-
You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Maco/ Brute 75
- Thread starter 238
- Start date
Jim,
A picture would surely help.
I believe this to be the input matching coil.
It would be adjusted with your SWR meter between your radio and the input of the amplifier. Adjust the coil for the lowest SWR reading. (Probably will be higher than 2.0:1 or so due to a lack of negative grid bias in this unit)
73
David
A picture would surely help.
I believe this to be the input matching coil.
It would be adjusted with your SWR meter between your radio and the input of the amplifier. Adjust the coil for the lowest SWR reading. (Probably will be higher than 2.0:1 or so due to a lack of negative grid bias in this unit)
73
David
The variable cap that has the shaft sticking up out of the chassis deck next to the coil is the Plate Tune control.
The one with the knob on the front is the Load control.
The Plate Tune should show a peak with the plates partly engaged. The cap in the pic has the plates all the way apart. This is the minimum-capacitance extreme of its adjustment range.
When the wattmeter shows a peak with the Plate Tune at this position, it's not really peaked. It just ran out of adjustment range at its low end.
Adjusting the coil between the two controls is how the Plate Tune can be returned to a true peak, between its end limits. Stretching it to increase the space between turns may do the trick.
Would be easier if the Plate Tune were on the front panel.
73
The one with the knob on the front is the Load control.
The Plate Tune should show a peak with the plates partly engaged. The cap in the pic has the plates all the way apart. This is the minimum-capacitance extreme of its adjustment range.
When the wattmeter shows a peak with the Plate Tune at this position, it's not really peaked. It just ran out of adjustment range at its low end.
Adjusting the coil between the two controls is how the Plate Tune can be returned to a true peak, between its end limits. Stretching it to increase the space between turns may do the trick.
Would be easier if the Plate Tune were on the front panel.
73
Removing and bypassing the board with the coils on it would be a good start. The marking "LPF" means that it's a low-pass filter, meant to reduce interference caused by harmonic frequencies coming out of the amplifier.
Just one problem. The parts on it are too small, and that board is famous for flaming out.
While you're at it, replacing the coax that runs from the load control to the relay will now be necessary if it won't reach the whole way to the relay.
The new coax really needs to have the shield grounded. Preferably at both ends. The factory coax is always installed with the shield not connected to anything.
At all. This is a bad idea and causes feedback problems.
If the old coax will reach to the lug on the relay, you can strip a quarter inch of the jacket from each end of the coax, wrap a piece of hookup wire around the exposed braid and (gently) solder it to the braid. Make the ground connection to the other end of the hookup wire, keeping it as short as you can.
And if it won't reach the lug on the relay, you need a new piece of coax. Just don't use one with foam dielectric. It won't hold up to heat. Foam will soften and eventually allow the center wire to short to the braid.
73
Just one problem. The parts on it are too small, and that board is famous for flaming out.
While you're at it, replacing the coax that runs from the load control to the relay will now be necessary if it won't reach the whole way to the relay.
The new coax really needs to have the shield grounded. Preferably at both ends. The factory coax is always installed with the shield not connected to anything.
At all. This is a bad idea and causes feedback problems.
If the old coax will reach to the lug on the relay, you can strip a quarter inch of the jacket from each end of the coax, wrap a piece of hookup wire around the exposed braid and (gently) solder it to the braid. Make the ground connection to the other end of the hookup wire, keeping it as short as you can.
And if it won't reach the lug on the relay, you need a new piece of coax. Just don't use one with foam dielectric. It won't hold up to heat. Foam will soften and eventually allow the center wire to short to the braid.
73
BJ radionut
Supporting Member and 6m addict
https://www.ebay.com/itm/Cornell-Du...098?_trksid=p2349526.m4383.l4275.c10#viTabs_0
This should work...I would think
NOMADE may check this later today...He may have other suggestions
This should work...I would think
NOMADE may check this later today...He may have other suggestions
Here is the capacitor that Maco used in most of their grid-driven amplifiers. It connects to the high-voltage transformer secondary on one end, and to two rectifier diodes on the other end. The diodes are wired to produce a negative DC voltage at fairly low current. This voltage is used to bias the control grid of a tube that's being used with grid drive like yours.
Thise are old Maco stock, best I can tell.
https://www.ebay.com/itm/LOT-10-22-...872023?hash=item4d6a5ba257:g:NR8AAOxyhlJRcDOk
The typical Maco grid-driven amplifier used a pair of these in series where yours has just the single capacitor. This boosts the effective voltage rating to 1200 Volts. Should do the trick.
73
Thise are old Maco stock, best I can tell.
https://www.ebay.com/itm/LOT-10-22-...872023?hash=item4d6a5ba257:g:NR8AAOxyhlJRcDOk
The typical Maco grid-driven amplifier used a pair of these in series where yours has just the single capacitor. This boosts the effective voltage rating to 1200 Volts. Should do the trick.
73
Last edited:
- No one is chatting at the moment.
-
-
dxBot:63Sprint has left the room.
-
dxBot:kennyjames 0151 has left the room.
-
-