Zenith Tube Radio + Altec Speaker = mono setup

[Snade]

Is this safe, or am I risking damaging the Zenith radio ?

Here is what I have done:

- Zenith 50's tube table radio, pulled the wires from the speaker and connected it to some speaker wire that connects to:

- Altec 601-8D speaker (12" duplex from early 70's), 8 ohms, efficiency 99dB with 1 watt.​

It sounds good.

(Update: Because of the shock risk noted by feedback below, I disconnected the speaker wire connects to the Altecs and reconnected them to the stock, internal speaker. It still sounds good in the stock setup.)

The Zenith radio on top of the Altec speaker in an Acousti-craft cabinet.

Back of the radio shows speaker wire connected to the Altec.

The Zenith radio.

Layout of the Zenith radio - 7 tubes.

View inside the Zenith radio.

The goal is a nice sounding mono setup for listening to classical music on FM radio.

Cheers, Snade

 

[Steve O]

You risk damaging yourself. That radio is a typical AC/DC unit where the chassis is either tied directly to one side of the power line (unlikely) or the chassis is tied to the powerline thru the famous "death cap". In either case there is risk of electric shock to the operator. If you want to continue to use this set-up you should probably use a good isolation transformer betw the wall socket and the radio.

No harm should come to the speaker or radio unless you connect something really wrong or there's a catrastrophic failure somewhere in the radio.

 

[Urizen]

That's sharp lookin', Snade.:thmbsp:

 

[Old1625]

That should sound pretty darn good. Zenith sets tended to have a pretty good OPT in them, so some surprising bass response may be had with a large external speaker.

No harm to the radio, but definitely a shock hazard exists from the externalized connection. If you have toddlers around you may want to put lots of tape over the speaker terminals.

 

[Snade]

No harm to the radio, but definitely a shock hazard exists from the externalized connection. If you have toddlers around you may want to put lots of tape over the speaker terminals.

Thanks for the warning, I will be very careful with that.

 

[Tom Bavis]

According to the Sams schematic, there are terminals for an external speaker, and it's isolated by the output transformer. But I don't see any... I suppose I could look at my OWN G-730...

 

[Snade]

According to the Sams schematic, there are terminals for an external speaker, and it's isolated by the output transformer. But I don't see any... I suppose I could look at my OWN G-730...

Right, I don't see any external speaker terminals.

After getting this feedback and thinking about it, I don't think this setup to an external speaker is a good idea.

I plan change it back to the stock internal speaker and delete this thread.

Thanks for the feedback.

Snade

 

[wa2ise]

Right, I don't see any external speaker terminals.

After getting this feedback and thinking about it, I don't think this setup to an external speaker is a good idea.

Check to see if the OPT offers isolation, or is there a feedback connection that would defeat such isolation. Also, I think that the power switch on that set may switch the hot side, and not the line that connects to the chassis. You could change it so the power switch does switch the hot side, and not the line going to the chassis, and then install on the power cord a polarized power plug, so the chassis is sure to connect to the powerline neutral. For added safety

 

[gadget73]

Well, it won't hurt anything running it on an external speaker as long as you aren't running both at the same time, and the impedance is close. That 35c5 output tube won't pump enough power to damage anything so you're safe there. The hot chassis thing is a bit of a concern, but as long as you use some common sense its perfectly fine. Don't touch the bare chassis while its plugged in, don't play with the speaker wires while its plugged in, and don't tie it to a ground.

 

[Old1625]

Right, I don't see any external speaker terminals.

After getting this feedback and thinking about it, I don't think this setup to an external speaker is a good idea.

I plan change it back to the stock internal speaker and delete this thread.

Thanks for the feedback.

Snade

Do what you feel, of course, but I don't think it'll come to harm you or anybody else if some precautions are taken. Often those sets had their on-off switch on the neutral side. Yours could be either way. But I don't see why one need bother with that tomfoolery. I can't remember whether or not the audio stage in these units had negative feedback, requiring referencing the secondary to the chassis ground and thus on a path with one side of the line cord. In any case if the speaker terminals on the back are covered up with a piece of heavy sheet plastic--such as from a blister pack--about the size of a playing card, and mounted with 4 screws--one at each corner, you could probably enjoy your new hi-fi set without a trace of guilt or fear thereafter. :thmbsp: Up to you....