300 a TUBE SWAP

[Sonar]

My Palomar 300a has two 6kd6's driving four 6lf6's.
I just got hold of six nos 6kd6's.
Is swapping the four 6lf6's out for the four 6kd6 finals okay?
If so is it a swap that consists of just removing the 6lf6's and plugging in the 6kd6's in without having to do anything else?
I know that some 300a's came with different drivers and finals but I believe this 300a to have the exact numbered tubes it came with from Palomar. They might even be the originals.
If it can be gone by just removing one and putting the others in, would there be any advantage (or disadvantage) to replacing the four 6lf6''s with the 6kd6?
I never tested the 6lf6's myself but I believe them to be good as I get about 450 with 11/2 swining 8/10 on AM which is what I us it on and believe that output to be what the manual calls for. Thanks. Ps If there's no other reason to swap them but for the fact the 6lf6' need to be replaced because it is that time then they'll make for good backup replacements. The were tested on a Hickock tube tester and we're show to be at 90% with other readings. I'm not sure what the other readings mean but they were within the numbers showing there in excellent shape.

 

[357]

6lf6 is the better tube.

the tubes need to be plate current matched within 10% or the strongest tube will suck up all the current and burn up.

eg: 110-108-112-109 would be a good match.
110-130-103-112 the 130 tube will not last long.
swapping the tubes might only show 50w more, they give good output all the way down to 60%

they are a direct drop-in, just the plate clips will need to be swapped

 

[BJ radionut]

6LF6's, 6MH6's, and 6LX6's are all pretty much the same tube. The only main difference is size. The 6LX6 tubes are usually taller that most 6LF6 / 6MH6 tubes.

The 6LF6 / 6MH6 Vacuum Tube is a duodecar type used in Linear Amplifiers and as a horizontal-deflection amplifier in color tv receivers. It requires a duodecar 12-contact socket.

Electrical Data:
Heater Voltage ................................ 6.3 V
Heater Current ................................ 2.0 A
Maximum Plate Dissipation ....................... 40 Watts

Preferred and Virtually Identical Substitutes: ........................ 6KD6, 6LX6, 6MH6

Substitutes ................................ 6JS6, 6KN6, 6LB6, 6LR6

WARNING ~ These tubes come in four different sizes! Even from the same manufacturer! Some of these tubes may not allow you to put your cover back on your radio or amplifier.

 

[Sonar]

6lf6 is the better tube.

the tubes need to be plate current matched within 10% or the strongest tube will suck up all the current and burn up.

eg: 110-108-112-109 would be a good match.
110-130-103-112 the 130 tube will not last long.
swapping the tubes might only show 50w more, they give good output all the way down to 60%

6LF6's, 6MH6's, and 6LX6's are all pretty much the same tube. The only main difference is size. The 6LX6 tubes are usually taller that most 6LF6 / 6MH6 tubes.

The 6LF6 / 6MH6 Vacuum Tube is a duodecar type used in Linear Amplifiers and as a horizontal-deflection amplifier in color tv receivers. It requires a duodecar 12-contact socket.

Electrical Data:
Heater Voltage ................................ 6.3 V
Heater Current ................................ 2.0 A
Maximum Plate Dissipation ....................... 40 Watts

Preferred and Virtually Identical Substitutes: ........................ 6KD6, 6LX6, 6MH6

Substitutes ................................ 6JS6, 6KN6, 6LB6, 6LR6

WARNING ~ These tubes come in four different sizes! Even from the same manufacturer! Some of these tubes may not allow you to put your cover back on your radio or amplifier.

Excellent information. Thank you. 73.

 

[357]

FYI
Check the top of the tubes, to to top cover clearance, especially the drivers.

I was told that the plastic tube spacers melt (and its confirmed) and the board gets loose, then people tighten the nuts and screws effectively RAISING the tubes doing it.
I took mine apart and added some washers to the spacer that was bent and melted shorter.

Otherwise you will short out the plates to the grounded top cover...bzzzzt
no good

 

[Sonar]

6lf6 is the better tube.

the tubes need to be plate current matched within 10% or the strongest tube will suck up all the current and burn up.

eg: 110-108-112-109 would be a good match.
110-130-103-112 the 130 tube will not last long.
swapping the tubes might only show 50w more, they give good output all the way down to 60%

they are a direct drop-in, just the plate clips will need to be swapped

I actually have no reason to change the the tubes in my 300 a.
You've given me some excellent information. I'll just hold on to these tubes. At the high prices there fetching I'm sure I'll be able to use them in the future. Thanks. 73

 

[Sonar]

FYI
Check the top of the tubes, to to top cover clearance, especially the drivers.

I was told that the plastic tube spacers melt (and its confirmed) and the board gets loose, then people tighten the nuts and screws effectively RAISING the tubes doing it.
I took mine apart and added some washers to the spacer that was bent and melted shorter.

Otherwise you will short out the plates to the grounded top cover...bzzzzt
no good


View attachment 18605 View attachment 18606 View attachment 18607

Thanks for the info and photos.
I can see the issue that can be caused with a taller tube.
My 300 a show's 450 with 1 watt from my 2340.
I've seen photos of other 300 A's with their top chrome cover raised using four individual pieces of straight metal brackets.
I'm wondering if the people who've done that did because of a taller replacement tube or for better heat dissipation.
I don't know about other 300 a's but mine gets hotter than hell itself.
I've been using this amp for 18 months now and am thinking of raising the cover.
I'd like to get as much life out of the two 6kd6's and four 6lf6's as I can and that heat can't help. The only issue I could think of by raising the cover is lots of dust getting in there.
I don't cover my stuff but am going to start.
It's amazing how much dust makes it's wat through the little holes in the cover of the 300a.
The same goes for the phantom and fs 2340. Thanks again. 73

 

[357]

You can see here, I guess there are some tall boys with top getters and grid heat radiators.
....now I see why mine are so close, they are the top getter style.