WARNING – foldback and tapering, a tale of caution and consequence (Part 1 & 2)

[peterb_2795]

Spoiler alert: NEVER mix wine, heat and Hammond plastics….. else, read on…


There have been many posts and advices given in regards to how to do both full-foldback and manual tapering for Spinet series organs (in my case a M100). I am sure that there are many that have been very successful in performing these modifications, and I am sure that there have been a number of stories where a job has gone horribly wrong resulting in a ruined manual.

I ordered an upper manual foldback kit off Ebay (Alan Dubois) just before Xmas with the intention of making the installation a nice little project between Xmas and New Year. The kit arrived as a well presented set of key contacts with clearly written instructions.

I was pleased to be able to make a start. The first thing that I did was create a new spreadsheet that clearly represented the works I was to do from the visual perspective that I would be working.

FOLDBACK
I set about the foldback activity first and found that inserting the new contacts was a relatively simple, if not Zen like activity to do. There was a certain ‘pleasure’ when one felt the new contact just ‘clicking’ into place without having to fiddle with a pick in order to get it through the correct guide hole. I approached the job based upon frequency order and when completed, soldered the ends off at the appropriate frequency lug.

First set of contacts installed, frequency 80, lots to go…



TAPERING
After inserting the 48 new key contacts for the foldback job, I then set about the tapering activity. This involves soldering 36 x 27 Ohm resistors in parallel with the existing 16 Ohm resistor wires to obtain the desired 10 Ohm resistance. Again, a job that I worked carefully and methodically through and found quite enjoyable as it was similarly Zen in nature.

After tidy up, I thought to myself that I had done a very neat/tidy job and deserved a glass of wine or two to celebrate my apparent success. See below:

Foldback and tapering complete... and with a nice tidy wiring loom



All in all, looking like a damn fine job.

Whilst having a well deserved glass of red, I thought that I might return to my work and just use a mini heat gun with a small nozzle to ‘tighten up’ the heat shrink and make an already tidy job into a ‘piece de resistance’. Thus, I very carefully applied some hot air to the heat shrink keeping in mind that I am working near plastics and was thus very careful to keep the nozzle pointing upwards. I then retired for the evening feeling very pleased with myself.

BAD MOVE
When I came to check continuity, I found that some of the key contacts had frequencies that spanned several frequency lugs. Knowing that this is definitely not correct, I took a careful look and discovered ‘horror of horrors’ that my upper contact support plastic had warped (due to the heat). I had one of those gut wrenching epiphanies that again told me never to mix heat (wine) and plastics!!


Oh dear, warped chassis plastics resulted in numerous key-contacts being in contact with the busbars.


I never thought to look at the actuators that had lifted because I assumed that they were pulled upwards due to the warping.

SOLUTION
If I were to be living in the US, then the solution would most likely have been to simply grab another upper manual from some ‘donor’ M100 (given that they still seem to be plentiful). However, I live in Australia and the story is much different. Hammonds and Leslies (and parts) are becoming scarcer than ‘hen’s teeth’ so it was once again off to the US to purchase some replacement chassis parts. This I managed to do and one week later they arrived.


THE FIX
I determined that I would need to be very careful in managing the key-contacts and resistance wires as I removed them. Previous experiences with the enameled wires told me that they can very quickly become a terminally tangled rats-nest. I resolved to use an additional piece of chassis plastic to act as the temporary storage bin of the individual contacts as I removed them from the damaged chassis. This scheme worked out very well and also provided the benefit of not having to label every key-contact removed.

Removing the key-contacts and storing to the temporary storage assembly



The forum only allows 5 attachments/images per post so please read on in Part 2..

[peterb_2795]

WARNING – foldback and tapering, a tale of caution and consequence (Part 2)

Spoiler alert: NEVER mix wine, heat and Hammond plastics….. else, read on…


continued from Part 1...

Key contacts and warped plastics removed, ready to replace with new plastics in the chassis



ADDITIONAL SURPRISES
As I was disassembling the chassis parts, I found it progressively difficult to remove some of the key contacts. The answer was soon to become obvious. As it turned out, not only did the key contacts guide plastic become warped, but also 8 of the 12 actuators were damaged. What is amazing is that in some cases the degree of shrinkage was also huge. In a few cases, I had to actually use cutters on the actuator in order to free out the key contacts.




Once I had cleared and safely stored the key contacts, I replaced the guide plastics and then started to re-insert the key-contacts by orderly transfer from temp storage assembly back into the chassis. Working from right to left, and from back to front, the job moved fairly quickly along and certainly aided by not having to remove labels etc.


