Topic: Garage Sale TUBES.

[faux fiddy]

I had to haul this thing home from a garage sale a few years ago.

I got a local 'ol boy who checked a capacitor on it (marginal)  and once I get him a schematic (already downloaded), I'm going to have him go through it. I found a couple extra tubes on e-bay already, might have one more in the house somewhere.

He said the thing is like an elephant. I guess people get killed sticking their finger in the wrong place when it's turned on.

It has to have preamps, anyone got anything old and RCA just sitting around?



http://docs.google.com/viewer?a=v&q=cache:rKEdFJ7g1BkJ:www.theused.com/manuals/rca/rca_mi-12234.pdf+mi-12245+schematic&hl=en&gl=us&pid=bl&srcid=ADGEESgp6U0S3Ovnv5BlEmX3AWCiClTM6RAIbyAWzQuh4qQFVarHqgNu-PQnfQuV6q2HFNFqgTy30uW5MNlt-0-3Yu4LNlW8mNoT3b9fSaRNNCq6iJ6oeP8s1Mh4obFI3Riv5evAvnpr&sig=AHIEtbQ1qNbbllrI03HELXhIpyofH0Krhw

[Frankencake]

You are going to need another one for stereo.  That thing is awesome though.  I fancy myself as the local tube amp repair guy in this one horse town.  Feel free to ask any questions.  I think that Industrial Dukiedook is into it too.  In fact there are a lot of guys here that put me to shame in the tube electronic department.  They actually know how they work while I just know how to fix them.

I do know that if you have a second one and actually have a tube stereo at 70 per channel, you will be predisposed go to jail for noise ordinance related offenses.

[mark]

I do know that if you have a second one and actually have a tube stereo at 70 per channel, you will be predisposed go to jail for noise ordinance related offenses.

type louder so folks can hear, eh?

[dave500]

is that one of them steam powered ones?

[faux fiddy]

You are going to need another one for stereo.  That thing is awesome though.  I fancy myself as the local tube amp repair guy in this one horse town.  Feel free to ask any questions.  I think that Industrial Dukiedook is into it too.  In fact there are a lot of guys here that put me to shame in the tube electronic department.  They actually know how they work while I just know how to fix them.

I do know that if you have a second one and actually have a tube stereo at 70 per channel, you will be predisposed go to jail for noise ordinance related offenses.

No more tv's now either at his place, it was a good business decision for him. Plays piano, tells jokes.
All I got is a picture of his cat which has been stolen by people who thought they had a stray. Cat had month long vacations to Dallas and sh8. Joe gets bunched up if Jack wanders off and keeps watch  real well now, but usually know's he's just gone to the mostest local tavern for airconditioning or commeradery.

bla bla bla,,,

[faux fiddy]

is that one of them steam powered ones?

Well, Joe called it an elephant, so I guess it would be grass  or then  other vegitation.

There was no visible way to plug it in to normal power.

[mark]

is that one of them steam powered ones?

Well, Joe called it an elephant, so I guess it would be grass  or then  other vegitation.

There was no visible way to plug it in to normal power.

the other name is boat anchor.

terminal strip on the back?

[dave500]

is it like for a pa at a train terminal?ALL ABOARD?

[faux fiddy]

is it like for a pa at a train terminal?ALL ABOARD?

Big PA horns in a circle around the pole maybe. Something happened to 70 watts since the good 'ol days, inflation got watts just like currency.

I have seen them sold as pairs, I guess you can't just plug in a pair of channels to the same machine and expect stereo separation.

[Duke McDukiedook]

http://www.theused.com/manuals/rca/rca_mi-12234.pdf

Wow, uses (4) 807's and tube rectification and regulation.
As usual with RCA designs of those days it is built like a friggin tank, looks like it was probably used as a PA amp and probably a theater amp also.

You will want to check all the tubes for shorts and emissions minimum and swap out the paper and electrolytic capacitors on this unit. As long as the transformers and most of the resistors are good it should be good to go.

If you could find a companion for this amp you could easily use these to run any kind of speakers you want to, Klipsch speakers are always good to mate to tube electronics.
 

[Duke McDukiedook]

Uh, did a little more reading about these- looks like they were used for PA systems and drive-in theaters- won't exactly make a decent hi-fi amplifier without some hacking- I think they were used to drive a bunch of the bakelite drive-in speakers at 70V- transformer at the pole speaker probably tamed the signal for a better load.
Probably rolled off around 200hz to save those small speakers from bass hell.

[Duke McDukiedook]

Looked a little more at the schematic and read the writing- looks like it should give somewhat flat response without a big rolloff as long as the filter caps are not removed or bypassed but I am not sure how high in frequency the output transformers go- the graph shows a rolloff before 15khz so I am pretty sure there is significant Rolloff before 20khz.

The trick would be figuring out which input tap you would want to use for your preamp and hooking up an RCA input to it- your music guy would be able to help you with that. Looks like it has 4 ohm and 8 ohm output taps so you should be OK there for most modern speakers.

You would of course have to find a matching amp for stereo amplification and probably a tube preamp to match the impedance.

[faux fiddy]

Looked a little more at the schematic and read the writing- looks like it should give somewhat flat response without a big rolloff as long as the filter caps are not removed or bypassed but I am not sure how high in frequency the output transformers go- the graph shows a rolloff before 15khz so I am pretty sure there is significant Rolloff before 20khz.

The trick would be figuring out which input tap you would want to use for your preamp and hooking up an RCA input to it- your music guy would be able to help you with that. Looks like it has 4 ohm and 8 ohm output taps so you should be OK there for most modern speakers.

You would of course have to find a matching amp for stereo amplification and probably a tube preamp to match the impedance.

Yeah,  mono is  kind of a bummer and I found these things can be hard to come by and often sold in pairs.

Somehow I think this was probably used with some old JAN projector with optical tracks and set up like that, as the box with it has a portable feel to it and inside the box is a sticker for a theater supply company.

Thanks for comments and anything you can figure out about mods to make it do better with music or home theater. I thought maybe use it mono if nothing shows up.

I'll have to post some pics when I get around to it.

[seanbarney41]

Trade it to a bass player for a Dyna Stereo 70 ...I had one for years until a transformer went bad...I really miss that thing