The Fine Things are Always Hand Made
So today I installed the re-capped Volume Range Expander into the AW23 receiver, as I had no way of testing it as a stand-alone unit. In addition to re-capping, I also took apart the control potentiometer and very lightly cleaned the wiping surface with a Q-tip sprayed with DEOXIT. Not sure this was a good idea or not. Although the Q-tip was completely black after cleaning, the wiping surface almost seems like it is made of paper or something similarly flimsy, so I don't know if I was removing dirt or dissolving the part. This potentiometer seems very cheaply constructed in my opinion. Also went through my (very limited) supply of 6A7 tubes and tested them all so as to use the two most closely matched. They aren't identical, but are definitely the closest of all that I have available, so they are the best I can manage until I have more to choose from. My current order has been delayed in shipping.
I followed the instructions for installation in the receiver, held my breath, and powered up the receiver. Nothing shorted/smoked/popped so I assume that there are no major problems with the unit. But I am wondering how to tell if it is performing correctly. Some observations after listening to a rebroadcast of an old Dick Clark program featuring the music of Phil and Don Everly:
-With the Expander knob turned all the way to "OFF" position, the regular volume control knob must be turned up higher than previously to hear a local station at ordinary listening volume.
-The VRE knob really has no apparent effect for the first quarter turn or so. At times it almost seems like it is working on a delay and the difference in sound happens gradually after turning the knob.
-There are no local AM stations broadcasting symphonies or opera music with wide dynamic range, so I cannot use music like that for testing purposes.
-Is there an objective way to know that the VRE is functioning as intended?
-Was this device actually more of a marketing gimmick in 1936/7, or does it really have a noticeable effect when fully functioning?
Thank you and best regards-
For my Pointer Philly with the control well advanced, the effect was very noticeable. It uses a different tube lineup than your outboard expander for the AW-23.
There is an audible time delay in it's action. An abrupt sound is initially softened and then volume ramps up of the rather noticeably. Thus - Without the expander, CHESTerfield. With the expander. cheSTRERfield.
The expander control pot is used to vary the effect. My RCA tube manual (RC-19 of 1959) among the various circuit descriptions in the front devotes most of a page to the volume expander.
No its not a gimmick at all.My pointer dial Philly expander when adjusted right adds a much better sound to the radio.Scott always improved his radios ,so your expander is different than the Philharmonics and may not work as well.Do a search on how expanders work.
I wrote this up about 20 years ago. Needs updated, but it will give you a feel for how the expander works.
Hummm. Guess if a volume expander were to be effective, it seems reasonable it would might reduce the low end of the volume range in a noticeable way if you were listening to a quieter program upon activation.
I always thought of the feature as making the soft parts softer and the loud parts louder. You can use the volume control to adjust the general volume level and the expander control to vary the degree of available expansion.
My pointer Philly is in line for some work so been awhile since I powered it up.
Been using my pointer dial Philly a lot of late.The expander sure makes it sound good.Thing is today radio stations use a lot of compression on the audio...RCA Radiotron Designer's handbook has 8 pages on volume expanders.Explains how each type works and has diagrams of each..
I had been listening to the AW23 with the VRE activated to various levels from 0-Full and just was not really impressed. This may have a lot to do with the fact that I primarily listen to radio shows and hockey games, not music with wide dynamic range on this set, especially this time of year. But there are no AM stations in the Seattle area that broadcast that kind of music at all anyway.
Anyway, the sound quality of the radio noticeably diminished this week, so I disconnected the VRE entirely and left it completely out of the circuit. The quality of the audio did not improve. I tested the 6C6 tubes in the first two audio stages and found one of them (in the second stage) to read less than 1/3 as good as the others. I find this odd, since they all tested equal when I first brought the radio up on the variac and then started regularly listening.
I do not think that approximately 3-4 hours of use per week should be enough to cause this much degredation of performance in a previously strong tube in the relatively short time that this radio has been back in service. So my question is: Could there be an undiscovered problem in the VRE that would cause one of the tubes it connects to to degrade so quickly? Or is it more likely just a coincidence that this tube failed so rapidly?
Thank you and best regards-
Probably just a coincidence, tubes do go bad in strange ways and not because of anything you did or didn't do.
The VRE probably had nothing to do with the tube going bad, unless there was a DC voltage on the grid, but the inputs and outputs to the VRE are isolated thru capacitors. Almost all of the Chicago stations have gone to the news/talk formats. We had one Disney station that played music, but it is also gone. I do pick up a Canadian station that plays music, and WSM from Nashville also plays music.
I would change the tube and reinstall the VRE and see what happens.
Hook up a phono, CD player or FM tuner into the Scott's phono input. Then you can choose music for getting the feel of the volume expander. Suggest classical music, because it can have sustained softer passages and sustained louder passages. In contrast, much of Rock, Pop and Country tend to have a sustained volume level for the entire track which with its delay action doesn't provide much for the volume expander to address.