Question for old timers - vintage vacuum tube electronics - speaker location - Page 1
Forum section: electronics / beginners

author: Hobby73
author_rank: Regular Contributor
timestamp: November 29, 2016, 08:40:45 pm
content: I acquired a shortwave radio receiver from the 50's- 60's era. Like other shortwave radios of that era, it contains tubes. Also, the speaker is in a separate cabinet that is connected to the receiver.I read that the speaker is kept separately from the tube receiver for a couple reasons: 1) the heat from the tubes can make the cabinet quite hot and adversely affect the speakers, and 2) the vibration from the speakers can be disruptive to the tubes. I don't know how true either of these assertions are, but they sound reasonable. In the late 60's onward, as shortwave radios replaced tubes with solid state components, they started including the speaker within the receiver itself.My question is, if these reasons for keeping the speaker separate from the tube receiver are true, why did television sets from that era contain the speaker within the set itself?

author: retrolefty
author_rank: Super Contributor
timestamp: November 29, 2016, 10:14:12 pm
content: Quote from: Hobby73 on November 29, 2016, 08:40:45 pmMany shortwave and ham tube gear from the time did include built-in speaker. Mostly a style thing on the more upscale equipment. Matching speaker cab could and did include more functions like phone patch attachment, metering, etc.

author: sbennett1298
author_rank: Contributor
timestamp: November 29, 2016, 11:04:28 pm
content: Everything has pros and cons. Just because there are some advantages to having the speaker separate there are also advantages to keeping it all one unit.Cost and space savings.I can tell you tubes can be sensitive to vibration especially as they age.A tube can start acting like a microphone and cause horrible feedback.We used to call them "Microphonic tubes" when they would start behaving this way.You could tap on them to find the culprit.-Steve

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: November 30, 2016, 02:08:04 am
content: 1) makes sense. The heat might dry out the speaker surround.2) makes sense. Tubes can be "microphonic". Although sound doesn't travel in a vacuum, you can get vibrations through the metal leads and it vibrates the frilly grid inside, varying tube characteristics in-sync with the sound.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 30, 2016, 04:37:42 am
content: Having lived through the tail end of the era, I don't recall any of those reasons being touted as the reason for the separate speaker. I wasn't able to read every publication of the time though, so those may have been out there. I always thought it was just a cost and space savings for folks who would most often be using headphones anyway.SWL and Ham are not often group functions, so a speaker to allow more than one person to listen at once is seldom needed. Headphones to block outside noise and allow concentration on an often noisy signal are almost always a benefit. The choice then became one of comfort. Some find wearing headphones (particularly those of that era which were much heavier and not so adroitly padded as those of today) to be uncomfortable, and are willing to trade the acoustic advantages of the headphone for a speaker.I am sure that there were many reasons for this marketing approach. Another might be that huge numbers of those participating in SWL and/or Ham began their hobby careers during a stint in the military, where headphones were almost always the answer because of outside noise, and other factors. They were just used to that mode of operation.

author: Grateful6595
author_rank: Newbie
timestamp: November 30, 2016, 04:57:33 am
content: The speaker placement may have had something to do with the way the old electromagnetic dynamic speakers work in that the output transformer/choke was mounted directly on the speaker and it is not desirable to run these elements of the circuit in the proximity of the receiver.

author: Hobby73
author_rank: Regular Contributor
timestamp: December 05, 2016, 10:05:54 pm
content: Do any of you old-time Ham radio operators or SWL'ers know why the external speakers were so large? The one I just acquired is huge ... much bigger speaker than is needed for a single person in a room.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 06, 2016, 12:28:05 am
content: In the two cases I am aware of it was a partly a style thing. The speaker enclosure was the same height as the radio it went with. That meant there was no reason to pay extra for a smaller speaker. Small speakers didn't really become common until the transistor and TV era. Transistors because one of the things they were selling was compactness. TV because by the time you got the CRT and all the video electronics crammed into the box there wasn't a lot of room in anything less than a console size TV.