A friend of mine always admired my 7G605 on campouts and such, and was trying to get me to trade for it (not!) ; so when a nicely restored example showed up on eBay I pointed it out to him, and he won. It's gorgeous, has new "alligator" covering, handle, professional recap, wiring, all brand new tested strong tubes, the whole nine yards. I think it may well be a Joe Magi restoration by the looks of it.

The listing said it didn't work though, came from an estate sale. Well, I opened my big mouth and said "no problem", will take care of it. Well have been out of the hobby for a couple years so am awfully rusty, busy with work.

The first thing I did, was run it up with battery power - figuring there's some problem with the AC power supply. Just a "phono" type hum. I ran it up on a variac, past the typical 110-115 - still nothing.

Poking and prodding doesn't seem to find any bad connections. Eventually, it will start to work (excellent, with good tone and AVC action) on all bands, w/ good sensitivity and selectivity. I can switch to battery power, and it works fine, again. Shut it off for a few minutes, works fine still.

It seems to go inop after sitting overnight or several hours, say. It doesn't seem to "pop" into operation, but just kind of fade into working again. I let it play overnight, and half-hoped it was "fixed" but of course we know better by now. It still exhibits the on again/off again feature.

Any ideas?

When it exhibits the problem is the Oscillator tube oscillating?

Corby

No, I don't believe so - just tried sniffing it out with another radio. Oscillator is dead, when switched on the AM band. That's 1LE3 on this set. I did say I was rusty, right?

Radio working on 49 meters though? That's been typical - it will start to work on SW, then after some (hours) the AM band will work too.

Yep, the 1LE3. Can you check the 1LE3 filament voltage working and not?

Are the loctal pins clean, they are a problem area.

Corby

That's where I'm rusty - pins 1 and 8 are filament iirc. Problem is, I only have an iPhone these days, the schematics have access to online are pretty much hard to read!

I really don't want to roast any tubes and it's easy to do. Have both a VTVM and a modern Triplett. What's the safe way to check the filament? Can't believe how much I've forgotten. Scary.

Edit - yes, swapped out tubes, tested, just to be sure, cleaned pins, etc. I was figuring an easy fix something like that. It "sounds" just like a set with a marginal string voltage, because loctals just won't work well at all with too low a voltage. That's why I was surprised when it didn't work on battery power, and really surprised when I kept ramping up the AC voltage on the variac and it still wouldn't oscillate.

Yes pins 1 and 8 are the filament. Either voltmeter should work AC of course if using line and DC for battery. See what the filament voltage is working and not.

Corby

This set has the 117Z6 tube rectifier. If it has been converted to either a selenium or silicon rectifier, the 17Z3 could be weak.

You didn't mention voltage checks in the set. Low voltages to the tubes, both filament and B+, could give the smptoms you describe.

Low voltages will cause this problem that's why I was puzzled when I used a battery pack for troubleshooting as well - it eliminates the AC power supply components as part of the problem, and yet it has the same symptoms as using AC power.

Let me see if I can get some voltage readings without zapping anything. I have the Zenith data sheet for these.

Checked the 1LN5 RF, schematic should be 10.5 at the filament/B- reads 8.25.. This is total string voltage, and way too low.

Take a look at this post.

http://www.antiqueradios.com/forums/vie ... hp?t=30307

Corby

Also I have found reference to a maximum filament supply voltage of 8.5 volts. It looks like the 3 volt tube is in parellel with a few of the 1.4 V tubes!


Corby

Ooops. Padgetts site does indeed show 10.5 V for the total filament string.

Corby

That's an interesting archive post, OZ had problems with his set. For some reason my reply is gone, but had recommended he change out the 100pf mica cap at the oscillator tube. Was leaning towards something this (it can't hurt anything) but hoped to get this nailed down without throwing parts at it. Those vintage micas can be strange beasts though.

Also check or just replace resistors in oscillater amd rf circuits. If they are original you will find they have all drifted up significantly. No good way to check mica's unless they are dead shorted or completely open, just replace them with recent production silver micas. Take pictures, and do not change the lead dress positions. Good Luck.

Yep. All the resistors are original, as are the square micas. Can't hurt anything by replacing them, though I am now remembering just what a PITA this particular set is to work on!

It will be worth it though! Beautiful restoration of a unique set.

Success! Replaced two 100pf Micamold caps on the oscillator tube and the radio is working well. Both original caps tested fine for value and no leakage at 450 VDC on my 950B. Hm.

Aye.