Author Topic: Bad transmitter (model 500) - what are my options?  (Read 1951 times)

Offline 1138

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Bad transmitter (model 500) - what are my options?
« on: September 02, 2009, 10:16:05 PM »
I have a Model 500 that I've cleaned up and intend on using as a regular phone. Everything works but the transmitter is bad: there's some sizzling and people can't hear me properly unless I have the transmitter positioned just right. I've tapped the transmitter out and it doesn't help. Handset cord seems to be good (there's no intermittency when I move it) and I have cleaned all the contacts (I disassembled the entire phone and cleaned everything). I tried another transmitter from a different phone but it has even more sizzling.

I think the transmitter is bad and I want to replace it. I was hoping to get some help as to what's the best replacement option. I'm not as much interested in keeping this phone in original condition as I am in getting it to work properly so I can use it. I've found the following options:

1) Order a new T1 transmitter from e.g. Oldphoneworks. These are still carbon transmitters, so I don't know whether they already have moisture or other problems. Plus, carbon transmitters seem to have a poor frequency response (at least both of mine do).
2) Order a "carbon compatible" electronic transmitter. This should solve the moisture and frequency response problems. Mike Sandman has them, but when I called, they said that it's not just a T1 sized drop-in. It comes with the cup and everything. Since my 500 has a hardwired handset, I don't know if it will fit (the staff member I called wasn't familiar with hardwired handsets, so I couldn't confirm that).
3) Order a modular handset from e.g. Oldphoneworks and get the electronic transmitter from Sandman. My phone is not notched for modular. I'm sure I can rig something up with a modular cord and some cord restraints, but this is not ideal and also an expensive option ($90 with shipping due to the different vendors).

Do I have any other options to get this working? Are there any drop-in transmitters that are designed for hardwired handsets? Will getting a new T1 solve the problems?

Thanks in advance. I've put in a lot of effort to fix this phone up and this is the one remaining problem.
« Last Edit: September 02, 2009, 10:20:44 PM by 1138 »

Offline benhutcherson

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Re: Bad transmitter (model 500) - what are my options?
« Reply #1 on: September 02, 2009, 10:47:10 PM »
Hello and welcome!

Although carbon transmitters are lacking in frequency response, they're otherwise pretty much bulletproof.

Besides that, T1s are the pinnacle of the design of the carbon transmitter, and are very well sealed against moisture.

You mention tapping the transmitters-on really stubborn transmitters, it often takes more than a "tap" to get them loosened up and working. Sometimes, they take more of a bang.

If this doesn't work, and you still have the same problem with two separate transmitters, I would suspect a problem in the phone over one in the transmitter. You could be dealing with a bad wire in the handset cord, or possibly a loose connection somewhere in the phone. The dial contacts can be suspect, too.

Beyond that, T1s are easy enough to locate and inexpensive enough. I'd just go ahead and replace it. They're incredibly reliable-I've had probably 50 separate ones pass through my hands, and I've never seen a bad one.

Offline Phonesrfun

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Re: Bad transmitter (model 500) - what are my options?
« Reply #2 on: September 02, 2009, 10:56:14 PM »
Yes, I agree with Ben.  If there are two transmitters that both are scratchy and not when in another phone, then it probably isn't the transmitter.  The T1 was once the gold standard when it came to telephone transmitters and while they don't have the crisp response of a more modern transmitter like an electret, you cannot really hear the difference unless you are using the carbon transmitter over an PA system.  Phone to phone, they are still an excellent transmitter, and they do have moisture barriers in them.

So, since the hookswitch and the dial pulse contacts and the handset cord are all in series in the circuit, it is probably one of those that is causing the problem.  Wiggle the cord around and see if the scratching changes.  Tap on the hookswitch contacts and the dial pulse contacts too.  A mechanical tapping is usually the first way to try to isolate the problem.  I would not go to the expense of a new transmitter unless once you get it working static-free, you are still not happy with the sound.  Most of us old farts kind of like the older sound anyway.

Even with the more fuzzy frequency response of a carbon transmitter, a properly working 500 with its T1 transmitter is still one heck of a lot better than the cutting in and out you get on a cell phone or a VoIP circuit.  "Can you hear me now??"

