[TenTec] TT 422 Blowing Fuses

[Bob McGraw - K4TAX]

With the amp wired for 230 V, I doubt with only 120 V applied,  the low 
voltage {as it will be 1/2 of the volts needed for the filaments and the LV 
supply} will not be adequate to pull in the relays and thus get the HV 
going.

A couple of approaches;  one is using two 150 watt 120V light bulbs.  Wire 
each one of the 150 watt light bulbs in series with each side of the 230 
volt line.  If there is a major short the bulbs will light to full 
brilliance.  This basically will limit the inrush current.  However the amp 
still won't receive full voltage and will not be fully operational.  A 
second approach is using a Variac.  This way you can control the voltage 
applied and bring it up slowly and under control.  You should measure the 
voltage applied as you increase it and also the AC current, watching for any 
unusual or rapid changes.  For this you'll need a 230 volt Variac rated at 
10 amps minimum.

73
Bob, K4TAX








----- Original Message ----- 
From: "Bry Carling" <bcarling at cfl.rr.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Sunday, February 02, 2014 9:31 PM
Subject: Re: [TenTec] TT 422 Blowing Fuses


> Thanks guys,
>
> It does appear that I was partly mistaken about how the soft start circuit 
> works with the three
> relays.
>
> Power is indeed applied to the transformer whenever AC Power switch is 
> turned on and the
> interlock is closed and the 12V is applied.
>
> I think this amp has some quite a complex circuits. it is a device that I 
> had not studied at all
> before. Having so many interacting PC boards, I may have misunderstood the 
> sequence at
> turn on for the two main switches. I hope that I have enough smarts left 
> in me to figure this
> out carefully, and understand what is going on when the HV transformer 
> gets back to me in a
> few weeks from Gary Brown. I will leave no stone unturned in checking all 
> of the diodes,
> caps, transistors etc. before I start getting ready to apply any power.
>
> What I do know is that he 12V supply works, the filaments and pilot lamps 
> light up when they
> should. HV Transformer had an intact secondary. One primary shorted.
>
> When the transformer gets back to me rewound, I plan to start it up on 
> 120V at first, as one
> peson suggested and make sure I can get at least 800V or so of HT before 
> proceeding
> further.
>
> Again huge thanks to everyone (including Robb) who has made efforts to 
> guide me in this
> troubleshooting and repair. You guys' knowledge and experience are a huge 
> help for
> somoene looking at this for the first time and pondering what the heck 
> goes on in this
> wonderful box of tricks!
>
> 73 from AF4K
> Bry
>
> On 2 Feb 2014 at 18:28, Robb Urie wrote:
>
>> On 2/2/2014 2:03 PM, Bry Carling wrote:
>> > Nope. The power switch only sends power to pilot lamps and
>> filaments on mine. The standby switch energizes relays that apply
>> primary power up the HV transformer.
>>
>>
>> Then this amp is certainly not stock...High voltage is applied via
>> the high voltage rectifier board 81538, there are no relays in the
>> original design.  Perhaps the ham who sold it to you modified it
>> without either documenting it or failing to tell you.  Before
>> complaining about poor quality transformers from Ten Tec, maybe a
>> better understanding of exactly what your amp really is would have
>> been better.
>>
>> Your original post did state "Only blows the fuse when switched to
>> operate" caught my attention.  I also found that strange, but did
>> not respond as you seemed to have found the primary shorted.  I have
>> had two 422's, a late one that went "Bang" resulting in a new set of
>> HV caps and an early model that seems to be working just fine.  At
>> one time, the 422 was a good value, but now at the current price
>> point I would have to look elsewhere if I was in the market.
>>
>> Keep us posted when you get your transformer back.
>>
>> 73,
>>
>> Robb N0RU
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>
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