6A7 tube substitutes?
 

Popped the top off my 6A7 tube and may not be able to mend it

I have some digit tubes 77,78 ,58, etc.

Just wondering if i have a sub in my pile before i go online and order a new one..

Thanks..

SR

Better order one. None of your others will fit into the socket. 6a7 /2a7 are odd balls. Electrically they are the same as a 6a8 but they are octals.
GL
Terry

What i meant was 6C6 will sub a 77 and a 6D6 will sub a 78, is there a # that will sub a 6A7?? :D

SR

The 6A7 is a pentagrid converter tube and the only one that I know of, with the same characteristics in a UX7 base. More modern counterparts are the 6A8, 6SA7, even 6BE6.
I'm surprised that the prices went that high. :thumbsdn:

IIRC, the 6A7 was the first pentagrid converter tube and not really an oddball tube. They were being used from around late 1934 to the late 30's.
Some firms adopted the octal based tubes earlier. Many still used the UX bases much later, Philco especially.
The pentagrid tube replaced the use of the separate oscillator and mixer tube or the autodyne converter setup. :scratch2:

Steve, In case this link is dead where I saw them on ebay and I have three myself. https://www.ebay.com/i/262346461158?...SABEgLPgPD_BwE

Is the wire broke off completely flush with the glass?

For that price, he should buy two! They should only charge one shipping charge?
Those 6AF6G's look pretty interesting. I wonder if they could sub the 6E5 just by changing the socket? :scratch2:

A good 6E5 was in an RCA victor console's RC-1192 tuner, but I needed it for a Crosley 1127 (1937 Dynatrol 11) console radio I was restoring and found a way to make a 1629 eye tube work in the RCA.

I had to change tube sockets, then swapped a 6BE6 for the 12BE6, and moved some series heater wiring. Probably cant do this in too many radios, but this one's wacky design made it a no-brainer, since I have several 1629s and few 6U5/6G5 and 6E5s sub for those.

Yep, it broke flush with the glass, i had enough to test with and the tube is marginal, so i bit the bullet and bought a NOS one off the bay..

While im inside this radio, is there a good sub for a .25MFD cap? :D

SR

A new .25MFD cap :D

.25 costs a bit more than the .22 And...that may not matter if its a bypass cap and not in an RC network

In parallel heater sets you can make a 1629 socket adapter with a voltage doubler on the heater to convert 6.3VAC to 12.6VDC...Heater don't care if it has AC or DC as long as it has enough of it...I've done this more than once.

If you have a .22 and .03 you can wire them in parallel. Some restorers get pissy when they see it but it works fine.

In just about any radio, any spot ... either a 0.22 or 0.27 uF cap.
In fact, they would be OK in just about any TV, even in a timing circuit.
Normally use a 0.27.

Only in real hi-fi audio filters would it matter.

Some restorers wouldn't like me at all. I never re-stuff capacitors, except Bakelite blocks. My CTC21 still has the original multisection electrolytics attached to the chassis, but the leads are cut off and the new discrete electrolytics are under the chassis :nono:

And I woulda just used a .22 or .27uf cap, it's probably just used for a tone control/bypass/coupling anyways. Only the silver mica picofarad capacitors in the tuning/IF circuit have to be exact.

Fortunately, i found a .25 in my odd cap batch. In fact, i found useful matches from previous builds where i ordered extras..

The radio in question is a Fairbanks Morse model 56.. Now all i need is a safety cap for the line to chassis. I was thinking of yanking a pair out of a DIRECTV DVR power supply board i have been scavenging parts from..

SR

How perfect the recap job needs to be for a restoration depends on how desirable/important the set. My best stuff I restuff with quality new parts, worthless trash I want to play with gets used caps pulled from junked BPC sets lazily tacked in...and there's plenty of shades in-between.

The .25 is a filter and decoupling cap for the fixed grid bias. It really does need
to be that big, but whether its 0.22 or 0.25 or 0.27 is immaterial.

Never had a radio act negatively with a new 6A7 installed.. It receives better with the old one. (new tube makes it whistle around certain areas of the SW tuning spectrum....... And the new tube tests strong with no shorts..
That and the fact the volume is still pretty loud in the Minimum position.. An odd acting radio i must say, but its alive.. :D

SR