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Author Topic: Need help with my Ten Tec Centurion 422b  (Read 1493 times)
KB4MNG
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Posts: 217




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« on: December 14, 2016, 04:27:33 PM »

I noticed after transmitting a few cqs on 40 ssb. I got up out of the chair and noticed the two 3-500zs were super orange with a lot of heat dissipation. I thought the bias had went out. I quickly cut the unit off. Now when I cut the amp on, with out transmitting, I get a plate reading just below two. After about 30 secs the center part of the tubes bottom half gets orange. Prior to this, it would start getting orange while transmitting only. It will transmitt and put out the wattage fine during this.

I have had to replace the bias transistor before. Once you cut the unit on, the whole center of the tube will glow orange immediately. That was about a year ago and have used it several times since.

thanks
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KB4MNG
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Posts: 217




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« Reply #1 on: December 14, 2016, 04:36:22 PM »

This one was manufactored in 2006.
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N4ATS
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Posts: 1128




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« Reply #2 on: December 14, 2016, 04:49:09 PM »

Some Ten Tec versions have grounded grid , some had grounded grid thru a resistor and coil. Look at the tube siockets and see which version you have. If you have the resistor/coil version , most likely they are open
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W1QJ
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Posts: 2341




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« Reply #3 on: December 14, 2016, 04:49:40 PM »

Do you have negative grid meter reading?  If not then it seems like you lost cut off bias.
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KB4MNG
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Posts: 217




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« Reply #4 on: December 14, 2016, 05:11:47 PM »

It seems like a bias problem. It acts like it did when i replaced the common transistor that went out. That time, the whole tube would get hot. This time its the bottom half.

I bought some additional transistors. i may pull the board this weekend and check it. I know this is the third time the transistor has failed, what could cause this!!!?
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KB4MNG
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« Reply #5 on: December 14, 2016, 05:12:30 PM »

I do not see any grid reading.
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W1QJ
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« Reply #6 on: December 15, 2016, 12:30:19 AM »

Are both tubes getting hot or just one?
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K8AC
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Posts: 1691




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« Reply #7 on: December 15, 2016, 05:07:57 AM »

I recently went through this with my Centurion.  Unless you make circuit modifications, components in the bias circuit are highly likely to be damaged anytime there is a HV fault, whether it's a tube shorting, or the cabinet interlock activating.  I'll let the others focus on how to tell if you have a bad tube and restrict my comments to the bias circuit.

When I acquired my unit, the resting plate current was somewhere below 200 ma with the tubes glowing a nice orange with no excitation.  I downloaded the Centurion manual from the Tentec site and compared the schematic dates and levels to the levels printed on the boards, verifying that I had the latest boards installed.  That's important because of the several changes they made in the bias circuit.  Since your amp was made in 2006, you should have all the latest boards installed and they should match the downloadable manual.

The bias transistor you replaced (Q1 on the Filament/AC board) is the last in a chain of components that could have been damaged.  In my case, Q1 was fine, but Q2 (which drives Q1) was shorted as were some active components back on the QSK board which connects to Q2 via connector #22.  I replaced Q2 as well as all the active components on the QSK board, rather than troubleshoot them one at a time.  That restored the bias circuit to proper operation.

Based on the advice of someone else on this forum, I also installed a new component, a 5KP60A transorb, from the K terminal to ground.  That should limit the voltage at K to 60 v for future failures.  The original failure in my amp was a shorted tube, according to the person who sold it to me.  After fixing the bias circuit, I accidentally caused another fault involving the cabinet interlock switch and that episode took out just Q1 (that was prior to the transorb installation). 

I've heard that the new Tentec may again be servicing the Centurion, but don't know if that's true. 
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NI0C
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Posts: 2840




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« Reply #8 on: December 15, 2016, 05:51:08 AM »

Likewise, I had the same thing happen with my Centurion just before the CQ WW CW Contest in 2014.  Back then, Ten Tec was servicing these amps.  I sent it in to the factory, and they replaced the bias transistor and the QSK board.  I had them send me a spare QSK board, and I also replaced the tubes after I got the amp back.  The amp worked great for just under two years, then it failed again (same way) at the beginning of the 2016 CQ WW CW Contest!  I replaced the QSK board, but that didn't fix it.

I'm selling the broken amp (at a low cost) to a local who wants to repair it.  Meanwhile, I've replaced the amp with a new ACOM 1010, that I'm very happy with so far..

This bias failure with the Centurion is very scary, and occurs without warning.  In 2014, my Centurion cabinet got blistering hot during a few minutes when I left the room with the amp on standby.  I recommend anyone using the Centurion turn power off before leaving the shack. 

I suspect K8AC's transzorb mod would work-- wish I had done that to mine (someone on eHam recommended using an NE-2 to limit the C-E voltage on the bias transistor, but I never got around to it).
73 & GL,
Chuck  NI0C   
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KB4MNG
Member

Posts: 217




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« Reply #9 on: December 15, 2016, 05:26:46 PM »

Both tubes glow. I am very gun shy using this amp and would never leave it for an extended time while on. the only way I caught this was because I make it a habit to periodically look at the tubes for this very reason. I may just sell the amp.

Its a shame, its and awesome amp. My al 80 a is nowhere as neat but has never let me down.
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KB4MNG
Member

Posts: 217




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« Reply #10 on: December 21, 2016, 03:55:43 PM »

I recently went through this with my Centurion.  Unless you make circuit modifications, components in the bias circuit are highly likely to be damaged anytime there is a HV fault, whether it's a tube shorting, or the cabinet interlock activating.  I'll let the others focus on how to tell if you have a bad tube and restrict my comments to the bias circuit.

When I acquired my unit, the resting plate current was somewhere below 200 ma with the tubes glowing a nice orange with no excitation.  I downloaded the Centurion manual from the Tentec site and compared the schematic dates and levels to the levels printed on the boards, verifying that I had the latest boards installed.  That's important because of the several changes they made in the bias circuit.  Since your amp was made in 2006, you should have all the latest boards installed and they should match the downloadable manual.

The bias transistor you replaced (Q1 on the Filament/AC board) is the last in a chain of components that could have been damaged.  In my case, Q1 was fine, but Q2 (which drives Q1) was shorted as were some active components back on the QSK board which connects to Q2 via connector #22.  I replaced Q2 as well as all the active components on the QSK board, rather than troubleshoot them one at a time.  That restored the bias circuit to proper operation.

Based on the advice of someone else on this forum, I also installed a new component, a 5KP60A transorb, from the K terminal to ground.  That should limit the voltage at K to 60 v for future failures.  The original failure in my amp was a shorted tube, according to the person who sold it to me.  After fixing the bias circuit, I accidentally caused another fault involving the cabinet interlock switch and that episode took out just Q1 (that was prior to the transorb installation). 

I've heard that the new Tentec may again be servicing the Centurion, but don't know if that's true. 

Which is the k terminal on the MJ15001? I could not find a reference to the k terminal on the data sheet.

Thanks
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W1QJ
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Posts: 2341




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« Reply #11 on: December 22, 2016, 06:45:53 AM »

I would think the transorb would limit the collector voltage.
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K8AC
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Posts: 1691




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« Reply #12 on: December 23, 2016, 08:44:44 AM »

The "K" terminal is on the circuit board.  See the schematic.
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KB4MNG
Member

Posts: 217




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« Reply #13 on: January 01, 2017, 06:56:16 PM »

I looked at the k terminal in the schematic. It looks like the k terminal is the collector. So the end of the transorb would go directly to k and the banded end to ground? Sorry for all the questions but want to be certain.
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