[Amps] TL-922 Troubles

[R.Measures]

On Jan 29, 2005, at 7:09 PM, Robert F.((Bob)) Jones wrote:

>
> ----- Original Message -----
> From: "R. Measures" <r at somis.org>
> To: "W0OXJ" <rfjones at ris.net>
> Cc: <amps at contesting.com>
> Sent: Saturday, January 29, 2005 6:33 PM
> Subject: Re: [Amps] TL-922 Troubles
>
>
>>
>> On Jan 29, 2005, at 4:33 PM, W0OXJ wrote:
>>
>>> I have been running a balanced pair of 3-500ZG's for 3 years.Recently
>>> the
>>> amp made a loud pop and began arcing while at idle.I turned it back 
>>> on
>>> after
>>> a period of time and noticed a loud hum and the filament transformaer
>>> was
>>> getting warm.
>>
>> A filament got pushed sideways and shorted against the grid cage.  Are
>> you using the stock vhf suppressors?  Did you install a glitch R?
>
> The amp is 100 percent stock,Richard.What is a glitch R?

Robert -- A glitch-R is a resistor in series with the HV+ that safely 
limits peak discharge current during an anomaly.  A glitch resistor 
must be able to withstand a direct short to ground (the" big 
screwdriver test") without damage of any kind or it will fail to do 
it's job.  A glitch-R is definitely not supposed to act like a fuse.
As to the value, I like to limit discharge current to 100A-peak in 
1500w-out heater-type tube amplifiers and 200A-pk in 1500W 
filament-type tube amplifiers.  In 3-500Z amplifiers, a glitch R helps 
to prevent filament-helix bending and fil/grid shorts.

>
>
>>> One tube has fresh paint on it and the other had faded paint which
>>> seemed
>>> strange.The tube with fresh paint does not look used at all.The tube
>>> with
>>> faded paint had a red plate after 45 seconds of excitation under low
>>> drive
>>> and a loaded final.I swapped out tubes with a spare Eimac 3-500 and
>>> the tube
>>> with fresh paint proved to be causing the heavy draw on the filament
>>> transformer.I also notice no idle current where I used to have 150 
>>> ma.
>>>
>>> The amp seems normal,it loads but I didn't try to load it fully.The
>>> relay
>>> seems to operate OK,the 3-500ZG plate stills glows faintly red.
>>>
>>> In the past I have noticed one tube would turn red after a period of
>>> keydown
>>> but was not concerned as the amp has delivered 800 watts out for 
>>> three
>>> years
>>> .
>>>
>>> Now I plan on replacing the defective 3-500ZG but would like to know
>>> what
>>> could be causing the imbalance? and is this the reason for the failed
>>> tube.Will a new tube be matched enough to give good service with the
>>> existing tube?Why no idle current?
>>> Both tubes check out with an ohm meter,no shorts between the three
>>> elements.
>>
>> The tube with the bent filament only shorts when the filament is hot.
>> Operating a stock 922 with a grid-fil shorted tube will destroy T2.
>> There is an article on the 922 on my Web site.
>
> I'll take a look at your website and certainly consider the 
> suppressors.
>
>>> I can't do any voltage checks until I replace the 3-500ZG and will
>>> follow
>>> the instructions in the service manual.They mention a bad zener,bad
>>> relay
>>> and a bad tube as causes for this condition.
>>
>> The bad tube is the result of an intermittent oscillation c. 120MHz.
>> Good luck, Bob.
>
> As always thanks Richard.
>
>>> Any advice or experiences would sure help as I would like to insure a
>>> few
>>> more years of reliable operation.
>>>
>>> Many thanks and 73,
>>>
>>> Bob
>>> W0OXJ
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>
>> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>>
>
>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org