can i use drive tube 12by7a inplace of 12by7

[johnny9]

i just got my new swr meter and swrs,are flat.best they can be.but noticed i was only dead keying 1/2 watt and swinging less than a watt on my tram d201.

so i propped the lid open and turn the light out"since i no sqaut about electronics lol" and all the tubes had a glow and looked ok..but when i keyed the mic i noticed one tube"the small driver 12x7" got a pretty blue color in it when keyed up..
so read on line that the tube ws gassed and leaking and wad bad..cool,my first fix with no tools..
i have a d201a also and the tube in it is a 12by7a,,i read that i could swap the 12by7 with a 12by7a and want to confirm before i do this as my hand wired d201 is in 99 percent new cond and pristine..im gonna copy below what i read,thanks,john

The difference between a 12BY7 and a 12BY7A is the "A" version has a controlled filament heating time. The resistance of the filament changes as it heats up and if the filament is one in a series string of filaments (ie like in a TV set), the voltage across each filament in the string will be varying in an unpredictable way. This could reduce filament life across the filaments with the highest overvoltages. If on the other hand all the filaments in the string heat up uniformly, the voltage across each filament should remain relatively stable. This is why the "A" version was made. As a driver in most ham rigs, the filament supply is 12V. Since the 12BY7's filament is not in series with anything (It's actually the 2 6V filaments of the 6146's that are in series and perhaps could benefit from controlled heat up time), it gains nothing by having a controlled heat up time. A 12BY7 will work as well as a 12BY7A for almost all ham applications.

 

[johnny9]

well ive installed the 12by7a tube and its doing the same thing..less than a watt dead key on my new astatic pdc2 meter and only swings a fraction,and the tube still has a light blue color when i key the mic. my meter on the radio has not been working correct either and in the manuel theres a few diff tubes that relate to the meter,but i dont think its those tubes,as when i turn the radio on the meter goes all the way to the right,then back to the left like supposed to,but it never goes left past the 1/4 way point and seems like it just has a sticky spot..

but did i read correct when i read the blue in the tube means it is gassed and no good? strange i had 2 of the same tube bad in 2 different radios to me..
id hate to order another one then it still be blue when keyed up.
id think another problem could poss be the reason for the blue color,or am i thinking wrong?

i can listen 2700 miles and every state in the usa past week,just dont have no watts according to the meter to talk except a couple miles..

my dad may have had a amp hooked to it 30 yrs ago,but i wouldnt think it could just come out of tune sitting in the closet..surely it wouldnt be turned down that low for a linear,as i read 4 watts dead key is a good match for a amp .
i was gonna play with the tune and load screws in the back but i figure that cant really change from sitting in the closet? any help is apreciated,john

 

[johnny9]

ok i swapped the tubes back to original since there both the same"light up a lil blue when keyed up"
dad came over and said that was normal for the small driver to look like that when keyed up..not what i read tho at all..

so if anyone has read any of this,,should i tune the test and load knobs on the back of the radio?
i just kinda assume they should be the same as they were 25 yrs ago myself,but since im only dead keying less than a watt im thinking about doing it anyway as i guess it cant hurt...i do have the manuels and easy to follow instructions.

dad said he always went by the modulation light,and when talking it def gets brighter and works like it should..

ANYONE ever have meter problems on these radios? as in changing the tubes that the manuel point to in the pull out section, for when the meter is not working correct?

 

[GnG8d]

If it's been sitting 25 years it probably needs recapped.

 

[GnG8d]

If it's been sitting for 25 years it probably needs recapped.

 

[johnny9]

this radio has not been used much in its life..ive heard before they need replaced but most folks ive talked to with in good cond radios as this say theres is fine..
if my electrolytic caps are bad would i still be able to hear 2600 miles in almost every direction? the radio recieves and talks great and everything on it works so far.just havent talked real far at all so far..

the problem is that i hooked up a new swr/watt meter and the meter says its less than 1 watt dead key and modulation..
should i adjust the test and plate load to see if it brings the watts up?
or is it because it needs new caps?
everything inside this radio looks new honestly..but i have no problem having these replaced..the only thing that dont work right is the meter in the center of the radio..can that be because of the caps also,,thanks very much for the reply btw..thought i wasnt gettin out

