Gary - if the drift is only on 160 - for hell of it -add another 2000 pfd or so
plate bypass at cold end of the plate RFC - I had that happen in another amp
on 160 - allegedly an "unauthorized" factory change had put a pair of 1000 pfd
Z5U
in instead of X7R. Those lousy Z5U were actually dropping to about 500 pfd at
80 C .
(yes I bought into the tale that that amp typically had bad padders and I
upgraded them
all first - did not change a thing !!!! thats when I started looking elsewhere
-BINGO. )
Hank K7HP
Message: 3
Date: Sun, 17 Mar 2019 16:31:27 -0400
From: "Gary Smith" < Gary@ka1j.com >
To: amps@contesting.com
Subject: [Amps] Replacing padder caps on an Alpha 77DX/SX
Message-ID: < 5C8EAE9F.20487.19DF0C6D@Gary.ka1j.com >
Content-Type: text/plain; charset=US-ASCII
Folks,
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.
----- On Mar 18, 2019, at 10:00 AM, <amps-request@contesting.com> wrote:
| Today's Topics:
| 1. Re: 3CX800A7 low grid current version? (Steve London)
| 2. Re: QRO 2500 MARK lll (John Bodine)
| 3. Replacing padder caps on an Alpha 77DX/SX (Gary Smith)
| 4. Re: Replacing padder caps on an Alpha 77DX/SX (Gary Smith)
| 5. Re: Replacing padder caps on an Alpha 77DX/SX (Jim)
| 6. Re: Question about grid current in 4CX or 3CX (Peter Voelpel)
| ----------------------------------------------------------------------
| Message: 1
| Date: Sun, 17 Mar 2019 14:18:38 -0600
| From: Steve London <n2icarrl@gmail.com>
| To: amps@contesting.com
| Subject: Re: [Amps] 3CX800A7 low grid current version?
| Message-ID: <121ccba3-78d1-e23b-6122-24af452cd1bf@arrl.net>
| Content-Type: text/plain; charset=utf-8; format=flowed
| This sounds like the same tube that Alpha was selling a few years ago. It was
| also touted as "low grid current". The specs are exactly the same as the
| standard tube, as far as I could tell. Alpha specifically did not recommend
| using it in the Alpha 87.
| The designation on the Alpha tube is:
| VTU-3CX800A7LG "Alpha Tubes" 1450
| BTW, in my converted 76PA, I do NOT find the pair of 3CX800A7LG's particularly
| easy to drive with the Alpha broadband input transformer. It typically takes
| 60-70 watts for 1500 watts output, depending on the band.
| 73,
| Steve, N2IC
| On 03/16/2019 02:33 PM, Floyd Sense wrote:
| > I see that RF Parts carries a "low grid current version" of the 3CX800A7
tube,
| > but haven't been able to locate any technical info on the tube.? I assume
that
| > this version of the tube might result in lower grid current than the
standard
| > version, at a given power level with all other things being equal.? Can
someone
| > verify that and are there any other considerations when using such tubes in
my
| > Alpha 89 amp?
| > 73, K8AC
| > _______________________________________________
| > Amps mailing list
| > Amps@contesting.com
| > http://lists.contesting.com/mailman/listinfo/amps
| ------------------------------
| Message: 2
| Date: Sun, 17 Mar 2019 16:21:31 -0400
| From: John Bodine <john.bodine@gmail.com>
| To: Amps Amps <amps@contesting.com>
| Subject: Re: [Amps] QRO 2500 MARK lll
| Message-ID:
| <CAFJ4jdbWEUkr2u=QYjsjZrCuYkY=UkNpaaaSY6biKCxVz4dR-A@mail.gmail.com>
| Content-Type: text/plain; charset="UTF-8"
| Try one tube at a time. Probably just one tube went.
| On Sun, Mar 17, 2019, 9:29 AM gudguyham--- via Amps <amps@contesting.com>
| wrote:
| > Sounds like a bad tube
| > Sent from AOL Mobile Mail
| > Get the new AOL app: mail.mobile.aol.com
| > On Saturday, March 16, 2019, Bob Gibson via Amps <amps@contesting.com
| > > wrote:
| > I have a problem that just came up with my QRO amp..First I blew a 1/2a
| > fuse on the bias board..I replaced it turned it back on then a 1/2a fuse
| > blew on the LV and bias board again but not the same fuse..Screen voltage
| > is OK and HV is OK. When I hit with 10 watts the fault light comes on and
| > kicks the amp off and I see the grid current meter go all the way over..I
| > see no burnt parts or smell parts...could this be a grid short in one of
| > the tubes? I have pulled the tubes and nothing looks bad below..I think I
| > will send the tubes down and have them check just to make sure it is not a
| > problem with one of them..Bob W5RG
| > _______________________________________________
| > Amps mailing list
| > Amps@contesting.com
| > http://lists.contesting.com/mailman/listinfo/amps
| > _______________________________________________
| > Amps mailing list
| > Amps@contesting.com
| > http://lists.contesting.com/mailman/listinfo/amps
| ------------------------------
| Message: 3
| Date: Sun, 17 Mar 2019 16:31:27 -0400
| From: "Gary Smith" <Gary@ka1j.com>
| To: amps@contesting.com
| Subject: [Amps] Replacing padder caps on an Alpha 77DX/SX
| Message-ID: <5C8EAE9F.20487.19DF0C6D@Gary.ka1j.com>
| Content-Type: text/plain; charset=US-ASCII
| Folks,
| 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
| http://doctorgary.net/toroid-1.jpg
| http://doctorgary.net/toroid-2.jpg
| Upper band transformer L6
| http://doctorgary.net/toroid-3.jpg
| 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
| http://doctorgary.net/100pF.jpg
| 1000pF band position B
| http://doctorgary.net/1000pF.jpg
| 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
| effort?
