A440B Preamp - parts replacement

After being in My Southern Exposure for a few weeks in June, I am back to work on the audio projects.

Over the last few weeks, the complete inventory took place for all audio units to see what capacitors needed to be ordered, what parts were in-house, and which parts would be left “as-is”. Since the most notorious component in vintage electronic equipment is the Electrolytic, paper, and non-ceramic capacitors, most of those were targeted to be replaced and ordered if not in-house.

The 440 has two can type Multi-section electrolytic capacitors. I could only find a suitable replacement for one of them – a 40/40/20/10 UF @ 300VDC can. The closest I could find was 40/40/20/20 UF @ 450VDC. This slightly taller replacement model could also replace cans in the tuner and power amp units so I went ahead and bought five of them for $38 each. Back in the day, I could probably have gotten one of these for $15 each, so this is just the [extra] cost of time past.

Picture of original (left) and new Electrolytic Capacitors

Anyway, three other electrolytic capacitors in the 440 were on the list, one I ordered (40 UF @ 250VDC), and the other two were "in stock" (50 UF @ 3VDC being replaced by 47 UF @ 16-and-20VDC respectively).

After receiving the ordered caps, I sat down with soldering iron in hand to swap them out. This is a skill you probably do not lose, even after some 20 years of not being in the trenches (what we used to call “smelling some rosin!”). It took about two hours to complete the replacements. 

 New Electrolytic Capacitor installed (right)

As can be seen above, the new can was almost too high to fit and I had to remove some screws that held the base in place to get it situated. The new one had twist tabs to hold it in place but they seemed to not have tab edges to lock it in place so it wobbles a little right now. I will probably glue the base to the Bakelite riveted mounting. I also had to bend the tabs over on one of the accessory power outlets so it would not hit the top of the can. It does clear it but I will probably put a piece of electrical tape on top of the can. 

The left hand electrolytic cap has a spec that I have been unable to locate a close match (1000/1000 Uf @ 15VDC) so at the moment, I am going with this one. I did order some small radial 1000 UF at 16VDC caps, which I may figure out how to use instead of the can. Amazing the tech advance!

Cleaning

After completing the retrofit, I could not help looking at the grunge so I decided to clean out the tube compartment and wipe down the tubes. Of course, the printing on the tubes mostly came off as I rubbed them lightly with a Que-tip dipped in water. Assuming the tubes are still good, I may hold onto them for now, and consider replacing later.

Still to work on before power up

Besides more cleaning, the two wire A/C power cable will be replaced with a new 3 wire plug (with ground). Hopefully, I will be ready to power up in a week or so.