Looking to build 80/40TX

[M1ECY]

Hi All,

My first post, so be friendly

I am looking to build a valve (Tube) tx here, following these sort of specs....

100W Carrier, High Level mod, VFO control, oh, and Rack and panel type of construction.

I have the following parts to hand.

2 off TY2-125, complete with bases and anode connectors (these are Triodes, and I only enviasge needing one)

Lots of iron, HT wise, 1500-0-1500 at about 200ma, 550-0-550 at 900ma, various smaller units as needed.

I also have a smallish selsction of large chokes.

Mod Iron isnt nailed down as yet, but I am thinking along the lines of a complete modulator that uses TZ40/DA41 class B triodes

At present I am thinking 6J5 VFO, 6AG7 buffer/doubler, 6L6 driver, and TY2-125 as the output.

Modulator will look something like this.

EF37a mic amp, 6SN7 preamp/phase splitter, 807/6L6 driver DA41/TZ40 modulators.

Any pointers, or design ideas would be handy (bearing in mind that this little island isnt exactly overrun with decent Am type stuff!)

Cheers de Sean
M1ECY

[W7TFO]

Sounds like a good lineup.

Build it!

73DG

[WQ9E]

Greetings Sean,

You have on hand a good lineup of parts.  I would suggest looking through some of the older handbooks and magazines for circuit ideas.  You may find something that you like or you can modify a design to meet your specific needs.

Some of the older handbooks are available online:

http://www.tubebooks.org/technical_books_online.htm

[M1ECY]

I have a good number of ARRL books from the 40s thru to present day, as well as some other stuff to draw from.

There aren't many triode designs - I guess the low gain compared to tetrodes was a reason behind this.

That site has lots to look at though - thanks.

I'm currently looking at the pi output stage (unless there is a good reason not to) assuming the following is correct I arrive at the following results.

Va 1500
Ia 150ma

So, 150W dc input

Assuming 60% efficiency (hoping for better)

This gives around 90W carrier, and is well within the dissipation of the tube.

From this I have calculated RL to be 5000r (assuming a class C stage)

In that case this gives me

Tune cap 100pf
Load cap 500pf
Inductor 20uH

I wonder how far off my calculations are?

Cheers
Sean

[KM1H]

Is there any reason you dont want a tetrode/pentode?

There are many WW2 era tubes still available in the UK such as the 803, 813, 814 that would make life a lot easier than a triode. The 803 is very seriously underated in the manuals and the others can also be considered very conservatively rated.

Ive recently rebuilt an old US TX that someone had tried to convert to an 813 and have been able to get an easy 150-175W out at 1100V on 160-20M with a 2E26 driver and a lot more on 40-10 with a 6146 which states the RF components/wiring/switching used are pretty inefficient.

A 6L6 will drive a 814 at 1000V to 120W out as used in the Hallicrafters HT-9.
http://bama.edebris.com/manuals/hallicra/ht9/

Triodes belong in modulators or in grounded grid

Carl

[M1ECY]

Hi Carl,

No reason - I just happen to have these laying around.

Of course, if the assembled experts reckon Tetrodes are the way to go, I am happy to listen - I might be able to source some here.

Im looking to use as much of the junk I have laying around, for several reasons - 1, between jobs, 2, falling over stuff that "might come in handy", and 3, recycling rules!

Cheers
Sean

[KL7OF]

Triodes are very cool...It sounds to me like you have a good lineup of tubes and the iron is OK as well.  i'm not familar with some of the UK tube numbers...The Arrl hanbook from the late 40's early 50's has some speech amps that I have used..  like 6sj7 to 6sn7 tx coupled to 6ls's / negative feedback and another 6sn7 to 2a3 model that had a very high rms vrms output...those schematics are adaptable to different tubes ...Is your iron big enough to handle 2 tubes in the fina???.... more strap is better...Good Luck...Steve

[M1ECY]

Just to muddy the water a little, I have also got access to a single TT100 tetrode.....

Any thoughts on using this tube in the PA?

Cheers
Sean

on second thoughts, scrub that - only 800v on the anodes in class C......

[KA2DZT]

Sean,

Probably the best tube for this power level is the 813, if you can dig one up.  There are plenty of them around.  Your 1500V xfmr will be just right and you will be able to get 120-150 watts output.

Fred

[M1ECY]

Thanks Fred,

I was just bouncing a couple of ideas around - something different....

Perhaps an 813 is the way to go then - I can probably grab one with a base on eBlag.

Then the TY2-125 can be used in the modulator I guess....

Cheers
Sean

[KM1H]

Sean, you need to provide data sheet links to those EU tubes. Some may be identical to US versions as often happened.

The TY2-125 triode is an odd duck that doesnt perform very well at low voltage. In that respect its a lot like the Eimac tetrodes such as the 4-125A.

Carl

[M1ECY]

Ah, yes, the TT100 is difficult for datasheets - nowt on the web...

As you say the TY2-125 isn't 100% happy with low HT - I am beginning to think life will be much easier sticking to tubes that are available from the US - there is not a huge homebrew following over here, and decent sized AM stuff is the exception rather than the rule.

in the meantime for those that have not seen it, data for the TY2-125 is attached below.

If any of you have something suitable and are happy with overseas shipping I would be pleased to hear about it

[KM1H]

The tubes I mentioned earlier are about as common in the UK as here and that includes the 811 or 811A.

With an 813 modulated by 811/811A's you wind up with convenient load impedances suported by many fixed ratio mod transformers. The surplus ATC/ART-13 version is often on Ebay from Europe.

[M1ECY]

The Mod Iron I have access to is ex RAF ground VHF gear - it used to modulate a 100w transmitter called the T1131

Uses a pair of either TZ40, or DA41 class B triodes as output bottles - as soon as I dig it out I will test the tranny

Cheers
Sean

[KM1H]

The TZ-40 is pretty much the same as the original 811 except for filament, I have the spec sheet if needed. Its midway between a 809 and 811A. The ART-13 used the 811.