Protecting the FL2100z against 572b tube flashover

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Protecting the FL2100z against 572b tube flashover

Postby VE7ALQ » Sat Mar 18, 2006 4:42 pm

I was wondering what I could do in advance to protect my Yaesu FL2100z in the event
that one of the 572b tubes decided to flash over. My first concern was the meters
and I have a pile of 1N5408 diodes on order from http://www.mouser.com with the
intent of placing two across each meter as a shunt. This should protect my scarce
meters from mortal damage. Anything else I should consider upgrading?

73's de VE7ALQ
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Postby VE7ALQ » Sun Mar 19, 2006 3:47 am

Hi! I have been poring over the FL2100z circuit diagram, and figure that if there
is a flashover, then R7 and/or R8 will be toast, depending on which tube arced.
These resistors go in series with each grid and are currently 33 ohms 3 watts each.
I was wondering aboutreplacing them with 33 ohm 10 watts each or higher. The
idea is to set it up such that a flashover will cause zero damage except to the fuse.
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Parasitic Chokes

Postby W4CLM » Sun Mar 19, 2006 5:21 am

Make sure your parasitic chokes are in good condition too!
Most important they not have any cracks in them or arcing going on or the amplifier can run away on you and or destroy a band switch too which puts you in a world of hurt.
Regards
Carol
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Re: Parasitic Chokes

Postby VE7ALQ » Mon Mar 20, 2006 6:33 pm

W4CLM wrote:Make sure your parasitic chokes are in good condition too!
Most important they not have any cracks in them or arcing going on or the amplifier can run away on you and or destroy a band switch too which puts you in a world of hurt.
Regards
Carol


I already have the mod for the parasitic chokes, complete with silver solder and
heftily rated resistors. I haven't gotten around to installing them yet.

I have ordered the 1N5408 silicon diodes from http://www.mouser.com to go back
to back across the two FL2100z meters, and also ordered two 30 ohm 12 watt
oxide thick film resistors from http://www/digikey.ca as beefed up replacements for
R7 and R8. I am expecting these items RSN (Real Soon Now) and then when I can
get a friend over here to open up the linear, he will do the necessary soldering.

I am not overly concerned about the parasitic chokes, as the resistors absorb
significant power only at the highest frequencies. I use the linear on 40 meters
and 30 meters exclusively (here in Canada QRO on 30 meters is legal) and in
any case, going into the 52 ohm dummy load, there are no problems with
stability. Even on 10 meters, the plate current rises smoothly and symmetrically
on both sides of the PLATE dip.

Do tell me about the bandswitch. I can get a replacement for a (few) hundred
dollars from http://www.multi-tech-industries.com I would prefer not to damage
the bandswitch that is in there for starters...
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amp parts

Postby W4CLM » Tue Mar 21, 2006 4:11 am

Give us the direct link for those chokes you bought? I'd like to see those. For some reason the digikey link you posted is not working for me, the page did not come up.

Just be careful with the band switch. If they arc over you can
literally burn the contacts right off the switch and that band won't work

Carol
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Postby VE7ALQ » Tue Mar 21, 2006 2:37 pm

Q) Where to get the super parasitic suppressors
A) The kit is put out by Mr. Richard L. Measures
mailto:measures@vc.net
and he charges USD$16.75 for enough parts to
stabilize two 572b tubes, like in FL2100/b/z He
even includes silver solder, and flux for solder.
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Location: Vancouver, British Columbia, Canada

Re: amp parts

Postby VE7ALQ » Tue Mar 21, 2006 2:43 pm

W4CLM wrote:Give us the direct link for those chokes you bought? I'd like to see those. For some reason the digikey link you posted is not working for me, the page did not come up.

Just be careful with the band switch. If they arc over you can
literally burn the contacts right off the switch and that band won't work

Carol


Typo on my part, the digikey link should be

http://www.digikey.ca (for Canada)
http://www.digikey.com (for USA)

I just checked and both links are working.
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Postby btbcopperclad1 » Tue Mar 21, 2006 8:52 pm

I don't really think a bandswitch from multi-tech will work in the yaesu amp.I had to move the band(rf?) coil with the taps to make room for a two wafer switch from them in my Swan Mark 1 amp. I've seen photos where some have even stood the coil on end to make room for it in the Swan. Since these multi-tech switches are so large, I doubt if there's room at all for one with 5 wafers in the 2100 amps. But I don't have one in front of me to inspect, or find out if there's a way to move things around like in my cabinet. By memory, the photos I've seen of the 2100's, they're a little cramped for space.
If someone were brave enough, and not caring about original looks, the whole shebang could be mounted in a larger cabinet with room for one of the beefiest switches around.
I especially like the spacing between the contacts with the large diameter multi-tech. Less chance of arc-overs between them.This old 40? yr old amp still going good after the replacement last yr.

Ron KD8AMT SKCC #259
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parasitic suppressors

Postby W4CLM » Tue Mar 21, 2006 10:11 pm

Thanks for the update on the parasitic chokes.
What exactly does his kit consist of ??

Carol
W4CLM


Q) Where to get the super parasitic suppressors
A) The kit is put out by Mr. Richard L. Measures
mailto:measures@vc.net
and he charges USD$16.75 for enough parts to
stabilize two 572b tubes, like in FL2100/b/z He
even includes silver solder, and flux for solder.
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Re: parasitic suppressors

Postby VE7ALQ » Wed Mar 22, 2006 10:46 am

W4CLM wrote:Thanks for the update on the parasitic chokes.
What exactly does his kit consist of ??

This kit consists of higher power rating resistors for plate
parasitic suppressors. He says to install two suppressors
in series for each plate lead to the 572b tubes.

Q) Where to get the super parasitic suppressors
A) The kit is put out by Mr. Richard L. Measures
mailto:measures@vc.net
and he charges USD$16.75 for enough parts to
stabilize two 572b tubes, like in FL2100/b/z He
even includes silver solder, and flux for solder.


The kit contains four 100 ohm three watt resistors,
each of which is to have six turns of wire wound
around the outside. Two of these three watt
parasitic suppressors are to go in series with the
plate lead for each 572b tube.
In a world without walls and fences, who needs windows and gates?
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Location: Vancouver, British Columbia, Canada

Re: parasitic suppressors

Postby g0fvt » Wed Nov 08, 2006 6:24 pm

Hi All, I think it is fair to say that a great deal of controversy surrounds Richard Measures parasitic stoppers, his use loops of nichrome wire in an attempt to "de Q" the PA. Some people seem to swear by them, but the controversy continues...


Regards David G0FVT
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Postby VK3YM » Fri Jun 01, 2007 8:22 am

Please take note...do not under any circumstances increase the wattage of the two resistors R7 & R8 (33 ohms 3 watts) because that wattage is important.
I have repaired many Yaesu amps over the years where people have had an arc over and these resistors have burnt out, so they have increased the wattage to 5 or even 10 watts in some cases. In all cases where these resistors have had their wattage increased the next time they had an arc over the resistors survived BUT THE TUBES BLEW.
Even those that increased them to 5w blew the tubes and not the resistors due to the fact the the time it takes the resistors to burn far exceeds the time it takes the tubes to blow.
The resistors act like fuses in this circuit.
Is it not better to spend a dollar replacing the resistors than $100+ to replace the tubes.
Do not act rashly and increase the wattage of R7 & R8. Keep them acting as a fuse.
Regards Rick VK3YM
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