I bought a Bogen Presto off Ebay with
the intention of rebuilding it into a guitar amp. I haven't gotten
around to that yet but I started a thread on Ampage about Bogen
transformer codes that resulted good Bogen output transformer color
codes. Here ya go:
From:
Regis
Subject: Output transformer color code question
Hi Guys,
I have an old Bogen Presto I am going to rebuild, and need some help on
identifying the color codes on the Output transformer. I was partially
dismantled when I got it.
Here are the wires:
Black: Ground ?
Yellow: 4 ohm tap ?
Green: 8 ohm tap ?
Blue: Plate ?
Brown: Plate ?
Red: B+ ?
Blue/White: ?
Brown/White: ?
I am going to try to rebuild it into a 5E5 Pro.
Thanks for any help.
Regis
From: steve
Subject:Re: Output transformer color code question
Regis,
Schematics are notoriously hard to find for Bogen tube amps. I couldn't
find any OT colors that matched the ones you listed exactly.
Does your OT have a part number on it? For example the CHB-100 PA amp
has 83-340-000 for it's OT. The MO200A has part number 83-349-010 and
83-349-000 for both of its OTs.
Also, what tubes are in the amp?
Steve
http://www.diycustomamps.com
From: Regis
Subject: Re: Output transformer color code question
Hi Steve,
The number on the transformer is 83-320-000.
The amp originally had two 12AX7'S, 7355 power tubes, and a GZ34/5AR4
rectifier.
From: steve
Subject: Re: Output transformer color code question (long)
Regis,
None of the Bogen schematics I have has that part number.
Here's the info on the ones I have:
CHB100 83-340-000 (4x 7868)
green/white: 70v & negative feedback
black/white: ground
green: 16?
orange: 8? (25v)
yellow: 4?
black/yellow: 2?
black: common
blue & brown: plate
red: B+
M120 83-371-000 (4x 8417)
green/white: 70v
black/white: common 2
green: 16?
yellow: 8?
orange: 25v (5.2? )
black/orange: 25VCT
black: common 1
brown/green: neg. feedback
brown/?: ground
blue & brown: plate
red: B+
M0100A 83-349-000 (4x 8417)
green/yellow: (132? ) & 115v output
orange/black: 70v (49? )
black/red: 70VCT
black/white: common 2
green: 16?
yellow: 25v (6? )
orange: 25VCT
black: common 1
red/blue: neg. feedback (49? )
blue/white: ground
blue & brown: plate
red: B+
MO200A: 83-349-010 & 83-349-000
green/yellow: 115v output & 66?
orange/black: 70v & (24.5? )
black/red: 70VCT
black/white: common 2
green: 8?
yellow: 25v (3? )
orange: 25VCT
black: common 1
red/blue: neg. feedback
blue/white: ground
blue & brown: plate
red: B+
Here is another online schematic for the DO30A:
http://www.triodeel.com/dbdo30.gif
HTH helps.
Steve
http://www.diycustomamps.com
From: Enzo
Subject:Re: Output transformer color code question
Your guesses are probably right. The white wires are probably the CV
windings for 25v and 70v.
From: Regis
Subject:Re: Output transformer color code question
Steve, thanks for the info.
Enzo, if that is the case, can I just shrink wrap those up and
fuggedabout them?
thanks,
regis
From: MBSetzer
Subject:Re: Output transformer color code question
I would check for continutity of the white striped wires with the OPT
primary blue & brown in case they are ultralinear taps.
Otherwise if they are the 25V & 70V secondary taps, the 70V one
especially makes a very nice low impedance output to a slave power amp.
Coming straight from the OPT this line out has much more of the full
amp tone (when the amp is driving a real speaker on one of its regular
4, 8, or 16ohm taps at the same time rather than a dummy load) than you
would normally expect from a line out.
Mike
From: Enzo
Subject:Re: Output transformer color code question
Good call on the UL taps. I wouldn't expect them on a Bogen, but you
never know. If the amp has 25 and 70v terminals on the rear panel, then
they have to come from somewhere.
And yes, you can tape them off if not in use. Continuity tests will
tell you if the white wires are part of the primary winding or not.