Total posts : 45366
Interesting story, Carl, about the recorder motor. Now that’s major surgery!
The parts arrived yesterday and I spent about 8 hours last night replacing the power supply electrolytics. What sounds like a simple task wasn’t so simple after all since one thing led to another such as removing parts to gain access to the circuit areas needed to replace the caps.
Another gotcha was that the circuit didn’t exactly match the published schematic and some of the resistor values did not match the parts list. Crosley is known for making design changes during the life of a production model so this is not surprising but it does slow down the process since the circuit changes had to be reconciled with what I know about what works and what doesn’t in tube equipment.
Most of the resistors and dipped wax capacitors were way off values marked. For example, a 15K resistor measured 22K, a 150K resistor checked as 90K. The caps were so leaky that a reliable measurement with my meter was not possible. These are being replaced.
One of the major problems concerned the three terminal wax caps which have two leads and a metal band around the body of the part (you can see one in the first post picture at the lower left.) According to information on web sites about this these were built with two caps in series with a common terminal at the strip connected to the junction and most of them were, but comparing this type of connection with the schematic and prior knowledge showed that some of them were wired differently internally. At least half of the time was spent pondering the schematic and reconciling the wiring to accommodate the new parts.
Presently, I have replaced about two thirds of the caps and resistors but I just had to fire it up (maybe I shouldn’t say “fire”) and check things. I installed a permanent line fuse just in case of problems and it held with the power on. The B+ and screen supply voltages came up nicely and settled close to spec and held steady indicating no apparent problems.
However, there was absolutely no sound from the speaker, not even the slightest hum. Applying an old radio man’s trick I touched the grid pin of the final amplifier and heard the reassuring 60 cycle hum (remember….old radio men think cycles since Hertz is what happens when you touch the wrong pin…don’t want that). Checking further revealed that one of the three terminal caps wasn’t built for bypass to ground but rather to function as a feedthrough. This is how I discovered they are not all built the same way. Fixed this and was treated to glorious audio which sounds better than it ever had despite that most of the audio circuit caps have yet to be replaced. This is very encouraging since it can only get better when these are replaced.
It is written that Powell Crosley Jr. followed the David Sarnoff model and constructed both a radio station (WLW) and a factory to build radios so people could listen to his station and would buy his radios. It was a successful strategy. Crosley developed a modulation method which gave very good fidelity for WLW. I recall they used to identify as “The nation’s highest fidelity radio station”.
For this fidelity to be important, the receivers had to have good audio systems and an IF bandpass wide enough to give good frequency response. The receivers also had to be sensitive since in the 1930s there were very few local stations in a given area and listeners needed to tune to distant stations for programming. Selectivity was also needed to keep the distant stations separated from those nearby and both characteristics are evident in this receiver. Such quality was necessary to induce buyers to spend one to two week’s pay for such a receiver. After WW Two the price and quality of many receivers was cut as I witnessed while repairing late 40s and early 50s radios.
Enough rambling for now but I expect to have this finished in a couple of days and will report more then.