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I scored a tube console!

WillVT

WillVT

Super Member
I have been on the hunt for a while now for a tube amp to power my Quad els57's that my wife's uncle gave me last year. I finally found something that may work.

I got this Zenith stereo console on craig's list for $20. I believe it is model SF2580. Cosmetically, besides some dust, it's in pretty pristine condition. It powers up, and other than some scratchy controls, everything seems to work flawlessly. Even the stylus on the record changer sounds really good.

I guess my question is, is this thing too nice to tear apart? Also, it seems from what I have researched, that the power amp is tied to the pre/tuner in such a way that it would be difficult to separate, especially for an amateur like me.

I am completely new to tubes, so please keep your answers simple. Here are some pics:

IMG_20131012_115850_412.jpg


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iiU7aQtu95gDTLL2qErrVRKrcDkP_XIAIzG8S3pKULE=w1463-h823-no


IMG_20131013_100144_270.jpg
 
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First, congratulations!

Second, front-loading consoles are great for resto-modding because you can put modern equipment in them and it will still look nice, plus, you can put stuff on top of them; hard to do with top-loaders and their coffin lids.

Third, I think that amp will work stand-alone if you wish to remove it. You would probably need to do some work to replace the inputs/outputs on that umbilical cord between the pre and amp, but I don't think it's impossible. Some consoles have half the power amp on the tuner and the other half offboard, which does indeed make it difficult.

I would see this console as a keeper; it's very nice. But it entirely up to you.
 
You got yourself a real nice stereo console.

I see that same model vintage console on my local CL and now I know what it looks like inside.

Thanks for posting

To part or not to part, that is the question...

but it seems like a great piece to learn on, just saying
 
Make sure you re-cap it and change the electrolytics before you use it. If you don't know what I'm talking about, send a PM and I can help you out. Both need to be done; if you don't do it, the amp is liable to die or start operating poorly at any time.
 
Very cool. I always liked the Zenith products. Do you think you'll refurbish it all, or use the amp for something else?
 
Does it have the 7D31 power amp?

I've got an SFD2565 that is very similar. I kept my console intact, complete restoration of the amp, the tuner/pre, the turntable and the cabinet. The Cobra-matic record changer is cool looking but sonically inferior, I'm afraid.

The amp and tuner/pre are meant to be used together, as the Presence control and the Stereo Separation control circuits span both chassis. Not impossible to separate but they do require a working knowledge of the schematic to make the amp into a standalone.

Some owners of this model replace the output transformers and from there, essentially copy a Magnavox 9300 amp, which is also push/pull 6BQ5s. So that is a possibility, too.

Note that the FM here is mono, the Tape-In and Phono are stereo, and the phono is line-level (ceramic cartridge.)

Let us know what direction you are leaning to go with this.


RWood
 
Diverted said:
Make sure you re-cap it and change the electrolytics before you use it. If you don't know what I'm talking about, send a PM and I can help you out. Both need to be done; if you don't do it, the amp is liable to die or start operating poorly at any time.
Click to expand...

Are the caps in the power amp the most important to change?

RWood said:
Does it have the 7D31 power amp?

I've got an SFD2565 that is very similar. I kept my console intact, complete restoration of the amp, the tuner/pre, the turntable and the cabinet. The Cobra-matic record changer is cool looking but sonically inferior, I'm afraid.

The amp and tuner/pre are meant to be used together, as the Presence control and the Stereo Separation control circuits span both chassis. Not impossible to separate but they do require a working knowledge of the schematic to make the amp into a standalone.

Some owners of this model replace the output transformers and from there, essentially copy a Magnavox 9300 amp, which is also push/pull 6BQ5s. So that is a possibility, too.

Note that the FM here is mono, the Tape-In and Phono are stereo, and the phono is line-level (ceramic cartridge.)

Let us know what direction you are leaning to go with this.


RWood
Click to expand...

The chassis number is partly rubbed off. I believe it is 7b31. I am leaning toward keeping it whole. I don't think I have the skills to take it apart.
Is it possible to just somehow wire my Quads directly from the console, bypassing the internal speakers?
 
7B31 might be a little easier to work with than 7D31. Are there connections on the back of the console for the external (Radial Sound) speakers? It might be that your unit was not so equipped, which is a good thing. You should have two wires going to each speaker crossover (If you do have Radial Sound jacks you would have three wires there). Route those wires to your own speakers and you'll be good.

I would not run the amp for long, though, until you can rebuild the power supply capacitors and change out the old paper coupling caps. Degree of difficulty for that job for a newcomer is probably 6 out of 10, and the amp has a lot of room underneath to mount the new filter caps. We can give you the guidance you'll need, if you want to tackle the job and learn how tube stuff works.
 
