Fleetwood model 4068... Advice?

[VintagePC]

Yep... We'll see how it goes.

I'm waiting for a nice sunny (and insect-free) day so I can finish derusting the chassis and power transformer casing, and I hope to get in an order for some replacement capacitors once I've tested for out-of-spec resistors.

Thanks for all your help!

[VintagePC]

Just finished re-winding the coil (pic below) and I'm waiting for the wax to harden. The CRT yoke had perfectly salvageable wire (and more than enough on just one winding- I nearly filled an 800 yard thread spool!

[VintagePC]

I reinstalled the coil and looked at the circuit diagram- it seems that there are some differences- (or someone has already "serviced" the radio.

Particularly, C25 and C26 are 0.01 µF (vs .03) and one of the filter caps in the can is 100 µF as opposed to 40 on the schematic.

R5 and R31 are completely absent.

Regarding replacements, I take it aluminum caps are fine for the electrolytics, and ceramics to replace the plastic and paper ones?

Also, can someone confirm whether C12,22,16, and 17 are electrolytic? They have the same schematic symbol as the filter caps, but like kinda like the plastic jobbies. (or just leave them alone?)

[electroking]

>Particularly, C25 and C26 are 0.01 µF (vs .03) and one of the filter caps in
>the can is 100 µF as opposed to 40 on the schematic.

Those 2 capacitors bypass the power line to the chassis to filter out some
interference. They are sometimes called 'death caps', because while
they are useful for their stated purpose, they also increase the leakage
between the power line and chassis, and bring up some shock hazard.
The lower value is possibly a production change, you need not worry,
but make sure good capacitors are in those spots. The 100 µF can
is probably fine for C23, but at C24 it may overstress the rectifier tube.
Better limit this one to 40 or 50 µF.

>R5 and R31 are completely absent.

Maybe they were removed by someone who wanted to disable the
radio section; these resistors provide the proper voltage and current
to tubes 6BE6 and 6DC8. The node between R3 and C5 should
definitely not be connected directly to the function switch, or the
tubes may be overloaded. You could replace R5 and R31 by a single
10 kohm, 3 to 5 W resistor. (note added afterwards: maybe the
resistors were moved to the part of the supply line on the other
side of the switch, somewhere to the right of C11)

>Regarding replacements, I take it aluminum caps are fine for the
>electrolytics, and ceramics to replace the plastic and paper ones?

Well electrolytics and aluminum electrolytics are essentially the same
(although there are also tantalum electrolytics, not very often used
in tube gear). Ceramic capacitors don't usually come in large values
(0.1 microF) and reasonably high voltage ratings. But in this radio,
probably anything with correct voltage and capacitance rating will do.

>Also, can someone confirm whether C12,22,16, and 17 are electrolytic?
>They have the same schematic symbol as the filter caps, but like kinda like
>the plastic jobbies. (or just leave them alone?)

Those cathode bypass capacitors are definitely electrolytic, but they
are low voltage units, that is why they are smaller. 6- to 15- volt
units would be fine for C12/C22, and 25-V units for C16/C17. You
can read the cathode voltages on the schematic, respectively 1.1 and
12 volts. These should be replaced, as any leakage will screw up
the bias on the tubes. P.S.: modern plastic units for C12/C22 would
be fine if not too physically big; some audiophiles will even tell you they
will improve the sound!

Good night.

[VintagePC]

The 100 µF can is indeed C23, so I'll see what I can get and may change it for a 40 if circumstances require.

I'll also look in to good replacements for the death caps; chassis ground is also turntable ground, so it is a big issue.

It turns out that R31 and R5 are present after all; they are before the function switch and tucked away, so I did not see them until I searched thoroughly.

I'm placing an order with Digi-key for other electronics supplies, so I'll get as many of the caps as I can there... if all goes well, I may be able to do a preliminary test next week! *crosses fingers*

Not much other radio progress, but after an afternoon with some steel wool and rust remover, I think I've eliminated all the rust. The line cord has also been replaced (the prongs on the old one were bent up and corroded.)

[electroking]

Hello again,

Regarding the death caps and shock hazards, it might be a good idea to
install a polarized plug (maybe cannibalized from a dead TV) with the
neutral (wide blade) connected to the lower side of the power
transformer and the live (narrow blade) connected to the upper
side (the one with the power switch). This would ensure that the
resistive link to the chassis (R55) would remain on the neutral side
of the line. R55 is part of the filter along with the death caps.

[VintagePC]

I found the polarized line cord I had; and installed it.

I'm currently re-painting the transformer case and have removed the filter cap can (and gutted it) for re-stuffing.

Capacitors have been ordered and are on the way!

[VintagePC]

There's a bit of a lull in activity now, since I'm waiting for my caps to arrive. More photos have been posted and updates made to the restore log on my site.

http://vintagepc.co.nr/site/index.php/stuff/radio/

Hope it tides everyone over!