After completing the re-insertion of key-contacts, I put some tie-down wires across the wiring loom and again tidied the job up with the following end result:



Once completed, I retested all contacts –vs- frequency and all contacts –vs- busbar. I was happy to find that I did not have a single error or problem resulting from the repair.

I am certainly not particularly quick when working on these organs (I like to work methodically and neatly), thus the time that it took to initially install the foldback and all of the tapering was 8 hours. The time taken for the repair (which could have been gainfully used elsewhere) was 10 hours. A very painful lesson indeed which thankfully was paid out in time rather than dollars! The warped and shrunken plastics are now to become a ‘decorator’ item in my workspace asa permanent visual reminder of that moment of red wine induced lack of clarity in thought.

I thought that my tale of foldback and tapering on the later (non Bakelite) based Hammonds could serve as both a reminder and a useful warning to others contemplating these modifications. I am fortunate in that I am modestly used to working within the wiring looms having fixed broken resistance wires after defoaming a few Hammonds (I am NOT a tech but I do love these instruments and do what I can to preserve these beasts and the tonewheel Hammond/Leslie sound for future generations). If I were to have been less adept at working in this space, the result could have been a write-off disaster – so that alone deserves a word or two of warning to those who might consider using a heat gun to shrink any heat-shrink around resistor connections when doing the Tapering modification.

BUT, more generically … THE MORAL OF THE STORY IS …

NEVER mix wine, heat and Hammond plastics … EVER !!
NEVER mix heat and Hammond plastics … EVER !!

NEVER mix wine and what appears to be a good idea until you have had further thought about it the next day … LOL


BE WARNED .. :o

[nonreverb]

Very informative post!
I hate the green plastic. I remember one of the first B3's I had to do a foam job on. It was a late '74. Busbars were stiff and when I tried to move them with the shifter, the f*ckin' green plastic shifter plate broke in half!!....fortunately, I had a couple of the older phenolic ones in stock. Problem cured.
I had to reconnect a few broken manual wires in it and remember being somewhat terrified that if the iron slipped it would sail through that stuff like a hot knife through butter.
I suspect that plastic will degrade as time goes on...it might get so brittle that it literally falls apart.

[KC9UDX]

This would have been easier to read if both parts were in the same thread..

[peterb_2795]

This would have been easier to read if both parts were in the same thread..

Problem is, the forum only allows you to upload 5 images per post. I had 10 for the story so hence two posts. my bad ..:)

[Admin]

The limit is 5 images per post, not 5 images per thread. You could have posted the additional images as another post in the same thread. I've merged the threads for convenience.

[Jaim]

When I do this sort of thing, I dip the ends of the key contacts in a metal cleaner to get a good solder connection to the wire, add the resistor, heatshrink - then install. Been using 28g computer wire-wrap wire with good results.

You deserve an 11 on the stick-to-it-ness scale.

Jim

[peterb_2795]

The limit is 5 images per post, not 5 images per thread. You could have posted the additional images as another post in the same thread. I've merged the threads for convenience.

Much appreciated, I didn't know that. Next time I will ... tks

[peterb_2795]

When I do this sort of thing, I dip the ends of the key contacts in a metal cleaner to get a good solder connection to the wire, add the resistor, heatshrink - then install. Been using 28g computer wire-wrap wire with good results.

You deserve an 11 on the stick-to-it-ness scale.

Jim

I would certainly have used your approach if I were to have been creating (say) new contacts to insert (ie. a 16 Ohm resistor soldered onto the end of a contact, apply heatshrink and then insert). For that part of the exercise (foldback), I had already acquired a whole bunch of key-contacts with 16 Ohm resistance wire attached. In the latter case (tapering), I was paralleling already in place contacts that have 16 Ohm resistor wires attached, and at that time, I didn't want to remove them, add the parallel resistor (or completely replace with a 10 Ohm directly) and then re-insert. I sure paid the price!!

I also use a touch of flux separately on the key contacts to get a good solder 'bite'. Have to clean up carefully afterwards though.

Being in AU and not having easy access to replacement keyboards, we have no choice but to do what is necessary to fix our little faux-pas! In all honesty, I was surprised that it worked out so well by using the extra plastic to organise the removed contacts.

Thanks for the 11 score on the stick-to-it-ness (aka Hammond nutcase) scale comment ... :-)

[geoffbrown]

well done. a mistake is only a mistake, if you can't fix it

[Thor Hammerdahl]

Problem is, the forum only allows you to upload 5 images per post. I had 10 for the story so hence two posts. my bad ..:)

I like the 2 parts; it was like a masterful play script, with story board, in two acts with a brief intermission. your good..:-)