Six Meter Amplifier




Boring Stuff: Here's another amplifier project of mine. And still learning lots of thing as I build. I suddenly got the Six Meter bug so why not build a 6 meter amplifier. I did lots of research on Six meter amps and look at all the different designs and schematic I could fine. And with that I will try an incorporate some of these into my own project.

If your thinking of building your first amp. Be prepare to do a lot of metal work, and this is were you'll be spending a lot of time. And be sure to plan out your project as much a possible. It will help I
you throw out your project.

The first thing I've learn when starting a amplifier project is to decide on what tube or tubes your going to use. And then start with your power supply section. The transformer for this project came from a old beat up Heathkit SB-200 amp I've had for 20 some years. Also made use of other parts from this amp.

Tube's for this project is a pair of Russian GI7B tubes. Ok so Let me get started. One thing you need to do before using these tubes is to burn in the filament for at lease 48 hours before applying
any High voltage to them.


 Power Supply:

The first part of this project is to build the power supply section and get it all working correctly. The transformer is from my beat up old Heathkit SB-200 amplifier. The capacitor and rectifier board is also from the Heathkit SB-200 amp along with the breaker. Since I decide not to re-build it, I decided to make use of the parts.

The transformer was check out and still working. I then clean it up and repainted it. The filter capacitor and rectifier PCB is being re-used. I remove all the components and clean up the board.  Image 1 shows the PCB before removing all of the components and before cleaning. Image #4 shows the bottom of the board before cleaning and image #5 shows after. The same goes for the top of the PCB.

As you can see from the images 6 and 7 there's nothing I can do about the burn or heat marks left on the board which was cause by heat from the 30K 7 watt bleeder resistors.
I replace the 30K 7 watts bleeder's with 30K 10 watts resistor because this it what I had on hand. I should have replace them with another type of resistor what would product much least heat and a lower wattage. Since the power supply section of the amplifier will not be enclose and will be rack mounted the heat will not be trap inside the case. Hopefully this will help to keep things cooler.
The original 16 rectifier diodes were replace with 1N4007 diodes. The capacitor bank are 390uf 450 volts. The reason I choose this value was to stiff up the voltage and in turn to keep from having a big voltage drop under full load.

Pictures 8 and 9 show how the newer capacitors were fitting to the old PCB. I used the ends from some very old resistor I have. Cutting the ends of the resistors and then wrapping them around each leg of the new capacitors and then soldering them to the old sb-200 PCB. This was not my idea I have seen this on another site some where.

Testing The Board:

Next step was testing out  the PCB board. Looking at pictures 10 and 11 you can see with 124.8 volts ac input the supply is delivering 2,335 VDC
out. My line voltage vary from 122vac to 125vac.

New Components:
Pictures 12, 13,14,15 shows the capacitor board with all new components added.

This is just a re-built SB-200 power supply with bigger components. The schematic is the same other then some small changes.

Clicking on a image will give a larger view. You may have to scroll down the screen a bit to view. Still trying to figure out how to fix this.

SB200 Transformer
Heathkit SB-200 Transformer

SB200 PCB Filter Cap Board
SB-200 PCB (1)

Another View PCB Filter Cap Board
SB-200 PCB (2)

Another View SB200 PCB Filter Cap Board
SB-200 PCB (3)

Before Cleaning PCB Filter Cap Board
Bottom Before Cleaning (4)


Bottom after cleaning PCB Filter Cap Board
After Cleaning (5)

Top Of PCB After cleaning
Top After Cleaning (6)

Top after cleaning PCB Filter Cap Board
Top After Cleaning (7)

Fitting new capacitor to board

Fitting new capacitor to board


Testing the power supply 124.8vac in 2335vdc out
HV Test (10)

Testing the power supply 124.8vac in 2335vdc out
HV Test (11)

Capacitor board with new parts 390uf caps
New Parts (12)

Capacitor board with new parts 390uf caps
New Parts (13)

Capacitor board with new parts 390uf caps
New Parts (14)

Chassis Construction:

I won't going into a lot of detail on how to build a chassis as this is all up to the builder. I will show some details was to what I did. I must say this. You will need to
put a lot of though into your construction. And where your going to mount your parts ahead of time. And try to drill out most of your holes before
placing them into the chassis if possible. I used aluminum angle for my frame work. Also found a large piece of steel sheeting that I think came out of some type of
locker of file cabinet laying around at work. This was used to make the bottom panel in the chassis. I had to cut the bottom sheet into two piece because after putting the frame work together, I could not place the hole bottom panel in place. The frame work was all riveted together.  The aluminum angle was purchase from Home Depot. The aluminum used to make the rack mount front panel was purchase from Metal By The Inch. You can do a internet search to fine them. And there price's
I fine to be must better other online metal companies.

So far I have found a few miss stack in my own construction but I can work around them LOL. Still learning.

Frame Work for amplifier
Frame Work (1)

Frame Work for amplifier
Frame Work (2)

Frame Work for amplifier
Frame (3)

Grin Paint away for good grounding
Bottom Plate In Frame (4)

Checking placement of capacitor board
Capacitor Placement (5)

Hole cutting for 120mm x 120mm fan
Cutting Hole for Fan (6)

Meter hole and switch cut out
Meter & Switch Hole Cut (7)

Miscellaneous Stuff:

Plate Voltage & Plate Current Metering:
I put together a voltage dropping resistor for the HV metering circuit which consist of (4) 750k ohm 3 watt resistor for a total of  3 meg ohm. The resistor are connected in series. This is so the meter will read up to 3kv DC. Fig 1 show the dropping resistors on  perforated board with stand off soon to be mounted. Fig 2 shows meter with the original scale.
Fig 3 Plate voltage and plate current meter with new scale.

Fig 4 Grid  current meter with new face plate.
All meters are 0-1ma purchase from All Electronic Corp.

Fig 5 Plate Choke:  The plate choke is home brew, wound with number 22ga enamel wire about 55 turns on a

 Fig 6 Filament Choke: Filament choke is also homebrew on a 7 1/2" ferrite rod. You don't need this long of a rod it's what I had on hand. Has you can see from the picture I'm not using the
complete rod. The rod is wound using #14ga house wire some 40 turns using tie wraps to hole the ends together.


Meter Dropping Resistor
Meter Dropping Resistors (1)

Meter 0-1ma
Meter Dropping Resistors (2)

Picture To Be Added
Meter With New Scale

Picture To Be Added
Meter With New Scale

HomeBrew Plate Choke
Plate Choke (5)