Type 51 Ericsson

[unbeldi]

That 1947 handset was only used for a little while on the type 1951. Only a year or so. I haven't been able to establish when they changed it. PTT also has retrofitted the newer design on almost all the early phones, so to find one with its Original handset is rare. After restoring about 50 of them and still with 30 of them in my house at this time, I only have one with the Original handset.

The Ericsson "F1" handset has in most cases the logo on the underside of the handgrip. But there are versions too without the logo. The Ericsson handset has flat ends, where as the true F1's have pointy ends.

NSEM (Standard) made a real copy of the F1, just like BTMC and ATEA.

Does your Type 1951 have a production date on it, Karl?

Well, I have recorded it as 1951, because I thought with that handset should be early, likely, but I am not sure now, whether I had better reasons. For some reason I have not recorded all data from the components.

But it's not obvious that there is a date from my pics.   The best date candidate is usually on the condenser, I think, but  the printing on the condenser is partially covered with the mounting bracket, so I have to open it some time and remove the metal mounting strap.  I do have a picture of it though (attached).  Perhaps you can tell whether the style of print is early.  The condenser canister also seems to use a lot more metal than later versions.

On the bottom is a gold decal "CE 51", which I suppose is the official PTT type and model number. But, I am not sure these were applied like this anymore in later years, at least I have not observed them often.

The circuit diagram was taped by someone on the outside of the bottom plate, and I have never removed it to see what is underneath.

[AL_as_needed]

It's a bit hard to make out the dark shades in the pictures, but your handset appears to be the later type that looks a lot like the Bell version, which is in turn quite similar to the WECo F1

Yes mine is of the F1 style, no logo or dates that I could find however. The rest of the phone is a 63/68, showing signs of a refurb in 68 with the dial and elements being the latter vintage. I have seen one of these phones with an actual F1 handset with WE elements inside, not sure if it worked. It did look good though 

[Matilo Telephones]

Does it have flat ends? Or pointy ones?

Left is flat, Ericsson. The pointy one is Standard (NSEM), on the right.

[AL_as_needed]

Does it have flat ends? Or pointy ones?

Left is flat, Ericsson. The pointy one is Standard (NSEM), on the right.

Pointy ends. Here are some better pictures of the handset. I did find a date under the receiver contacts, looks like 8-52 if I'm reading it right. And no PPT or other company markings.

[AL_as_needed]

Here is something I noticed just now: I now have the T-51 plugged into a split line with a 554 wall set. Each time I pick up the handset on the 554 to dial, the t-51 gives a slight "ding" from the ringer. Same occurs when I hang up the 554. This normal?

[unbeldi]

Here is something I noticed just now: I now have the T-51 plugged into a split line with a 554 wall set. Each time I pick up the handset on the 554 to dial, the t-51 gives a slight "ding" from the ringer. Same occurs when I hang up the 554. This normal?

From what I recall about the ringers in these, they are unbiased, meaning they do not have a mechanical means, such as a coiled spring to keep the clapper on one side when no ringing current is applied.

So, when someone makes or breaks the local loop, the induced current spikes are sufficient to move the clapper so that it strikes a gong.

All Bell System ringers have this feature, because the Bell System telephones never disconnect the ringer from the line when taking a set off-hook.  The PTT devices, on the other hand, are designed to first break the ringer connection before the rest of the telephone set is connected to the line.

[AL_as_needed]

From what I recall about the ringers in these, they are unbiased, meaning they do not have a mechanical means, such as a coiled spring to keep the clapper on one side when no ringing current is applied.

So, when someone makes or breaks the local loop, the induced current spikes are sufficient to move the clapper so that it strikes a gong.

If that is the case, then it should also ring when i dial out on the 554 with each digit.... This could make for some fun ghost call pranks.

[unbeldi]

If that is the case, then it should also ring when i dial out on the 554 with each digit.... This could make for some fun ghost call pranks.

In principle that is true, but the dial pulse contacts in the 500-series telephones are protected with a capacitor and resistor network across the gap, which quenches spikes and protects the contacts from arcing.

[andre_janew]

I think when he dials out on the 554, the Type 51 will ding.  For example if he dials a 5 on the 554, the Type 51 will ding 5 times.

[unbeldi]

I think when he dials out on the 554, the Type 51 will ding.  For example if he dials a 5 on the 554, the Type 51 will ding 5 times.

That's not what he described.


But the bell tap is still possible when dialing even with a filtered dial, it depends on the precise line conditions, distance between sets, the line polarity, the instantaneous position of the offending clapper. After all, the filter does not and cannot smooth out the pulses themselves, and they still cause changes in loop current as they must.   The filter should kill the high-voltage spikes, and reduced the pulses to the nominal battery voltage.  The 48 V battery has a much weaker effect.

[AL_as_needed]

After some toying around with the T-51 and a few 500s on the same line, the t-51 "dings" with each digit dialed, as well as when a 500 goes on or off hook. Quite funny to hear.

[andre_janew]

I take it that the T-51 dings 5 times when you dial a 5 on another rotary phone.  Years ago, I had a cheap Asian made touchtone telephone behave the same way whenever I dialed out on a rotary phone.  I guess the ringer on it didn't have a bias spring either.

[Matilo Telephones]

Strange that it does that. I have had many of them over the years and have never had one that did that. I had one that rang to its own dial, but it had a short somewhere.

[AL_as_needed]

I take it that the T-51 dings 5 times when you dial a 5 on another rotary phone.  Years ago, I had a cheap Asian made touchtone telephone behave the same way whenever I dialed out on a rotary phone.  I guess the ringer on it didn't have a bias spring either.

Yes the T-51 dings with each digit pulse, I can almost simulate a ring on it by repeatedly dialing zrero on another rotary (nothing happens when I use my 2500).

Matilo: I have checked over the wiring a few times now, and based on the wiring diagrams it should be correct. Could it be something in the ringer? I'm not sure what the voltage difference for telecoms would be US vs EU, if there is one? Outside of your side there is a real lack of info on these in English. (Sorry but the Dutch language was lost to the family in the 1800s  )

[Matilo Telephones]

I'll have a look this evening. I know the Heemaf ringer has an adjustment screw, that cause the the mechanism to react more or less easy to pulses on the line. Perhaps a similar adjustment is possible with the Ericsson ringer.