Here is a comparison of some of the amplifiers found on eBay.

I have been comparing the specifications of some of the amplifiers that I have worked with:

L-10 Amplifier:

Size: 200x41.5x?? mm

8 Ohm 100 Watts

4 Ohm 200 Watts

2 Ohm 350 Watts +-55VDC

Gain: ?? 

Output Transistors - 3 EA: A1943 C5200

L-15 Amplifier

L-15 Amplifier:

Size: 150x40x?? mm

Size: 5.9x1.57x??"

8 Ohm 150 Watts

4 Ohm 300 Watts

2 Ohm 600 Watts +-55VDC

Gain: 36x

Output Transistors - 3 EA: IRFP240/IRFP9240

L-20 Amplifier

L-20/28 Amplifier:

Size: 110x65mm (L-20)

8 Ohm 200 Watts +-65V

4 Ohm 350 Watts +-60V

2 Ohm

Gain: 34x

Output Transistors - 4 ea D1047 B817

Note: L-20-SE has 2SA1943 2SC5200 transistors

Note: L-28 Includes capacitors and speaker protection

PR-800 Amplifier

PR-800 Amplifier:

Size: 245x65x30mm (or 195x90 with 4 Capacitors)

Size: 9.64x2.55x1.18"

8 Ohm 500 Watts +- 95VDC

4 Ohm 1000 Watts +-90VDC

2 Ohm 1000 Watts +-65VDC

Gain: 40x

Output Transistors - 4 ea TTA1943 TTC5200

Note: Includes Capacitors and Speaker protection

Note there are 2 sizes; one with 2 large filter capacitors and one with 4 large filter capacitors.

NJW0281/NJW0302 Amplifier

NJW0281/NJW0302 450W+450W HIF

Size: 259x73mm

8 Ohm

4 Ohm 450 Watts +-85VDC

2 Ohm

Gain: Very Low - needs preamplifier

Output Transistors - 4 ea NJW0281/NJW0302

Note: ATX power supply pins fit the connectors on the right side.

Rebuilding some old speakers

I was given some speakers that I had built back in the 70's and that had been in use at a churhc for about 20 years or more.  They were made to look nice, but I will rebuild them to look tough.  I also want to upgrade them from 25 watts to about 150 watts or more.

This is what I bought at a Hamfest to rebuild the speakers with.

This picture compares an old speaker with one of the new ones.

 Initially this is what initially had to work with.  I only had one of these bass speakers.

 Here is one cabinet stripped down and the old speakers sitting on top of it.

I painted the front plywood black and started reassembling the speakers. I traded something for some tweeters.  They are rated at 75 watts.  I also added some grills to protect the woofers.

Rebuilding LAB Series LS800 Amplifier with a PR-800 Amplifier

I had rebuilt this LS800 amplifier with a L-15 amplifier but I decided to upgrade to PR-800 amplifiers for much more power.  This is a picture of the old amplifier dissembled.

This is a picture the old power amplifier section.  It was really cobbled.

This is how the PR-800 amplifier boards arrived.  Note that the power output transistors will have to be soldered on.

Pr-800 as it arrives

Here I have added the output power transistors.  I also moved the driver transistors to the top side of the board for mounting on the heat sinks that I have.  Their leads barely reach the tops of their holes.

PR-800 with power transistors

This is what it looks like mounted on the heat sink.  I went back and added washers under the heads of the 3/4 inch 4-40 screws.  Note that little plastic washers must be installed in the two To-220 transistors (Q12 and Q15).  Make sure to check for shorts to the heatsink with a voltmeter!

PR-800 Mounted on heatsink

WARNING!!  Something was really wrong, it tripped the circuit breaker and shorted the output transistors!!!  I eventually found the problem.  The 2SD669 (Center transistor Q13) has to be soldered UPSIDE DOWN on the top board!

Upside Down Transistor on PR800

Here is the schematic of the output section.  Note that the 2SC5200 (Q16, Q17, Q18, Q19) transistors are connected to the + power source and the 2SA1943's (Q20, Q21, Q22, Q23) are connected to the negative power source.  Also not that the two boards are the opposite of each other.  The 2SA1943's will always be next to the power filter capacitors.

The schematic was derived from this schematic found on the internet.  The protection circuits do not match what I received.

Here is a labeled picture

I have both channels working fine now, but only one at a time.

PR-800's mounted on heat sinks

As you can see I cut off one side of the heatsink.  I also switched to silicone insulators because they are less messy.  One channel is missing two power transistors because they were fried when I installed the 2SD669 right side up.

This project is finally done!  The cooling fan was mounted to the front cover to make working on the amps easier.  The heatsinks were mounted to the bottom of the cabinet.  The LM3915 LED VU meters have the bottom LED always on and the top two red ones are in parallel thus giving 12 LED's per channel.

2018 Chaffee NY Hamfest

I was at the 2018 Chaffee NY Hamfest.  It is a smaller one but I got some great deals. This is what it looked like.  It is a smaller Hamfest but it is less than 5 miles away for me.

Here is my table.  I failed to get rid of my free stuff!

I bought a metal locator and some speakers.  Here are the 12 inch speakers that I will use to rebuild my speakers with.

Niles ZR 4630 tear down and rebuild

A friend has a Niles ZR-4630 that he wants made into independent amplifiers.  There are six stereo amplifiers based on the LM3886 IC.  I have been reverse engineering it.  By default the mute is "on" for the amplifier modules.  Here are some pictures of the guts.

This shows the amplifier modules and the power transformer.  We could not get the power on by the on off switch so we hot wired power to the transformer.

This is another view of the transformer and amplifiers.

This is a view of the back side of the guts.

So far I have been able to confirm the pins of the amplifiers. There is more to come.

Here is a picture of one of the amplifiers running on the workbench.