
> in the right direction.
>
> First, there was an arc over between the chassis and the bottom of the
> plate choke where the HV connects. This caused R106 in the HV supply
> to blow. I had spare 25 ohm 25 watt wire wounds and replaced R106.
>
> The HV came back after replacing the resistor, however now my grid
> current goes way high. Even keying the amp with no audio on SSB shows
> about 15 to 20 mils of grid current.
>
> When I applied some excitation (maybe 5-10 watts), it did indicate
> output and plate current, however not knowing if the meter was reading
> correct or not, I did not take much time to measure actual output for
> fear of losing the grid. With 20 to 40 watts of drive, the grid
> reading nearly goes off scale with no effect turning the load cap.
> SWR is 1:1, so no problem there.
>
> I swapped the tube with a spare known to be good and the results were the
> same.
>
> At this point, my ideas on the problem are guesswork. I suspect the
> bias diode for the cathode, or the metering circuit for the grid
> meter. Oddly, the schematic shows only one diode D1 for the bias,
> however in my amp, there are clearly two in series that appear to be
> OEM, so that in itself throws me off. I plan to take the diodes out
> of circuit today and check them for lack of any other ideas. BTW, are
> these Zeners? The manual just calls it "bias diode".
>
> Also, can anyone tell me what D105 is for? This is a small metal can
> diode hooked directly to R106 on the HV- lead. When I replaced R106,
> I failed to check this diode, and since it is physically attached to
> R106 parallel to ground, I suspect it could have been damaged when
> R106 blew up.
>
> As you can probably tell, I'm sort of pulling at straws right now, so
> forgive the ramblings.
>
> I would really appreciate hearing from any experienced 3K folks that
> may shed some light on what I need to be looking at. In the meantime,
> I'm going to find some corona dope and patch up the point of arcing so
> that doesn't happen again.
>
> Thanks,
> Brian / w5ami
>
>
>
>
> --
> "There is nothing more uncommon than common sense." -- Frank Lloyd Wright
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>
>
>
>
--
"There is nothing more uncommon than common sense." -- Frank Lloyd Wright
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