 

[wavrider]

Yes adjust the tune and load for maximum output on your watt meter

this radio has not been used much in its life..ive heard before they need replaced but most folks ive talked to with in good cond radios as this say theres is fine..
if my electrolytic caps are bad would i still be able to hear 2600 miles in almost every direction? the radio recieves and talks great and everything on it works so far.just havent talked real far at all so far..

the problem is that i hooked up a new swr/watt meter and the meter says its less than 1 watt dead key and modulation..
should i adjust the test and plate load to see if it brings the watts up?
or is it because it needs new caps?
everything inside this radio looks new honestly..but i have no problem having these replaced..the only thing that dont work right is the meter in the center of the radio..can that be because of the caps also,,thanks very much for the reply btw..thought i wasnt gettin out

 

[johnny9]

sorry if i sound silly,,im a gearhead and only have talked on cb,s ,never worked on them lol..
ok,i adjust the test and load,,WOW,they are pretty touchy and makes sense they could have been out of tune now that ive done it..

didnt take much back and forth with the knobs"per instructions" and its dead keying the normal 4 watts..
the pdc2 meter i got dont show any swing,just the dead key watts.i guess this could be normal? cheap lil meter..

but since i also adjusted/zeroed the meter in the radio <gotproof>
it reads 4 watt dk and just over 15 swing..meter only goes to 15 so prob like 16 watt swing id guess..
thanks fellas for giving me the needed push,as i was chicken shizzit to touch this thing..
now i been reading for hrs on the schematics to find these electolytic caps..says theres 4 of one and 3 of the other..i did see there cheap on ebay.

now to find someone in fla that has skills in replacing them and tuning the radio..the stuff i recieve ups leads me to think it would be real scarry shipping my radio a few states north to have this done.

anyone have a idea of a price it should cost to have these caps replaced?
or anyone in fla familiar with these radios?
thanks again,john

 

[wavrider]

http://www.worldwidedx.com/amplifiers/26225-how-tune-tube-amp.html


CK posted a "how to".

It applies to your radio also as you have a tube final in it.

Also if the radio is working, and you get good reports on the air then I would not worry about replacing the caps yet.

This is of course up to you if you want them replaced or not.

If it is an older radio as you described then a re cap and proper alignment would be of benefit.

Glad you got the old tuber working, now get on the air and make some contacts, and have fun

 

[johnny9]

thanks wavrider! gonna check out that thread after this post..yes,my old hand wired tram has made its first contacts tonight but nothing real far.
most ive talked was about 20 miles and they said i sounded outstanding on there end..
on my end it was all i could do to hear them lol,but the radio waves are very quite tonight compared to the past week..
in the am i can hear montana to ny and cali very well,but i can tell thems some big radios im hearing as they love to fight over the air waves.

since my radio is doing ok now will i really hurt anything running a 300-450 watt kicker?
the old avanti astroplane from the 70,s has dead flat swr,s and im running the big boy coax,that dont bend around corners lol.
i could really use some "receive" to hear better when the waves are quite like tonight,and would love to get out and talk further.
but dont wanna harm this handed down radio either..
i can get a nitro 300 in pristine cond,or can also get a varmit 450 in very good shape and putting out 95 percent i was told.
just dont no enough as to if they can harm the ole tram radio?
goodnight wwdx

 

[wavrider]

You will not hurt the radio using an amp, but encourage you to improve the antenna system first.

Seems like the radio may have low receive issues after reading your last post. Or it may be the height of your antenna.

 

[johnny9]

the old astroplane is only apro 14-15ft to the bottom ring and i need 25-30 more ft to get above the trees lol..its actually 12ft from my full metal roof on the house and trees all around.my old pres grant hears just as good with a k40 on it at the moment also.
id like to think its kicking butt for where its at since i do here 2600 miles or so every morning but thats big radios i hear for sure..

i just got a crank up tower that should get me 40ft when ever get time to repair the cable and make a fold down bracket for it..i dont wanna think about climbing it even when lowered,im a wuss when it comes to that

as a kid i watched my dad install them for a living back when cable tv got popular,and one morning climbed about 40 ft up ours at home and the amount it swayed really changed me for life

i do no where a heathkit sb221 is at a great price also