firestone: Air Chief R-1661 Issues

Hi all. I have acquired about two dozen old receivers, mostly older Hallicrafters.

But one radio that I have a particular interest in is the Firestone Air Chief R-1661. My mother owned one and I kept it after she passed away. That particular radio is stored in my garage.

I have since bought two other R-1661s and just started testing tubes today. I looked at the schematic posted here and immediately ran into a snafu. The tube in the schematic is a 6F5. But the tube in the radio is a 6Q7 two obviously different tubes.

There is a note on the page that reads: Note: There are a few minor production changes noted on the Riders schematic (Page FIRESTONE 7-3) for receivers with serial numbers 453,400 and above. (Note again: I added the FIRESTONE to the page name.)

So I looked at that page. It looks just like the schematic posted on Radiomuseum. It does not have a 6Q7 tube in the schematic.

I am now assuming I have an earlier model of the R-1661. Or do I?

Here are some pics.

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The triode part of the 6Q7 is very similar to the 6F5, so the only change needed to use a 6Q7 instead of a 6F5 would be to move the anode connection from pin 4 to pin 3.

Is anything connected to any of the diode anode pins (pin 4 and 5) of the 6Q7 in your radios? If not, it might be a change just for production economy, i guess that the 6Q7 was produced in much larger quantities than the 6F5 and hence had a slightly lower price.

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Hi James

I can see at the chassis a 6H6. That’s a two-diode tube. In so far, a 6Q7 don’t make sense because it has also two diodes. So, either somebody put the 6Q7 by mistake in the radio or the manufacturer had a surplus of this tube and use them off. In this case the anode is connected to pin 3 and pin 4 and 5 are free.

Regards

Rolf

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Thanks for the answers.

So it could have been a mistake or if deliberate, there may have been a change made to the socket.

I guess I'll be taking the chassis out now (it needs to be cleaned) to look at the hidden components.

I have ordered some replacement tubes. It's a slow process but I am retired and have always had a fascination for old radios. I was an electrical engineer at one time but all I can remember really is:

Better

Be

Right

Or

Your

Great

Big

Venture

Goes

Wrong

Remember this?

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Ok, the chassis is out. I have a few pics of the socket and chassis.

By the way, is this the right place to work on a chassis and comment about it?

The chassis:

The socket:

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Please measure at the socket (see your lower pic) on pin 3 and pin 4. On one of the pins, you must measure the anode voltage, This is somewhere between 60 and 100 volt. Then you know what tube needs to be in the socket

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Cleaned the chassis with an electronic board cleaner. Checked all tubes. Turned it on.

Nothing but hum!

Time to troubleshoot. I am guessing capacitors are first.

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Indeed, typically all paper (wax) capacitors have expired long time ago in a such radio and its better to replace them before even trying to power the radio on.

Some electrolytics might be in useable condition if you are very lucky, but they have to be carefully reformed before trying to switch on full voltage on them. Usually, small low-voltage electrolytics are completely dried out and have to be replaced, the bigger high-voltage units might be salvageable.

Other kinds of capacitors, like ceramic or mica, are usually in good condition.

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Thanks.

Any idea where the best place is to order components online? And figuring out some of these parts is a doozy. Like what are good replacement parts for mica's and paper, etc.

I should try replacing these components before I look for other concerns.

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Generally, you can use ordinary polyester film capacitors instead of old paper capacitors. Just watch out for the rated voltages. A capacitor from the 1930's is often not marked with the working voltage but with the test voltage that the capacitor could withstand for one second or one minute when it was new, it might be 3 or 5 times the maximum working voltage. So its very common to find capacitors with 1500 V rating where they just are subjected to 250 V in operation.  Its a good idea to study the schematic and figure out which voltages may occur across which capacitors, before ordering new ones.

Paper capacitors that are connected directly to mains voltage or that mostly are subjected to high AC voltages (for example, a capacitor across the anode voltage winding of the mains transformer) should be replaced with safety capacitors with an X2 approval.  Capacitors connected from mains voltage to chassis or else crossing the insulation barrier should have Y2 approval and usually of no more capacitance than 4,7 nF in case of 200-250 V mains, 10 nF in case of 100-130 V mains.  X2 capacitors can have either polyester or polypropylene dielectric, polyester is good enough in these cases. Y2 are often ceramic nowadays, and that will be ok.

As mentioned before, mica capacitors seldom need replacement. If a such capacitor anyway has to be replaced, and a new mica is too expensive, use a ceramic with C0G (older designation: NP0) dieelectric. Other kinds of ceramic dielectrics like X7R, Z5U etc have much inferior stability and RF properties, and should be avoided where the original designer chose a mica.

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I'm still planning my restoration of the chassis.

In the meantime, I bought an old Riders Volume VII and made a high-def copy of the schematic page for the R-1661.

I put them on a website because they are probably too large to upload here. Let me know if I am wrong. Oh, I control the website.

You can really see the detail with these scans. I have created a webpage to view or download these really large images. The detail is so good that you can differentiate between a period and a dash in the part numbers.

Firestone Air Chief R-1661

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I know it's been a while. I've received the replacement parts and would love to start.

Life, as you know, does get in the way sometimes.

I hope to start work on it in early September.

I'll post updates and pics at the time.

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I'm back. I still want to restore my R-1661.

More later.

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