| Also, I'll probably get the HT58 padders
| from RF Parts, any other worthy places I
| might also check into?
| Thanks & 73,
| Gary
| KA1J
| ------------------------------
| Message: 4
| Date: Sun, 17 Mar 2019 19:02:58 -0400
| From: "Gary Smith" <Gary@ka1j.com>
| To: Amps@contesting.com
| Subject: Re: [Amps] Replacing padder caps on an Alpha 77DX/SX
| Message-ID: <5C8ED222.12990.2936F6@Gary.ka1j.com>
| Content-Type: text/plain; charset=US-ASCII
| Folks,
| > 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 should have said ETO instead of Alpha,
| even though we all know the current Alpha
| group did not make these old amps, I
| should have been more clear.
| 73,
| Gary
| KA1J
| ------------------------------
| Message: 5
| Date: Sun, 17 Mar 2019 21:12:14 -0500
| From: Jim <jimw7ry@gmail.com>
| To: amps@contesting.com
| Subject: Re: [Amps] Replacing padder caps on an Alpha 77DX/SX
| Message-ID: <50f6cf1f-9d74-361a-1f51-edec27577337@gmail.com>
| Content-Type: text/plain; charset=utf-8; format=flowed
| I just rebuilt a Ten-Tec Titan 435 that had horrible drift issues on 160
| meters. The RF current in the load cap on 160 is very high!
| I used strings of 100 pF 3KV CERAMIC disk caps. *No more drift.* Mouser
| part number is: 80-c330c101JHG. Replace a 500 pF doorknob with 5 of
| these in parallel.
| Don't waste your time with doorknobs, they cant handle the current. I
| just ripped the original doorknobs out of the Titan 425 and replaced
| them with strings of these. 20 second key-downs now no issue on the
| Titan 425 on 160 meters.
| I would stay below 1.5:1 SWR to keep the voltage down. With high SWR,
| the voltage *can be* quite high on the loading caps.
| Don't use mica caps either. I tried them. They just blew up.
| Some info in the archives of the amps reflector about this subject. Do a
| search from contesting.com amps archives. There also some info on W8JI's
| site, www.w8ji.com
| Email me privately and I can send you some pictures of what I did in the
| Titan. I'll try to post the pictures on my photo site later this week
| and share the link.
| Thanks
| 73
| Jim W7RY
| On 3/17/2019 3:31 PM, Gary Smith wrote:
| > Folks,
| > 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
| > http://doctorgary.net/toroid-1.jpg
| > http://doctorgary.net/toroid-2.jpg
| > Upper band transformer L6
| > http://doctorgary.net/toroid-3.jpg
| > 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
| > http://doctorgary.net/100pF.jpg
| > 1000pF band position B
| > http://doctorgary.net/1000pF.jpg
| > 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
| > effort?
| > Also, I'll probably get the HT58 padders
| > from RF Parts, any other worthy places I
| > might also check into?
| > Thanks & 73,
| > Gary
| > KA1J
| > _______________________________________________
| > Amps mailing list
| > Amps@contesting.com
| > http://lists.contesting.com/mailman/listinfo/amps
| ------------------------------
| Message: 6
| Date: Mon, 18 Mar 2019 09:19:36 +0100
| From: "Peter Voelpel" <dj7ww@t-online.de>
| To: <donroden@hiwaay.net>, <amps@contesting.com>
| Subject: Re: [Amps] Question about grid current in 4CX or 3CX
| Message-ID: <B4151E78081946A0BA36EE4E8A8C1CE1@SHACK>
| Content-Type: text/plain; charset="iso-8859-1"
| Hi Don,
| The grid dissipation of the 4CX10000D is 75W.
| It takes 150W of drive for 250mA of grid current with that tube in class-c
| with anode and screen voltage supplied.
| Are you thinking of a different tube?
| 73
| Peter
| -----Original Message-----
| From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of
| donroden@hiwaay.net
| Sent: Freitag, 15. M?rz 2019 16:38
| To: amps@contesting.com
| Subject: [Amps] Question about grid current in 4CX or 3CX
| Question :
| For the larger tubes with handles ( commercial service )
| Does grid current increase or decrease as plate voltage and screen
| voltage is removed. ?
| If it takes 250 watts to produce 100ma of grid current in a 4CX10,000.
| is the grid just a big dummy load and is it doing the tube harm to
| dump 250 watts into it when both plate and screen voltages are removed ?
| Don W4DNR
| _______________________________________________
| Amps mailing list
| Amps@contesting.com
| http://lists.contesting.com/mailman/listinfo/amps
| ------------------------------
| Subject: Digest Footer
| _______________________________________________
| Amps mailing list
| Amps@contesting.com
| http://lists.contesting.com/mailman/listinfo/amps
| ------------------------------
| End of Amps Digest, Vol 195, Issue 10
| *************************************
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