Thanks to Steve, Mike, Vic, and Lou,
I've checked the tubes. I also purchased NEW tubes as stated in
my post. Steve the R11 resistor might be my problem. Who ever owned
this amp before replaced this with a 15k pot. Not sure about the
wattage. Mike I will be checking these resistors. It's been a little
challenging getting the R11 resistor and the R8 resistor. It seems
they don't make these type of resistor that much anymore.
73,
Kevin
w2fa
On Nov 21, 2007, at 2:08 PM, Steve Scoggins wrote:
> Hello Kevin
>
> A common failure in 3-500Z tubes is a filament to grid short which
> may be intermittent.
> This type of failure may be detected by the incidence of negative
> grid current (usually some plate current) during standby. Observing
> the safety procedures in your manual. Remove the tubes then use a
> VOM to check the tubes for grid to filament shorts.
>
> Good tubes will have infinite resistance from each of the grid pins
> to the filament pins.
> You can tap the tube lightly while doing the check for intermittent
> shorts.
> The tube check procedure described above is from the Drake L-7
> manual in section 5-8.
>
> Also, check the 120V bias resistor labeled R11.
> This is the 5K 7Watt power resistor located on the bottom of the PS.
>
> The 120Vdc is switched in via Pin 5 of the RF Deck connector
> when not transmitting in order to reduce the idle currents in the
> 3-500Z.
> Pin 6 is the negative return for the plate HV and the 120Vdc bias.
>
> Steve
>
> ----- Original Message ----- From: "Kevin G. Wagner"
> <w2fa@comcast.net>
> To: <amps@contesting.com>
> Sent: Wednesday, November 21, 2007 10:52 AM
> Subject: [Amps] [AMPS] Drake L-4 negative grid current reading on
> meter
>
>
>> All,
>>
>> I'm having a problem with my Drake L-4 amplifier. A few weeks ago
>> the .082 resister blew because one of the cap's let go in the power
>> supply. I replaced all the cap's, diodes and the .082 resister in the
>> power supply and whet to check out the amp. When I turned it on I
>> have a negative grid current reading on the meter. It slams to the
>> left at rest and when I key the amp it reads zero. I have purchased
>> new tubes (3-500Z's) and I still have the problem. I then tried to
>> calibrate the grid meter using the procedure in the Drake manual with
>> no luck. I'm thinking it's a meter problem.
>> Please help.
>>
>> 73,
>> Kevin
>> w2fa
>>
>>
>>
>> _______________________________________________
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>> http://lists.contesting.com/mailman/listinfo/amps
>
>
73,
Kevin
w2fa
Cell - 732-608-4749
E-Mail - w2fa@comcast.net
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