[WallaceRoger]

I see I need to pick up a signal generator to align my Model 20 (and future projects).

Any recommendations? I'm not picky about whether it's tube or solid state, but the area I have to work in is the living room of my apartment, so relative compactness and ease of use would be ideal.

[Radioroslyn]

Hi Greg,
Don't really need a sg to align the model as there is no IF stages or local osc. If you have a station near the high end of the band (1500kc). Tune it in then peak the trimmers on the tuning cap for max signal. Done.

[morzh]

As it was pointed in the your 20 thread, it is a very simple radio to align, no oscillator.
Do as Terry directed you.
All three 24A stages have to be tuned.

[WallaceRoger]

The reason I asked is because I downloaded a book "Aligning Philco Receivers" by John F. Rider that describes using a signal gen and a .0002 mf cap inline to the antenna post while tuned to 1400kc. I swear I'm not making this up...

I'll use Terry's method.

I'd still like to hear folks recommendations for signal generators, as I have a couple other radios I'm starting on that aren't TRFs.

[morzh]

A simple two-tube job can be had for $20 or, during a Kutztown auction, $5.

This said, John F. Rider et all describes the "proper", lab type alignment, but, again, for a TRF set like 20 and such the tune-to-a-station type will do just fine and will yield as good a result as anything.

For a superhet alignment a generator is highly desirable.

[Radioroslyn]

For just tuning up BC sets something like a Heathkit SG-6,7,or 8 is OK. There are a lot of service grade sg around. Heath,Eico, and Knight all made them back in the '50s and 60's. The big draw back is frequency accuracy is lousy and the attenuator isn't calibrated along with the fact they leak rf badly. So you can't do any meaningful sensitivity measurements. But that aspect doesn't matter much w/the type of service we're talking about.

Two simple ways to work around the calibration issue is to use a modern digital receiver to check the sg output frequency. Or buy one of those inexpensive frequency counter ($10) and hook it to the sg  output. It will display the output frequency.

Price wise you are looking around $20 or so. Make sure it comes w/the output cable, w/o it you can add $5-10 more to find the proper connector and make one up.

Next time ur in Philly stop by and I'll give one. Hmmm reminds me I found an old Philco 077 or 088 sg the other day when tiding up and I feel I should be doing something constructive. Maybe I'll have a go at it. Now where did I leave that catsup???

[morzh]

I use a BK Precision frequency counter to measure the generator's frequency after it stabilizes a bit when doing the alignment.

Of course a built-in meter is the most convenient.

[WallaceRoger]

I found an RCA WR-49B for next to nothing, figured I'd grab it for non Model 20 projects. I'm currently recapping and going through it, the unit itself is very clean and in nice shape. All pots turn freely, the couple tubes inside tested strong, etc.

I noticed it has an old selenium rectifier. What are the chances I'll need to replace this? It also has some kind of odd (to me) setup with a 1 watt, 10meg resistor with a coil winding around it. Hard to explain... I was going to just leave that and hope it worked ok.

[Radioroslyn]

> It also has some kind of odd (to me) setup with a 1 watt, 10meg resistor with a coil winding around it. Hard to explain...

Would think that the resistor is going to be rather invisible compared to the coil. In other words the resistor is a coil form. It may be used to stop parasitic oscillation. I would leave it be also.

[WallaceRoger]

I probably didn't describe it very well. Here are some photos. It's part L7, listed as a choke.

Thanks Terry.

[Image: https://i.imgur.com/YkQ2jK7.jpg]

[Image: https://i.imgur.com/lSwdEc4.jpg]

[Image: https://i.imgur.com/8y36rve.jpg]

[Ron Ramirez]

> I noticed it has an old selenium rectifier. What are the chances I'll need to replace this?

100% chance of replacing it. Seleniums go bad. When they do, they may emit a noxious odor that is not good for you.

Alan Douglas once wrote (not an exact quote, going from memory here), "If you throw a selenium rectifier in a trash can and hear it go 'clunk' as it hits the bottom, then it is bad."

Just replace it.

[morzh]

I thought selenium was an essential micro-element, important for proper nutrition? so a bit of selenium-infused fumes can't be all that bad?

[WallaceRoger]

Maybe when I remove it I should grind it up and add to my breakfast shredded wheat? LOL

So, I'll need a diode and guessing I'll need to add a resistor. Any suggestions for diode and new resistor value?

[Eliot Ness]

1N4007 should do the trick.  R10 shows 135 volts so just add resistance to maintain that.  Here's a good read on Selenium's:

http://w3hwj.com/index_files/RBSelenium2.pdf

I saw a burned out selenium in an old teletype stink up a whole Comm Center at NAHA Air Base in Okinawa 

[morzh]

Nothing beats a dead skunk or a bottle of freshly open Heineken beer that was stored awhile before being sold. Or a CCFL bulb that decided to smoke while still in your bedroom.
Selenium's child play.