The AM Forum

50 Watts, Four Tubes and No Mod Iron


http://www.amwindow.org/tech/htm/wb9eckseriesmod.htm

Hey , that's a nice little design, S!

Looks like a grown up and more sophisticated version of
the 6AQ5 PW series modulated rig.

I'll bet it will do really hi hi FB audio response.

T

Is that really a #47 bulb in the 1100 volt B+ line?

#47 rated for 150 mills..... aughta werk ok   klc

You could replace it with a meter.

Steve,

 Question on the output Tank came in locally here, one of my local buds called and wondered the values of the Two Variable condensers and the two Inductors.

Any way to edit that and add the Values in..?

I like it. Should sound better than with iron. And many types of sweep tubes from color TVs may be used.

There is an Excel spreadsheet available on the Web that will calculate Pi and Pi-Net values for you. Google is your friend. I think I have DLed it in the past. I will look for it tonight or tomorrow and run for 160. That should cover all the bands.

Yep - 6KD6s, 6DQ5, 6HF5s all should probably work FB. I suppose you could sub a 6146 for the 807 too.

Thank You Steven..FB.

Hi Steve;

Nice simple design. Anyone heard it on the air? probably sounds great!.

Do you suppose I could sub a couple of 6L6's for the sweep tubes? or a more common (cheaper) tube? Sweeps are getting rare and expensive.

Thanks!

Wonder how a second 807 would play in place of the paralleled 6lf6s ?

You get a better saturation voltage with sweep tubes in the modulsator. I run 60 volts on the screens of the 6DQ5s in my PDM viking that gives me just under 100 volts saturation voltage. A higher Z tube may not swing the monkey that low limiting the positive modulation peak. A fet with a source resistor would work even better but has no heater pins.

The required component values for the Pi-network output circuit should be approximately as follows.

160 Meters (Lowest f=1.8 MHz)

C1=350 pF
C2=1550 pF
L=25 uH

For 75 Meters (Lowest f=3.8 MHz)

C1=170 pF
C2=1000 pF
L= 12 uH

C1 is the tune cap, C2 the load cap. Operating parameters were as follows.

807 Plate Voltage = 500 VDC
Power Output = 40 watts
Tank Q = 12

I am collecting parts to build one of these*, with plans to make it bandswitched for 160/80/40. I have a power transformer from a Johnson Valiant I that I could use, but I don't know the specs for it. Does anyone have any information on this piece? I know it is gross overkill for a single 807 transmitter, but it's what I've got.

Might do some trading for a more suitable transformer.

So far I have an 807 (good? ... who knows), a  10.5 in rack panel, and the Valiant iron. Plus some misc little parts that will work scattered throughout my junkbox.

73,
Theo K4MO


* The actual crazy idea is to build it as an exicter stage for a Globe King "look alike", with three chassis. The exciter (this stage of the project) will be the middle unit with a linear amp in the top (single 3-1000Z since I know where I can get one for $0), and the power supply in the bottom with a VFO. The whole thing would be in a bud rack the same size and style as a Globe King 500.

Don't ask why I won't just build  a normal transmitter. I have no idea.

JOHNSON VALIANT LOW VOLTAGE
POWER TRANSFORMER, (T-2) SNC P/N 3068
CORE) EI-150 X 2             STYLE #) 05  E-I LAMINATED CORE
PR) 117 VAC 60 HZ

S1) 310-215-0-215-310 VAC @ 250 MA CCS

S2) 6.3 VAC @ 12A CCS

S3) 2.5 VAC @ 10A CCS

S4) 5.0 VAC @ 2A CCS




JOHNSON VALIANT PLATE
FOR JOHNSON VALIANT TRANSMITTER
CORE) EI-150 X 3.5" 29GM6X   STYLE #) 05  E-I LAMINATED CORE
PR) 120 VAC 60 HZ 1 PH

S1) 1520 VCT @ 400MA CCS

for a series cathode mod rig. How about a 6080 or 6AS7G for the series modder tube,
they are usually found cheap at festers and swaps and have the lowest Mu and plate resistance of any triode out there. After all they were designed to be series regulators. I would think a 6080 with both sections in parallel could cathode modulate a pretty serious strapping final. Just my $.02 worth.

                                                                         The Slab Bacon

The 807 was my Dad's favorite final tube. Every time I ran the 807 rig he would pound his shoe on the livingroom floor. I would take out the tv picture.
you gotta love cable.

        That reminds me,  I wanted to hot rod a DX-60 for AM.  I left off wondering if
 series modulation would be an improvement over the usual mods for the DX-60.
 With the one I have here now, maybe it would be a single bander.
        Hope I have not changed the subject too much. Would like to show up on
 10 meters with something unusual.
                                                       tnx,
                                                             Ed WA4NJY
                                                             Bradenton, Fl

Theo,
Did u see my reply about the transformers??????
Your welcome.......

Bill ... my appologies. I did, and I have been searching through my junk box(es) to determine which one it is. Thanks very much for the timely info!

No problem Theo.....I was just wondering if u saw my post.
Good luck with the project.
Bill

Here's an approach from the other end, the B+ side. Not as much power from the RF section, 5W carrier/20W peak, but that is because there is only one 807 and more could be paralleled. It's more complicated as well, but this can make use of one of the adjustable DC power supplies with the many parallel pass tubes with very little modification.

http://www.montagar.com/~patj/amxmtr_dc_classamod.html

Hi all...New on this site but already impressed..

I like this article and have decided to add it to my winter time workshop activities.I will have to use 6DQ5 tubes in the modulator.I thought I would make it monoband for 160 meters as there is quite some AM activity in VK on that freq.I will also add a VFO to the transmitter.I would appreciate any further info..It will be a change from constructing amplifiers..

73..Bob..VK3ZL..

Stevie, Huz 'esq. and Bob, WB9ECK
Look at the 50k pot in the grid circuit of the 12AU7's 2nd triode, the one that adjusts the lower end of the 470k bias resistor from ground to -75 volts.  I'm curious what Bob got for the actual voltages at the grid and cathode.  Are you looking at about about 5 volts neg. grid to cathode because cathode is lifted far from ground by a 10k resistor?  Cathode wise, you have probably 10ma going through 10k which is 100 volts.  Now I'm not sure that -75 is sufficient.  Some of it must be from grid leak through the 470k.  Do you have measured voltages? Current through 12AU7 at E_bb = 300? Maybe the current through the 10k is way less (minimal that it is in a voltage amp.) than required to support the AF power required?

Well it must work since Stout built it, relay switching and all.  I'm just wondering what might be good bogie set points failing having a distortion meter.  - and the operating voltages throughout the circuit

For fun I tried Bob's circuit inserted into the cathode of a Viking I. I used two 6CD6 tubes since I had them handy. This worked excellent at moderate power, but I would have needed maybe 4 of the 6CD6's to push 100W peaks from the 4D32. I am impressed it seemed quite linear, yet so few parts were needed. I ran the screens at 50V on the 6CD6's. Cool!