[VintagePC]

Still twiddling my thumbs. I'd hoped the caps would arrive today, but probably will on Monday (because of the holiday Thursday).

Can't do much else until I have those, but I did rig up an external RCA input using a dual-pole dual-throw switch and some RCA jacks, plugs, and shielded audio cable... so when the set is done, I'll be able to switch between the internal turntable and an external source at the push of a button!

The only issue I could see is with the set's floating ground- Would it cause an issue if I plugged in an audio source with a hard-wired ground?

Anyway, once I've recapped, what would be the best way to power up the set? I don't have a variac (alas) but I'd thought to pull all the tubes, check the transformer output voltages, and then put the tubes back in one by one, testing voltages (indicated on the schematic) as I go.

[electroking]

Originally Posted by VintagePC

Still twiddling my thumbs.

...
The only issue I could see is with the set's floating ground- Would it cause an issue if I plugged in an audio source with a hard-wired ground?

Anyway, once I've recapped, what would be the best way to power up the set? I don't have a variac (alas) but I'd thought to pull all the tubes, check the transformer output voltages, and then put the tubes back in one by one, testing voltages (indicated on the schematic) as I go.

No problem with ground floating ground, it will just cease to be floating
when connected to a grounded source. This is not really a hot chassis,
the power transformer does provide isolation. You can ground the chassis
to earth if you make sure you have the correct power line polarity as
discussed before, end even with incorrect polarity, the leakage will
be small and tolerable as long as the line filter components (one
resistor and two capacitors) are OK.

Do not plug the tubes one by one! Instead, install all the tubes
except the rectifier. It would be best to start up with a variac
(do a bit of research with this word), or with an incandescent
bulb in series, but in a pinch the line fuse will do. With power
applied, tube heaters should light up (not very bright, but visible
in the dark). Let the set run (while watching) for maybe 30 minutes.
The power transformer should get mildly warm, but not any hotter.
Without rectifier, no DC will be generated, so no voltage measurements
to be done at this point.

You may use your old tubes for this test (hope you did not discard
them), many or all are likely to be good. Bad tubes would be
detected later by measurements and substitutions.

Now with power off, install the rectifier tube. The time for the
full test is approaching. Securely hook up your DC voltmeter to C23 and
ground. Turn on power, and watch the meter. The situation
is now the same as before, so no sparks are expected, but as
the rectifier warms up, the correct DC voltage (275) should appear.
If the value is substantially lower, it means you have a short somewhere
down the road from the rectifier, HIT THE POWER SWITCH. Otherwise,
listen for some hum in the speaker, etc. You may start doing the
voltage measurements you suggested.

This should get you going for a while. Good night.

[VintagePC]

Yes, I did keep the tubes that were in there I'm not tossing anything until I know for sure it's bad.

Regarding the variac... I might be able to borrow one from work... I'll have to ask. If not, then I should have enough stuff to make a dim-bulb tester.

[VintagePC]

Good news- I've sourced a variac that I can borrow.

With this, I've read that the procedure is to bring the set up in steps (typically 10v steps/30 min?) Can someone confirm or provide a link to a good guide for doing this? I've found a few, but those all discuss re-forming the original filter caps and precautions if you're bringing the set up with the original paper caps- I'll have replaced all of those by then, so I don't know if the process differs much.

There's also something about a point around 40-50V where things get near the minimum operating voltage to run, and that it should be left there for longer.

Thanks!

[electroking]

Re-forming applies to the power supply electrolytics. If they are new and
correctly wired, there should be no problem with those capacitors.

Without the rectifier, you can turn up the variac as slowly as you wish, but
when you do the test with the rectifier in place, dont run the unit under
say 80% of nominal voltage for more than a few minutes. If it seems
to be idling OK at 80%, you can get it up to 100%. This radio is much simpler
than a TV, where for instance lack of horizontal drive could fry the sweep tube.

Also, in addition to what I wrote to you last time, you should do the initial testing
with rectifier with the function switch in PHONO or STEREO, rather than
RADIO (or BC). This will keep the two radio tubes off the high voltage.
Of course, this test should be done with the speakers (or load resistors) connected.
After checking the high voltage at C23, the next measurements should be
the cathode voltage at the output tubes (pin 2 of each 6AQ5, 12 volts) and
at each of the driver tubes (pin 7 of each 6AU6, 1.1 volts). Correct values
at these four points will almost certainly guarantee that the tubes are correctly
biased.

Once you get the audio section working, we'll have a look at the radio part.
Good luck.

[VintagePC]

Thanks for the info- good thing I asked too- since sometimes being to cautious is just as dangerous as not.

My capacitors arrived today... So I'm going to have me a restuffing party!

[VintagePC]

Just spent an afternoon recapping... what an experience.

Nothing quite like trying to figure out how the leads are attached when they all run in to a giant glob of solder.

Anyway, pictures and more info posted in the build log.

I'm waiting to get that variac before I test it... that should be next Monday.