[Amps] Amps Digest, Vol 170, Issue 5

[Robert Paluf]

Dear Mr Steve Wright,

Thank you for taking the time to respond to my posting requesting assistance with my new (to me) Titan amplifier.  You should not be so quick to judge others. I have with the expert advice received off of this forum successfully overcome all of the problems that I have had so far.  I am an electrical engineer with in depth analog design experience.  I may be older but not worn out yet!  When advice is requested do not tell me to give up and seek help from "professionals", I have all the necessary skills but simply need some experienced guidance that I have graciously gotten.

Best 73,
Bob KV4JO

> On Feb 5, 2017, at 12:01 PM, "amps-request at contesting.com" <amps-request at contesting.com> wrote:
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> Today's Topics:
> 
>   1. Re: Amps Digest, Vol 170, Issue 4 (Steve Wright)
>   2. Re: TenTec 425 Plate Current at Standby (Mark Robinson)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Sun, 5 Feb 2017 09:54:33 +1300
> From: Steve Wright <stevewrightnz at gmail.com>
> To: amps at contesting.com
> Subject: Re: [Amps] Amps Digest, Vol 170, Issue 4
> Message-ID:
>    <CABSSkBU+8TiAqURsZPAsLtdWaN2VCAnUP8PsUczv628F1hQzCw at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
> 
> On Sun, Feb 5, 2017 at 5:03 AM, Robert Paluf <robert_paluf at hotmail.com
>> wrote:
> 
> Unfortunately, I am 66 years old
> 
> 
> Strike 1
> 
> 
>> this is my first HF Amplifier
> 
> 
> Strike 2!
> 
> 
>> so I have zero experience with big power amplifiers
> 
> 
> Strrrrike three!!!  Aaaand you're out!
> 
> Sell it, or get professional help.  Don't fiddle.
> 
> Sorry.
> 
> Steve
> 
> 
> ------------------------------
> 
> Message: 2
> Date: Sat, 4 Feb 2017 16:07:48 -0500
> From: Mark Robinson <markrob at mindspring.com>
> To: amps at contesting.com
> Subject: Re: [Amps] TenTec 425 Plate Current at Standby
> Message-ID: <3d42be50-c2ec-ad36-b799-be90941947ff at mindspring.com>
> Content-Type: text/plain; charset=utf-8; format=flowed
> 
> I have a Tentec 425 as well (Golden Series) and I love this amplifier.
> 
> 
> I have had this plate current problem twice in the last two years and 
> both times it was a bad Chinese Matchlett tube.
> 
> I hope it turns out to be a bias problem as K2XX has described. I tried 
> the tube swap first as it was easier and I had some spare Eimac tubes on 
> hand.
> 
> When using this amp watch the grid current at all times. I like to keep 
> mine at 30mA. If you are showing too much grid current when tuned then I 
> increase the Tune setting by maybe 0.5 and then reload for max RF.  This 
> gives less amp gain and you will see less grid current.   I keep a table 
> handy with all the settings for the different bands and spot 
> frequencies   My amp is a later model and has grid current protection. 
> I  don't think some of the earlier models had this protection. It is a 
> quite simple circuit where the current monitoring voltage is applied to 
> the base of a transistor through a resistor and once the current drive 
> voltage gets too high it turns off the bias to the tubes.
> 
> 73 Mark N1UK
> 
> 
>> On 04-Feb-17 11:03 AM, Joe via Amps wrote:
>> While I sold my two 425s some time ago, I believe that this is a 
>> common problem when the amp is over-driven.  R17 on the bias board 
>> opens up.  It is a 4.7 ohm, 5% resistor and is accessible by removing 
>> the small metal plate from under the RF compartment. Then disconnect 
>> four Molex connectors and three(?) mounting screws to remove the board.
>> 
>> THERE'S A 50:50 chance that this is your problem.
>> 
>> I agree with Jim that these are excellent amps.  They're easy to work 
>> on because each lead is numbered and keyed to the schematic. Jim's 
>> complete one page schematic is also a real boon.
>> 
>> 73, Joe
>> 
>> K2XX
>> 
>> P.S. If it does turn out that you need new 3CX800s, I have two unused 
>> for sale.  They were checked out in my 425s before I sold them.
>> 
>> 
> 
> 
> 
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> End of Amps Digest, Vol 170, Issue 5
> ************************************