I have an old Delmonico PB-742

When I bought it I noticed the Stereo indicator light wasn't working, when I took it apart the previous owner seemed to have rigged another tube in the slot.


They had even cut out all but two pins to make it work


I purchased the 6ME5 listed on the diagram (expensive) and now my radio won't work. I can't find the old tube that was in there. Anyone have an idea as to what it was, its a Hitachi 6A...Or anyone have a suggestion as to what I should do, I don't feel like dropping another $30 for a tube for it to not work.

Ok , here's my best guess ..........

It's a series string radio . The original , expensive eye tube burnt out . Since it's not needed for proper radio functioning , the person decided to "jump out" the tube , and used whatever spare tube he had kicking around to keep continuity in the heater string .

The tube he used has different heater pins than the original eye tube did , and so he "reworked" the tube socket , rewiring the heater circuit to the "jumper" tube's heater pins ...

That's why when ya plug in the right tube , it won't work , cause the socket has been rewired to match the "jumper" tube's heater connection .....

Howz THAT sound ???

That sounds like it is a probability....NOW.....how to fix it? Anyone have a wire diagram for the 6ME5 socket? I can try to snap a pic of the socket itself to see if anyone can help with it. Thanks a ton Init, I'd love to have this back to glory. It played great, I had to go and muff it up by trying to fix it.

Well, start from here. Kind of doubt anything was changed if everything but pins 3 and 4 (filament) was snipped off on the dud. That 1 eg resistor is notoriously bad on eye tube sockets. Change it out.

http://www.diyaudio.com/forums/tubes-va ... agram.html

One flaw in your theory, excepting for some of the early battery types, the 6ME5 & virtually ALL other 7pin tubes use pins 3&4 as the heater connection...

The tube with the clipped pins is probably a 6AQ5, which because of it's 450ma heater vs the 150ma of the 6ME5, would have been a poor choice... Might as well have used a jumper wire...

Tom

Take an Ohm meter to the 6ME5 and make sure that her filament is intact.

Here's the original (pre-hacked) 6M-E5 base:

http://www.radiomuseum.org/tubes/tube_6m-e5.html

Hi Tom ,

On second thought , my guess could be wrong for not only the current difference that you mention , but also because if someone were of a mind to cut all the other pins off of the tube (to make sure the "jumper" didn't interact with the circuit it don't belong in) then they would have no need to rewire the socket , since any orientation is kinda meaningless when the tube only has two pins

Course , just seein a tube with 5 of 7 pins removed like that sure don't inspire a lot of faith in what was goin on in the "repairman's" mind ... Anythings possible with regards to this "repair" .........

I have an Ohm meter, but how its got a whole bunch of settings. I'm not sure how to check it? Any instructions or suggestions. Thanks

Pull out the instruction sheet for your meter, and become familiar with it first. They are all different,. Then come back and we can help then.

One of the first things to understand about troubleshooting is that if you take an action such as changing a tube, and you get an unexpected result (e.g. now the radio doesn't work), go back a step. In this case, it would mean putting the old, chopped up tube back the way it was.

There are only a couple of possibilities here. One is that the new tube is defective. If so, putting the old tube back should get you back to where you were before: a radio that plays, but no tuning indicator. If you put the old tube back and the radio still doesn't work, it means that something else has gone wrong, and you need to start troubleshooting. That's the other possibility.

Since you indicate that you no longer have the old tube, you can use your meter on the ohms scale to at least verify that the new tube has heater continuity. Put the meter on Ohms (if it is a modern autoranging DMM), or ohms X1 if not. Hold the new 6ME5 with the pins up and the keyway (blank space where there is no pin) facing you. Pin 1 is the first one on the bottom left. They then go clockwise around to pin 7, which is on the bottom at the right.

If the tube has a good heater, you will read a low resistance (a few ohms) between pins 3 and 4. All the other pins will show high (infinite) resistance, but that's okay. If you do not get a low resistance between 3 and 4, it means the tube is a dud.

Thanks for your help Chris, I'll try this when I get home. Does the tube have to be plugged in or just out in the open. I'll try both ways if I don't hear back first. Thanks again.

Ideally when you check the heater of a tube with an ohmmeter, the tube should be out of the socket. That way the reading does not get thrown off by anything else that might be connected in the heater circuit.

Ok so checked and met with a zero on the ohmeter. I'll have to check the other tubes, I'll also snap a pic of the 6ME5 socket to see if someone can tell if its been rewired in any way.

Thanks

When you say "zero," do you mean zero Ohms, as with the probes shorted together, or zero as in the thing didn't budge off infinity?

If you did get a resistance reading on the order of a few ohms from pin 3 to pin 4 of the tube, it would indicate that the heater has continuity. This would suggest that the problem is elsewhere in the set. Re-wiring of the socket might still have occurred, but the 6AQ5 tube you found in the socket also had its heater on pins 3 and 4, so one would not expect the wiring to them to be changed.

On the other hand, if the meter did not budge off infinity when you measured the tube, it would mean that the heater in the tube is open. In that case, another tube would have to be obtained, or the heater would have to be bypassed, which is what it appears the 6AQ5 was in there for.

Thank you guys for all your help, I narrowed down three tubes that weren't registering resistance on the heater pins, the first one I replaced was the 50C5 and boom, started to hum and fired up in seconds. Metallica blasting from a unit like this just seems unholy. The Magic Eye works perfectly when tuning, AM doesn't work, I'd assume its one of the other tubes that needs replacing or the antenna isn't connected I didn't look at the antenna scematics yet. I just have to figure out where to put it....my wife says "Basement...for when you work down there...you know not up here..." I have a cabinet stereo refurbished with a 6-disc changer & mp3 player hook up in our foyer, and the house is equiped with an intercom radio system from the early 80's.
I don't even know the value of a radio like this beings I haven't seen any others on sites. Anyone have a clue as to its worth. Might keep this baby outta the basement and into my office area.

Again thanks so much for your kindness and help. This was a great project. This is a great forum and community.