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Old 01-17-2018, 10:36 AM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,743
So....A lot of stuff has happened since I last posted...



Back on new years eve, I decided: "dagnabbit I'm at least going to start the resto this year!".
I took shots of the chassis organized my parts and got ready to rebuild some caps.
Before pictures:


I knew I'd have to find paper shells to stuff to sub for the bumblebees and white ceramic tubulars, but what eventually really frazzled me was the realization all the 'paper caps' were Dumont Duramold Bakelitized tubulars....Essentially bumblebees with a paper jacket molded on. I had some samples from other sets that I attacked with various methods (heat and dremmel), and after a few tries, I concluded there is no practical means of separating the guts and the paper sleeve without ruining the sleave. After nearly giving up on restuffing (part of me wishes I had since restuffing that many caps is a LOT of work) I came to the conclusion "heck if I was going to find alternate caps to restuff for ~6-10 of them, why not just do it for all of them?", and off I went. (hoarder alert! )I've got a bankers box worth of can lytics, paper caps, vintage molded plugs, and other interesting defective parts I've saved since the beginning of my resto work. From that box, I was able to pull re-stuffable paper caps to restuff in place of the originals. Since I found Sprague and Aerovox in the set I tried to stick as much as I could to those as the new shells. I gutted MANY paper shells, saving the wax and altering a few label numbers as needed, selected shells slightly smaller than original where possible to open up chassis space, and placed modern caps of the correct value in the shells filling some of the extra internal space with paper towel scraps (to conserve wax) than sealing the ends with the saved wax.
There were 3 orange drops from vintage repair work that I decided to leave alone. And in the HV cage I basically decided to not restuff anything (I figure smaller caps are harder to arc to)...Except the .22uF cap since I had one restuffed cap laying around.
Every restuffed cap has a red band on it, to denote the restuff.
The original paper caps are labeled with the Sam's ID number in the 'bad parts' bag.
I decided to mimic Christ Riggot's cap rebuilding technique on the multi-section lytics making a central wire bundle for the cap pack and substituting a piece oa aluminum from spare cans for his PVC section. The 4 cans under the seleniums I did my way: drill one hole per lead of the replacement cap through the wafer near the terminals and wire them up....Also since 2 had cardboard tubes I simply pulled the cardboard off, beheaded the can, put the new cap in and placed the cardboard tube over the topless can...I then decided to copy that on the metal cans by stealing the cardboard off other spare caps I had...It is easier and you barely see those caps anyway.
The result:


I need to order more parts...All the tubular lytics 50V and under on the underside of the main chassis are still untouched, the 4uF 350V cap on the RED video amp board consists of 2 10uF 150V parts in series tacked in since I mistakenly ordered 2 3.9uF 450V caps instead of the 3 I needed, and the ballast resistor is dead (I kludged together a sub with series-parallel parts but it is not worthy of the final work).

All the white peaking coils were predictably wide open and got replaced...With 2 exceptions: The one under the IF shield was fine, and one of the demod-matrix coupling coils was a brown replacement probably from the 60's (shows how lousy those coils were that techs were changing them back then).

Powering it up on saturday got me a raster, sound and 10KV of HV...After some head scratching I finally pulled the 6BK4 completely out (it's top is so close the HV rect cathode that disconnecting the 6BK4 top cap had no effect!). The grid of the 6BK4 was too positive, and tacking in some parallel resistance with the 4.7M got grid voltage back in a range where the HV pot works decently. With the reg out it can do about 28KV. With the reg in I had it set at 25KV. Based on the grid voltage that was producing that regulation VS the listed voltage on the schematic I probably need to replace the HV reg tube and do more work on the circuit. The 6BK4 is one of the oldest I've seen. It sort of looks like they soldered the plate together and then it redplated or something.
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Tom C.

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Last edited by Electronic M; 01-17-2018 at 01:51 PM. Reason: add pictures and split the post to add more pictures/info
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