CHICAGO RADIO TUBE AMPLIFIER

[srini1785]

Hello,

I'm trying to restore a vintage Chicago Radio Tube amplifier (mostly used as a PA system). Presently, it has on its chassis a ECC83 pre amp and NEC valve (details not visible) in the amplifier stages. The amp is mostly intact except someone has changed the power stage from tube to diode (IN4007). I did send a message to Motwani communications (Present name of Chicago Radio) but no reply from them. What I need is more info on this amp and if possible any schematic. I want to restore it back to original specs.

Thanks

 

[Hiten]

I would recommend to check power and audio output transformer to see if they are working or not. Good transformers will increase your budget significantly in restoration.
regds.

 

[Hiten]

Addition : Also if this is PA amplifier system. there are good chances of its audio output transformer will be band limited. So dont go for specifications just see if it can be restored as a working amplifier.

 

[yogibear]

Iron seems to be completely rusted so no point working on it. 5881 tubes ?Chicago iron is well regarded and particularly for Push Pull circuits.

I restored and fired mine recently, a mono 6L6 PP amplifier which doesn't sound an iota like a PP but SE. It's a Heathkit W4 AM based on all Chicago iron. Excellent sound.

 

[srini1785]

Yes, I'll test it shortly with a pilot bulb. The rust seems to be only on the surface. I'm working on another tube amp and will update this thread shortly. So, I guess there is no point trying to get schematics?

 

[yogibear]

If iron is fine, and no issues under load, I would rather build an amp around them. Strip and use the same chassis. 6L6 PP would be excellent choice.

 

[analogadikt]

Iron seems to be completely rusted so no point working on it. 5881 tubes ?Chicago iron is well regarded and particularly for Push Pull circuits.

I restored and fired mine recently, a mono 6L6 PP amplifier which doesn't sound an iota like a PP but SE. It's a Heathkit W4 AM based on all Chicago iron. Excellent sound.

View attachment 93554

Good evening Yogi,

Heathkit and other reputed American valve amp manufacturers used " Chicago Transformer Company" iron. That company was actually based in Chicago, USA.

The OP has a vintage Indian made PA amp that was manufactured by Chicago Radio of India. It is not known if this Indian entity had any connection with the aforementioned American business.

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The OP's amp is 6L6gc PPP mono amp pushing out about 100 watts. My suggestion would be to strip the chassis completely, repaint it , retain the power transformer and replace the OPT with a pair of decent OPTs suitable for 6L6PP operation to rebuild this as a stereo amp.

Regards,

 

[srini1785]

Some update: We connected the amp to mains using a pilot bulb and it seems to work fine with and without the pilot. So no shorting or anything and the tubes lit up fine. Components are, IMO, quiet OK. My guess is that there is separate preamp for tone and audio,

Although i'm not sure. We have bought the caps and knobs recently. I'll keep the thread updated.