A1 with 302 as subset - pop when taken off hook

[mariepr]

The wiring of an A1 to a 302 chassis really deviled me, but I finally decided to let the 302 wiring scheme predominate.  (This is not canonical BSP, but I much prefer the compact desktop subset that can be made from a 302 base.)  Long story short it sounds great, dials out, rings.  But when I lift or put down the the receiver I get loud metallic "pop" in the handset.  Not when dialing - I managed to wire the shut contacts working right. 

I usually rely on Steve Hilsz's wiring diagrams but a 302 has no "B" or "RR" terminal.  Might the more technically inclined take a look at my attachment?  I've made an illustrated "how to do it" guide sheet that I'd like to make available to the collector community but don't want to widely disseminate it if it has a major electrical flaw.  I've already tried if using BK/Y terminals for the switch hook instead of GN/W would help but no difference. 

Maybe this "pop" is unavoidable since I am mating two generations of equipment?  The phone is for my personal use not resale - and at the moment I'm feeling rather content on figuring it out this far.

(Attachment removed - refer to Revision 1 below.)

[unbeldi]

I looked briefly at your pictures and you do not seem to have the correct dial on your instrument.
As a customer substation the required dial for a handset telephone is the 2H, 4H, or 5H dial, which has an extra contact pair over the switchboard dials.

If you draw a circuit diagram of your wiring, the problem will become immediately clear when you compare it with the diagram for a 302 of which you used the base.

Also, the pop when operating the hookswitch implies that the hook switch is not properly disconnecting the receiver.   The 302 has both a hookswitch pair, as well as a off-normal dial switch pair in its immediate connection.

PS: I also noticed in the headline that you are using a five-conductor mounting cord.  A four-conductor cord should be sufficient, which function is performed by the fifth conductor?

[unbeldi]

Here is a circuit diagram that shows all connections and all switches in a 302 without the complexity of lines crossing all over the place, which makes the standard BSP diagrams almost incomprehensible without a lot of study.

The two hookswitches are designated as HS, and the dial switches are DS (off-normal switches), and DP (dial pulse).

If you follow the white wire from the receiver (RX) on the right-hand site, you see that it is first switched by the W-BB contacts of DS, which is normally closed, and then by the hookswitch HS, before terminating at point GN on the induction coil.
If you do have a hookswitch in this circuit, make sure it closes LAST, as indicated, when taking the set off-hook.

[poplar1]

You can use the same diagram as a 202 connected to a 684A subset. I don't understand why you chose to change the designated colors, though. And I agree that 4 conductors of the 5 in the mounting cord will be enough.

Handset:
Black (transmitter) to BK on dial (Dial should be 2H, 4H, 5H, or 6A -- not G)
Red (common) to R on dial
White (receiver) to W on dial

Jumper from BK on hookswitch to Y on dial
Jumper from W on hookswitch to BB on dial

Mounting cord:
YELLOW From Y on hookswitch to L2-Y on induction coil
GREEN From GN on hookswitch to GN on induction coil
RED from R on dial to R on induction coil
BLACK to spare terminal in 302 base (equivalent to BK terminal in 684A subset)

Line:
Red to L1
Green to L2-Y

There should not be mounting cord wire on L1 on the induction coil.

[poplar1]

Also, you don't need to connect the yellow wire from the wall to GND.

You are using the "GND" terminal to connect the slate condenser wire and the black ringer wire. On the diagrams, this would be the "K" terminal, but since it is just a convenient "blind terminal", the designation doesn't really matter.

[mariepr]

I've delayed following up on this in order to check out and address some of the issues raised.

The A1 has been stored for a while and if memory serves it came with the 2GB dial.  Not quite akin to buying a dial stick with what turned out to be a #1 dial but it was nonetheless quite a haul.  (Lousy seller photographs can sometimes yield good surprises!)  If not using a 2HB will cause some performance issues then I'll gladly live with those issues. 

As for "changing the wire colors" – the colors are meaningless to me other than as a guide to what should connect to where. But I can well understand that anyone who has spent their entire professional career following company installation protocols would find any changes to the standard color coding disturbing.   I have rarely worked with subsets as I'm the queen of AE mini-network installations.  Maybe, just maybe, a mini-network would fit into a manual A1 but there's just no room in a dial A1.   

I followed the outline in post #4 as an A1 would connect to a subset:  Zip, zero, nada.  I had been trying to mate the 302 while referring to existing subset diagrams and it was driving me to frustration.  But pretending that the A1 desk set was the dial and handset of a 302 did work.   
It was mentioned that there should be no mounting cord on Induction coil L1.  When consulting the wiring for a 302 EW-HW there is most definitely a direct connection between dial R and Induction coil L1. (ref. http://www.beatriceco.com/bti/porticus/bell/images/WE-302E_HW.jpg).  This is in contradiction to the standard subset wiring of dial R going to IC R.  The "5th wire" was the one to connect handset common to IC R as without it the volume is very low. 

According to my multi-tester the BK/Y switches made first, the GN/W switches made last.  So, I used BK/Y as the hook switch.  End result – there is no longer a loud metallic pop when the phone is taken off hook.  A livable "click" but not that loud pop. 

So, I have a mounting cord connection each on L1, L2, GN, R, and condenser Black. Will it work if I use 4 wires - take the handset red off the connection to IC R and instead place it on dial GN?  (I don't have "BB".) Nope.   

So, I've modified my instructions and shot new images to more closely follow established color coding.  But as it was said at the railroad museum:  There is restoration for historic accuracy, and there is restoration for use but the two are rarely compatible. 

I may try it with a B1 or D1 that has a 4H or 5H dial and see if I can get by with 4 conductors instead of 5 as those are more typical dials.  I suspect many others are also stymied at this conversion.  Was it Ray or Paul who made the subset conversion covers?  If more people find this helpful for converting a 302 then one of them might earn some money back on his investment.