RWood said:
7B31 might be a little easier to work with than 7D31. Are there connections on the back of the console for the external (Radial Sound) speakers? It might be that your unit was not so equipped, which is a good thing. You should have two wires going to each speaker crossover (If you do have Radial Sound jacks you would have three wires there). Route those wires to your own speakers and you'll be good.

I would not run the amp for long, though, until you can rebuild the power supply capacitors and change out the old paper coupling caps. Degree of difficulty for that job for a newcomer is probably 6 out of 10, and the amp has a lot of room underneath to mount the new filter caps. We can give you the guidance you'll need, if you want to tackle the job and learn how tube stuff works.
Click to expand...

There are no speaker connections on the back. It seems there are 4 wires on each side of the amp labeled Speakers, with various labeled color wires.

I would love some help replacing the caps. Thank you. I have never replaced a cap, but I am fairly handy with a soldering iron. It will probably be pretty slow going though. I can really only work on weekends.

As far as the final set up, would another option be to remove both the amp and the tuner/pre, and maybe mount them together on their own, still wired as they are?
 
WillVT said:
There are no speaker connections on the back. It seems there are 4 wires on each side of the amp labeled Speakers, with various labeled color wires.
Click to expand...

Ok, that's good. Take a look at each Output Transformer (arrows below) and let us know what wires are coming off each one.

IMG_20131012_122951_405_zps661403d0.jpg


Maybe Tom Bavis will come along and post a scheme for a 7B31 :yes:
 
RWood said:
Ok, that's good. Take a look at each Output Transformer (arrows below) and let us know what wires are coming off each one.
Click to expand...

There are 2 wires coming off each Transformer, going to the four clips I mentioned, which I now see are tied together somehow. So am I right in assuming that I could run speakers off those wires coming directly off the transformers?

This brings up another question, which is probably the biggest; would this amp be suitable, at least in terms of safety, for Quad esl57's? My understanding is that most tube amps are, but I am by no means sure of that assertion.
 
I'd feel more confident if we had a schematic to verify the color of the wires and the way the crossover network is configured, but it does sound like the two wires from the OT are the speaker ground reference (often black) and the hot lead, en route to the crossover. If so, you would divert them from the crossover and send them to the external speakers.

I am not familiar with your speakers but the main considerations are the nominal impedance and the power handling requirements. The Zenith, with push/pull 6BQ5s, will give you 12 - 15 watts per channel. Whether or not that is adequate for the ESLs is another question, but I doubt you could harm them with too little power.

Since they are vintage, desirable, etc, I recommend getting the amp recapped and running with either the stock speakers or an inexpensive (expendable) set, before trying them out on the ESLs.

RWood
 
Here is the schematic.
http://www.radiomuseum.org/r/zenith_sf2580h_ch_9b25_7b31.html

Unfortunately, I have no idea how to read such a thing. I am already in over my head a little with this project, but that's where all the fun happens, right? I really do appreciate all the help that is available here, so thank you all.

Yes, I would definitely recap it and make sure it was ready before I let it near my Quads. From what I've heard, that is a decent wattage range for them.

Edit: Hmmm. I guess you have to be a member of Radiomuseum to view those...
 
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nice console! the horn looks like jensen.

anyways, the amp should work fine with the esl 57 i think. won't hurt to try. i used dynakit, heathkit, and eico mono blocks for my 57 and worked great. as you probably know, 57's are notorious for amp eating impedance curve.
 
I have been lurking around AK for a month and a half reading all sorts of advice from the likes of RWood and others, as I've been working to restore an almost identical but for the style model, SFR2560.

I found the schematic posted by another AK member right here: http://www.audiokarma.org/forums/showpost.php?p=5378445&postcount=7

I replaced basically all the caps and resistors in the amp and now it works like a champ. One of my bias pots/resistors was fried so I replaced the both resistors/pots with a 180 ohm power resistor and 22uF 50V electrolytic capacitor in parallel as RWood suggested somewhere for a 7D31 (a slightly different version of the amp chassis you and I have).
 
keymo said:
I have been lurking around AK for a month and a half reading all sorts of advice from the likes of RWood and others, as I've been working to restore an almost identical but for the style model, SFR2560.

I found the schematic posted by another AK member right here: http://www.audiokarma.org/forums/showpost.php?p=5378445&postcount=7

I replaced basically all the caps and resistors in the amp and now it works like a champ. One of my bias pots/resistors was fried so I replaced the both resistors/pots with a 180 ohm power resistor and 22uF 50V electrolytic capacitor in parallel as RWood suggested somewhere for a 7D31 (a slightly different version of the amp chassis you and I have).
Click to expand...

That's awesome, thanks!

I have been sidetracked by another project, so I haven't gotten under the hood of the console yet. I am a little nervous, to be honest. I have never changed a cap in my life. I can solder, but I would need some help buying the correct caps.
 
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