[Amps] Amps Digest, Vol 195, Issue 10--Replacing padder caps on an Alpha 77DX/SX

Fri Mar 22 11:40:42 EDT 2019

Ive used the Ameritron (never paid extra from RFP) as high as ~4KW + SSB/CW 
in modified LK-800A's using the 3CPX tubes and with the LK-550 transformer. 
And also 2 holer AL-1500's which was as simple as using the AL-82 tube 
chassis and a filament transformer. JI pioneered that swap for his own use.

Never had a report of any failures.

Carl

----- Original Message ----- 
From: "Paul Christensen" <w9ac at arrl.net>
To: <amps at contesting.com>
Sent: Thursday, March 21, 2019 2:20 PM
Subject: Re: [Amps] Amps Digest, Vol 195, Issue 10--Replacing padder caps on 
an Alpha 77DX/SX

> >"The 802 was a bit better and its been awhile since Ive been into those
> amps so dont know if the big Ameritron will fit. Carl"
>
> As I recall, the Ameritron choke and RF Parts RFC3 are the same.  I have
> replaced the B&W 800 series chokes with the RFC3 in Alpha 77Dx, 70V, and 
> 70A
> amps.  There's ample room for the new choke although accessing the choke
> support screw is difficult.  On my 77Dx, I used a thin metal machinist's
> ruler, pressed against the threads to hold the screw into position long
> enough for the screw to grip the threaded ceramic post.  Then, it's just a
> matter of hand-tightening the choke to the point that the fiber washer
> between the ceramic and chassis is slightly compressed.  The RFC3 has a
> small wire gauge so not sure how well it would hold up in the 2-8877 77Sx 
> if
> used well above 1500W.
>
> The new choke works great on all HF bands, including WARC.
>
> Paul, W9AC
>
> ----- Original Message -----
> From: "HP" <pfizenmayer at q.com>
> To: <amps at contesting.com>
> Sent: Monday, March 18, 2019 3:24 PM
> Subject: Re: [Amps] Amps Digest, Vol 195, Issue 10--Replacing padder caps 
> on
> an Alpha 77DX/SX
>
>
>> 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 at ka1j.com >
>> To: amps at contesting.com
>> Subject: [Amps] Replacing padder caps on an Alpha 77DX/SX
>> Message-ID: < 5C8EAE9F.20487.19DF0C6D at 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 at 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 at gmail.com>
>> | To: amps at contesting.com
>> | Subject: Re: [Amps] 3CX800A7 low grid current version?
>> | Message-ID: <121ccba3-78d1-e23b-6122-24af452cd1bf at 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 at 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 at gmail.com>
>> | To: Amps Amps <amps at contesting.com>
>> | Subject: Re: [Amps] QRO 2500 MARK lll
>> | Message-ID:
>> | <CAFJ4jdbWEUkr2u=QYjsjZrCuYkY=UkNpaaaSY6biKCxVz4dR-A at 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 at 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 at 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 at contesting.com
>> | > http://lists.contesting.com/mailman/listinfo/amps
>>
>> | > _______________________________________________
>> | > Amps mailing list
>> | > Amps at contesting.com
>> | > http://lists.contesting.com/mailman/listinfo/amps
>>
>>
>> | ------------------------------
>>
>> | Message: 3
>> | Date: Sun, 17 Mar 2019 16:31:27 -0400
>> | From: "Gary Smith" <Gary at ka1j.com>
>> | To: amps at contesting.com
>> | Subject: [Amps] Replacing padder caps on an Alpha 77DX/SX
>> | Message-ID: <5C8EAE9F.20487.19DF0C6D at 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 at ka1j.com>
>> | To: Amps at contesting.com
>> | Subject: Re: [Amps] Replacing padder caps on an Alpha 77DX/SX
>> | Message-ID: <5C8ED222.12990.2936F6 at 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 at gmail.com>
>> | To: amps at contesting.com
>> | Subject: Re: [Amps] Replacing padder caps on an Alpha 77DX/SX
>> | Message-ID: <50f6cf1f-9d74-361a-1f51-edec27577337 at 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 at contesting.com
>> | > http://lists.contesting.com/mailman/listinfo/amps
>>
>> | ------------------------------
>>
>> | Message: 6
>> | Date: Mon, 18 Mar 2019 09:19:36 +0100
>> | From: "Peter Voelpel" <dj7ww at t-online.de>
>> | To: <donroden at hiwaay.net>, <amps at contesting.com>
>> | Subject: Re: [Amps] Question about grid current in 4CX or 3CX
>> | Message-ID: <B4151E78081946A0BA36EE4E8A8C1CE1 at 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 at contesting.com] On Behalf Of
>> | donroden at hiwaay.net
>> | Sent: Freitag, 15. M?rz 2019 16:38
>> | To: amps at 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 at contesting.com
>> | http://lists.contesting.com/mailman/listinfo/amps
>>
>> | ------------------------------
>>
>> | Subject: Digest Footer
>>
>> | _______________________________________________
>> | Amps mailing list
>> | Amps at contesting.com
>> | http://lists.contesting.com/mailman/listinfo/amps
>>
>> | ------------------------------
>>
>> | End of Amps Digest, Vol 195, Issue 10
>> | *************************************
>> _______________________________________________
>> Amps mailing list
>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>
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