The AM Forum

Here is what she looks like externally. There are three six foot racks. The one on the right side has the two HV power supplies, a rectifier deck, the modulator, the speech amp, and a 250V regulated power supply for the speech amp. The middle deck has two large variacs, one for the line voltage, and one for the plate transformer primary. There is also a control deck, the bias supply deck, and the meter panel. Above this is my external speech processing equipment consisting of a Grace Design mic preamp, a dbx graphic equalizer, and three CRL processing boxes. I use an EV RE20 mic. The rack on the left has the two RF decks, and the Viking II RF exciter. I am very pleased to have those beautiful vintage Hickok meters which have a 270 degree rotation. You don't see meters like these very often.
OK, done braggin'   8)  

It's very cool!

Parts is parts.

You did a good job getting them all together and working! ;)

73DG

Looks great Ron!  Maybe I missed the tube lineup, but what is it?

Joe-GMS 

Hi Joe,

The RF tube line up is simple. The Viking II exciter drives the final amplifier tubes directly. There are two RF decks that use the same power supply, modulator and so forth. On 160, 75, and 40 meters, the RF deck has a single 810 with a pi network tank circuit. It is capable of 300 watts of carrier on all three bands. On 20 meters, the RF deck uses old HK54 triodes (thank you W7TFO) in push pull with a swinging link tank circuit. It is capable of 225 watts of carrier. If the HK54's ever go bad, I have some 35TG's that would work at slightly lower power output.

For audio, the original design had an amplified D-104 going directly into the homebrew speech amp. Now I use an Electrovoice RE20 into the speech processing equipment as shown, and this then goes into the speech amp. The speech amp has a 6SJ7 feeding a 6C5 phase inverter, which goes to a 6N7 twin triode operating push pull to excite the grids of the 6A3 driver tubes. The 6A3's operate with cathode bias and are capable of about 5 watts of power output. They drive the grids of the 811A modulators through a UTC S9 driver transformer. The 811A's have 1400VDC on the plates and -2.4V battery bias on the grids. The mod transformer is a UTC S22 used in conjunction with a 50H Dahl modulation reactor. The secondary of the S22 has RF final plate voltage on it, but does not carry the plate current.

The RF final and the modulators have separate power supplies. I can vary the RF plate voltage from zero to 2500, but I never run it over 2000VDC to save the vintage Thordarson plate transformer from excess strain. If it ever went bad, I doubt that I would be able to find a direct replacement. It is capable of 2500VDC and 300mA, but I typically run it at 1750VDC and 200-250mA. Power supply rectifiers are 866's for the modulator tubes and 3B28's for the RF final.

Plate voltage is always on. There is about -120 volts of blocking bias from a bias power supply. Operating bias is from a grid leak rheostat which can vary from 0-15000 ohms.

Ron

Thanks for the details Ron and a great tube line-up.   

Concerning plate iron, I have an extra CG-309 should you ever need it!   The specs are in this vintage UTC catalog:

http://www.junkbox.com/electronics/utc_transformer_catalog_1963.pdf

One of these days when I get my antennas squared away and the beam up, we will have to work.  If memory serves me right, I think we had a brief QSO on 40 meters many years ago.

73,
Joe-GMS   

Here are some pics of the PP HK54 RF deck for 20 meters. Thanks Joe for the offer of the CG309. I am partial to UTC transformers and I'll keep it in mind.
Ron

Edit: I just looked at those specs. The CG 309 apparently weighs 253lb!!. It would have to be shipped via truck. I will be very careful with my Thordarson T19P65.

Looks like a FB old buzzard rig Ron!  That may be the same TX as you built some years back, not sure.  Love those National dials. 

I wonder what it would cost to ship you the CG-309?   At one time, I had 4 of them.  I only need one. 

Are you getting on for the Rollins event?  Maybe we could work on 40M CW later tonight.


Joe 

Hi Joe,
Yes, most of the chassis and parts were built several years ago. I have tried several types of tubes and have switched back and forth between push pull and single ended, and I have decided to leave it as it was originally designed with push pull HK54's. It is the same with the other RF deck. I have tried multiple configurations using different tubes, including a 250TH, a Taylor 822, and a 254W, but the 810 seems to be the easiest to tame on all three bands. The only other tube I would like to try is an 8000, which is a low mu version of the 810, but I don't have any at the moment, and they are getting pretty hard to find. The power output would be the same however, so there is no real advantage of the 8000 over the 810.

Anyway, I'm happy with the transmitter as it is. Time to stop trying to redesign it and just get it on the air with some regularity.

73, Ron

Hi Ron,

I think I have a couple good 8000's, will forward same in the near future.

You might as well give 'em a try, I'll never use them.

73DG

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That CG-309 is one sweetie of a transformer! There's a selfsame PA-309 here but in the other profile, as if the core is on its side and has larger end bells. It's sitting on a rack dolly to support easy movement, but hasn't been moved in a decade.

Truck shipping? Bah! It'll fit in the trunk of a 1973 Ventura just fine. Road trip!

Secondary has a usefully low DCR.
2x2 3-500Z or 833 transmitter?
PSUD drew the attached pictures about it
(YMMV & we now return to some sort of normalcy).

KD5OEI

2 of those beasts reside here at the radio ranch.

They protect the storeroom from high winds...

73DG

Hi Dennis,

Thanks for the 8000 tubes. Supposedly easier to drive than an 810, but power output is exactly the same. Similar to 811's and 812's, hi and low mu versions of the same tube.

73, Ron