GE 21T11 set - It's ALIVE!!! >:)

[nasadowsk]

Ok, the quick story- This was a 'freebie' I was given a few years ago - 21" rectangular tube, Bakelite tabletop set, with UHF tuner. It sat on it's side in the guy's backyard for a few years prior, looked like a total loss - a mouse moved into the chassis, etc.

I've been playing with it, and here's what I've got so far:

* A dead 21EP4, thanks to someone with a hammer.
* A nice bakelite cabinet, but a few missing knobs.
* A now cleaned up chassis.

I've got reception on it! I can get low VHF channels, with audio, and I've got picture. I've used an 8DP4 that's wasted (I need one of these too) as a 'test tube'. Not perfect, but it's ok enough to get the basics down. There's sweep, and a picture.

I recapped the bulk of the set, and I've got lock on both the horizontal (good) and vertical (good enough). And it's stable enough to watch the set. The picture looks all there, and not much noise, though I've got something noisy in the set.

Ok - here's the deal though:

* I need a 21EP4.
* The high voltage isn't. With the listed tube (6BQ6) in the horizontal, I get a rip roaring 10kv, at best. Now, if I slip in a secret weapon, a/k/a a 6DQ6, I get about 20kv with no CRT plugged in. Now, I know GE did running changes to this set (oh, did they do changes!), could they have changed the horizontal tube and not marked it anywhere, or am I looking at an actual horizontal problem (Or a sloshed horz output?)?

I'm going to temporarilly pull my only 21EP4 and install everything into the cabinet and see how the set looks, but it's a really dim tube. It's slated for a rebuild, but I still need another tube, because the one that came with the set got wacked by someone's hammer...

I'll see, if the tube swap and HV thing gets fixed, if I can post up a pic or two. It's at least working, which is something for a set that sat under a bush upside down for a few years....

[Chad Hauris]

I was going to say that maybe the transconductance was higher on 6DQ6...but, consulting the tube manual, the specs on 6BQ6 and 6DQ6 are quite similar. Maybe your 6BQ6 is just weak? Check the b+, boost voltage, and screen and negative grid voltage on the HO tube with the photofact and see if any are abnormal. Off-value resistors could be causing voltage problems in the H.O., perhaps in the screen.

[nasadowsk]

UGH

I have the set in it's cabinet now with the 1/2 dud 21EP4. I have to REALLY give it volts to the filliment to get a raster - like 10V. Looks like a pilot light in the back

It's got a pretty good picture, but only the lo band channels work so far, and to add to the fun, the AGC won't AGC. I have a meter on the AGC test point - it's at 0 all day, antenna or no. Naturally, this means local channels overload, which looks bad and does worse things to the sync.

Here's the thing - I'm tracing the AGC section, and it looks NOTHING like the schematic at all! At first, I figured a benchtop EE got to the set, but this all looks pretty origional.

My Sam's is for a 21TF chassis, which covers a 21T14 and 21C something. The set's a 21T11, but no chassis stamp I can make out on it. Anyone know what chassis this thing's supposed to have? My Sam's follows it pretty closely, but in some places it's way off, and this is one of them

[Chad Hauris]

I have a 1955 GE which is a 21...something chassis and there is a range control on the front panel which you have to set according to the channel strength...I don't know if this sets the AGC level or if it is just a manual gain control.

Sometimes you can see an improvement in CRT performance if you switch back to the 6.3 crt filament voltage after applying the boosted voltage to shock it back to life....if you return to the 6.3 volts you can prolong the life of the tube. On some sets with weak CRTs I have added a switch to go to the boosted heater voltage when needed...I leave it on the "boost" position for several minutes, and this will rejuvenate it for a while before you have to do it again. This may not work on your CRT if it doesn't really show anything on the normal heater voltage, though.

[nasadowsk]

Well, this CRT is basically 'shot' at 6.3 volts....

As for my chassis? No clue. It's got TF stamped on it, but no numbers in front of or behind. The annoying thing is the chassis is pretty much working perfectly, save for the AGC issue and the horizontal output issue. But I can't figure out the AGC section, as it doesn't match the schematic