[Amps] Mangian

[Jim Thomson]

Date: Sun, 28 Feb 2010 14:16:42 -0800
From: MIKE DURKIN <patriot121 at msn.com>
Subject: [Amps] Mangian wire

Ok .. do you really need the Mangeian Wire from the B- of the Filter board to the shunted amp meter??

##  The B-  from the  HV supply, has to ultimately find it's way back to the CATHODE. 


 I have my amp up and running with a GS-35b now and im sure that my bias isnt working right .... mabey it is ... but as it sits now .. i should have 30V bias keyed and im showing 60ma idle ... now this is why i think i still have a problem with metering - when driving with 30W im getting an output of 600W (carrier/cw -what ever) and the uA meter is showing only about 120 mili-amps of plate current. 

##  are u sure the current isn't finding an alternate path ?     You don't want stuff like unwanted V drops  turning on  RVS  connected safety  diodes, and diverting current through back door path's.    Amp will work fine, just the metering is screwed up.  




Second question is do you need plate voltage on the plate to complete the bias voltages (im talking through the tube) to the heater?? 

##  YES.  It's the cathode current   [ = combined grid + plate current]  flowing through your zener's that creates the zener voltage. 


My DC at the heater is 120VDC cutoff and 4V DC key'd state (no drive). My Bias supply is not sagging and the collector of the pass transistor is tied to the CENTER TAP OF THE HEATER TRANSFORMER ...... Please leave out comments about using a center taped heater transformer and the differences of using a bifilar wound rod for RF blocking - its simply what i have and plan on using for now.

##  Maybe try a different meter, or remove stock meter....and bench test it.      Or temp substitute a Fluke 87 DVM.     If the  amp is  functioning fine, the current is flowing... somewhere... and only a portion of it may be flowing through the meter. The current may well be flowing through multiple paths.. then back to the cathode.      I'd be checking everything  between the B-.... and the cathode.

Later... Jim   VE7RF




If your wondering what amp again its a Yokagawa P93 blah blah blah.... i have posted the schematic (a scan of it- and a poor one at that) . Im thinking that the Bias supply needs to supply voltage at the collector via a blocking diode and say a 1K 5W resistor so that when the emitter is pulled to ground the Zeners are reversed by the Bias supply and not the tube leakage ..... at the current configuration im thinking that the 30V zener that i used to replace the pair of 4.1V zeners will never be properly reversed for the wanted 30VDC Bias ....

Mike
KC7NOA