1950 portable phono retrofit!

[davestradamus]

i recently picked up a funtioning 1950 Webster Chicago 100-621 phonograph from a junk store. the old girl still works great when the tubes heat up! it plays 33, 45 and 78 rpm records and has a 45w 3 tube amplifier. the stylus isnt great, but it makes noise!

my plans:
aux in (stereo rca, or maybe headphone port style)
instrument in (for my guitar)
switches and crossfader (in case i want to jam with a record)
new speaker
beefier wiring and resoldering

i think i have the input circuit under control. i added some wiring and hooked up my mp3 player yesterday.

my question:
i attached an 8ohm speaker to the amp and it played at half the volume of the original speaker.

there are no markings on the speaker

4ohm?
3ohm?
something crazy?

keep in mind, this was made in 1950.

ill post pics when i get the time.

HELP!!

-davestradamus

 

[highfigh]

i recently picked up a funtioning 1950 Webster Chicago 100-621 phonograph from a junk store. the old girl still works great when the tubes heat up! it plays 33, 45 and 78 rpm records and has a 45w 3 tube amplifier. the stylus isnt great, but it makes noise!

my plans:
aux in (stereo rca, or maybe headphone port style)
instrument in (for my guitar)
switches and crossfader (in case i want to jam with a record)
new speaker
beefier wiring and resoldering

i think i have the input circuit under control. i added some wiring and hooked up my mp3 player yesterday.

my question:
i attached an 8ohm speaker to the amp and it played at half the volume of the original speaker.

there are no markings on the speaker

4ohm?
3ohm?
something crazy?

keep in mind, this was made in 1950.

ill post pics when i get the time.

HELP!!

-davestradamus

Post some photos- if the speaker has a transformer near or on it, it may be a 'field coil' speaker, which uses a separate coil to create the magnetic field for driving the voice coil. Usually, a field coil speaker's impedance is completely different from a regular speaker. There weren't a lot of speakers with permanent magnets at that time.

 

[davestradamus]

ahh! there is a transformer mounted on the amp and attached to the speaker! i have never heard of such field coil drivers. hmm.... not many replacement options online. the speaker and transformer are in good shape, but by todays standards sound awful.

oh well, i guess its "character".

pics as promised.

thanks!!!

-d@v3str@mu5

 

[son-yah-tive]

I never thought I would ever say those were cool.....But I am. That is COOL!!

 

[davestradamus]

hah, thanks!

i think it will be a good little guitar amp. the sound has plenty of "color". which isnt the greatest for accurate music reproduction, but can sound great with an instrument.

i wish i still had pics of the TV stand i built for my parents. i used a 1940s philco radio phonograph and retro-fitted a HTIB in place of the phono. refinished the mahogany vaneer and put some nice speakers in it. they couldnt have been happier with their xmas gift that year. they wouldnt let me do a 5.1, buts its got 2 speakers and a really small sub.....

any encouragement would be awesome!!!

ill keep you updated if anyone cares...

-davestradamus

 

[highfigh]

ahh! there is a transformer mounted on the amp and attached to the speaker! i have never heard of such field coil drivers. hmm.... not many replacement options online. the speaker and transformer are in good shape, but by todays standards sound awful.

oh well, i guess its "character".
thanks!!!

-d@v3str@mu5

If the speaker isn't making any sound, it could be the transformer, a tube, cap, etc. Old tube amps need maintenance if they sit for a long time. The caps tend to become electrically leaky, which means they're no longer a capacitor. Shorted caps will usually blow a fuse, while open ones will cause hum or very compressed sound.

Field coil speakers are repairable- Weber, in Indiana, can do it and I had communicated with Ted not long before he passed. His son is running the company now and Ted passed along the info he had, so they should be able to get it running if it's actually a speaker issue. The old speakers were assembled using hide glue and it becomes brittle over time, so it's possible that the voice coil former separated from the cone. I have seen some on ebay but the impedance is important. The field coil is important, too, because it's part of the power supply.

That would definitely make a nice little guitar amp. I used an old 1950s RCA amp when I decided that the little practice amp I had wasn't enough and in my non-electronically knowledgeable mind, it made sense to just take the speaker wires off of the speaker, connect them to the RCA amp's input and connect that to the speaker. Then, I decided to use one of the Jensen C12-R speakers I got from the music store where I worked and it was sweet. I had no idea that it was a bit risky, but it sounded great.

Here's an Oahu lap steel amp, from the late '30s. It has a field coil speaker, too.

Be careful poking around in there- the plate voltage, power transformer secondary and B+ from the rectifier are lethal. Make sure that, if you work on it and need to probe anything, it's non-conductive. A wooden or bamboo chopstick works well for this. If you're going to do anything when it's on (a bad idea if you don't know what's going on inside), keep one hand in your pocket- if you happen to touch something with high voltage, you won't electrocute yourself. If you touch anything with your hand and touch he chassis with any part of the other side of your body, well, it may be the last thing you do.

 

[highfigh]

GET YOUR PHONE OFF OF THE RECORD!!!