Cheers
-Bill G

Offline 1138

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Re: Bad transmitter (model 500) - what are my options?
« Reply #3 on: September 02, 2009, 11:18:57 PM »
I know the problem isn't the cord. I've tried wiggling the cord, and there's no change. I've also tried taking out the transmitter and shorting the two contacts together and the sizzling was gone on from my own receiver, which is what led me to suspect the transmitter in the first place.

Which ones are the dial pulse contacts? I'll have to try testing them too. I've tried the same handset on two different phones with the two transmitters, but I haven't tried the other handset with the transmitters.

I really like this phone, it's just the constant "you need to speak up" I get from people that drives me crazy!

Offline Phonesrfun

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Re: Bad transmitter (model 500) - what are my options?
« Reply #4 on: September 02, 2009, 11:45:43 PM »
The dial pusle contacts are the green and blue wires from the dial.  If you have a jumper wire try jumpering where they connect at the network at terminals F and RR.

You can aslo bypass the hookswitch wires by jumpering also.  There are two sets of contacts.  Jumper between L1 and RR for one and try between L2 and C for the other.

I was a little unclear about your trying the other transmitter from the other phone.  Is that from a transmitter and phone that works ok, but when the transmitter is in this phone there is static?  If you tried the transmitter from this phone in the other phone is there static?

BTW, if you can follow a diagram, here is a link to the 500:

http://telephonecollectors.org/library/weco/500cd.pdf

For some, however, this may be too much information.
-Bill G

Offline rp2813

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Re: Bad transmitter (model 500) - what are my options?
« Reply #5 on: September 06, 2009, 12:24:33 PM »
I'm tending to agree with others here that the problem may not be the transmitter.  Have you checked every connection at both ends of the handset cord?  I had issues that I thought were transmitter-related and ended up finding problems at spade connectors on each end of the handset cord, one where it connected to the network block and the another where it connected to the receiver element.  Just a little jiggling of the wires at the spade connectors while off-hook produced the static and isolated the problem.  The dial mechanism/contacts are additional places to check, along with the switch hook contacts, as has been advised by others here.

This doesn't mean you don't have a bad T1.  After fixing my problem, I still had occassional static.  What I found is that my 1953 T1 seemed to have a carbon granule or clump of them rattling around, and no amount of rapping or tapping would fix it.  It's possible that you have a similar problem.  While it's unusual to have another random T1 act the same way, I suppose it could happen.  But if the interference sounds exactly the same with either T1 in place, that would indicate a problem elsewhere in the system.

Interesting that an "electret" transmitter requires its own cup in the handset.  I was considering retrofitting my daily driver 500 set with one of those, but won't go that route if it means replacing the cup.  The handset in question has the moulded cord holder with flat-bottom cup so I can't use a later style cup with cord holder on it.  I recently picked up a re-furbed 1963 500 that had been updated in 1979 and it appears that it went into storage and was never used.  It's like brand new and the 1979 T1 is the clearest I've ever heard.  You might want to try a replacement T1 since they're not that expensive, and I presume OPW tests theirs out for proper operation, but only after you've made sure the problem isn't being caused by something else.

Ralph
Ralph

Offline McHeath

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Re: Bad transmitter (model 500) - what are my options?
« Reply #6 on: September 06, 2009, 04:43:29 PM »
You can get new transmitters for cheap here:

http://www.fivestarphones.com/index.php?cPath=59_181&page=5

These are new made units.

Offline 1138

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Re: Bad transmitter (model 500) - what are my options?
« Reply #7 on: September 12, 2009, 01:19:30 AM »
Thanks everyone. I'm going to have to sit down one day and do some major debugging of the phone.

The model 500 connection diagram helps. I can tell what everything is now.

I'll probably put together some pictures and send them off to Sandman.com and see if their electret drop ins can possibly fit. It's sometimes hard to describe things over the phone.

Offline rp2813

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Re: Bad transmitter (model 500) - what are my options?
« Reply #8 on: September 14, 2009, 02:42:15 PM »
Do report back on the electret drop-in capsule.  It would be good to know there's an easily retrofitable alternative to the carbon element T1.

Ralph
Ralph