The AM Forum

Hi All

I’m starting restoration of my Valiant transmitter and I have a few questions.

I plan on solid stating the entire unit.    My calculations for dropping resistors are as follows:

5V4: Tung-Sol data sheet shows 23V drop @ 175 ma per plate
23/.175 =  131 Ohms  4W --  Use 130 ohms 10W

6BY5: Tung-Sol data sheet shows 32V drop @ 175 mA per plate
32/.175 = 182 ohms   5.6W – Use 180 ohms 10W.

This is a bias circuit.  175 mA is steep to use for a bias circuit, but I have no idea what this value is for a Valiant.   Comments?

866: RCA data sheet shows 15V drop.    Not worth compensating for in HV circuit.

Chernobyl resistor:   Replace with 18K   5+W  (I’m using 20K because I have one…..).

Do the chirp mods…….

VFO Compartment.

I’m using the manual from BAMA and have a good one on order from Pete.   However, tracing the components on the side of the VFO compartment near R3 shows some very different connections than my schematic.   Here’s a pix:

I’m showing Pin 4 of the VFO tube goes to one side of “L?” which is in series with “C?”.   The other end of “C?” goes to a terminal strip which then proceeds to Pin 7 of the VFO tube and (what I think) is L3.         I like to know what those unknown components are.    I know that L20 is under the chassis.    I ran across this as I’m measuring as many resistors in the VFO compartment as I can…..

Thanks

This would make more sense if you were counting the V1 (oscillator) tube socket pins in the other direction so that pin 4 (heater hot lead) becomes pin 7 (cathode). In that case, your "L?" becomes L3 and "C?" (which is also an inductor) is L19. There should be a bypass cap, C20, between the junction of the inductors and ground.

You can verify my guess by measuring the resistance to ground at either of the leads of either of those inductors and switching the OSCILLATOR switch between VFO and ZERO. The former should be high resistance and the latter a closed circuit.

As for solid stating the supplies, keep in mind that the voltages listed in the documentation were based on 1950s 117vac line voltage. Today's can be higher and you'll want to be sure that the unloaded supplies don't surpass the voltage rating of components, such as filter caps, until the tubes warm up and begin to draw current.

That "soft start" feature of using vacuum tube rectifiers is gentle on components.

RF and AF bias are adjustable from pots on the side of the chassis, and the keyer and clamper (which use the bias voltage) are adjustable on top of the chassis. They may offer enough adjustment range to not need a dropping resistor in the bias supply.

The issue was I was viewing Pin 4 and Pin 5 from an angle that made me think they were the same pin.   

I believe the following photo is correct:

Greetings All....

Well, the Chernobyl resistor is replaced.... my restoration log for your viewing pleasure...

http://www.k3msb.com/valiant/valiant.html (http://www.k3msb.com/valiant/valiant.html)

I was doing the Chirp fixes as per w8ji  (https://www.w8ji.com/johnson_vfo_chirp_jump.htm (https://www.w8ji.com/johnson_vfo_chirp_jump.htm) ).   His photo is a bit confusing for me.

Here's a photo of my chassis.   I replaced insulated washers at points 1 and 2,  but his photo seems to indicate  points 1 and 3.    I mistakenly did 2 as point 3 was already done.   I don't see any particular harm in doing point 2 as well (on the other hand, I can't see any particular good either).  Comments?

Work is progressing, but slowly........

I've a question about solid stating the 5V4.  For the 5V4, my Tung-Sol data sheet shows 23V drop @ 175 ma per plate.   Even though both plates will be used,  it will be only one side at a time so the current through the single dropping resistor should be computed based on 175 mA.

I've see some computations on a Valiant site showing 2x175 mA.    I think it should be just 175 mA,  but want to make sure.

Before Solid Stating anything, first make sure everything works with the tube rectifiers.




Phil - AC0OB