270??? Judging from the manual for the military version, I'd expect 170V there. How large is the first filter capacitor? What's the voltage on the 6V heater winding?

C31 is made up of two 20mf. Reading 270 off the first one (same point as pin 8 on V5) and 205 on the second one. Or am I misunderstanding your question? Am not at my bench at the moment so can't get a reading on the heater. The schematic is on page two of this thread for quick reference.

270 is much too high, but where is it coming from? What's the AC voltage from the transformer? Supposed to be 175 each side of centertap, acording to the military schematic.

Made the measurements this morning...

Measurements taken with the rectifier V5 removed

Secondary:
CT to pin 3 and 5 of V5 measured 230vac each

Heater 7.5vac

Resistance
CT to pin 3 and 5 is 220ohms

Did notice this about the transformer. The parts list called for a 20800-58. The one installed is a -95

Ray

Is that 7.5V under load?

Alan, I do appreciate the help. The rectifier V5 was the only tube that was removed. Al the other tubes were in. So essentially yes, it is under load.

Ray

Found a thread on Nostalgia Air about the 288x power transformer.

http://www.nostalgiaair.org/Forums/Mess ... 098171.htm

Here is the recommend transformer from that discussion.

http://www.edcorusa.com/products/616-xpwr024_120.aspx



Ray

Evidently the transformer is putting out too much voltage, which means the primary has too few turns. That's very odd. You can run it from a variac and see what it wants, and then I suppose use a bucking transformer to supply whatever that turns out to be. 100 Volts at a guess. The only country that uses 100V is one half of Japan.

Possibly part of the primary is shorted, but I'd expect the transformer to be smoking, in that case.

Or maybe it was made to run with a ballast resistor in series? Or a line-adjust pot, like a Hickok tube tester? Tube testers use 100V transformers. Was there a line-adjust pot installed in this thing once?

Doesn't appear to have ever had any type of pot. I'm still curious about the different part number on the tranformer and the added resistor in the filter caps. I'll do some more digging and check to see if there are any other changes with regards to components being used compared to what the parts list says.

Tube line up is the same as the schematic EXCEPT the is a 6SK7 installed instead of a 6SJ7.

I did remove all teh tubes and measured the secondary voltages again. Same as before.

Found out a little more on the 20800-95 power transformer. It is used in a Hickok Model 620 Pattern Generator. Its output is 200 volts where the -58 that is called for in the parts list outputs 175. Now whether or not the -95 was/is orginal I don't know. I would feel better if I could locate a revised schematic that showed this.

Ray

You could live with the 200V; it's easy enough to add some series resistance in the B+. But the tube heaters won't like running on 7.5V.

Hi Folks
I found this subject doing a search, and I am in the same mess trying to get a 288x up and running. My generator has a tube lineup of V1-6c4, V2-6sn7, V3-6sn7, V4-6sc7, V5-6x5, V6-6sg7. There is a 4.7K ohm resistor from pin 5 at V2. There is also a 1.8K resistor across the dual 20 mfd filter cap.
I realize that this is a old topic, but I would really like to find the right schematic for this signal generator. I have the manual from Bama and it is 617W also I have a preliminary hand book that was also on Bama.
This Signal Generator still has the serial number tag 16281 if that will help any.
Any help would be appreciated, I can replace the components that are installed and feel confident that the magic soldering gun has not violated this piece of equipment. The solder joints are too good.
Thanks in advance as I am still learning.
Lynn

After doing some checking I found that v-4 should be a 6sj7 the same as the 617W schematic.posting.php?mode=edit&f=8&p=1522318#

That lineup doesn't match the military equivalents, which are all I have schematics for. A pox on Hickok and their undocumented changes. I once heard that there was a man there who did all the final cal on the 288s and after he retired Hickok had to discontinue the model since nobody else could get them to work.

Tinkerbell,

I had the same problem, and although it was an old post, another poster sent me a copy of drawing 999 which turned out to be the schematic version I needed - mine also has that 4.7k ohm resistor.

Give me a couple of days and I'll post that schematic on the thread for All.
cheers
jeffrey

All,

Here's the schematic drawing #999 that another poster on this thread sent me. Sorry that I don't have any image editing software to stitch them together!
Hope this helps - it turned out to be nearly the correct drawing for my 288x.


If the resolution isn't good enough I'm happy to email these out - PM me.

Thanks
The Schematic looks ok. I appreciate your help with this project.

Lynn

Hello,

I too am looking for the correct schematic for my 288X. The tube lineup I have is the same as the one on bama, but with differences around V2. The "999" schematic someone else posted doesnt match either. Does someone else have another schematic they could send me?