I am working on restoring an Emud T7 and the current issue I have is low audio output. I tested the EL84/6BQ5 and although it tests good on my TV7B/U it also shows shorts. Does this mean the tube is bad? I don't have another one to swap with it to test so thought some of you tube guys might know.

Thanks,
Frank

Frank

This tube has 3 pins, 1, 6 and 8 that are internally connected. These pins should not be used but might show shorts to others. Some tube testers indicate shorts are ok on certain pins. Your tester might be showing shorts on these pins? If that's the case tube is good.

http://frank.pocnet.net/sheets/127/6/6BQ5.pdf

Thanks Norm, most of the time when a tube shows shorts the TV7 book indicates that the short is normal. There are no notes about that on this one, It shows short on all pins. Seems kinda weird to me but maybe I am just grasping at straws because it would explain the low audio out on the set. I am lookinng for another tube now so I can rule that out as a cause.

Thanks,
Frank

I wouldn't use that suspected bad one anymore, as it might cost you a transformer. That being said, test a known good one when you get it in the same tester and see what you find.

H.mmm Those IC on pins 1.6.8 mean these pins cannot be used for tie points.

Frank

Since pins are shown as IC no guarantee another tube will be the same. IC just means connected internally to something, not necessarily the same thing between different manufacturers.

Normally we wouldn't use a shorted tube as mentioned by codefox. Since the radio works shorts are most likely related to those three pins.

Check setup for 6CW5. It uses the same basing as 6BQ5.

Norm, is a 6CW5 a replacement for the 6BQ5?

Frank

No, it has lower voltage ratings.

I have noticed that the pins showing "short" vary on the EL84... some brands have different internal connections.

OK,I replaced the filters and got full volume so I guess there is nothing wrong with the EL84? The radio is playing well on AM and FM now.

All I need now is for someone to tell me how to adjust the IF cans. It looks like they are covered in wax. I started a thread in the repair forum but no one has responded yet. Anyone know how to remove the wax seals on these cans?

Thanks,

Frank

I lovingly dig the worst of it out. If things don't nicely free up, then I gently heat a nail and ease it in there just long enough to free things up. Then make the tweak and move on.. You don't want to get a bunch of wax locking the threads up on you and preventing future service.
Remember, ferrite cores can be rather brittle.

Anybody else have a better approach?

Mecalero, what about turning the chassis upside down while you put the heat to the can. That way the wax wouldn't run down beside the coils?

Thanks,
Frank

Never thought of that. Hmmm.. Capillary action may render the effort futile at times. But, that could exist with gravity either aiding or opposing.
Might be worth a try. I'd still ease out the worst of it cold just because.

BTW: Don't shove a heated nail or other object in there. Ferrets (stupid phone spell-changer) are brittle. In a past life, I kept a set of ball-end Allen wrenches in my screen room. They were exclusively for heating waxed cores. Then I used proper tuning tools to make adjustments.

I had the same observation last weekend when testing a batch of tubes. So I went to my usual reference:

Nolan Lee, the (late) well known TV-7 expert, compiled a fantastic listing for all TV-7 test setttings. That included updates on shorts, listing corrections, etc. I think that's still out there if you search for it. Anyway, from his compilation it's noted for the 6BQ5: Short on 1, 2, 3, and 5.

All the data is in an xls worksheet. Here's the full entry for that tube (sorry, cut/paste doesn't do so pretty):


Tube Type Fil. Voltage Selector Positions Bias Shunt Range Press to Test Minimum Value Notations Settings Data Source


6BQ5 6.3 EV2-7930 30 - C 3 50 Short on 1, 2, 3, and 5. T.O. 33AA21-5-31G

I hope this helps you as much as it's helped me.

Best regards,
Grid2

More Hickok stuff here:
http://6007.us/

Nolan's stuff reposted:
http://www.antiqueairwaves.com/nlee/tv-7_index.html

Thanks guys. I found another 6BQ5 and it showed the shorts on 1,2, 3 and 5 as well. Good to have that data Codefox.

Thanks,
Frank