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Author Topic: Apollo 300X Base Amplifier Schematic  (Read 3683 times)
KB8ASO
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« on: September 28, 2010, 08:06:47 AM »

Hello all,

I just picked one of these up @ the local hamfest in good condition for the grand sum of $5.00. It is a late 60's 6-10-15 meter (CB) amp that uses a single 6LQ6 in a grounded grid configuration.  (I have stashed several new 6LQ6's so tube cost is not an issue.)  I am interested in reforming this amp from the CB bands to use on 6 meters with a MFJ-9406 for a little more power when needed. Anyone have a schematic for this or a generic one tube 6LQ6 amp?

Thanks,
Randy AB9GO  
« Last Edit: September 28, 2010, 08:10:11 AM by Randy E. Randall » Logged
K0BG
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« Reply #1 on: September 28, 2010, 12:15:11 PM »

There is no practical way to convert this amplifier to 6 meters, if for no other reason than getting the tube to go that high! What's more, 6LQ6s, and all the rest of the sweep tubes just don't do well as grounded grid. The first amp I ever built, used 4-6KD6s, and it was for 20 meters. The plans were right out of the ARRL Handbook, but even then, I'd bet it was IMD city!
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N2EY
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« Reply #2 on: September 28, 2010, 05:14:22 PM »

QST for April, 1970. Pages 32-35, "Building A Skinnier Linear".

Uses a single 6LF6 in grounded grid to boost the output of a QRP rig on 80 through 15 meters. The 6LF6 is a beefier tube than the 6LQ6 so you would run the latter at lower power.

6 meters is another story, though. The problem is the capacitances of the tube look like short circuits to the RF. You might be able to get it to work with a tuned input circuit and some tricks in the output, such as link coupling instead of a pi-net. But as K0BG points out, the result may be IMD-city. (What was considered acceptable transmitted IMD 40+ years ago may not be acceptable today).

The makers and users of illegal CB amps didn't care about minimizing transmitted IMD. In fact, they *liked* it, because it gave the signal a distinctive sound!

Note that the "Skinnier Linear" was being used for CW.

If you want to try it, I'd suggest first trying to convert the amp for one HF band (say, 75 meters) and seeing how it will work there.

73 de Jim, N2EY
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KB8ASO
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« Reply #3 on: September 28, 2010, 05:28:30 PM »

Knight used the 6dq6 in the t-60 and a sweep tube in the t-175 2x 6JE6 both sweep tubes on 6 meters.  Will they be as efficient as a purpose built RF tube?  No, but they may work well enough.  

Still looking for the schematic.

Randy AB9GO
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KB8ASO
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« Reply #4 on: September 28, 2010, 05:38:42 PM »

QST for April, 1970. Pages 32-35, "Building A Skinnier Linear".

Uses a single 6LF6 in grounded grid to boost the output of a QRP rig on 80 through 15 meters. The 6LF6 is a beefier tube than the 6LQ6 so you would run the latter at lower power.

6 meters is another story, though.

If you want to try it, I'd suggest first trying to convert the amp for one HF band (say, 75 meters) and seeing how it will work there.

73 de Jim, N2EY

I do not have to mod it for a HF band as it can do 15 meters now. Smiley  The output network is 15, 10, and 6.

Randy AB9GO
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KB8ASO
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« Reply #5 on: September 28, 2010, 05:44:18 PM »

I did notice that there is no -grid bias.  Now I have to make a supply. Cry

Randy AB9GO
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W8JI
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« Reply #6 on: September 29, 2010, 01:48:55 AM »

I once made a six meter amplifier with four 6LQ6 tubes on a bet. It was very touchy to make work, but when adjusted properly it worked OK. Amp Supply turned it into a product.

I would say a single tube would be easy **IF** the builder knows enough about RF to do a good RF layout and if the sweep tube is a compact design with very short lead lengths inside the envelope.
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W3LK
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« Reply #7 on: September 29, 2010, 08:05:23 AM »

I once made a six meter amplifier with four 6LQ6 tubes on a bet. It was very touchy to make work, but when adjusted properly it worked OK. Amp Supply turned it into a product.I would say a single tube would be easy **IF** the builder knows enough about RF to do a good RF layout and if the sweep tube is a compact design with very short lead lengths inside the envelope.

Was this a case of "Just because it can be done, doesn't mean it should be done"?  Smiley
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WB2WIK
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« Reply #8 on: September 29, 2010, 09:26:00 AM »

I did notice that there is no -grid bias.  Now I have to make a supply. Cry

Randy AB9GO

Is it really grounded grid (with grids connected directly to the chassis)?

If so, you wouldn't want a -grid bias supply, really.  You'd want a +cathode bias supply (same thing, really, but you can't apply a voltage to something that's already grounded).

And if it is grounded grid, I'd think there would be a relay that switches bias between "cutoff/standby" and "operate," or it never would have worked to begin with.
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KA5N
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« Reply #9 on: September 29, 2010, 06:35:43 PM »

Is there something that I am missing?  Supposedly this amp is for 6-10-15 meters.  So why does it
have to be converted to 6 meters?  Does it not work on 6?  If it is really an amplifier then maybe all
it needs is a few simple input output circuit tweaks.
Basically anything build for CB use is a waste of time.  Consider the old addage:  " Anything worth
doing is worth doing well."

Allen
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N2EY
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« Reply #10 on: September 29, 2010, 06:50:49 PM »

Is there something that I am missing?  Supposedly this amp is for 6-10-15 meters.  So why does it
have to be converted to 6 meters? 

I think the issue is that the amp was originally meant for 11 meters, and it sort-of works on the other bands. Meaning it has some gain. But it probably doesn't make much RF and sounds terrible.

I think the amp could be fixed up for 6 meters but it would be a lot of work. Basically you'd redesign it from the ground up, using the available parts where possible - mostly the cabinet and power supply.

73 de Jim, N2EY
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