OT - Way OT - Antique radio speaker replacement

Re: OT - Way OT - Antique radio speaker replacemen

Dan Donaldson

>One question: A lot of the old radios used electromagnets instead of permanent ones. Some of them also had a matching transformer on the speaker. You need to make sure you don't have one of those. If it is a permanent magnet speaker, with no transformer, then you should be able to use a normal 8 ohm speaker. Is the cone blown or is it electrically bad? If it is a unique type speaker and it is just the cone bad, you can probably get it reconed.

Re: OT - Way OT - Antique radio speaker replacemen

wilbur

>Yes, impedence matching is important for tube amplifiers as well. (I know, you have a radio, but here we're just interested in the part that drives the speaker.)

You have a couple of ways of figuring out what impedance speaker you need. One is to look at the speaker itself -- there may be a label that tells you if it is a 4 ohm or 8 ohm speaker. The second is to look at the output transformer, which is where the wires to the speaker will be connecting to. The transformer may have a label that tells you if it has a 4 ohm or 8 ohm tap, and you'll need a speaker that matches it. You could also experiment by hooking up a 4 ohm and an 8 ohm speaker to the amplifier, and listening to see which one sounds better. If this is a brief test, you won't burn out your radio.

Finally, if you google for "Motorola 5t tube radio", you may be able to find a service diagram. I looked briefly, and there is one for sale on eBay. That would be the best thing, since with one of those, you'll be able to fix anything else that goes wrong with the radio.

Re: Original speaker gone.

Al Stokka - Cambridge, Iowa

>Dan,

Thanks for the advice. After I posted, I wondered if I should have mentioned that the original speaker was GONE when I got the radio. Finding a replacement would be a lot easier if I had the old speaker as a starting point.

Al

Old radio web page *LINK*

wilbur

>After doing some more googling, I found this web page, with schematics and service manuals for old tube radios. They list an RCA 5T, which could very well be identical to the radio that you have. Back in the day, RCA had many tube radio and tube amplifier plans, which were rebadged by other manufacturers -- kind of like the Asian machinery manufacturer of their day.

Hmm. Maybe things don't change that much.


RCA tube radio schematics

Re: OT - Way OT - Antique radio speaker replacemen

Jerry Nicholson

>Unless you know that the radio is still in operating condition, the speaker might be the least of your problems. Tubes go bad, filter capacitors dry out, coupling capacitors can short out, resistors can change value, etc. If you don't have a background in this stuff, you might see there is a local amateur radio club where you could find someone that would like to help. And lots of "hams" have piles of old parts such as speakers and tubes laying around. Especially the old guys!

Jerry

Re: OT - Way OT - Antique radio speaker replacemen

Ken Garlock Collin County Texas

>Hi Al.

There is a good chance that your radio is a pretty standard configuration. Nearly all the little desk top or kitchen radios had 5 tubes with the tube filaments strung in series. Tube filament voltages were chosen so that the total of all the individual filaments added up to 110 volts. This configuration usually had a 50L6 audio output tube. All the little radio permanent magnetic speakers of that era used a 4 inch 4 ohm speaker.

IF your radio has a power transformer, then the tube filaments would be 6 volts. You can tell this type radio because there will be a black power transformer at one end of the chassis. The little output transformer that drives the speaker will be about the size of an English walnut.

IN either case there is a high likelihood that the electrolytic capacitors are shot. Seventy years is an extraordinary life time for a capacitor of that era.

Al, unless you are experienced in radio repair, your best bet would be to clean it up and set it on a shelf.

Have fun,

Ken

Re: Schematic

Al Stokka - Cambridge, Iowa

>Ken,

Does this schematic help?

Yes, the radio has a power transformer.

Al

Re: Schematic

Al Stokka - Cambridge, Iowa

>Ken,

Does this schematic help?

Yes, the radio has a power transformer.

Al

Re: Schematic

Ken Garlock Collin County Texas

>Hi Al. What you have is a radio that is at least one generation older than I had thought. You also have a tuning eye, sometimes called a magic eye. The rectifier is a number 80 tube. The audio output is a #41. These tubes are so old that about the only way you can find one is as a used one.

I am guessing that the speaker is mounted separate from the radio chassis. I think I see a pointer to a speaker plug at the top of the pictorial. (A pictorial is a drawing of the layout of a chassis, where the schematic is a symbolic description of the components and how they are connected.)

Since there doesn't appear to be an output transformer mounted on the chassis, it was probably mounted on the back of the speaker. Radios that far back frequently used the output from the rectifier to both provide the electromagnet for the speaker and as an electrical choke to reduce the hum in the DC voltage, along with the electrolytic condensers. (One possible interpretation is that you will have a very slim chance of finding a speaker assembly for the radio. Like the paper dog chasing the asbestos cat through h****)

The next step might be to search the Internet for your radio brand and the time frame. There appears to be a chassis number in the lower right corner, and a serial number in the lower left corner.

When I was in grade school, we had a Silvertone console radio that had a shortwave band and the standard AM broadcast band.

Happy Hunting,

Ken

Not so OT - Antique radio capacitors

Frank House

>Things to bear in mind about old electrolytic capacitors:

1. they contained corrosive substances, including iron salts, when new (may have dried out by now).

2. the cases tend to leak when they get old (just like ... err let's drop that)

3. if in bad condition and not used for a while they can explode when power is applied. The electrolytics in a radio will not do much damage, but could make a mess. (I have seen a hole blown in the plywood side of an old television from that era when an electrolytic failed).

In short, stand it on a tray for storage, and particularly if you try to use it - I have a lovely solid oak sideboard with large black stains on the top from an old raido left there unattended for a couple of years :( .

Frank.

Re: OT - Way OT - Antique radio speaker replacemen

del schisler

>i been in repair for 50 yrs Get the model number and find a schematic and see what the output transformer say's It will also tell you if it is a electro magnet speaker or a 4 ohm or 8 ohm perment magnet style speaker Not a big problum you can get them easy That is the easest way to do it a Schematic make's the difference tell's you want you want to know instead of guessing del

Re: OT - Way OT - Antique radio speaker replacemen

Dan Donaldson

>Just an interesting side note. The school that I went to had a complete set of the Ryder's repair manuals. For those that don't know what they are, Ryders was the predecessor to the Sams's schematics. There was some interesting stuff in them. I had an old TRF radio from the 1920's and the schematic was there, as was the one for a 1929 Steinite that I worked on at the time.

Tube layout

Jerry Nicholson

>What you have there is the tube layout diagram. The schematic shows the circuitry that connects all those tubes, transformers, etc together. I agree with Ken's comments - the speaker has the output transformer attached and is probably used as a filter choke. If there is a plug for the speaker on the back of the chassis, does it have 2 pins, or 4 or more pins? 4 or more would make it very likely that the speaker has an electromagnet acting as a filter choke. In the deep dark past, I threw away dozens of speakers like that, many of them probably in good working order.

Jerry

Re: Speaker plug has 5 holes

Al Stokka - Cambridge, Iowa

>