Skip to main content

Heathkit A7-E


The HeathKit A7-E amplifier is an interesting amplifier. As you can see this model uses only 4 tubes and a rectifier tube. This is seen on the schematic below. The yellow indicates parts the have been verified as correct.

On the particular amplifier the output transformer has been replaced. I do not know anything about the one in there now, but once the amplifier is up an running I will find out if it needs to be replaced again.  One big issue is that some one removed all 200MMF ceramic caps. I am going to have to put all of those back.
This is a  look at the underside. I am only beginning the work on putting this back to the way it should be.

I will update this post as I make some progress.
Finished Link
Labels:

Comments

Post a Comment

Popular posts from this blog

Seeburg Digital Control Center

The Seeburg Digital Control Center came into use around the 1970's. This was model DDC1. Seeburg continued the use to the digital control center line until around 1977. The last model used was a DCC42-56. The DCC is used to supply 27 volts DC, -27 volts  DC and -13 volts DC to the jukebox. The DCC has test points on the side to measure these voltages.  Below you can see a DCC3. Once you flip over the DCC you will see two circuit boards. The top board is the data buffer board. Generally you will not have any issue with it. The second board (on bottom) is the power supply board. This where you may have issues. The power supply board is where the DC voltages are created and regulated. Below is the power supply board removed. The first thing I always do when working on a DCC is start by replacing all electrolytic capacitors. Below is the schematic.  In my case as you can see below I had other issues. As you can see transistor Q3120 has been repla
Post a Comment
Read more

Seeburg SHP3 Repair July 2017

I have just finished repairing this Seeburg SHP3 for a friend. My friend collects and refurbished jukeboxes and he occasionally brings me the amplifiers. Initial Photos : The above photos show the amplifier as I received it. It was obvious someone had done some work before. The driver transistors as well as the output transistors were not originals. Also, Q5114 had been changed. It is the big silver transistor you see on the driver board. The initial power up  using a dim bulb tester showed that the right channel was not working and too much current was being drawn. Why I use a dim bulb Tester:  Notice the red enamel wire running along the top edge of the driver board. A trace should be there, but someone ran the amplifier with shorted transistors and burnt the 32+ volt trace off the board. Repairs: Replaced Q115 and Q116 (Driver Transistors Right Channel) -Shorted Replaced Q5117 and Q5118 (Output Transistors Right Channel)- Shorted Replaced Q5114 (Signal
Post a Comment
Read more

Bell & Howell Oscilloscope Model 34 DeVry Tech

The Bell & Howell Oscilloscope Model 34 was purchased at an auction and then give to me. It was made by Heathkit for DeVry Tech (DeVry University). Below is a photo of the front after I finished electronically going through it. There was nothing interesting that came up while working on it. Below you can see some before and after of the underside. Below is the top side. The 2 filter cans were 4 sections of 20mfd for a total of eight 20mfd capacitors.  Below is the solution I came up with to replace them. It consists of eight 22 mfd on a PCB that is zipped tied to the bottom of the chassis.   Overall this is a simple oscilloscope and was a simple electronic restore.  Here is the schematic.
3 comments
Read more