FW: [Elecraft] 1.8 MHz VCO tuning voltage in K2 / Problems with Drake TR7

Wed Nov 5 08:27:01 2003

-----Original Message-----
From: Roy Vickers [mailto:[email protected]]
Sent: Wednesday, November 05, 2003 7:21 AM
To: zu
Subject: RE: [Elecraft] 1.8 MHz VCO tuning voltage in K2 / Problems with
Drake TR7

Do you know about the drake list? [email protected] I subscribe to them
also since I tinker with older Drakes and you can subscribe at
http://www.zerobeat.net/drakelist/. I was operating on 40 mtrs last nite
using a Drake 2-NT ant a 2-C since my K2 bit the dust this weekend. Good
Luck
Roy Vickers KF5YU

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of zu
Sent: Wednesday, November 05, 2003 7:04 AM
To: [email protected]
Subject: [Elecraft] 1.8 MHz VCO tuning voltage in K2 / Problems with
Drake TR7

Good morning from HB9MFK

1.8 MHz VCO tuning voltage in K2
K2 (No. 3680) with K160RX, KDSP2, KAT2, KSB2 and KNB is now on the air.
The K2 is indeed an excellent rig and it was a great pleasure to assemble
it. The K2 receiver outplays my other receivers as TR7, R-4C and NRD525.
In my K2 the VCO tuning voltage at 1.8 MHz was only 0.9 V. Too low to
operate varicaps! In order to keep the VCO tuning voltages on all bands in a
2 to 6 volt limit, I had to add 39pF in parallel with C75 and 4.7pF in
parallel with C71.

Looking for expertise on Drake TR7 transmitter instability! (Sorry for using
this forum for a non ELECRAFT item)
My TR7 (Model 1337) showes instabilities on 15 meters when tuning an antenna
with the Drake MN-200 matchbox. With 20 W and 1:2 VSWR the output power
suddenly hookes to >150W due to parasitic oscillations. Operating the TR7 in
CW tune mode on 15 meters into a 50 Ohm load showes instabilities at output
power >50W.
Does anyone has experience with TR7 instabilities and their cure?
My first try was the insertion of a 4 dB T-attenuator between driver and PA
stage and ALC realignement to bring the output power to 120W. No power
snapping was obseved on any band with this attenuator at VSWR up to 1:6.
Does anyone know a better remedy?
Does anyone know where I could get a copy of the TR7 service manual?

Many thanks for any assistence.

Best 73 de Ueli, HB9MFK

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