Looks like a 6V6GT output tube. Very common, very inexpensive. I doubt the other tubes will be hard to find, if they go bad. The caps can be found at Antique Electronic Supply and many other places- they're not expensive, either.

 

[TLS Guy]

i recently picked up a funtioning 1950 Webster Chicago 100-621 phonograph from a junk store. the old girl still works great when the tubes heat up! it plays 33, 45 and 78 rpm records and has a 45w 3 tube amplifier. the stylus isnt great, but it makes noise!

my plans:
aux in (stereo rca, or maybe headphone port style)
instrument in (for my guitar)
switches and crossfader (in case i want to jam with a record)
new speaker
beefier wiring and resoldering

i think i have the input circuit under control. i added some wiring and hooked up my mp3 player yesterday.

my question:
i attached an 8ohm speaker to the amp and it played at half the volume of the original speaker.

there are no markings on the speaker

4ohm?
3ohm?
something crazy?

keep in mind, this was made in 1950.

ill post pics when i get the time.

HELP!!

-davestradamus

Most speakers in that era were 16 ohms. 8 ohms and less did not become prevalent until the solid state era.

 

[highfigh]

Most speakers in that era were 16 ohms.

If it has a permanent magnet, I would agree but that was because permanent magnets made speakers more interchangeable (not taking sensitivity into account). The field coil speaker in my Oahu amp shows 7500 Ohms on the label, but that's the field coil itself. When I measured the DC resistance, it was in the single digit range, but I'd need to check my info to verify that.

 

[davestradamus]

the speaker and transformer are both in good working order. i just wished they sounded better. thanks for everyones kind words and helpfull input!!

i will be getting the parts for my input circuit today.

pics when done!


cheers!
-davestradamus

 

[highfigh]

the speaker and transformer are both in good working order. i just wished they sounded better. thanks for everyones kind words and helpfull input!!

i will be getting the parts for my input circuit today.

pics when done!


cheers!
-davestradamus

Have you measured the voice coil yet? I would do that first and google the speaker's part number/manufacturer code (it will be a 6 digit number, possibly with a hyphen).

If you want a manual, here's a link-
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=360173085626

Does it lack bass, or treble? If the impedance is too low, the bass goes away, although it's a small OEM speaker and I don't know what you used for the 8 Ohm speaker. Is it distorted, more than usual (at all volumes)?

I think I would hold off on your decision about the sound until the re-cap is done. I would also put a grounded power cord on it if you plan to use it for guitar and it may be connected to other electronics. There's no guarantee that the chassis won't be hot when the other is grounded, which causes all kinds of problems- not only for the electronics, but if you were to touch a mic or something that's grounded when you're touching the strings, it's easy to drop like a sack of flour from the jolt, or worse.

BTW- I don't know if you have worked on tube stuff before, but the electrolytic caps need to be discharged before you touch them. You can usually go to V1 and connect a jumper from ground to the pin going to the plate.

These should be the tubes in it:
http://www.radiomuseum.org/tubes/tube_12sj7.html
http://www.radiomuseum.org/tubes/tube_50l6gt.html
http://www.radiomuseum.org/tubes/tube_35z5gt.html

Here's a link fro just about any tube info you may need, including substitutions for others that may not be available-
http://tdsl.duncanamps.com/tubesearch.php

 

[TLS Guy]

hah, thanks!

i think it will be a good little guitar amp. the sound has plenty of "color". which isnt the greatest for accurate music reproduction, but can sound great with an instrument.

i wish i still had pics of the TV stand i built for my parents. i used a 1940s philco radio phonograph and retro-fitted a HTIB in place of the phono. refinished the mahogany vaneer and put some nice speakers in it. they couldnt have been happier with their xmas gift that year. they wouldnt let me do a 5.1, buts its got 2 speakers and a really small sub.....

any encouragement would be awesome!!!

ill keep you updated if anyone cares...

-davestradamus

I don't think it will make a good guitar amp. Those sort of units had single ended triode amps giving a power of two to three watts. It will have plenty of color alright.

It is a nice piece of nostalgia but a relic of the worst type of consumer goods of that era.

It was the risk of being condemned to that type of product, that got me into DIY at a very young age!

 

[highfigh]

I don't think it will make a good guitar amp. Those sort of units had single ended triode amps giving a power of two to three watts. It will have plenty of color alright.

It is a nice piece of nostalgia but a relic of the worst type of consumer goods of that era.

It was the risk of being condemned to that type of product, that got me into DIY at a very young age!

Define 'good guitar amp'.

As a guitar amp, pristine sound isn't desired by anyone other than jazz players. It's not necessarily for playing at high volume levels but 3.5W from a single-ended amp can often fill a room very well. The Oahu in my post is single-ended 6L6G and it was made when Americans were on a Hawaiian music kick. For playing with a lap steel guitar that has a lower output pickup, it was probably clean all the time but many guitar players made do with what they had or could get so, small, low power amps have always been popular.

I know you listen to mainly Classical music and because of the instruments used in that genre, along with their voicing, it's hard to convey how an amp like this could sound good to a guitar player. For a lot of Rock and Blues players, the main word to describe the sound they want is usually 'crunchy'.