304tl-big-rig

RESURRECTION OF A

HOMEBREW 304TL

AM PLATE MODULATED RIG

Well, I saw what looked like a 304TL homebrew rig on the E-bay place, didn't think I would get it because

there was a Millen R.F. Amplifier thrown in for good measure. Short story I did win, and picked the items

up at the 2003 June Butler Hamfest in PA. Follows are the pictures from E-bay to show what caught my

Eye.

The HV Power Supply




The supply consists of the H.V. Transformer
a high current swinging choke
a high current smoothing choke
two high voltage oil filled capacitors
a pair of 3B28 rectifiers and the
filament transformer for them.

Here is a recreated version

of the schematic for this

component layout.

The pair of 805 Triodes Modulator Section
Front View

The 805 Triodes

in the Class "B" Plate Modulator




The Modulator components consists
of
Black transformer at the left is the Filament
transformer for the 805s.
Grey transformer center rear of chassis is
the driver input transformer.
the HUGE transformer to the right of the 805 tubes
is an RCA 500 Watt modulation
transformer.

Check out the "Large" RCA Modulation transformer

Here is a recreated version

of the schematic for the

component layout
of the Modulator.

.
The Speech amplifier
and
Modulator Driver,
Modulator Bias
and AC Control
Circuitry.




  Rear View
of
Speech Amp.




The 304TL R.F. Deck
Front View

And of course the

Single 304TL

with B&W-850 plate circuit coil & Bandswitch




Also the B&W 800 plate RF Choke


Finally a close-up view of the
Plate and Grid Current Meters
the grid meter is using the
0 - 100 MA scale.

Well the first thought was, if you know me, lets see if it fires up! However since there was dust and dirt, I

started by buzzing everything out, to see where things went, find bad components etc. While doing that I

came to the conclusion that new panels and chassis were in order so first I have to get them and set out

putting the parts in a cleaner and more organized environment. I might note here, I will NEVER run out of

304TL/TH tubes for this rig. Last count was 8 tested and working tubes.

The specifications for using the 304TL/TH can be found here. This unit will be running with 1500 VDC
on the 304TL and the 805 modulator tubes. The power supply provides a total of 500 Ma at this level
and should be quite adequate for the rig in its final form.

The specifications for using the 805 can be found here.

The HV transformer input voltage is controlled by a 120 VAC Superior Powerstat variac, with a 15 amp
rating. so that the voltage output of the High Voltage supply can be set to the proper level.

Also needed are tube sockets, these are made by E.F. Johnson.

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