1x3 tube amp mod to 4 tube

[Se7en]

hi, i would like to modify this amp to be run on all four tubes instead of 1 driving 3.
i was told where the white wire is on the driver tube needs to be jumped to the center of the three tubes to by pass the tuning pot in the rear.
any help would be greatly appreciated​

it would be cool if i could remove the bottom inside the amp where its all dirty/dusty have it chromed and make a top cover out of acrylic so you can see the tubes glow.

 

[Se7en]

Bump, anyone?

 

[Atlasta]

I've been wanting to do the same thing to my 1x3, but I'm wondering if the gain would be worth the effort.

Right now I'm getting 300 - 350 out of the 1x3. Would converting it to a straight 4 provide any appreciable or notable gain?

 

[ExitThirteen]

You can do the conversion from 1 x 3 to a 4 tube, but keep in mind that if you do so, you'll have to drive it with a radio capable of doing 60-100W to drive the amp full output. In my opinion, it's not worth the trouble, you might gain 50-75W more on total output, but you'll have to have an extra 50-75W more on the input to gain that 50-75W on output, plus all the time and extra funding you may have to put into it for the conversion process.

Keep it stock, you're better off in the long run. Keep it at about 20W input, and the amp will be just fine.


~Cheers~

 

[Se7en]

You can do the conversion from 1 x 3 to a 4 tube, but keep in mind that if you do so, you'll have to drive it with a radio capable of doing 60-100W to drive the amp full output. In my opinion, it's not worth the trouble, you might gain 50-75W more on total output, but you'll have to have an extra 50-75W more on the input to gain that 50-75W on output, plus all the time and extra funding you may have to put into it for the conversion process.

Keep it stock, you're better off in the long run. Keep it at about 20W input, and the amp will be just fine.


~Cheers~

the only resean why i aksd this was cause im driving the single 6lb6 tube (driver) with 20w which i was told is WAY too much for that tube. i have noticed brown burnt material more and more on the (driver) tube each day i use it. if its not a simple mod or worth the trouble thenn i wont bother.
i guess its time to go big. havent found a good 8-10 tube box on ebay yet worth the $

 

[wavrider]

Lower the drive from the rig or pad the input to the driver stage and all is good.

 

[ElectronTubesRule]

3.5 watts should drive that driver just fine the driver then pumps out 30-60 watts from your 3.5 watt dead key plus any swing pushing the rest of the tubes to their rms limit with some spikes from the swing on AM. 10-12watts SSB will like wise be ideal. I am going to guess that at 20 watts dead key you are a splater box at this point. Just turn down the radio's power that is far easier then doing the mod you wish to do.

First it is not as easy as just jumpering the wire fromt he driver to the other's. Your entire Pi network is designed to work with the values of that one tube....When you look at a data sheet full of meaningless numbers to you for a tube most of that data is used to design the Pi-Network so you can match your radio's output to what the tubes want to see as a load for that freq. you are attempting to broadcast on. Not only do you have 3 tubes in the output section they are more then likely not the same tube as the driver so you have different vales for the tubes and you have 3 sets of combined values to work with. So all the caps in your tuning network would need to be changed to the appropriated values among other things like the coils maybe needing to be slightly. different.

If you get a single final CB and gently peak it so you have 3-3.5 watts dead key with some moderate swing it will work perfectly.

Keep in mind that when that unit was built the legal limit for CB was at an all time high of 4Watt's most units left the factory keying 3-3.5 watts especially the units that left with Motorola Final transistors. I have never seen a stock unit with motorola finals key more then 3.5 watts from the factory. So they designed these amps to work with that type of power. Their where no dual final radio's and the 2SC1969 was not the norm either. So they gave you an extra tube that could put out the 25-60 watts needed to drive what ever tubes they decided to use for finals.Today we have monster chasis's with Mosfet trans putting out 200-400 watts. Never mind they do not fit well in anything made since the 1980's short of Big Rigs and Farm Equipment. They also look like a growth on a dash.....Like a Mushroom from Super Mario Brother's is sprouting out of your dash! LOL So the unit was not made for how you useing it. I would suggest you match the radio to the unit.

 

[ExitThirteen]

By 20W input, I'm referring to SSB. For AM, definitely no more than 4W... 2-3W is plenty. 20W is about max for that amp on SSB. the 6LB6 tube is rated at 30W plate dissipation, so you're running 66% of the max plate dissipation of the tube. Anything beyond 70-75% or so will shorten tube life and cause some nasty modulation.

~Cheers~

 

[Se7en]

Good to know guys thanks for the write up ETR, funny bout the mushroom yea )

ExitThir.... true. i didn't mean 20w DEADKEY. just simply 2.5 DK with a modulated of 20w peak into the driver tube. the mic gain isnt something id try to use for my "swing"... ill back down the rig to 12w PEP. i DONOT use this linear for SSB no point really unless i like killing10 channels up and down 40 blocks away. i simply want the box to do a steady 500w. it does it but its slowly dropping a watt. thus why i asked about 4 tube rather then a 1x3 config. i understand the Pi network and see why it is not as "easy" as "said" done.

73s guys thanks.

 

[wavrider]

Good to know guys thanks for the write up ETR, funny bout the mushroom yea )

ExitThir.... true. i didn't mean 20w DEADKEY. just simply 2.5 DK with a modulated of 20w peak into the driver tube. the mic gain isnt something id try to use for my "swing"... ill back down the rig to 12w PEP. i DONOT use this linear for SSB no point really unless i like killing10 channels up and down 40 blocks away. i simply want the box to do a steady 500w. it does it but its slowly dropping a watt. thus why i asked about 4 tube rather then a 1x3 config. i understand the Pi network and see why it is not as "easy" as "said" done.

73s guys thanks.

500 watts is asking a lot from those three tubes.

I use 6lb6 for converting old 8950 pa finals to 6lb6. The 6lb6 is less expensive and easy to locate.

I set the drive up so that a single 6lb6 will put out 60 watts of PEP power, At that output the tubes basically last for many many years.

If you lower your drive into the amp, keep your pep swing down around 12 watts. you will have a cleaner sounding signal on the air, less splatter and that old amp will continue to give you good service for many years providing you have upgraded the filter caps.

The difference between 250 watts output and 500 watts output is 3DB or around 1/2 an S meter, the difference between 250 watts and 500 watts on those tubes means years of service.

 

[ElectronTubesRule]

I can see 20 watts on SSB still pushing it a bit but that depends on the tubes, the power supply the transformer voltage etc......So I can see it in some but I would not drive it past 12 on SSB myself I like a super clean sound with plenty of headroom and I like tubes to last.

If I really wanted power I would not look to a sweep tube for it. For the power hungry with the price of sweep tubes being so high today you are so much better off using a tube designed for RF use. I have two sweep tube amps and one is a fantastic little amp the other is well just looks like something I would built in 5th grade following plans from a book for my Boy Scout Ham Radio Merit badge.

So if all you have is a 1 driving 2 up to about a 1 driving 4 the cost is not bad you can live with it. If it is more then that just get a different amp. Those amps that are able to make 1KW or more with sweep tubes are money pits. The only way I would ever buy one is if it was dirt cheap and then I would convert it to a one or two tube rf tube set up. Now if you bought a ton of tubes in the 1980's getting ready for the Cold War to turn Hot well then it is a different story. Their are plenty of tubes designed for RF amplification that can make 350-1kw easy on a single tube in a compact chasis and even be broad band. Just something to think about.