T-368/C problem

[n5ama]

I have a recently acquired T-368/C transmitter that was previously working and determined on the initial power up, it has a problem. It was transported a long distance in the back of a truck (all 3 drawers sitting on moving blankets).
I've checked off the start up procedure and all seems to be ok up to the point of keying the transmitter on the tune switch position. When keyed, I get about 100ma plate current but no power out. Additionally, the plate current doesn't
respond to dipping the load or tune controls. I checked the contact on the rf deck to the case going to the output connector and it seems to be making contact. I didn't check the relay going from the case connector to the case rf
output connector. I'm reluctant to do this with the rf deck in place and the multipin cable plugged in.
 
Where else do I need to look for a problem?
Thanks in advance for any help,
Tom N5AMA

[WBear2GCR]

Does the ANT relay operate?

Does the exciter module deliver RF drive?

You did not check its operation prior to the acquisition?

[n5ama]

Does the ANT relay operate?

Does the exciter module deliver RF drive?

You did not check its operation prior to the acquisition?

Good questions. The rig was knocked down when I arrived to pick it up. I drove 1500 miles one way and didn't have time to operate it and then knock it down and load for transportation back. I barely had time for the 1/2 hour it took to load it in my truck and drive back with the given time.

The exciter "module" probably works but it really doesn't matter because I'm driving it at the external excitation input. I do have a bunch of spares for the entire rig including 4-5 6000 tubes.

The antenna relay was my first suspect given 100ma plate current with absolutely no output. Not even a meter twitch.

I'm a 4 hour drive to the transmitter and trying to put together ideas for my next visit.

Thanks,
Tom

[WBear2GCR]

Ouch... 4hrs to get to ur xmitr??

Well, assuming all voltages present to the finals, it may not be being keyed!
That sounds like quiescent current from bias... just thinking about it now...

                 _-_-

[K8DI]

I’m not familiar with the T368, but a look at the schematic leaves me with three questions:  is there grid current or is the 100mA what it flows when clamped due to loss of drive?  If it’s clamped is it because there’s no drive, or because the clamp tube is shorted? Is it clamped because the screen bypass is shorted?  And, have you verified that HV voltage is actually there at a reasonable voltage?

Ed

[KA3EKH]

PA Grid current? If you have no grid current you got no drive. I always thought that if the clamper is working that tube sucked down the screen of the PA to the point where you have very little plate current but never had the Balls to run the amplifier up with no drive and see what happens. Lot of spring contacts and if they are not working that’s an issue and one thing, I have seen is that a lot of the 368 that have been out in the community for decades now have been hacked with all sort of “Ham” improvements like disabling the interlocks or relocation of the plate current meter to the cathode side of the PA so all that’s suspect. Some people have also changed the HV feed around so most of the tank is not at HV potential. Don’t get me started on the modulation hacks, but that’s just me. I tend to think the audio restricted base version of the B and C models are the best.
Also, every time on the T-368 I always caution about never pulling out two drawers at a time along with another Ham modification of removing the outriggers on the base and installing stupid things like carpet coasters on the bottom of the case.
The 368 can not just kill you by high voltage, it can also kill you by falling on you!

[n5ama]

I really appreciate the leads and will give them a shot when I return to the transmitter in 2 weeks.

There has been some audio hacks but I’m getting the documentation soon, I hope. The rest of the old girl seems un-molested including the interlocks and the modulation toobs. It’s a clean unit and the only thing I plan to do with it is put it on the air with a Johnson KW matchbox and a 6” (on steroids) muffin fan hung off the rear panel.

[KA3EKH]

Don’t mean to be a Dick or anything but also remember that the service selector has to be in AM or CW, if its in External you won’t get any drive. Don’t remember if in the FSK mode if you had to have the external FSK box attached or not.

[n5ama]

I understand. Thanks for the reminder!!
Tom

[n5ama]

Ok, finally got back to the T3 and after poking around a bit noticed the small connector on the rf deck wasn’t fully inserted. Seating the connector brought the tx to life and quickly tuned up to just short of 500w out.

There is still a problem with the exciter input. When placed from AM to exciter, the rig keys but no drive or output, The front connector was modified to plug in a PTT using a D104 and it works fine on AM but not with the exciter input selected. I’m putting a 5 volt signal into the exciter input.

Any ideas what I’m doing wrong?

Tom N5AMA

[WBear2GCR]

how do you know the exciter input circuit is connected or properly switched?

[n5ama]

Thanks for the reply. When I switch over to the external exciter, the rig keys without the PPT being depressed on the D104. I’m getting 600w into the dummy load and have to really reduce the load control to get the power back to where it’s suppose to be.

I expected the rig to key with the D104 just as it does when in the AM position.

Tom