[morzh]

Most resistors could be measured in-circuit as often times they end up driving a tube's electrode and have no DC path to complete the circuit. If a resistor measures slightly below the declared value it is most likely OK and can be left in place; if it settles above the value outside 10-20% it then has surely drifted by that much. If over 20% it should be replaced, especially if it is a part of a divider where precision matter more than in, say, being a grid stopper.

[WallaceRoger]

I'm making slow but sure progress, mostly waiting for the capacitor and resistor assortments I bought on ebay to arrive. I rebuilt a couple of the easiest capacitors and now I've pulled out part #8 bakelite capacitor of .05mfd , which the parts list notes as also containing a 250ohm resistor. I haven't cleaned the old tarry gunk out yet. Is there really a resistor inside here? I'm assuming a regular old 1 watt metal film resistor is fine?

EDIT: Yep, I found it. Heating up the bakelite block with a heat gun and pushing through a rivet hold with an old 1/16 drill bit got it out nice and easy. I kind of messed up and now trying to figure out what the other end of the resistor attached to...

[GarySP]

Hello WallaceRoger.  The particular bakelite block you are referring to doesn't have a resistor, but a small bundle of resistor wire approximating 250 ohms.  I replaced the resistor wire with a 1/2 watt 250 ohm resistor when I rebuilt mine.  Take care, Gary

[WallaceRoger]

Hello WallaceRoger.  The particular bakelite block you are referring to doesn't have a resistor, but a small bundle of resistor wire approximating 250 ohms.  I replaced the resistor wire with a 1/2 watt 250 ohm resistor when I rebuilt mine.  Take care, Gary

Thanks, Gary. I have a huge batch of resistors and have some 270ohm, but no 250ohm. I know it's considered ok to replace old capacitor values (like .05) with modern common ones (like .047). Is the same true of resistors? If not I can just find the 250, but if I can use 270 I'd like to. Thanks again, I'm learning a lot as I go.

[morzh]

I think 270 ohm is fine there.

[WallaceRoger]

I paid a guy out in CT to restore a small Trav-Ler clock radio alarm for me several years ago and he installed an inrush limiter. I'd kind of like to do that here, as well as install a fuse at the power to help prevent damage (especially since this is my first project and I might screw something up).

What are your thoughts on this? Are the two together overkill? What fuse amp rating did some of you other guys use on your Model 20?

[morzh]

I do not have a fuse on my 20 radios, I might have it on one radio I restored for my dad.
At any event, I would rate a fuse at 1.5x the radio's max current rating, and make it a slo-blo (time-lag) type.
An inrush limiter, in my opinion, is an overkill for this type of application.
I used them in AC/DC switching supplies as there is a very sizeable inrush due to an unprotected discharged capacitance essentially in parallel (disregard the rect bridge) to the AC supply. In a radio with a transformer there is essentially an inductance (which is what an unloaded transformer is) and this does not result in a very strong inrush.
There is one possibility when a switch gets made exactly at the point of the AC voltage crossing zero, that could result in some DC-like behavior and saturation by the transformer, but not for a long time as there is some finite loss resistance there.

This said, the peace of mind is a priceless thing and if it makes you sleep better at nights, by all means the limiter is good.
The fuse is a good idea in any case.

[WallaceRoger]

Thanks again, Morzh

[WallaceRoger]

I got my last resistors put in, replaced the power cord with a new one from Radio Daze, added a fuse. I'm waiting for my variac to arrive before I try powering it up.

In the meantime, I pulled the speaker out and it needs a recone. What have you guys paid on average for a re-cone? We have a couple places here in Chicago who do speaker work.

[WallaceRoger]

I almost forgot the photos

[Image: http://i18.photobucket.com/albums/b145/s...124319.jpg]

[Image: http://i18.photobucket.com/albums/b145/s...125407.jpg]

[Image: http://i18.photobucket.com/albums/b145/s...0714_1.jpg]

[WallaceRoger]

Ok! Today I got my variac, so I powered up slowly. The good news is, no smoke and nothing else visually seems to be an issue. The fuse I installed didn't blow.

The bad news is, it produces nothing but a steady hum, the volume knob appears to have no effect on it, and the display lamp doesn't light.

Where would you guys recommend I start checking? I have not replaced anything in this except caps and resistors, so everything else is original (including the long, tubular resistor).

[Kenneth F. Besso Jr.]

DID you rebuilt that Big,,square ,,oblong silver can ,,,next to the Black transformer,,,that holds capacitors inside ????

[WallaceRoger]

Yep, I heated and slowly worked all the old stuff out, all new caps in there.

[morzh]

Tubes tested?

[Steve Davis]

Start by checking voltage on all the tube pins. Compare them to the voltage chart on the schematic.

Steve