Re: Drake W4 wattmeter woes...
¿ªÔÆÌåÓýHi Mike, ? Don¡¯t forget that R1 is in the circuit.? If that goes high in value, it could throw everything off. ? PIN diodes should work well in these meters.? They work well into the VHF range and have low forward voltage drops.? The 1N34 and other geranium diodes were used because they performed better than silicon did at the beginning.? Things have changed now. ? 73, Clint, VE3CMQ ? From: [email protected] <[email protected]>
On Behalf Of Mike Bryce via groups.io
Sent: Friday, 19 January 2024 19:25 To: [email protected] Subject: Re: [DRAKE-RADIO] Drake W4 wattmeter woes... ? Hi, Ron, ? already checked the meter movements and they all seem to be working fine. ? I¡¯ve been poking around with one of the meters. ? Trimmer R4 sets the calibration for the 200W scale. Voltage from D1, (from the pickup generated by D1) goes through R4 to the meter switch and then through the 2.2K resistor to the meter. It¡¯s that simple! However, I can¡¯t set the meter to 100W with 100W from the transmitter (using a bird wattmeter and correct slug)? ? When the 2000W position is selected, voltage ?goes through R4, then R3 and R2. R2 set the 2000W scale. ? I put in a 5K trimmer for R4, and I can somewhat set the meter. Even with R4 out of the circuit, the meter can¡¯t quite make full 100W deflection.? ? What¡¯s that mean? I don¡¯t know. I suspect the D1 isn¡¯t up to snuff, it tests fine. Resistor R5 is good, too. ? So far, I can¡¯t find any of the 1N295 diodes, although I¡¯m sure the 1N34A diodes will work. I don¡¯t have any of those either, and the chinese imports are $2 a pop. ? It¡¯s a real head scratcher! ? ? Mike, WB8VGE ? ? ? |