[TenTec] Titan 425 troubles, R1 and blown 20a fuses

[Denton]

I have an older 220 ten tec L network transmatch I am rebuilding, and I 
notice that ten tec uses high voltage disk ceramic paddling caps in series 
with the main tuning air paddler...
I notice that under some tuning conditions, the swr will drift and some of 
the ceramic caps will get rather warm, even with barefoot power applied...
I am wondering if substuting the original ceramic caps with 2nF type caps 
will stablized the swr drift.
----- Original Message ----- 
From: "Jason Cooper" <jbear45 at msn.com>
To: <n5oe at nctwb.net>; "Discussion of Ten-Tec Equipment" 
<tentec at contesting.com>
Sent: Saturday, July 21, 2007 3:18 PM
Subject: Re: [TenTec] Titan 425 troubles, R1 and blown 20a fuses


> If one capacitor went south, there is a very good possibility that some 
> others were also very close to failure.  You are doing the right thing by 
> ordering some new ones.  There is a possibility of a transformer failure, 
> however, a Peter Dahl replacement is very expensive and you would have to 
> replace the caps if you cannot test them at high voltage.  I restored a 
> 425 about 6 months ago and tested each capacitor with a variable HV power 
> supply and an ammeter.  After re-forming them, all my caps were well under 
> 200uA at 500V so I did not replace them.  If you can get to a HV supply or 
> a HV curve tracer, you could test the caps and that would give you some 
> reasonable input if the failure was caused by the caps.  Also an ESR test 
> is useful if you can find someone with an ESR meter.  If I remember 
> correctly, R1 (It's R2 on my schematic) is in the soft-start circuit and 
> would certainly blow if one of the caps was drawing excess current.
>
> By the way, I just bought a whole lot of 2nF 10KV ceramic capacitors to 
> replace the plate blocking caps (C6 and C7)  These caps have the X5R 
> dialectric and will drift very little with heat unlike the OEM caps that 
> Ten-Tec used.  This will fix the tuning drift problem on 80M and 160M.  I 
> would be willing to sell off the excess if there is any interest
>
> Good luck fixing your 425.  Jason KN7AZ
>
>
> ----- Original Message ----- 
>  From: Carlin Royal<mailto:n5oe at nctwb.net>
>  To: tentec at contesting.com<mailto:tentec at contesting.com>
>  Sent: Friday, July 20, 2007 2:45 PM
>  Subject: [TenTec] Titan 425 troubles, R1 and blown 20a fuses
>
>
>
>  I have a Ten Tec Titan 425 that I have only had myself for about 6 months 
> now. The amp when I received it had 1 bad HV capacitor in the power 
> supply. Due to lack of funds at the time I replaced the one known bad 
> capacitor. A few months later I was operating the amplifier during a cw 
> pileup for about 30 minutes, I set everything on standby and went to 
> lunch. When I returned to the shack I find the amp had blown one of the 
> 20amp fuses in the supply.
>  After checking in the PS, I found that R1 the 10ohm 25watt wire wound 
> resistor on the rectifier board had went open. I replaced the blown 
> resistor and powered the amp back up, this time again blowing a 20ampfuse 
> and the same resistor. Ten Tec advised to replace the original rectifer 
> board with a new one, (82112 rev E I beleive) since they thought some 
> diodes were probably leaking and was the cause of all my troubles. Now 
> after replacing the old rectifier board with the new one from Ten TEc, I 
> power the amp on and it blows another 20amp fuse but did not appear to fry 
> the resistor this time. Here is the main question to the list; Could I 
> have another bad capacitor that is failing under high voltage since they 
> do not read any shorts on the VOM when individually beng tested. I have on 
> order 8 new 400uf 450v caps from Newark Electronics and will be replacing 
> them this week, but I am looking for more input as to the trouble. It just 
> seems odd to me that when sitting idle for just
>  3
>   0 minutes the thing went south and now I have had all this trouble. 
> Hopefully I am on the right track and it will be one of the caps in the 
> PS, but would be interested to hear any other areas that I might could 
> check within reason here on the very limited bench. Thanks for any 
> advise/comments.
>  73
>
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