This is a multi-part message in MIME format.
------=_NextPart_000_0233_01BFF961.60A47DC0
Content-Type: text/plain;
charset="Windows-1252"
Content-Transfer-Encoding: quoted-printable
As you can probably guess by my posts, I am refurbishing
a Dentron MLA-2500B amp.
This model, and most of the Dentron power transformers
were wound for 234 volt mains. (Alpha's were also, for that matter) I =
measured 6.75 volts on the tube pins of
those expensive 8875's in the 2500B. I wound six turns
of #22 teflon covered wire on a one inch form and placed it in series =
with the side of the filament winding that goes to ground. This reduced =
the voltage at the tube pins to a comfortable 6.18 volts. This will also =
serve as a "bump" for any in-rush current that may or may not be there. =
(I don't have anything to measure inrush with)
I am very interested to chat with anyone that has played with =
MLA-2500B's. The padder door knob caps vary from model to model, and =
even within a model. Since the load cap is only 500 pf, this presents a =
very narrow "window"
for matching various loads on 160 meters, as most of the
capacitance is fixed in the padders. Also, various values
of padders on the tune cap are used from model to model=20
depending on what value it is...140 pf on the older models and 170 pf on =
the "B" model.
All in all, the MLA-2500B is a sweet, compact, legal-limit
amp with no bad habits and very smooth tune-up. Too bad
that the 8875's are becoming extinct!
(((73)))
Phil, K5PC
Phil Clements
410 VZ CR 4903
Ben Wheeler, TX 75754
------=_NextPart_000_0233_01BFF961.60A47DC0
Content-Type: text/html;
charset="Windows-1252"
Content-Transfer-Encoding: quoted-printable
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Dwindows-1252"><BASE=20
href=3D"file://C:\Program Files\Common Files\Microsoft =
Shared\Stationery\">
<STYLE>BODY {
BACKGROUND-POSITION: left top; FONT-SIZE: 10pt; COLOR: #000000; =
BACKGROUND-REPEAT: no-repeat; FONT-FAMILY: Comic Sans MS
}
</STYLE>
<META content=3D"MSHTML 5.50.4134.600" name=3DGENERATOR></HEAD>
<BODY bgColor=3D#ffffff>
<DIV>As you can probably guess by my posts, I am refurbishing</DIV>
<DIV>a Dentron MLA-2500B amp.</DIV>
<DIV> </DIV>
<DIV>This model, and most of the Dentron power transformers</DIV>
<DIV>were wound for 234 volt mains. (Alpha's were also, for that matter) =
I=20
measured 6.75 volts on the tube pins of</DIV>
<DIV>those expensive 8875's in the 2500B. I wound six turns</DIV>
<DIV>of #22 teflon covered wire on a one inch form and placed it in =
series with=20
the side of the filament winding that goes to ground. This reduced the =
voltage=20
at the tube pins to a comfortable 6.18 volts. This will also serve as a =
"bump"=20
for any in-rush current that may or may not be there. (I don't have =
anything to=20
measure inrush with)</DIV>
<DIV> </DIV>
<DIV>I am very interested to chat with anyone that has played with =
MLA-2500B's.=20
The padder door knob caps vary from model to model, and even within a =
model.=20
Since the load cap is only 500 pf, this presents a very narrow =
"window"</DIV>
<DIV>for matching various loads on 160 meters, as most of the</DIV>
<DIV>capacitance is fixed in the padders. Also, various values</DIV>
<DIV>of padders on the tune cap are used from model to model </DIV>
<DIV>depending on what value it is...140 pf on the older models and 170 =
pf on=20
the "B" model.</DIV>
<DIV> </DIV>
<DIV>All in all, the MLA-2500B is a sweet, compact, legal-limit</DIV>
<DIV>amp with no bad habits and very smooth tune-up. Too bad</DIV>
<DIV>that the 8875's are becoming extinct!</DIV>
<DIV> </DIV>
<DIV>(((73)))<BR>Phil, K5PC<BR></DIV>
<DIV> </DIV>
<DIV>Phil Clements<BR>410 VZ CR 4903<BR>Ben Wheeler, TX=20
75754<BR></DIV></BODY></HTML>
------=_NextPart_000_0233_01BFF961.60A47DC0--
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|