On September 9, 2014 at 13:41, Ernie Gilman said...
Glad to hear that. When you called them "tube covers" and "extra grid wire" it didn't seem like you knew.
It didn't even occur to me that those might be octal sockets. The chassis I've seen that looked like that had six pin sockets with no center pin and tubes with numbers like the 35 or 37; the rectifier would be the 80 with four pins. The pins connected to the filaments on those tubes were thicker than the rest, making it hard to put them in wrong, but not impossible. The center pin of the octal and loctal tubes could not be put in wrong.
Well, no offense meant. When I write, I write for the person I'm commenting to as well as to the rest of the guys who might run across this. To some it's a novel idea that ground is a DC potential of zero, just as it doesn't occur to most us that DC is a signal with a frequency of zero Hertz. I added that comment to answer their question "what do you mean by grounded or held at some other DC potential? How is ground a DC potential?"
There's a further argument that could be brought up, that "potential" can't be zero because potential indicates the presence of a level of energy. But if you can have positive energy levels that are potentials, and negative energy levels that are potentials, it makes no sense to define potential as discontinuous, with the zero point not being potential. And zero is a level.
I also figure you know all that stuff I wrote above about earlier tube pins, but some others might not know it. And there were no nonal tubes as large as the ones in the chassis you showed.
Yup, early 80s. Maybe started in the late 70s.
The rectifier is 80, V1 is 6C8G and the mixer is 6Q7G and as I think I mentioned, the output tube is 6L6G. I recapped it and replaced the power cord and fired it up without tubes, to make sure the power transformer secondary and heater voltage was correct, then loaded the rectifier. Bupkis. No B+, so I went to Ebay and looked- found someone selling three which, according to him, all worked. Got them for $18.50, shipped. Put the first one in and saw it glow, so I let it warm up before checking the B+, which was right where it should be, according to the data for the other tubes. I then inserted V1, V2 and V3, checking voltages as I went. Once they were all in and warmed up, I plugged a cable in and touched the tip- not much. Bummer. Went up to my computer to look at the data for V1 and V2- turns out, they had been in the wrong positions- I removed them and placed them on my bench in the same order as they were in the amp. I swapped them and when I touched the tip, it was a lot louder. The volume control has a spot that's a bit crunchy from sitting for who know how long, but it sounds great. I assume the rectifier went bad and the owner removed the tubes and took them to the local drug store or TV repair shop to have them tested, giving up when they may not have been able to buy one, or afford it. At some point, someone was shooting BBs at it and I found a few inside of the chassis. I noticed the little dents on the front before I heard them rolling around.
It came with a full set of KenRad tubes, which were probably original and they look very good- not bad for almost 80 years old.
I don't assume others know tube amps, so I called them 'covers'.
According to this site (
[Link: tdsl.duncanamps.com]), the 80, 6Q7G and 6L6G were introduced in 1936 and the 6C8G was introduced in 1937- I don't know how long they were available before the would have been used in products brought to market, but it's possible that this amp was made in '37. Since it has 1/4" jacks, using the tubes for dating it seems to be the most accurate, due to the lack of EIA product codes (which began in 1941).
Nonal (often called 'noval') tubes seem to have been produced after this amp was made. It also would have been produced during the Hawaiian music fad of the 1920s-1930s.
WRT ground and potential, if the chassis is used as the shield and grounding plane, any points with connections to it should be at ground potential or, as it's sometimes known, equipotential, meaning no potential difference and therefore, OV between the connections because voltage is potential energy. I think some become confused when discussing LowZ balanced audio when the ground plane for the audio is "floated" above the ground plane for the power supply.
