Author Archive

B12NC/B15NC Schematic

October 18th, 2009 No comments

I finally got around to redrawing my B15NC schematics, something that I have been wanting to do for quite awhile.  I have redrawn 3 different versions of the NC schematic, which are shown here.  These drawings are based on originals that I have, and I have tried to replicate the original’s appearance as closely as I could.

The first is dated 1/64.  This is an early NC schematic and does not have circuit voltages shown on it yet.

B15NC Schematic 1/64 (PDF)

The second is dated 11/64.  It has various voltages shown in the circuit, and there have been a few capacitor additions and deletions.

B15NC Schematic 11/64 (PDF)

The third is dated 9/64.  It is the same as the 11/64 schematic except for the center tap on the hum control pot.  Rather than attaching to point “K”, this symbol has been marked over by hand and changed to a ground symbol.

B15NC Schematic 9/64 (PDF)

Because of the size of the original schematics, these drawings are formatted to be printed on 8.5″ x 14″ paper.  When printed, they should be the size of the originals, as long as no resizing occurs within Adobe Acrobat.

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New power resistors

October 15th, 2009 1 comment

The new power resistors arrived today and I swapped them out with the ones I originally had on the board.

New Ohmite power resistors

New Ohmite power resistors

It may seem like a silly detail but I am so much happier with how the new ones look.  The previous ones had been bothering me ever since I put them in.

(edit: I just had to replace the new 1K resistor with another new one.  I just double checked it with a meter and it read about 10M to begin with, and kept climbing the longer I kept the test leads on it.  I’m pretty sure I checked it before installing it, so I guess I damaged it while soldering it.  I was extra careful with heat-sinking the leads on the latest one and it seems fine)

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B15NC eyelet board layout

October 15th, 2009 No comments

Here is a drawing I did of the eyelet board in my B15NC.  It just shows the components on the board; it does not show any of the control wires, etc. that also connect to it.

1964 B15NC Eyelet Board (PDF)

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Output transformer, etc.

October 11th, 2009 2 comments

I finally got the output transformer potted and then remounted onto the chassis.  The 3 primary leads were too short so I had to extend them.  I also soldered leads to the multi-cap and just curled them up for now.  With that done I installed the fuse holder and finished wiring the power supply.

Before going much further I needed to get the 2 logo lamps installed so that any future wiring could be routed around them.  Since this started out as a B15NF, the lamp holders were different from what was used in the B15NC.  These holders were originally mounted to the larger B15NF printed circuit board.  Since I am using a turret board that is much smaller, I had to find a different method for attaching the holders.  A couple of new holes and some #4-40 machine screws took care of that.  I also installed a new rubber light shield over the logo slot, since the original had come loose and was in poor shape.

The chassis gets a little more crowded

The chassis gets a little more crowded

This was intended to be a learning experience for me and so far it has been.  I look at what I’ve done so far and sometimes see things that I wish I had done better.  There have been a couple of things already that I have gone back and changed.  The key has been whether I thought I could perform the change without ultimately making things worse.  One thing that has been bothering me for quite awhile are the (2) 10W resistors – they are larger than what I was expecting and I have never been happy with how they look on the board.  I will be replacing them with shorter ones which should arrive later this week.

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The turret board and components

October 4th, 2009 2 comments

Well, I came close to getting all the components soldered to the turret board today.  Unfortunately, I miscounted and did not order enough .022 mf capacitors (needed 7, ordered 6).  For this project I decided to go with slightly higher quality components, so I was using Solen fast caps for all but the electrolytics (which are Sprague Atoms).  I have other caps here that I could pull from but I really don’t want to mix brands.  I’ll just have to wait until I get the last one in.  That’s what I get for not ordering a few extra to begin with!

Here’s what the board looks like with everything except the one missing cap:

New turret board w/components

New turret board w/components

For comparison, here is the board on a 1964 B15NC:

1964 B15NC eyelet board

1964 B15NC eyelet board

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The turret board

October 2nd, 2009 No comments

I am close to the point where I need to start installing components on to the new turret board.  Before I do, I thought I would show a photo of the board while it is still nice and untouched.  It is made from 1/8″ thick G10/FR4 board, so it feels nice and strong.  This was my first time making a board and I’m really pleased with how it turned out.


New turret board

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Continuing with the power supply

October 1st, 2009 No comments

I got a little more of the power transformer wiring done tonight, including partially wiring the switches, as well as the power cord socket.  I also made some improvements to the wiring I had done previously.


Additional power supply wiring

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Starting the power supply wiring

September 30th, 2009 No comments

I got a modest start on the power supply tonight.  I installed the newly potted power transformer, as well as the new multi-cap can and 3 new switches.  I got the 5v and 6.3v heater wires, and the power transformer secondary wires connected to the tube sockets.  I temporarily mounted the new turret board, in order to get the transformer leads run in an orderly manor.

Heater and secondary leads connected

Heater and secondary leads connected

My next step will be to wire the primary side of the transformer.  I will hold off wiring-in the fuse holder until I have everything wired to the cap can, since that’s easier to do with the fuse holder out of the way.

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B12XT / B18X Manual (includes schematic)

September 29th, 2009 2 comments

This is a service manual for the B12XT and B18X Portaflex amplifiers.  I have redrawn it from a photocopy and have tried to match the look of the original as best as I could.

B12XT/B18X Service Manual (PDF)

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B12NF/B15NF Schematic (1966)

September 29th, 2009 No comments

Here is a schematic of an Ampeg B15NF, dated 1-66.  I redrew it from an original I have and tried to closely match its appearance.

B15NF, 1-66 (PDF)

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