Found. A new/old Hammarlund. It's now working great.

badrestorer · Member Joined: 17 Mar 2008 Posts: 2362 Location: Arkansas

Ed,
Later tonight there will be a lot of switch cleaning. But before leaving for work I did get to trace a 455kc signal I sent through it. Things were fine until it entered the 3rd IF tube (6SS7). It never came out on the plate. That was as far as I got. After the switch cleaning I'll also make a few voltage checks on that tube. If needed, I have (I think) a 6SK7 that can be used a temporary sub.
Thanks for the info on that wire.
_________________
Regards,
John

They don't know the power of the radio side.

Burnt Fingers · Posted: Oct Thu 29, 2009 1:43 am

If that tube is cold and you dont have the spare take the one out of the RF stage. You will at least have noise from the mixer back to check operation, do IF and oscillator alignments.

Carl

Kent Kershaw · Posted: Oct Thu 29, 2009 2:25 am

In case you need it, the factory manual is here: http://bama.edebris.com/manuals/hammarlu/ I didn't see if it was in a previous post.

badrestorer · Member Joined: 17 Mar 2008 Posts: 2362 Location: Arkansas

Carl,
Using the RF tube was on my mind, if I don't have the 6SK7, but I think I do have one. The apparently bad 6SS7 tube does heat up.
You know...I think somewhere along the line these tubes were checked with a tube tester and the results scratched on the tops. One or two have 76. Another has 74. I'm at work right now and can't remember which tube has what number scratched on its top.
_________________
Regards,
John

They don't know the power of the radio side.

w3jn · Posted: Oct Thu 29, 2009 4:33 am

Check plate and screen voltage of that 3rd IF.

You say "everything went fine until you got to the third IF tube" - does that mean you started at the detector with the 455 KHZ signal? Or you injected a 455 at the mixer and used a scope to trace it forward?

badrestorer · Member Joined: 17 Mar 2008 Posts: 2362 Location: Arkansas

It looks like I have more problems than I thought. The B+ voltage is very low. It's enough to allow a sig. gen. signal to be heard (injecting it at the 6K8 grid cap), but not enough to make things totally operational. Either the rectifier tube is bad or something has been wired wrong. Someone has done a little messing around with the rectifier socket. I'll know more in a day or two. Not to worry...I'll figure it out. Rolling Eyes

But right now I'm working on two radios and need to get back to the first one for a while.
_________________
Regards,
John

They don't know the power of the radio side.

gvel · Posted: Nov Sat 07, 2009 4:26 pm

Thought I'd get this back up top. Laughing

_________________
There's always next year!
WD8PHW

badrestorer · Member Joined: 17 Mar 2008 Posts: 2362 Location: Arkansas

Here's the findings, folks (voltages taken pin to ground):
Definite power supply problem. Very low B+. Voltage readings at the rectifier:
Pin# 4...300vac
Pin# 6...298vac

Pin#2...starts out at 22vdc, then slowly lowers to 13vdc as the tube heats up.
Pin# 8...same as pin#2.

What's the verdict? Tube or transformer? I do get continuity across pins 2 & 8 with the rectifier removed. I also get continuity on those tube pins.
I'll take a swag...the tube is bonkers.

http://www.nostalgiaair.org/Pa ... 008997.pdf

http://www.nostalgiaair.org/tubes/5u4g.htm
_________________
Regards,
John

They don't know the power of the radio side.

Dave Doughty · Posted: Nov Sat 07, 2009 6:42 pm

If the tube were good, the plates would be glowing red-hot because of a short somewhere. If the filaments light and the plates aren't glowing, I think the tube is bad.

Dave

gvel · Posted: Nov Sat 07, 2009 6:54 pm

It seems that your power transformer is fine, John.

I'm betting on the Rectifier Tube, since you've change the electrolytics.
_________________
There's always next year!
WD8PHW

Curt Reed · Posted: Nov Sat 07, 2009 7:02 pm

I would start all over and take resistance readings to the B- starting at the rectifier filament after the filter capacitors have been discharged. I would suspect that something in the order of 10 K ohms or greater should be the reading. If you are showing something in the order of a few hundred ohms or less, it means you have a short in the B+ line to ground somewhere.

Also make sure the center tap connection of the power transformer high voltage winding is connected to the B-. It may run thru a switch to put the set in standby, so make sure that is all working like it should.

Then if all resistance readings are in the ball park, it is time to do voltage checks with the set turned on and in the receive mode. I can not begin to guess the times I have run into difficulties either with others or even myself when the receive/standby switch got thrown to standby without knowing about it.
Curt
_________________
Curt, N7AH
(Connoisseur of the cold 807) CW forever!

gvel · Posted: Nov Sat 07, 2009 7:15 pm

While in stand-by, shouldn't he still see HV, at the filaments of the rectifier?
_________________
There's always next year!
WD8PHW

Curt Reed · Posted: Nov Sat 07, 2009 7:17 pm

If the standby switch opens the center tap of the transformer, all B+ is killed when the switch is open. There is no return for the current flow when it is open.
Curt
_________________
Curt, N7AH
(Connoisseur of the cold 807) CW forever!

Dave Doughty · Posted: Nov Sat 07, 2009 7:40 pm

Standby switch doesn't open the CT of the power transformer in this case. Some circuits stay powered during standby.

I agree that resistance measurements should be taken before a new tube is tried.

Dave

badrestorer · Member Joined: 17 Mar 2008 Posts: 2362 Location: Arkansas

The latest:

1. Both rectifier filaments light up and the plates do not glow.

2. Both filament pins, 2 & 8, to chassis ground read 62K each.

3. Receive/send switch is in the receive mode.

4. Pins 4 & 6 readings (300/298 vac) are center tap to ground. Across the pins reads 598vac.

Did I forget anything?
_________________
Regards,
John

They don't know the power of the radio side.

Dave Doughty · Posted: Nov Sat 07, 2009 7:56 pm

Do you have another tube to try? I say go for it!

Dave

badrestorer · Member Joined: 17 Mar 2008 Posts: 2362 Location: Arkansas

Curt Reed · Posted: Nov Sat 07, 2009 9:31 pm

OK, you have AC voltage to the plates of the rectifier tube. How much DC do you have coming off the filaments of the rectifier tube?
Curt
_________________
Curt, N7AH
(Connoisseur of the cold 807) CW forever!

gvel · Posted: Nov Sat 07, 2009 10:12 pm

Curt...he has 23 V at start-up and it drops to 13V after warm-up.
_________________
There's always next year!
WD8PHW

badrestorer · Member Joined: 17 Mar 2008 Posts: 2362 Location: Arkansas

Curt,
I decided to let things really warm up and the filament voltages dropped another volt, to 12vdc. I'll play around with it a little longer. Maybe I'll find a bad apple or something will change. If so, I'll get back to y'all.
_________________
Regards,
John

They don't know the power of the radio side.