T-368 Arcing Problems

[W1UJR]

HV overload trips, need to flip reset; sometimes plate relay sticks needs whack to release.

I am still suspicious of the K6 relay sticking and the HV still on after the load has been removed from the final. Even if it does not require a "whack" to release it, it still may be releasing very slowly while arcing. The more this happens the worse K6 will get.

K6 sticking could be a result of another problem or it could be the problem.

I thought the "F" series had sealed relays. Not that a sealed relay would not stick, but should be less trouble.

[flintstone mop]

I'll look thru my junque and see if I kept a K-6 relay. Help my memory banks.....it's a grey metal plug-in type on the HV chassis???
If I have one from a former T-3, I'll send you one fer free.


Fred

[W1UJR]

Slow release relay, K1A?

The test I mention should tell you if the T/R relay is dropping out too soon.

Check your service manual, used in early series of TX, not sure if its still there on the F model.

See page 39 of depot service manual, the heory is explained there.
You'll have to check with someone who has the "F' supplement to see if it still applies.
Go back and check your work, see if you might have disabled said circuit on your rig.

http://atlanticmotorcar.com/w1ujr/t3.jpg

[K1HH]

I'm at the shop now and will start checking some things again. 
Bruce:
I'll look and see if I have the timing circuit.

Fred:
K6 in this F Series rig is a sealed relay, apparently is bolted in with three bolts.
In this rig it is a 2 X 2 and 1/4 X 3 inch relay made by Price Electric, Type 5701-37HS 115v 220 ohm relay with 20 amp 120 volt contactor rating.

[WA1GFZ]

Bruce's test is the first thing you should do to verify the TR relay is opening too quickly. If that is true then you can find out why. Define the problem before you try to solve it. Also with the relay shorted you will see how much time it takes to discharge the system giving you a clue as to the delay you will need need.
A sealed relay will stick if it has been stressed too many times.

[flintstone mop]

I do have a T-3 K-6 relay. If you need it PM me.
I think it's ok, but I may have shotgunned it and used a Potter Brumfield just as an insurance type thing. The problem you are working on has been around since we started picking up on these T-3's when they were within reach of reality $$$$. Middle 1990's. I paid $750 + shipping from Fair Radio and it worked right off the pallet.


Lemme know

Fred

[W1UJR]

Haven't heard from Rodger for a couple of days, hopefully all is all right? 

Keep away from the HV OM.

[K1HH]

Thanks for your concern. I have avoided the HV. I try to be real cautious around the stuff. Earlier in my life as an engineer for 50KW-9 tower WDGY in Minneapolis two other senior engineers always let me clean the arc blocks each week. And I had to use the chicken stick to discharge the HV caps before reaching to get the blocks. I knew it was going to spark, and each time I discharged the caps, I'd jump.They'd laugh. Every week.  Actually I am spending some time with the XYL this weekend. It also gives me a little time to think about the T-3. Friday I did swap out the tubes in the timing circuit (page 40 for the lettered model units) and varied the pot but noticed no difference. Plate relay hung up again. May get to the shop Monday or Tuesday. I'll keep everyone posted.

Rodger

[K1HH]

Hello all:

I'm still alive and I have replaced K6, the high voltage relay.
Relay is in and works well. In the CW mode at full power it goes in and out of transmit with no arcing and no relay sticking.

In AM mode still having the same problems. I have disconnected the plate leads to the mod tubes and removed the audio driver tube from the speech amp and still have the arcing problems. So I don't think its any mod I made to the speech amp. Maybe its the HV routing through the mod deck.

I still have not confirmed the antenna switching relay timing, although I am not currently having a problem in continuous carrier mode.  I'm not using a key, but turning the carrier on with the plate relay switch, which is in parallel with the push to talk switch.

I'll keep plugging away.

Going to Hamcation in Orlando this weekend. See what other junk I can acquire.

Again thanks for the relay and support.

Rodger
K1HH

[K1HH]

Today I finally solved my arcing problems, and the solution was far simpler to solve than see. My thanks again to all who resonded to this forum and especially to Mark KA4JVY who brought his T-368 RF deck 150 miles to my place so we could confirm I had an RF deck problem rather than a mod deck problem, since I had modded both. I walked away from the T-368 for a while but it came to be yesterday and took 15 minutes to fix today. It had to do with where I was feeding the HV and I have taken before and after photos and hopefully its easy to see the error of my ways.

Rodger
K1HH

[WA1GFZ]

Wow, no wonder.
You could have just moved the suppressor to the other end of the strap near the caps. This would have reduced the lead length to the plate tuning cap. Consider that if you have any stability problems

[flintstone mop]

WOW!
That would have been a looong time for me to pcik up on that. A lot of long head scratching.

Fred

[Todd, KA1KAQ]

Glad you found it Rodger. This illustrates why it's important not to shotgun an entire rig - receiver or transmitter - but better to work on each section and then stop to test functionality before moving forward. It's always easier and faster to go back to the circuit you just repaired or changed when a problem crops up.

Should be pretty much bullet-proof going forward as you've checked everything else.

[K1HH]

Thanks guys! During this whole procedure, I actually tried a National 175A plate choke and, of course the original 470 pf Russian caps. When that didn't work I searched for the 500 pf 30KV caps that are in there now. And I've had other caps clipped leaded in various places convinced it was a bypass problem.

In my original, stock T-368 the supressor was connected directly to the plate on one end and the other end connected to the tank coil because B Plus is fed in from a low imedance point instead of the high impedance point where it now comes in. For some reason, (brain flagalation, I suspect), I hooked it up the way I did. It would send out RF fine, but it didn't like coming out of transmit. In hindsight, I wish I had posted my original configuration photo. One of you guys would have spotted itin a heartbeat, I'm sure.

Rodger
K1HH

[WA1GFZ]

DC was fed into the low Z end of the tank coil for a reason. When you change to the high Z end the RF choke can resonate and fail. This is not an issue for the ham bands but operating over the whole range there could be a frequency that turns the choke into a fuse. It is good to get high voltage off all the caps and switches but there is a price. It is a good idea to check the circuit with a grid dip meter to make sure there are no issues on the ham bands. This could be the reason the R175A failed.

[flintstone mop]

So, there was a method to their madness in the design of the T-3.
The same can be said for the modulator and its "shortcomings". (For Ham A.M. there were hurdles there to overcome)

Fred

[K1HH]

This entire project started with the idea removing high voltage from the Ip meter by making it a cathode current meter, and to remove B Plus from the tank circuit, and along the way decrease some of the shunt capacitance in the tank circuit. Also implemented are some changes to the audio driver circuits, to hopefully, expand the unit's frequency response. The only way to really know if this works is to run "proof of performance" tests before and after the modifications. I did not "proof" it in its stock shape, but I hope to in it's current state. Just need to borrow a THD meter. I didn't burn out the R-175A choke; I only inserted it in place of my home wound coil and obtained the same results (arcing). Had the R-175A been installed in the correct configuration by me, I think it would have probably worked for the 80-10m amateur bands. I do acknowledge that the designers of the T-368 knew what they were doing when the fed DC in at the low impedance part of the circuit. Their choke design setup offerred wide frequency coverage in a very rugged package. My 1947 Ford worked just fine as it came from the factory, but I had to put Edelbrock heads and multiple carbs on it too.

Rodger
K1HH