8950 tube ??

[ExitThirteen]

Ahh, yes... the venerable MaCo Amps... I couldn't even begin to count how many of these I retubed over the years... it is kind of a pain, but once they are re-wired to accept 6 volt tubes, it allows you to retube it with several different tubes. I do agree that if you're unsure about re-wiring the sockets to accept 6 volt tubes, you're best off to take it to a tech that can do this for you. Good luck!

~Cheers~

 

[tramdr]

Maco

Though they have similar voltage ratings, seems that the further you go down in dissipation, the quicker they will flashover and kill the tubes, even with less drive and power out.

 

[High Voltage Mobile NJ]

I have been doing some researce,and I see if not mistaken. I can take a 8950 tube and exchange the heater pins 1 & pin 12 from the socket,and place a 6lf6 in and use it in place of the 8950! 6LF6 is just a broke down verson of the 8950 but at 6 volts........any thoughts

do a mod an upgrade to 2057 tubes its like a 8950 on steroids . its not to expense to upgrade .

 

[mackmobile43]

do a mod an upgrade to 2057 tubes its like a 8950 on steroids . its not to expense to upgrade .

Do you have any examples of mod upgrade?

 

[AudioShockwav]

Unplug the 8950 and plug in the more expensive M2057.
The only advantage that the M2057 has over the 8950 is 7 more watts of plate dissipation .
That is about it.
The G.E. 6LB6 is 30 Watts Plate dissipation ( 6 volt heaters)
The G.E. 8950 is 33 Watts Plate dissipation ( 12 volt heaters )
The M2057 is 40 Watts Plate dissipation ( 12 volt heaters)
The Maco Brand M2057 was made by G.E., they also sold many under the G.E. brand...... some of them are about 1/4 of an inch taller than the 8950...depending on the run of the tubes.
I have seen M2057`s go for anywhere from $80 to $100 a tube.
You can find the 8950 for half that depending on were you look.

http://tubedata.milbert.com/sheets/084/m/M2057.pdf

http://scottbecker.net/tube/sheets/084/8/8950.pdf




73
Jeff

 

[ak3383]

old thread

I know it's an old thread but initially the poster stated he wanted to swap-out the 8950 with a 6lf6 and change the pin configuration but the replies were in regards to the 6lb6 tube and made no mention of the 6lf6 tube he wanted to use because he already had some that were good. Perhaps the 6lf6 and 6lb6 is the same tube, I just couldn't make any sense out of the tread because no-one addressed his question as stated. Just sayin

 

[LeapFrog]

To convert from a 12v filament tube to a 6 volt filament tube two of the 6 volt will be wired in series.

6+6=12

Two 6lb6 will use 12v for filament
One 8950 will use 12 volt for filament.

Since there is an odd number of tubes, not even. You will need to keep one 8950 at 12v filament.

then the other eight 6lb6 can be wired in series. Using two 6lb6 wired together for 12v filament from transformer.

Hope that did not confuse you as I re read it may be confusing.

I would sell the 8950's and then you would have enough $$ to buy 6lb6 to last a lifetime for that amp.

Pin 1 and pin 12 are heaters.
8950 pin 1 will have 12v and pin 12 will be at ground.

to make it work for 6lb6 two tubes are required.
Pin one will have 12 volts on tube A.
then on tube A pin 12 jumper it to pin 1 of tube B.
Pin 12 of tube B will go to ground.

I would put a cap at tube A pin one to ground for RF bypass.

hope that clarifies it better.

If you are unsure of how to do this modification then please take it to...

I know this thread is old, I've just finished what I think is a conversion on a 2 tube (8950 to 6v) amplifier following the description.

I would like to know, would it be a problem if I also placed a decoupling capacitor @ at tube B from Pin 1 to ground, instead of just the one at tube A?

Or would I be okay to just go ahead and add decouping caps on both ends of the jumper wire?
I am not sure if the extra caps are going to be an issue but I am hoping it is an improvement.

Thank You & Best Regards
-LeapFrog

 

[nomadradio]

One decoupling cap at the "hot" end where 12 Volts feeds the two series-connected heaters, plus one at the jumper point between them should be fine. Unless the wire that goes between the two heaters is long, it should not matter which end of the wire where it's placed.

73

 

[LeapFrog]

Thank You nomadradio, I appreciate your help. I can get the wire a little shorter yet.
[photo=medium]4972[/photo].

 

[nomadradio]

Looks just fine the way it is.

73

 

[LeapFrog]

Thank You NomadRadio

 

[BlowinSmoke]

Why in this day and age would anyone still deal with expensive wimpy sweep tube type amps when newer tubes made for RF use are cheaper and will make much more power? A pair of 572b tubes will blow any of these sweep tubes away or a single 3-500.

 

[LeapFrog]

Why in this day and age would anyone still deal with expensive wimpy sweep tube type amps when newer tubes made for RF use are cheaper and will make much more power? A pair of 572b tubes will blow any of these sweep tubes away or a single 3-500.

The amplifier came to me in a trade, I like it even though most would say it is a sweep tube junk box, to me it is my first two tube amplifier from the 70's.. I want a sb-220 but I gotta crawl before I can run. Besides adding metering circuits and filtering (plus a tuned input section) will be a great learning experience that would have been skipped over had I bought a nice amplifier from the jump.

I don't know if I got hosed on the tube purchase, but I am seeing 40-45 CW out so I think the tubes may be weak, but the amplifier lives.

Edit: with max plate dissipation rating of 30 watts, I am going to expect to get 15 watts carrier per tube. I can have the box produce a 30 watt carrier, and that should be ok, leaving head-room.
I appreciate all the people that are into radio that help others, thanks guys.

 

[RJB]

hi everyone,
I was give a PAL 351 BDX and the tubes were swapped out from 8950 to 6JM6A
the problem that i am have is i can't get the amp to amplify in xmit mode. i hope someone can help me

 

[nomadradio]

Not to put too fine a point on it, but has anyone done any of the last 40-plus years of maintenance? There are parts in the power supply that will only still work if the mileage is really, really low.

Kinda like having a 1979 car that just won't start. Except this amplifier has no odometer, so we don't know the mileage.

If the tubes have not been tested, that would be the next priority. Back in the day, books about electronic servicing would advise you to start with the most-likely failure items when you have nothing more obvious to blame.

Most common failure item is the tubes. Next most common is electrolytic capacitors, like the ones in the power supply.

Next on the list is moving parts, like the antenna relay or switches.

Which leads me to the first common question. Do you hear an audible "click" when you put the PAL into operate mode and key the mike? Or is it just silent? Identifying what's broke starts with identifying the parts of the system that aren't, one by one.

73